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Feeding structures of the white shark, Carcharodon Carcharias (Linnaeus), with notes on other species Powlik, James 1989

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FEEDING STRUCTURES OF THE WHITE SHARK, ( Carcharodon carcharias (Linnaeus), WITH NOTES ON OTHER SPECIES By JAMES JOHN POWLIK B.Sc.(Hon.) The University of B r i t i s h Columbia, 1988 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA DECEMBER, 1989 © James John Powlik, 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Z o o l o g y The University of British Columbia Vancouver, Canada Date 13/03/1990 DE-6 (2/88) ABSTRACT Fresh and prepared museum specimens of the white shark Carcharodon carcharias, b u l l shark Carcharhinus leucas, and salmon shark Lamna ditropis were measured and compared with respect to tooth p o s i t i o n and anter ior buccal cav i ty dimensions. Coordinates of funct iona l tooth p o s i t i o n were defined by 1) dev iat ion from the midl ine and 2) degree of e r e c t i o n . Tooth pos i t ions were not unique i n any region of the mouth/ but demonstrated less v a r i a b l i t y wi th in 3 0 ° of the mid l ine , p a r t i c u l a r l y for male specimens of a l l three species ( 7 1 . 4 8 ° +- 1 0 ° erect) and a l l Carcharhinus leucas specimens ( 4 6 . 5 8 ° + - . 9 6 ° e r e c t ) . Ana lys i s of high-speed videotape of white shark feeding ind ica ted a 1 5 . 7 ° reduct ion i n tooth cu t t ing angle with jaw adduction fo l lowing upper jaw p r o t r a c t i o n . It i s suggested that such changes i n tooth cu t t ing angles during feeding are p r i n c i p a l l y the r e s u l t of jaw f lexure , and may make the teeth more e f f ec t i ve by angl ing them inward towards the g u l l e t . Values for tooth removal from fresh- frozen white shark mater ia l using a t e n s i l e t e s t i n g apparatus ranged from 12 kg (for a 1 1 0 ° erect tooth) to 70 kg (for a 5 9 ° erect too th) . Removal load was appl ied d i r e c t l y outward from the mouth to simulate a re s i s tan t prey item, and was not s i g n i f i c a n t l y d i f f eren t for degree of erec t ion or tooth p o s i t i o n on the jaw margin. Tooth p o s i t i o n i s seen to change with jaw p r o t r a c t i o n , however t h i s change does not enhance tooth f u n c t i o n a l i t y by increas ing the load required to remove the tooth . iv TABLE OF CONTENTS page ABSTRACT i i ACKNOWLEDGEMENTS Tfiii TABLE OF CONTENTS iv. LIST OF TABLES v LIST OF FIGURES .vi, LIST OF SPECIES AND ABBREVIATIONS - V i i CHAPTER 1: GENERAL INTRODUCTION The Shark Feeding Apparatus 1 This Study 13 Study Animals 14 CHAPTER 2: MEASUREMENT OF TOOTH POSITION 2.1: Introduction 17 2.2: Materials and Methods 20 2.3: Results 41 2.4: Discussion 59 CHAPTER 3: FEEDING DYNAMICS 3.1: Introduction 65 3.2: Materials and Methods 71 3.3: Results 74 3.4: Discussion 83 CHAPTER 4: STRUCTURAL INTEGRITY 4.1: Introduction 90 4.2: Materials and Methods 91 4.3: Results 95 4.4: Discussion 104 CHAPTER 5: GENERAL DISCUSSION AND CONCLUSIONS The Position of Shark Teeth 111 Applications and Future Research 112 Conclusions 117 LITERATURE CITED 119 APPENDIX A: Specimen C o l l e c t i o n and Dimensions APPENDIX B: Selected Feeding Film Tracings 126 138 LIST OF TABLES TABLE page 1- 1 Landmark Studies i n Se lach i ian Oral Biology 3 2- 1 S t a t i s t i c a l Summary of Midl ine Displacement 45 2- 2 S t a t i s t i c a l Summary of Cutt ing Angles 47 2- 3 ANOVA resu l t s for MLD and ECA values 50 2- 4 Phase Calcu la t ions 53 2- 5 Chi-Square Analys i s of Fresh M a t e r i a l 57 3- 1 Summary of Feeding Analys i s 76 3- 2 Regression Analys i s of Feeding Footage 78 4-•1 Summary of Instron Experimentation 97 4- 2 Regression Analys i s of Instron Results 99 A-•1 Study Specimen C o l l e c t i o n 127 A-•2 Specimen Buccal Cavity Dimensions 131 A-•3 Summary of Midl ine Displacement Values 133 A-•4 Summary of Cutt ing Angles 135 v i LIST OF FIGURES FIGURE page 1- 1 The Shark Feeding Apparatus as a Lever 6 1- 2 Ske le ta l Elements of Shark Jaws 10 1- 3 Musculature of Shark Jaws 12 2- 1 The K i n e t i c Dentometer 23 2- 2 Dentometer Measurement of Gape Angle 25 2- 3 Dentometer Measurement of the Buccal Cavity 27 2- 4 Dentometer Measurement of Cutt ing Angle 27 2- 5 Tooth Enumeration System 31 2- 6 Measurement of Tooth Size 34 2- •7 Mouth Sections and Comparisons 39 2- •8 Mean Pos i t i on of Funct ional Teeth 55 3-•1 Pro trac t ion of the Upper Jaw 68 3- 2 ECA Change versus Absolute Gape Angle 80 3-•3 ECA Change versus Relat ive Gape Angle 82 3-•4 ECA Change with Jaw Flexure 87 4-•1 Instron Apparatus 93 4-•2 Force of Removal Versus Tooth Pos i t i on 101 4-•3 Cutt ing Angle Versus Force of Removal 103 5-•1 Summary of Feeding Events 114 B-•1 Rotation Tracings of Reference Jaws 139 B-•2 Tracings of V e r t i c a l Attack (sequence 1) 141 B-•3 Tracings of Angle Attack (sequence 2) 144 B-•4 Tracings of Angle Attack (sequence 3) 147 B-•5 Tracings of Straight Attack (sequence 4) 150 v i i x LIST OF SPECIES AND ABBREVIATIONS Species White shark Carcharodon carcharias (Linnaeus) B u l l (Zambezi) shark Carcharhinus leucas (Valenciennes) Salmon shark Lamna ditropis (Hubbs and F o l l e t t ) Blue shark Prionace glauca (Linnaeus) Bluntnose s i x g i l l shark Hexanchus griseus (Bonnaterre) Lemon shark Negaprion brevirostris (Poey) Tiger shark Galeocerdo cuvieri (Peron & LeSueur) Dusky shark Carcharhinus obscurus (LeSueur) Sandbar shark Carcharhinus milberti (Valenciennes) Smooth dogfish Mustelus canis (Mitchell) Grey reef shark Carcharhinus amblyrhynchos (Bleeker) Barracuda Sphyraena picuda (Bloch and Schneider) Pike Esox lucius (Linnaeus) Common Abbreviations PQL Palatoquadrate length (upper jaw length) MCL Meckel's c a r t i l a g e length (lower jaw length) DAL Dental Arc Length (length of jaw margin) MLD Midline Displacement (angle deviant from midline) MLD' Linear displacement from the midline (based on jaw margin length, divided by 180 degrees, to give a value expressed i n mm/degree) ECA E f f e c t i v e Cutting Angle (degree of tooth erection) TML Tooth Midline POR Point of Reference PR Protractor SA Scale A (of the dentometer) SB Scale B (of the dentometer) DRP Dentometer Reference Plane (as along scale) AA A u x i l i a r y Attachment SD (wrt dentometer) Scale Displacement SD/ STD DEV (wrt s t a t i s t i c s ) Standard Deviation SE Standard Error ACKNOWLEDGEMENTS v i i i This study could not have been completed without the assistance of a number of very fine people. The author wishes to thank: Robert Blake, John Gosline, and Geoffrey Scudder (University of British Columbia) for overseeing the development of the manuscript and providing laboratory f a c i l i t i e s ; Martin Adamson and Norman Wilimovsky for serving on the the thesis examination committee; Gavin Chalmers and Bruce G i l l e s p i e for t h e i r assistance with the laboratory equipment; Alex Peden (Royal B.C. Museum) and B i l l Eschmeyer (California Academy of Sciences) for allowing access to t h e i r museum c o l l e c t i o n s ; A l Giddings and Kim Dodd (Ocean Images) for providing access to t h e i r f i l m l i b r a r y ; Geremy C l i f f (Natal Sharks Board) for providing the fresh materials; and Richard Lund (Adelphi University) , Leonard Compagno (Cape Town Shark Research Center), John McCosker (California Academy of Sciences), and Gavin Naylor (American Museum) for providing insight and d i r e c t i o n when i t was greatly needed. The products of the Coca-Cola company are duly recognized for t h e i r n u t r i t i o n a l support. Dedicated to Perry W. Gi l b e r t and Sanford A. Moss for t h e i r innovations i n t h i s f i e l d . 1 CHAPTER 1; GENERAL INTRODUCTION  THE SHARK FEEDING APPARATUS In terms of body morphology, perhaps no feature of the Chondrichthyan form i s more d i s t i n c t i v e than the sub-terminal l o c a t i o n of the mouth. Although a v e n t r a l l y located mouth and a multitude of teeth are not unique to sharks among f i shes , i t i s t h i s s tructure which serves as the animal's p r i n c i p a l means of defence, predat ion , and environment sampling. Schaeffer (1967) even suggests that c l a r i f y i n g the development of the feeding mechanisms present i n l i v i n g sharks may e luc idate the evolut ion of the e n t i r e group. I t has been suggested that the shark sub-terminal mouth or ig ina ted i n the Mesozoic E r a , l i k e l y improving hydrodynamics by provid ing a p r e - o r a l p laning surface (Moss, 1977, 1984). Development of a v e n t r a l mouth s t r i c t l y to a s s i s t i n benthic feeding has general ly been refuted ( e . g . , Moss, 1984), however the advantages of a v e n t r a l mouth for maneuvering during feeding i s acknowledged ( e . g . , Spr inger , 1967) . An antero-ventra l p o s i t i o n of the jaws i s often considered i n e f f e c t i v e i n comparison to longer jawed 2 TABLE 1-1: S i g n i f i c a n t studies and methods contr ibut ing to the present understanding of Se lach i ian o r a l b io logy , as discussed i n the t ex t . TABLE 1-1: Landmark Studies i n Se lach i ian O r a l Biology RESEARCHER YEAR SUBJECT METHOD Luthor 1909 Anatomy,mechanic s Anatomical study Goodrich 1909 C l a s s i f i c a t i o n Anatomical study LeRiche 1910 1926 Tooth c l a s s i f i c a t i o n Anatomical study L i g h t o l l e r 1939 Comparative anatomy Anatomical study I f f t and Zinn 1948 Tooth replacement Ag-N03 s t a i n Springer 1961 Feeding mechanics F i l m G i l b e r t 1962 Feeding behavior F i l m Moss 1962 Feeding mechanics F i l m , e l e c t r i c a l s t imulat ion Strasburg 1963 Tooth p o s i t i o n Anatomical study Applegate 1965 Tooth c l a s s i f i c a t i o n Anatomical study Moss 1967 Tooth replacement C o n t r o l l e d growth Snodgrass & G i l b e r t 1967 Adduction p o t e n t i a l Al /PVC b i t e meter Moss 1972a Tooth replacement C o n t r o l l e d growth 1972b Feeding mechanics F i l m Nobi l ing 1977 Feeding mechanics F i l m , anatomical study Maisey 1980 Jaw suspension Anatomical study T r i c a s & McCosker 1984 Feeding mechanics and behavior High-speed f i l m T r i c a s 1985 . Feeding behavior High-speed f i l m Frazze t ta & Prange 1987 Feeding mechanics High-speed f i l m Frazze t ta 1988 Tooth form Anatomical study 4 f i shes such as barracuda (Sphyraena spp.) or pike (Esox s p p . ) . The shark cannot "look" prey i n t o i t s mouth s ince the u p l i f t of the snout sh ie lds i t s v i s i o n of the prey item, and t h i s has commonly been l a b e l l e d as a disadvantage, reducing prey capture e f f i c i e n c y . Mechanical ly , however, the advantages of a sub-terminal mouth are r e a d i l y apparent. Referr ing to Figure 1-1, a shortening of the jaws reduces the moment arm of t h i s type III l ever and allows a greater amount of force to be generated by the adductor muscles (Heemstra, 1980). Forces as high as 3 tonnes per square centimeter can be produced by such systems at the tooth t i p , as measured i n lemon and dusky sharks (Snodgrass and G i l b e r t , 1967). Consequently, with the appropriate tooth morphology, chunks may be gouged out of a prey organism. This increases the d i v e r s i t y of prey a v a i l a b l e to the shark since i t i s no longer l i m i t e d to feeding on organisms smaller than i t s e l f . In contras t , pike and barracuda have adopted a gulp feeding method, owing to the r e l a t i v e l y more l i m i t e d adduction p o t e n t i a l of t h e i r long jaws (Moss, 1984). Although quite adept at manipulating t h e i r prey to an o r i e n t a t i o n p a r a l l e l to t h e i r jaws and g u l l e t , these predators are l i m i t e d to feeding on prey smaller than themselves. 5 FIGURE 1-1: The shark feeding apparatus as a Type III lever. Pivoting i s produced at the fulcrum (jaw joint) [1]/ force i s generated by the jaw adductor muscles [2] , and r e s i s t i v e load i s provided by the food item [3]. Length of jaw and contraction force are inversely r e l a t e d : In shortening the moment arm (the lower jaw), more adduction force may be generated, at the expense of speed of closure and v i s i b i l i t y of prey. 6 7 A second r e s u l t , or perhaps concurrent event, of the movement of the mouth to a sub-terminal l o c a t i o n i s the enhanced development of the snout (Shaeffer, 1967). The e l e c t r o - and o l f a c t o r y s e n s i t i v i t y of the shark i s we l l documented ( e . g . , Hodgson and Mathewson, 1978; Kalmijn , 1974, 1977, 1982), with the p o t e n t i a l to sense concentrations of blood as low as 1 ppb, and e l e c t r i c a l voltage gradients as low as 0.005 mV per centimeter. A d d i t i o n a l l y , the snout i s the l o c a t i o n for the shark's mechanoreceptors and the h ighly s p e c i a l i z e d Ampullae of L o r e n z i n i . This enhanced r o s t r a l s e n s i t i v i t y i s one means of compensating for a ' b l i n d ' purchase on n e a r - f i e l d prey. The jaw anatomy and means of suspension i n sharks i s well-documented ( e . g . , Gegenbaur, 1872; Huxley, 1876; Luthor , 1909; Goodrich, 1930; L i g h t o l l e r , 1939; Holmgren, 1941; Moss, 1962; Maisey, 1980; Compagno, 1988). The jaw suspension i n l i v i n g sharks i s h y o s t y l i c by Huxley's (1876) o r i g i n a l d e f i n i t i o n (Maisey, 1980). Hybodont and cladont sharks possessed an amphisty l ic suspension, however hyostyly i s considered a subset of , rather than an a l t e r n a t i v e t o , amphistyly (Maisey, 1980). The s k e l e t a l elements are c a r t i l a g i n o u s , but become c a l c i f i e d at the p r i n c i p a l s tress points with growth and age. 8 The d i s a s s o c i a t i o n of the upper jaw (palatoquadrate) from the braincase permits the jaw complex to be protracted forward i n the act of b i t i n g ( e . g . , Moss, 1962, 1972, 1977, T r i c a s and McCosker, 1984; Frazze t ta and Prange, 1987). The palatoquadrate i s attached to the braincase only by the ethmopalatine l igaments, which connect to o r b i t a l processes on the jaw to prevent i t s overt downward movement (Figures 1-2 and 1-3). The processes may a l so act to s t a b i l i z e the jaw against sideways rocking when the upper jaw i s r e t r a c t e d . The palatoquadrate i s a r t i c u l a t e d to the lower jaw (Meckel's c a r t i l a g e ) at the jaw j o i n t . The prec ise s tructure of the j o i n t var i e s from species to species , but t y p i c a l l y the p o t e n t i a l for l a t e r a l movement i s reduced with increased toughness of the prey items i n the d i e t (Moss, 1984). This basic arrangement, described by Moss (pers. comm.) as "elegant i n i t s s i m p l i c i t y of design", has l ed to a mult i tude of v a r i a t i o n s among the 350 l i v i n g shark spec ies . Gregory (1933) c i t e s t h i s s i m p l i c i t y as the r e s u l t of degenerative processes, rather than pr imi t iveness ; not un l ike the s k u l l s of sturgeon and salmon. The above d e s c r i p t i o n i s not intended to represent the e n t i r e group, but i s i l l u s t r a t i v e of the p r i n c i p a l elements involved i n the feeding apparatus of a t y p i c a l Carharhinoid or Lamnoid shark. 9 FIGURE 1-2: [1] General p lan of the s k e l e t a l elements of the shark feeding apparatus. [2] Ske le ta l elements of the feeding apparatus i n a t y p i c a l shark (Squalus). [1] from Moss, 1984 [2] from Ashley , 1976 10 S P I R A C L E 11 FIGURE 1-3: Musculature of the shark jaws. [1] cjVf = quadratomandibularis muscle mass, which acts to c lose the jaw. preorb^&2 = p r e o r b i t a l i s muscles, which p u l l the jaw complex forward. l ev pq = l evator pa la toquadrat i , which p u l l s the jaw complex upward. [2] Movement of s k e l e t a l elements during jaw p r o t r a c t i o n . Downward movement of the palatoquadrate (pq) i s l i m i t e d by the ethmopalatine ligaments ( e l ) . Hyomandibula (hy) moves outward with downward movement of the Meckel's c a r t i l a g e (mc) . SOURCE: Moss, 1972 THIS STUDY Most studies on jaw protraction have examined only one component of the feeding apparatus (such as the jaws or teeth), or u t i l i z e d only one means of evaluation i n a single type of analysis (Motta, 1984). This study i s an attempt to compare r e l a t i v e tooth positions with the action of the jaws. The hypothesis tested i s that the protraction of the upper jaw repositions the teeth i n such a way as to make them f u n c t i o n a l l y superior. Functionality i s defined here as being more r e s i s t a n t to removal (less susceptible to loss) during feeding. In overview, t h i s study has three objectives: 1. To quantify the p o s i t i o n of the functional teeth i n the shark mouth. 2. To determine how these tooth positions become alter e d by the action of the jaws, p a r t i c u l a r l y by protraction of the palatoquadrate. 3. To determine the s t r u c t u r a l i n t e g r i t y of r e l a t i v e tooth positions and the adjustments made to them during b i t i n g . STUDY ANIMALS To evaluate use of the dentometer (sect ion 2 .2) , a p i l o t study was performed on a number of a v a i l a b l e Carcharhin id and Lamnid species . The c o l l e c t i v e abundance of these two Orders (approximately two-thirds of a l l l i v i n g shark species) permits the broadest a p p l i c a t i o n of t h i s study's r e s u l t s . J t The white shark, Carcharodon carcharias, i s the primary animal for t h i s study. The white shark i s found mostly i n temperate, t r o p i c a l , and subtrop ica l coas ta l regions and around cont inenta l and i n s u l a r she l f breaks. It may grow to 6 meters i n length and i s reputed to have the most attacks on humans of any shark species with a rate of 1.3 per year world-wide (Hughes, 1987). Adults feed p r i m a r i l y on marine mammals, while young feed on small f i s h (Tr icas and McCosker, 1984). As the larges t and most ferocious p i sc ivorous animal i n the world, the white shark has a feeding apparatus that provides an i d e a l t e s t i n g ground for the above hypothesis . The s ize of the animal permits easy measurement of the jaws, and i t s large teeth and independent d e n t i t i o n are e a s i l y measured. Access to footage of i t s feeding movements in situ i s a lso a v a i l a b l e . 15 The salmon shark (Lamna ditropis) i s a l so d iscussed . Also a Lamnid, the salmon shark i s found throughout the P a c i f i c Ocean (Hart, 1973). L.ditropis i s a fast-swimming, pe lag ic shark, growing to 3 meters and feeding p r i m a r i l y on salmon and tomcod (Hart, 1973). This d i e t of smaller f ishes contrasts sharply with the d i e tary j preference of adult white sharks wi th in the same Order. I The b u l l shark, Carcharhinus leucas, i s the t h i r d species inc luded i n t h i s study. Smaller than the white or the t i g e r shark, the b u l l shark's threat to humans i s often understated (Hughes, 1987), but i t i s nonetheless an impressive predator . The b u l l shark i s found p r i m a r i l y i n t r o p i c a l seas, but i t has been found as far as 3700 kilometers upstream i n large r i v e r s . I t has a robust body, growing to 3.4 meters (Hughes, 1987), and a strong feeding apparatus which may be l ikened to that of white sharks ( L . J . V . Compagno, pers . comm.) Museum specimens were used i n order to increase the s i ze and sampling area of the data set . Dried and preserved museum specimens were examined i n add i t i on to fresh and f i lmed specimens. Although t i s sue shrinkage and deformation i n c a r t i l a g i n o u s specimens are p o t e n t i a l problems i n preserved museum m a t e r i a l , the magnitude these w i l l be discussed i n l a t e r chapters . CHAPTER 2: MEASUREMENT OF TOOTH POSITION 2.1; INTRODUCTION The shark mouth possesses an abundance of teeth which are dynamically replaced (a polyphyodont c o n d i t i o n , Hi ldebrand, 1974). Shark teeth are comprised of apat i te (calcium phosphate) c r y s t a l s embedded i n a gelat inous pro te in matrix (Lisseau, 1977). These c r y s t a l s form f ibres which bend towards the c u t t i n g edge of the t ee th , thus supporting them. White sharks have the most complicated arrangement of these apat i te f ibres (Lisseau, 1977). Shark teeth are coated with enameloid, a r e s i l i e n t substance s i m i l a r to enamel, but d i s t ingui shed from the l a t t e r by i t s o r i g i n s from both the dermis and the epidermis (Lisseau, 1977) . Heemstra (1980) i d e n t i f i e s 3 tooth forms commonly found i n sharks: 1) broad, t r i a n g u l a r , b l a d e - l i k e t ee th , used for gouging chunks out of prey; 2) s lender , a w l - l i k e t ee th , used to hold small f i s h ; and 3) b lunt , pavement-like t ee th , used for crushing prey items such as crustaceans and mol luscs . The teeth are not attached to the jaws, but are mounted i n a co l lag inous tooth bed and are p u l l e d over the 1 jaw margin i n successive rows with the growth of the bed (a pleurodont c o n d i t i o n ) . Although the mechanism of tooth movement wi th in the tooth bed has long been debated (see Cawston, 1938, 1944), the teeth are c u r r e n t l y recognized to a r i s e as tooth buds wi th in the f l e sh of the anter ior buccal c a v i t y , emerging outward over the jaw. A tooth , once emerged, does not continue to grow, but successive teeth i n descendant rows w i l l be s l i g h t l y l arger as the animal grows (Moss, 1984). I f f t and Zinn (1948) used s i l v e r n i t r a t e s t a i n i n g t demonstrate that tooth replacement i n the smooth dogf ish occurs every 10 to 12 days. Wass (1973) measured tooth replacement of 18-38 days i n sandbar sharks and 22-32 days i n grey reef sharks. Moss (1967) c a l c u l a t e d a replacement rate of one funct iona l row per week i n lemon sharks, although Strasburg (1963) described the proport ion of teeth being replaced at any moment as h ighly v a r i a b l e , both i n t e r and i n t r a - s p e c i f i c a l l y . Genera l ly , replacement rates are estimated at e ig th to 30 days, with fas ter replacement occurr ing i n younger, more r a p i d l y growing animals (Moss, 1984, and pers . comm.). The intense pressure and abrasion associated with mandibulary forces necess i tates t h i s rap id replacement of t ee th . 19 Despite the nearly continuous movement of the teeth throughout the animal's l i f e t i m e , the func t iona l teeth assume only a l i m i t e d number of p o s i t i o n s . Larger-toothed species tend to have only one or two func t iona l tooth rows at any t ime, while smaller-toothed specimens may have three to f i v e concurrent funct iona l rows (Lisseau, 1977). The dental formulae of LeRiche (1905, 1910, 1926), and the modif icat ions to these by Applegate (1965) are attempts to describe the d e n t i t i o n of sharks. With these, terms such as a n t e r i o r , l a t e r a l , medial , and p o s t e r i o r are assigned to the teeth as a d e s c r i p t i o n of t h e i r p o s i t i o n along the jaw, with the numbers of each assigned to the species formulae. An accepted method to q u a n t i t a t i v e l y describe shark d e n t i t i o n has not prev ious ly been recognized ( L . J . V . Compagno, pers . comm.). With few exceptions, research studies on the o r a l b io logy of sharks have remained mutually exc lus ive i n examination of the jaws, the tee th , feeding dynamics, or r e s u l t s of shark at tack . A l l of these areas have s i m i l a r l y abounded i n q u a l i t a t i v e and subject ive evaluat ions of t h e i r var ious parameters. The in tent ion of t h i s por t ion of the study was to define a means of quant i fy ing the anatomical dimensions of the shark mouth. These dimensions w i l l then be compared both i n t e r - and i n t r a s p e c i f i c a l l y to t e s t for p o s s i l e d i f ferences among the specimens examined. An 20 attempt to r e l a t e the p o s i t i o n of the teeth with the a c t i v i t y of the jaws w i l l hopeful ly r e c t i f y the shortcomings of past s tudies , while at the same time u n i t i n g information from the various fact ions of o r a l b io logy . 2.2: MATERIALS AND METHODS  THE KINETIC DENTOMETER The dentometer, an invent ion of the author, i s shown i n Figures 2-1 to 2-4. I t cons i s t s of two mm scales jo ined perpendicu lar ly at a p ivot that serves as a point of reference for the seven measurements of the jaw apparatus used i n t h i s study. A protrac tor i s s i tuated at the p i v o t , and an a u x i l i a r y scale i s attached to one scale to measure the p o s i t i o n of each tooth . By a l i g n i n g scale A along the base of the lower teeth with the p ivot at the point of jaw a r t i c u l a t i o n , the (1) gape angle (GA) of the jaws i s provided by the p r o t r a c t o r when scale B i s a l igned along the base of the upper teeth (Figure 2-1) . Measuring gape angle i s important, e s p e c i a l l y i n fresh specimens, s ince t h i s w i l l r e l a t e to the degree of hyoid arch outswing, which i n turn e f fec ts gape width and maximum v e r t i c a l gape (Moss, 1977). 21 For the remaining measurements, scale A i s placed across the mouth and i s pressed p o s t e r i o r l y against the points of jaw a r t i c u l a t i o n with the p ivot centered i n the mouth (Figure 2 - 2 ) . Gape width (GW, 2) i s measured as the maximal distance on scale A between the ins ide edges of the jaw j o i n t s . Pos i t i on ing scale A so that the point of reference i s exact ly half-way across the gape, the dentometer i s clamped i n place to prevent the instrument from moving about. The clamps are made from standard Bul ldog^ or hardware clamps with extensions soldered onto them to increase t h e i r contact area with the specimen. I f necessary, a s t r i n g or wire can be attached to the ends of scale A and looped over the dorsa l f i n , act ing l i k e a b i t to hold the device i n p lace . Scale B i s attached to the p ivot 5 mm through the point of reference ( i . e . , h a l f the width of scale A) to compensate for the point of reference 's displacement a n t e r i o r l y from the jaw j o i n t by t h i s p o s i t i o n i n g . 22 FIGURE 2-1: The k i n e t i c dentometer, a device used to measure the anterior buccal c a v i t y . Two ruled scales (SA and SB) are joined at a pivot (PV). A protractor at t h i s point of reference (PR) provides measurement of each tooth's displacement from the midline (MLD) as scale B i s rotated to • • • • • R i n d i v i d u a l teeth (see Figure 2-3). Modified Bulldog 1^ clamps (C) anchor the device to the sides of the head. INSET: A u x i l i a r y attachment of the dentometer. The attachment i s placed on scale B and held at the tooth t i p by holding screw (HS). The attachment arm i s placed p a r a l l e l to the midline of the tooth to cal c u l a t e tooth c u t t i n g angle (degree of erec t i o n ) . See Figure 2-4. AA = a u x i l i a r y arm; AS = a u x i l i a r y scale, a r u l e r c a l i b r a t e d i n millimeters. 23 24 FIGURE 2-2: Dentometer measurement of gape angle (GA). Scales A and B (SA, SB) are a l igned with the base of the teeth i n each jaw, with the p ivot (POR = point of reference) at the point of jaw a r t i c u l a t i o n . NOTE: A s i m i l a r measurement i s used to der ive gape and tooth angles from fi lmed footage (see Chapter 3). 25 26 FIGURE 2-3: Dentometer measurement of the a n t e r i o r buccal c a v i t y . Scale B provides measure of palatoquadrate length (PQL) and Meckel's c a r t i l a g e length (MCL) i n d r i e d jaws, the distance from the jaw j o i n t to the anterior-most t ee th . Swivel led to each tooth , Scale B provides midl ine displacement (MLD) for each tooth , read as 90^ for maximum displacement on the r i g h t side of the head, and -90^ for maximum displacement on the l e f t side of the head, descr ib ing the shape of the jaw. FIGURE 2-4: The a u x i l i a r y arm, of known-length, i s at r i g h t angles to the a u x i l i a r y sca le , which i s d i sp laced along scale B when placed against the tooth (TML = tooth m i d l i n e ) . E f f e c t i v e c u t t i n g angle (ECA) i s measured r e l a t i v e to scale B, which extends caudal ly towards the jaw j o i n t . ECA = (AA length / S D ) l / c o s and i s read as 0 ° for maximum inward d e f l e c t i o n , to 180^ for maximum outward d e f l e c t i o n . 27 28 S c a l e B may t h e n b e s w i v e l l e d p e r p e n d i c u l a r l y t o s c a l e A t o g i v e (3) t h e u p p e r d e n t a l a r c l e n g t h , t a k e n a t t h e b a s e o f t h e a n t e r i o r - m o s t t o o t h o n t h e u p p e r j a w , a n d (4) t h e l o w e r d e n t a l a r c l e n g t h , t a k e n a t t h e b a s e o f t h e a n t e r i o r - m o s t t o o t h o f t h e l o w e r j a w . I f p r e p a r e d j a w s a r e b e i n g m e a s u r e d , t h e p a l a t o q u a d r a t e l e n g t h (PQL) a n d M e c k e l ' s c a r t i l a g e l e n g t h (MCL) c a n b e m e a s u r e d d i r e c t l y i n t h i s way ( F i g u r e 2-3) . T h e d i f f e r e n c e b e t w e e n jaw l e n g t h a n d d e n t a l a r c l e n g t h i s l i k e l y v a r i a b l e b e t w e e n s p e c i e s . S c a l e B c a n t h e n be s w i v e l l e d t o t h e t i p o f a n y o f t h e t e e t h i n t h e p r e d o m i n a n t f u n c t i o n a l s e r i e s . O t h e r s e r i e s c a n b e m e a s u r e d b y t h e d e v i c e , b u t t h e m o s t p r e d o m i n a n t t e e t h mus t b e r e m o v e d t o a l l o w p r o p e r p o s i t i o n i n g o f t h e d e v i c e . S c a l e B p r o v i d e s (5) t h e d i s t a n c e o f e a c h t o o t h f r o m t h e p o i n t o f r e f e r e n c e . T h e s e d i s t a n c e s f o r a l l t e e t h i n a p a r t i c u l a r s e r i e s may be u s e d t o d e s c r i b e t h e a r c o f t h e j a w m a r g i n . T h e p r o t r a c t o r now p r o v i d e s (6) t h e t o o t h ' s m i d l i n e d i s p l a c e m e n t ( M L D ) , o r d e v i a t i o n f r o m t h e f i s h ' s m i d l i n e , r e a d t o t h e n e a r e s t 1 ° . F o r a n a l y s i s , t h e m i d l i n e i s r e a d a s 0 ° , - 9 0 ° i s t a k e n a s p a r a l l e l t o s c a l e A a t m a x i m a l l e f t d i s p l a c e m e n t , a n d + 9 0 ° i s t a k e n a s p a r a l l e l t o s c a l e A a t m a x i m a l r i g h t d i s p l a c e m e n t . N e g a t i v e MLD v a l u e s d e n o t e t o o t h p o s i t i o n s on t h e l e f t s i d e o f t h e h e a d . The (7) e f f ec t i ve c u t t i n g angle (ECA) or degree of erec t ion of the tooth i s measured with the a u x i l i a r y attachment. Figure 2-4 shows the placement of the device against the tooth , and the attachment i s held i n place on scale B by a holdfast screw. The point of a r t i c u l a t i o n on the attachment i s a l igned with the t i p of the tooth so that the a u x i l i a r y arm (AA) describes a tangent to the c r o s s -s ec t iona l midl ine of the tooth (TML). The a u x i l i a r y scale (AS) i s d i sp laced along scale B with t h i s p o s i t i o n i n g (scale displacement = SD), and since the angle between the arm and the scale i s 90^, the ECA can then be der ived using the formula: ECA = (AA LENGTH/ S D ) 1 / c o s Here, 0 ° i s read for a tooth po in t ing maximally inwards, and 180^ i s read for a tooth po in t ing maximally outwards (an erect tooth would be taken as 90^). Using t h i s tr igonometric d e r i v a t i o n , the ECA can be r e l i a b l y ca l cu la ted to the nearest 0.1^ (see Figure 2-4) . A system of enumeration i s a l so suggested i n Figure 2-5 to describe the p o s i t i o n of each tooth i n a given func t iona l s e r i e s . The ser ies are numbered, i n order , from the anterior-most caudal ly to where the teeth disappear i n the mouth l i n i n g . This ser ies number precedes the tooth number, which i s assigned as i n Figure 2-5. Note tha t , though the designations of row and ser ies remain the same as Applegate's (1965) system, the designation for each tooth i s 30 FIGURE 2-5: System used to define p o s i t i o n of the func t iona l teeth during specimen measurement. Teeth on the l e f t s ide of the head are given odd numbers, increas ing from the mid l ine ; r i g h t s ide teeth are given even numbers. A denotes an upper jaw tooth , B denotes a lower jaw tooth . The number of the funct iona l row precedes the tooth number by a dash (see t e x t ) . Diagram from Moss, 1967, with permiss ion. 32 s i m p l i f i e d by referencing i t only to the jaw mid l ine , rather than c l a s s i f y i n g i t s p o s i t i o n as a n t e r i o r , l a t e r a l , medial , or p o s t e r i o r . The system proposed here does not attempt to compare specimens on the basis of the number of each tooth type present , but comparison of the specimen to such types of formulae gives information on the r e l a t i v e q u a l i t y of the specimen (and therefore the r e l i a b i l i t y of mean values c a l c u l a t e d from the number of teeth present ) . Tooth height (HT) and width (WD) were a lso taken with a r u l e r , using the method shown i n Figure 2-6. In add i t ion to the buccal c a v i t y dimensions, other data c o l l e c t e d for each specimen inc luded: sex, weight, t o t a l l ength , and date, l o c a t i o n , and means of c o l l e c t i o n (see Tables A - l and A - 2 ) . MEASUREMENT OF THE JAW APPARATUS Gape angle and MLD values for the study specimens were recorded to the nearest 1 degree, while ECA values were recorded to the nearest 0.1 degree. This contrasts with the method of Frazze t ta (1988), who groups angles measured from tooth form to the nearest 10-15 degrees, with r e l a t i v e + or - designations to f a c i l i t a t e eas ier comparison. Greater p r e c i s i o n i n tooth angle measurement was i n t e g r a l for t h i s study i n order to c l a r i f y poss ib le f i n e - s c a l e d i f ferences i n tooth p o s i t i o n between specimens. As a p i l o t study, 8 specimens from the c o l l e c t i o n of the Royal B . C . Museum, V i c t o r i a , B . C . , were examined i n 33 FIGURE 2-6: Measurement of tooth s i z e . Measurements were taken with a r u l e r as the maximum height (H) and width (W) of the enameloid cap of the tooth. Attempting to measure to the base of the tooth added s u b j e c t i v i t y to the method, as the r u l e r often had to be inserted i n t o the tooth bed. Teeth drawn for each specimen are upper jaw teeth of t y p i c a l size for the specimens examined. S C A L E : 3:2 November, 1988. A l l specimens were whole, and had been stored i n i sopropy l a lcohol fo l lowing f i x a t i o n i n 10% formalin so lu t ion (for durat ion of preservat ion , see Table A - l ) . The study included measurements from 5 salmon sharks, Lamna ditropis; 2 blue sharks, Prionace glauca; and 1 bluntnose s i x g i l l , Hexanchus griseus. The l a t t e r two species were described i n the i n i t i a l study i n order to tes t the performance of the dentometer on a v a r i e t y of jaw forms and d e n t i t i o n types on animals of markedly d i f f e r e n t feeding mechanisms. Many teeth on the two blue shark and one s i x g i l l specimens could not be measured d i r e c t l y , and so r e l i a b l e data on tooth p o s i t i o n could not be obtained from them. In d i s cus s ion , the animals of the p i l o t study w i l l be r e f e r r e d to as P l through P8 (see sect ion 2 .3 ) . Another 24 specimens, from the C a l i f o r n i a Academy of Sciences , San Franc i sco , C a l i f o r n i a , were measured i n June, 1989, and added to the extant data . These inc luded: 13 sets of d r i e d jaws from white sharks, 2 whole white sharks preserved i n i sopropy l s o l u t i o n , 4 sets of d r i e d b u l l shark jaws, 2 sets of d r i e d salmon shark jaws, 2 whole salmon sharks preserved i n i sopropy l s o l u t i o n , and 1 d r i e d jaw from Hexanchus griseus. One white shark jaw and the H. griseus jaw (specimens #3 and #1) were discarded from subsequent analysis of tooth p o s i t i o n , but are included i n the tables of Appendix A for the remaining data on t h e i r c o l l e c t i o n and buccal ca v i t y dimensions. The salmon shark was selected both as a representative Lamnid and to permit comparisons with the specimens of the p i l o t study. The b u l l shark was examined as a Carcharhinid with d e n t i t i o n and jaw robustness s i m i l a r to the white shark (L.J.V. Compagno, pers. comm.). The re s u l t s of these measurements are discussed i n section 2.3. For discussion, the C a l i f o r n i a Academy sharks w i l l be referred to as museum specimens 1 though 24. For a l l of the museum specimens, only the f i r s t (outermost) functional row was measured, as measurement of subsequent rows with the dentometer would require the removal of the f i r s t row and destruction of the specimen. STATISTICAL ANALYSIS OF DATA  ONE-WAY ANOVA For each specimen, the buccal ca v i t y was divided i n t o 6 sections; two l a t e r a l sections and one ce n t r a l section i n each jaw, designated r e l a t i v e to a d i v i d i n g l i n e 30^ on eithe r side of the midline (see Figure 2-7). Sections were then compared by c a l c u l a t i n g the mean MLD and ECA values for each and comparing sections 1) with in each jaw to t e s t for jaw symmetry, and 2) between jaws of the same specimen to tes t for jaw compliment. See Tables 2-1 and 2-2. One-way ANOVA comparisons were made at P=0.05, with the n u l l hypothesis that the mean angles between the sect ions were not s t a t i s t i c a l l y d i f f e r e n t ( i . e . , H Q : = 0) . In the event that the n u l l hypothesis was r e j e c t e d , a Tukey t e s t was performed on the data (see Table 2-3) . PERCENT OF PHASE As a second measure of the complimentation of tooth p o s i t i o n between jaws, the mean tooth s i ze and midl ine displacement were p lo t t ed for each species . A comparison of the phase d i f ference i n the tooth p o s i t i o n between the jaws was performed i n the fo l lowing manner: The jaw i s assumed to be the shape of a h a l f -e l l i p s e , whose hal f -per imeter i s taken as the length of the jaw margin. This distance equals: 2pi( ( . 5GW2+.5DAL2 ) 12 )1/'2 where GW i s the Gape Width, and DAL i s the Dental Arc Length (upper or lower jaw distance from the dentometer's point of reference to the base of the frontmost teeth i n the jaw). The area with both jaw margins are added to give the buccal c a v i t y areas of Table A - 2 . The jaw margin length i s then d iv ided by 1 8 0 ° to give the number of mi l l imeters along the margin represented 38 FIGURE 2-7: For s t a t i s t i c a l comparison (1-way ANOVA), the upper jaw i s d iv ided i n t o sections 1 (r ight s ide , l a t e r a l ) , 2 (middle), and 3 ( l e f t s ide , l a t e r a l ) ; the lower jaw i s d i v i d e d in to sect ions 4 (r ight s ide , l a t e r a l ) , 5 (middle), and 6 ( l e f t s ide , l a t e r a l ) . Sections 1 and 3, and 4 and 6 are compared for jaw symmetry; 1 and 4, 2 and 5, and 3 and 6 are compared for complimentation between jaws. L a t e r a l sect ions are compared to center sections for ECA (tooth c u t t i n g angle) only , s ince MLD (tooth p o s i t i o n r e l a t i v e to the midl ine) d i f f e r by d e f i n i t i o n . 39 1vs3 UPPER JAW 1vs4 2VJ 55 <- ECA „ . > LOWER JAW 4vs6 40 by one degree. The MLD value i s m u l t i p l i e d by t h i s mm/degree value to give the l i n e a r displacement from the midl ine (MLD'). Mean tooth height and width are drawn to scale at the appropriate MLD'. The t i p s of the teeth (1 for each sec t ion = 3 per jaw) are compared to those i n the opposing jaw. A 100% out of phase condi t ion i s ind ica ted by no dev ia t ion between the mean tooth t i p s of upper and lower jaws ( i . e . , the tooth t i p s are a l igned , preventing jaw c losure and thus are out of phase), while a 100% i n phase condi t ion r e s u l t s from a dev ia t ion between upper and lower tooth pos i t ions equal to ha l f the mean tooth width ( i . e . , maximal c u t t i n g edge). Percent out of phase i s the r a t i o of observed c u t t i n g edge to the maximum poss ib le c u t t i n g edge. Since very few s ing le specimens had enough measurable teeth to ca l cu la t e mean ECA and MLD values i n a l l 6 mouth sec t ions , a l l specimens for each species were averaged to derive the values of Table 2-4 and Figure 2 - 8 . CHI-SQUARE TEST Once the load required to remove teeth from various i n i t i a l pos i t ions had been derived (sect ion 2 . 3 ) , the MLD and ECA values for specimens 2-16 were compared to values from fresh white shark specimens by a Chi-square tes t (Zar, 1984) , where X^ = Z(o-e)^/e . Here, the expected value 41 (e) i s taken from the average value of Hi and H2, and the observed (o) values taken from specimens 2-16 (the museum white shark specimens). The assumption i n t h i s c a l c u l a t i o n i s that the observed p o s i t i o n of the teeth i n the fresh specimens i s representat ive of the average or 'expected' p o s i t i o n , against which the observed (museum) values are compared (see Table 2-5) . 2.3; RESULTS  PILOT STUDY The dentometer provided measures of the buccal c a v i t y dimensions to an accuracy of 2-2.5% on r e p l i c a t e measures of the 8 Royal BC Museum specimens. Problems i n p o s i t i o n i n g the device on the smaller specimens were evident , but r e c t i f i e d by increas ing the gape angle of the jaws. The tee th , p a r t i c u l a r l y of Prionace glauca and Hexanchus griseus are c h a r a c t e r i s t i c a l l y r e t r a c t i l e , and sink i n t o the l i n i n g of the mouth post mortem. This produced problems i n measuring tooth height and width d i r e c t l y , but i t was s t i l l poss ib le to make measurements a f t er p u l l i n g back the l a b i a l fo lds of sk in to expose the teeth and using the method of Figure 2-6. 42 For a l l specimens, midline displacements (mean MLD+- SD) ranged from 32.67° to 80.47° +- 10.51° f o r the l a t e r a l sections of both jaws (1,3,4, and 6, from Figure 2-7), and -2.78° to 4.89° +- 3.38° for the ce n t r a l sections (2 and 5). MLD values, by d e f i n i t i o n , are d i f f e r e n t between the c e n t r a l and l a t e r a l sections and were not compared. La t e r a l section MLDs did not d i f f e r s i g n i f i c a n t l y from one another. The l a t e r a l sections showed the greatest MLD -s i m i l a r i t y i n the upper jaw (sections 1 and 3), i n d i c a t i n g a tendency towards jaw symmetry rather than comparability between the upper and lower teeth (see Table 2-4). E f f e c t i v e cutting angles (mean ECA+-SD) ranged from 48.46° to 90.00° +- 11.17° o v e r a l l . Section 2 (the upper, center section) showed the lea s t v a r i a b i l i t y i n measured p o s i t i o n , ranging from 59.55° to 80.11° +- 14.06°. The s i g n i f i c a n c e of these r e s u l t s i s discussed i n section 2.4. MUSEUM SPECIMENS For measurement of the remaining specimens, which were much larger and included removed, dried jaws, the dentometer worked exceptionally we l l . Measured values were re p l i c a t e d and found to vary less than 2%. The larger and more prominent teeth of the white and b u l l sharks were p a r t i c u l a r l y easy to measure. 43 Results of MLD measurement are summarized i n Table 2-1, and given completely i n Table A - 3 . Middle , upper jaw (sect ion 2) teeth cons i s t ent ly demonstrated the lowest standard dev ia t ion among the groups examined i n Table 2-1, with the exception of the pre l iminary specimens, female specimens, and Carcharhinus leucas, which demonstrated the lowest v a r i a b i l i t y i n the teeth of the middle , lower jaw (sect ion 5) . The teeth of Sect ion 5 had the second lowest SD for the remaining groups, i n d i c a t i n g lowest o v e r a l l v a r i a b i l i t y i n p o s i t i o n among those teeth c loses t to the m i d l i n e . The male specimens of a l l species examined ( - . 3 ° + - ; 8 ° ; mean +- 1 SE) , and a l l white shark specimens examined ( 2 . 6 ° + - . 7 ° ) demonstrated the lowest v a r i a b i l i t y of a l l natura l groups for sect ion 2 tee th . Results of ECA measurement are given i n Tables 2-2 and A - 4 . The r i g h t side of the lower jaw (sect ion 6) demonstrated the lowest standard dev ia t ion for Lamna ditropis, Carcharodon carcharias, and the museum specimens (Pl through 24). A l l the Carcharhinus leucas and the remaining male specimens showed lowest v a r i a b i l i t y i n sect ion 2 (SD = 0 . 9 6 ° and 1 0 . 0 0 ° , r e s p e c t i v e l y ) . Sect ion 2 (middle, upper) teeth had the next lowest v a r i a t i o n for a l l specimens, Lamna ditropis, Carcharodon carcharias, whole, preserved, and fresh specimen groups (see Table 2-2) . 44 TABLE 2 -1: S t a t i s t i c a l summary of MLD values (angle deviant from the m i d l i n e ) . STD DEV = standard d e v i a t i o n , with the lowest value for each category i n bold type; n = number of specimens. Negative values denote pos i t i ons l e f t of the m i d l i n e . 45 TABLE 2-1: S t a t i s t i c a l summary of MLD values. CATEGORY MOUTH SECTION 1 2 3 4 5 6 ALL SPECIMENS AVG. MLD 39.8 1.4 -37.0 44.7 1.1 -37.8 STD DEV 15.54 2.90 15.81 12.53 3.30 20.47 n 23 26 24 25 24 22 PILOT STUDY AVG. MLD 46.5 -0.9 -54.3 57.3 2.3 -55.7 STD DEV 9.69 2.92 3.41 12.12 2.55 11.62 n 5 5 5 4 5 5 MUSEUM SPECIMENS AVG. MLD 34.9 1.8 -33.4 39.7 0.8 -29.7 STD DEV 12.88 2.76 12.55 6.70 3.52 15.01 n 18 21 19 21 19 17 MALE SPECIMENS AVG. MLD 36.0 -0.3 -36.8 42.7 2.1 -37.9 STD DEV 15.83 2.14 15.73 14.38 2.15 19.59 n 7 9 8 8 9 8 FEMALE SPECIMENS AVG. MLD 31.3 1.9 -25.8 24.9 1.3 -32.6 STD DEV 19.43 3.07 32.24 31.18 1.65 19.60 n 6 6 6 6 4 6 CARCHARODON CARCHARIAS AVG. MLD 37.0 1.5 -36.2 43.5 0.5 -34.3 STD DEV 19.09 2.56 14.45 12.79 3.93 21.96 n 9 12 11 12 10 9 LAMNA DITROPIS AVG. MLD 46.1 1.0 -51.2 51.3 1.0 -49.9 STD DEV 8.04 3.15 5.12 11.67 3.81 11.12 n 9 12 11 12 10 9 CARCHARHINUS LEUCAS AVG. MLD 37.5 1.6 -24.9 38.0 1.4 -26.3 STD DEV 2.78 3.18 14.55 2.09 1.44 15.24 n 4 4 3 4 4 3 WHOLE, PRESERVED AVG. MLD 43.8 0.7 -47.5 49.0 4.32 -47.5 STD DEV 8.76 3.44 8.24 12.18 4.60 12.03 n 9 10 10 9 10 10 DRIED JAWS AVG. MLD 37.1 1.7 -30.2 34.3 0.6 -34.0 STD DEV 6.40 2.62 18.73 19.37 3.97 5.38 n 14 16 16 16 16 16 FRESH SPECIMENS AVG. MLD 71.1 2.1 -55.0 72.2 1.2 -77.8 STD DEV 6.00 0.17 na 3.72 1.20 8.71 n 2 2 1 2 2 2 46 TABLE 2-2: S t a t i s t i c a l summary of ECA values (degree of tooth erect ion for a l l mouth sections and groups examined). STD DEV = standard dev ia t ion , with the lowest values for each group i n bold type; n = number of specimens. 132 TABLE A-3: Summary of midline displacement (MLD) values , n denotes the number of teeth i n each mouth sect ion . Negative values denote pos i t ions l e f t of the mid l ine . Specimens P l , P2, P8, 1, and 3 were omitted from analys is for i n s u f f i c i e n t measurements of tooth p o s i t i o n . 47 TABLE 2 -2 : S t a t i s t i c a l Summary o f ECA V a l u e s . CATEGORY MOUTH SECTION 1 2 3 4 5 6 ALL SPECIMENS AVG ECA 68.20 74.53 60.15 62.65 74.64 76.43 STD DEV 20.42 17.59 28.53 20.60 19.95 16.86 n 23 27 23 26 28 27 PILOT STUDY AVG ECA 78.58 69.88 84.14 72.35 61.86 84.30 STD DEV 9.19 8.30 9.03 6.51 7.67 2 .40 n 4 5 4 4 5 4 MUSEUM SPECIMENS AVG ECA 65.87 77.23 53.72 60.68 80.79 75.73 STD DEV 22.41 18.72 28.83 22.74 17.37 18.37 n 17 20 18 20 21 21 MALE SPECIMENS AVG ECA 64.82 71.48 57.56 55.44 70.83 76.38 STD DEV 18.94 10.00 28.69 20.70 11.41 13.86 n 7 9 8 8 9 8 FEMALE SPECIMENS AVG ECA 45.56 64.23 36.20 33.06 59.29 57.79 STD DEV 34.79 37.34 31.31 27.36 36.26 35.45 n 6 6 6 6 4 6 CARCHARODON CARCHARIAS AVG ECA 60.11 79.15 44.44 59.57 79.31 79.49 STD DEV 23.08 17.44 27.78 23.44 22.70 12.94 n 9 12 11 12 10 9 LAMNA DITROPIS AVG ECA 77.08 76.84 74.83 65.23 74.83 84.06 STD DEV 12.20 10.39 14.48 13.34 17.42 2.343 n 8 9 8 8 9 7 CARCHARHINUS LEUCAS AVG ECA 78.91 46.58 86.40 70.22 64.27 51.78 STD DEV 10.24 0.96 5.09 15.53 12.67 21.42 n 4 3 3 4 4 4 WHOLE, PRESERVED AVG ECA 71.48 77.04 65.39 54.42 73.41 83.97 STD DEV 16.70 9.83 24.60 18.35 13.92 3.77 n 9 10 10 9 10 10 DRIED JAWS AVG ECA 65.90 75.05 55.00 67.55 79.49 73.87 STD DEV 23.67 20.82 30.75 21.55 19.22 19.83 n 14 16 16 16 16 16 FRESH SPECIMENS AVG ECA 67.22 57.83 80.00 62.96 41.85 68.02 STD DEV 9.91 8.25 na 5.65 19.41 9.10 n 2 2 1 2 2 2 48 STATISTICAL ANALYSES Results of the 1-way Analysis of Variance (ANOVA) on a l l specimens demonstrated no s t a t i s t i c a l difference i n the MLD values f o r the l a t e r a l sections ( o v e r a l l mean MLD for section 1 = 40°, 3 = 40°, 4 = 41°, 6 = 42.5°). As stated previously, MLDs of l a t e r a l versus c e n t r a l sections were not compared (overall MLD for upper jaw, section 2 = 1.2°, lower jaw, section 5 = 1.3°). ANOVA on the ECA values for a l l specimens exceeded the c r i t i c a l F value, and so a Tukey t e s t was performed (Zar, 1984). Mean ECA values for sections 4, 1, 2, and 6 were not d i s t i n c t (with va lues of 62.63°, 68.29, 76.35°, and 77.10°, r e s p e c t i v e l y ) . Mean ECAs f o r sections 3 and 5 were d i s t i n c t , with means of 59.25°, and 77.15°, respectively (see Table 2-3). MEAN TOOTH POSITION The r e s u l t s of the percent of phase c a l c u l a t i o n s are summarized i n Table 2-4 and Figure 2-8. Mean tooth height and width are related to o v e r a l l gape width. The highest in-phase value was calculated for Lamna ditropis, with a value of 89.93. The lowest value was 51.16 for Carcharodon carcharias, i n d i c a t i n g a non-complimentary positioning of the teeth between upper and lower jaws. 49 TABLE 2-3: R e s u l t s o f one-way ANOVA c a l c u l a t i o n s f o r f u n c t i o n a l t o o t h p o s i t i o n (MLD, ang le from the m i d l i n e , and ECA, t o o t h c u t t i n g angle) f o r a l l specimens , from T a b l e s 2-1 and 2 -2 , A-3 and A-4. TABLE 2-3: Results of S t a t i s t i c a l Tests . One-way ANOVA of LATERAL SECTIONS (1,3,4,6) SECTION n MEAN VARIANCE SD 1 23 4 0 . 4 8 2 5 9 . 2 8 6 7 . 7 0 0 3 23 4 1 . 0 8 3 8 7 . 7 9 8 9 . 3 7 0 4 25 3 9 . 5 9 0 2 4 5 . 7 4 6 1 0 . 3 6 5 6 22 4 0 . 9 7 7 1 1 6 . 5 8 2 1 0 . 7 9 6 Source of V a r i a t i o n SS DF MS Tota l 1 1 6 1 4 . 5 0 92 Groups 3 3 . 1 2 3 1 1 . 0 5 7 Error 1 1 5 8 1 . 3 3 89 1 3 0 . 1 2 7 F - . 0 8 5 F 0 . 0 5 ( 1 ) , 3 , 8 9 ~ 2 , 7 2 Accept H Q (mean values are not d i f f erent at P = 0 (p > .25) One-way ANOVA of CENTER SECTION (2 and 5) MLD SECTION n MEAN VARIANCE SD 2 26 1.245 8.327 2.886 5 24 1.088 13.865 3.615 Source of V a r i a t i o n SS DF. MS Tota l 508.954 49 Group .304 1 .384 E r r o r 508.651 48 10.597 F = 0 . 0 2 9 F o . 0 5 ( 1 ) , 1 , 4 8 = 4 ' 0 6 Accept H Q (mean values are not d i f f erent at P = 0 (p > .25) 51 TABLE 2-3 (con't) One-way ANOVA of ECA VALUES SECTION n MEAN VARIANCE SD 1 21 68.292 469.818 21.675 2 25 76.350 322.514 17.959 3 22 59.252 871.989 29.528 4 24 62.625 476.943 21.839 5 26 77.147 323.005 17.972 6 25 77.102 386.344 17.503 Source of V a r i a t i o n SS DF MS Tota l 69311 .56 142 Groups Error 7467.88 61843.69 5 137 1493.575 451.414 F = 3.3087 r 0.05(1)5,137 = Reject H Q (mean values are not equal; .01 > p > .005) = 2.29 TUKEY TEST OF ECA VALUES C r i t i c a l q 0 . 0 5 , 6 / O o = 4 ' 0 9 6 SECTION 3 4 1 2 6 5 MEAN ECA 59.25 62.63 68.29 76.35 77.10 77.15 52 TABLE 2-4: Phase c a l c u l a t i o n s . Tooth measurement technique i s described i n the text . GW = gape width; PQL=palatoquadrate length; MCL = Meckel's c a r t i l a g e length (see t ex t ) ; MLD' = midline displacement, scaled to a proportion of the length of the jaw margin (see t e x t ) . Mean tooth p o s i t i o n , taken from th i s data, i s i l l u s t r a t e d i n Figure 2-8. 53 TABLE 2 -4 : Phase Ca lcu la t ions . MOUTH SECTION 1 Carcharodon carcharias (n= 2 14) 3 4 5 6 AVG TOOTH HT (mm) AVG TOOTH WD (mm) AVG MLD (degrees) 15.33 15.88 36.42 16. 15. 1. 39 60 45 13.86 13.79 -29 .51 12.77 11.47 34.14 15.07 11.33 2.14 11.67 11.29 -33 .91 AVG GAPE WIDTH(mm) AVG PQL (mm) AVG MCL (mm) 221 175 221 MLD' (mm) 63.01 2. 51 -51 .05 % 52.58 OF PHASE 3.30 < • 52.22 51.16 Lamna ditropis (n= 9) AVG TOOTH HT (mm) AVG TOOTH WD (mm) AVG MLD (degrees) 6.34 5.31 47.11 7. 5. - 0 . 95 23 86 7.05 5.21 - 5 4 . 3 6.45 5.81 57.34 8.59 6.66 2.30 6.73 5.61 -57 .01 AVG GW (mm) AVG PQL (mm) AVG MCL (mm) 83.11 81.56 69.89 MLD' (mm) 33.92 0. 62 39.10 38.42 1.54 -38 .20 % OF PHASE: 89.93 Carcharhinus leucas (n= 4) AVG TOOTH HT (mm) 11.49 13 .24 11 .53 8 .50 11 .40 10. 87 AVG TOOTH WD (mm) 14,74 13 .86 15 ,27 12 .30 12 .38 13. 72 AVG MLD (degrees) 37.45 1 .58 -33 .18 34 .72 1 .44 - 3 3 . 57 AVG GW (mm) 249 AVG PQL (mm) 163 AVG MCL (mm) 126 MLD' (mm) 67.04 2.83 -59 .4 56.94 2.36 % OF PHASE: 55.05 56.80 54 FIGURE 2-8: Mean p o s i t i o n of f u n c t i o n a l t e e t h . INSET: T h e o r e t i c a l arrangement of t e e t h [A] 0% i n phase (minimal c u t t i n g s u r f a c e ) , and [B] 100% i n phase (maximum c u t t i n g s u r f a c e ) . F i g u r e i s 3/4 l i f e s i z e . Teeth are drawn a c c o r d i n g t o average h e i g h t and width measurements. Displacement of t e e t h from the m i d l i n e are c a l c u l a t e d as MLD' (a c o n v e r s i o n of MLD t o account f o r the l e n g t h of the jaw margin). See Tab l e 2-3. [1] = Carcharodon carcharias (51.16% i n phase) [2] = Lamna ditropis (89.93% i n phase) [3] = Carcharhinus leucas (56.80% i n phase) A • 3 0 1 V MIDLINE - 3 0 ° SCALE* 3:4 1 V A. 56 TABLE 2-5: Chi-square analys is of Carcharodon carcharias fresh mater ia l (the 'expected' value from the average of 2 specimens, HI and H2) versus museum specimens (the 'observed' values from specimens 2-16), to tes t for differences i n tooth pos i t ion (see Tables A - l and A - 2 ) . MLD = midl ine displacement (angle deviant from the midl ine; ECA = e f fec t ive cut t ing angle (degree of tooth erec t ion) . 57 TABLE 2-5: X2 GOODNESS-OF-FIT VALUES OF CARCHARODON CARCHARIAS FRESH MATERIAL VERSUS MUSEUM SPECIMENS CHI-SQUARE FOR MLD VALUES SECTION 1 2 3 4 5 6 t o t a l H1/H2 (e) 71.1 2.1 55 72.2 1.2 77.8 SPECIMEN ( o - e ) 2 / e 2 20.63 4.88 5.32 17.55 1.2 21.46 71.04 4 18.43 .23 10.91 24.20 7.01 na 60.78 5 18.33 .11 10.13 22.94 3.33 na 54.84 6 16.45 7.62 10.04 18.35 .30 26.38 79.14 7 8.17 7.24 2.57 10.40 64.53 15.75 108.66 8 17.03 .93 4.26 4.10 158.70 21.71 206.73 9 na .58 8.80 22.61 6.07 na 38.07 10 10.33 5.83 9.79 13.83 4.80 na 44.58 11 19.88 .17 6.29 16.49 3.33 23.55 69.71 12 18.22 3.47 9.29 na 91.88 26.14 149.00 13 na .17 na 11.89 na 25.22 37.28 14 na 2.52 na 19.27 4.41 23.66 49.86 15 na .23 5.70 11.73 13.33 29.37 60.36 16 22.73 .48 na 19.37 2.70 26.96 72.24 u n c o r r . X* 170.21 33.91 83.09 212.73 361.60 240.13 58 TABLE 2-5 fcon't) CHI-SQUARE FOR ECA VALUES 1 2 3 H1/H2 (e) 68.2 57.8 80.0 SPECIMEN (o-e) 2 /2 2 43.05 17.94 57.44 4 13.95 78.13 5.64 5 11.67 5.33 .31 6 .38 15.25 15.31 7 14.54 13.74 54.43 8 4.13 6.71 10.08 9 na .14 3.89 10 na 2.08 na 11 4.87 6.71 61.43 12 3.00 14.52 70.31 13 na na na 14 na .48 42.25 15 na 23.94 na 16 2.99 17.94 0.00 SECTION 4 5 6 t o t a l 64.0 109.4 68.0 3.44 19.35 .30 141 .52 .01 3.51 20.02 121 .26 28.29 21.59 .30 67 .49 1.49 8.34 1.21 141 .98 23.09 .81 6.32 112 .93 15.92 7.19 5.58 149 .61 10.54 11.68 10.70 36 .95 na 13.34 4.24 19 .66 16.63 7.37 5.81 102 .82 15.02 6.20 1.43 110 .48 na na na 5 .11 .09 8.01 .24 51 .07 10.56 3.44 .52 38 .46 7.12 6.61 7.12 141 .78 uncorr. X z 98.55 202.91 321.10 132.18 117.44 69.0 59 CHI-SQUARE TESTS Tabl e 2-5 p r e s e n t s the r e s u l t s of the c h i - s q u a r e c a l c u l a t i o n s . A l l v a l u e s f o r a l l specimens exceeded the c r i t i c a l v a l u e s a t P=0.05 (DF = 13), i n d i c a t i n g a s i g n i f i c a n t d i f f e r e n c e i n t o o t h p o s i t i o n between the f r e s h and museum specimens. Lowest c h i - s q u a r e v a l u e s over a l l s e c t i o n s , were o b t a i n e d f o r specimens 6, 10, and 13. The s i g n i f i c a n c e o f t h i s i s d i s c u s s e d i n the next s e c t i o n . 2.4 DISCUSSION For t h i s study, the use of museum specimens was necessary f o r the d e s c r i p t i o n of f u n c t i o n a l t o o t h p o s i t i o n . The u s e f u l n e s s and r e l i a b i l i t y of these specimens should f i r s t be d i s c u s s e d . S i n c e t h e r e was no s i g n i f i c a n t d i f f e r e n c e between the t o o t h p o s i t i o n s i n the v a r i o u s museum p r e p a r a t i o n s , nor between these and the f r e s h m a t e r i a l s , the e f f e c t of shrink a g e on t o o t h p o s i t i o n i s l i k e l y s m a l l , and occurs soon a f t e r f i x i n g . T h i s i s suggested i n l i g h t of the o b s e r v a t i o n t h a t no obvious d i s c r e p a n c i e s i n t o o t h p o s i t i o n were e x h i b i t e d among the museum specimens, which ranged i n age from 2 t o 30 ye a r s s i n c e p r e p a r a t i o n . From the c h i - s q u a r e a n a l y s i s (Table 2-5), the f r e s h m a t e r i a l s d i f f e r e d l e a s t from museum specimens 6 and 11, both of which are 30 ye a r s o l d . The e f f e c t of shrinkage among the museum specimens 60 f a l l s w i t h i n the normal v a r i a t i o n i n t o o t h p o s i t i o n noted f o r a l l specimens, f r e s h and p r e s e r v e d . T h i s i s not t o say t h a t s i g n i f i c a n t deformation of c a r t i l a g i n o u s specimens does not occur, but t h a t the museum specimens s e l e c t e d f o r use i n t h i s study demonstrated no s i g n s of gross d e f o r m a t i o n . The f u n c t i o n a l t e e t h i n f r e s h m a t e r i a l are noted t o f l e x s l i g h t l y , p o s s i b l y t o reduce r e s i s t a n c e t o jaw c l o s u r e c r e a t e d by l o c a l i z e d b i n d i n g of i n d i v i d u a l t e e t h ( s e c t i o n 4.1). T h i s f l e x u r e was absent i n the d r i e d museum specimens, and was reduced c o n s i d e r a b l y i n the whole, p r e s e r v e d specimens. For c o n s i s t e n c y i n measurement, t o o t h c u t t i n g angles from the f r e s h specimens c o u l d e i t h e r have been taken a t the p o i n t of maximum inward o r maximum outward f l e x u r e . Maximum outward f l e x u r e was chosen f o r 1) a c l o s e r resemblance t o the degree of t o o t h e r e c t i o n observed i n the museum specimens, and 2) maximal ECA reduced the amount of s l a c k i n the a c t u a t o r arm when the t e e t h were m e c h a n i c a l l y t e s t e d (Chapter 4 ) . As a means of e v a l u a t i n g the use of f r e e jaws f o r measurement of the b u c c a l c a v i t y , the jaws were removed from specimen H2, measured, and the measurements compared t o those taken p r i o r t o removal. For t h i s Carcharodon carcharias specimen, the pa l a t o q u a d r a t e and Meckel's c a r t i l a g e l e n g t h s were seen t o be l e s s than 10 mm (5%) g r e a t e r than the v a l u e s measured p r i o r t o removal ( i . e . , the upper and lower d e n t a l a r c l e n g t h , see s e c t i o n 2.2). 61 S i m i l a r l y , the gape width was o n l y i n c r e a s e d by 15 mm (6%) f o l l o w i n g removal of the jaws. T h i s i n d i c a t e s t h a t m o r p h o l o g i c a l measurements taken from jaws alone are good approximates of such dimensions i n whole specimens, p r o v i d e d e x c e s s i v e shrinkage has not o c c u r r e d . In u s i n g the d e s c r i b e d method f o r measuring of MLD and ECA, i t should be noted t h a t the averages c a l c u l a t e d f o r each specimen are a f f e c t e d by the number of t e e t h measured i n the r e s p e c t i v e s e c t i o n s (or, a l t e r n a t e l y , by the number of m i s s i n g t e e t h ) . F o r t h i s reason, the number of t e e t h used t o d e r i v e each average i s i n c l u d e d i n T a b l e s 2-1 and 2-2, as w e l l as Ta b l e s A-3 and A-4. The e f f e c t of sm a l l numbers of t e e t h on the c a l c u l a t i o n of the averages i s most apparent i n the l a t e r a l s e c t i o n s o f the whole museum specimens. Here, the measurement of t e e t h w i t h MLDs exceeding 75° w i t h the dentometer was o f t e n impeded by s t i f f e n e d jaw j o i n t s . I t i s encouraging t o note, however, t h a t the f u n c t i o n a l t e e t h from the middle of the jaws ( s e c t i o n s 2 and 5) were e a s i l y measured, and t h e i r ECAs were not found t o be s i g n i f i c a n t l y d i f f e r e n t between c e n t r a l and l a t e r a l s e c t i o n s . The e f f e c t of l e s s e r numbers of t e e t h measured i n the l a t e r a l s e c t i o n s was t h e r e f o r e l i k e l y s m a l l , and probably o n l y c o n t r i b u t e d t o s h i f t i n g the p o s i t i o n of the l a t e r a l s e c t i o n t e e t h s l i g h t l y towards the m i d l i n e i n F i g u r e 2-8. 62 S t a t i s t i c a l a n a l y s es of the MLD and ECA da t a showed t h a t the t e e t h of any p a r t i c u l a r s e c t i o n are not s i g n i f i c a n t l y d i f f e r e n t than any o t h e r . The t e e t h of s e c t i o n 6 (the lower, r i g h t s i d e of the mouth), which showed the lowest s t a n d a r d d e v i a t i o n o v e r a l l , and s e c t i o n 2 (the middle o f the upper jaw), which showed the second lowest SD, are not unique i n t h e i r p o s i t i o n , but demonstrate l e s s v a r i a b i l i t y . T h i s suggests t h a t the f u n c t i o n a l t e e t h are not p o s i t i o n e d randomly on a l l s e c t i o n s of the jaw margin and supports the hy p o t h e s i s t h a t these t e e t h share some s i m i l a r i t i e s i n p o s i t i o n between the specimens examined. Determining the f i n e - s c a l e extent of these commonalities, however, would r e q u i r e a much l a r g e r data s e t . Average MLD was not r e l a t e d t o mean t o o t h s i z e . Teeth a l o n g the jaw margin were not d i s t r i b u t e d a c c o r d i n g t o the widths of t h e i r r e s p e c t i v e bases, as d i s c r e p a n c i e s between jaw margin l e n g t h and the average t o o t h s i z e w i l l a r i s e a c c o r d i n g t o the degree of o v e r l a p among the f u n c t i o n a l t e e t h . Both b u l l and white sharks had wider t e e t h i n the upper jaw and narrower t e e t h i n the lower jaw. T h i s arrangement l i k e l y a s s i s t s i n f e e d i n g , w i t h the lower jaw a c t i n g t o impale prey items, and the wider upper jaw t e e t h sawing i n t o the prey (Moss, 1984; T r i c a s and McCosker, 1984). The r e l a t i v e l y g r e a t e r area of attachment of the lo n g e r a x i s of the broad t o o t h base presumably makes the 63 t o o t h harder t o remove when p u l l e d i n a s i d e - t o - s i d e d i r e c t i o n . The low p e r c e n t of phase v a l u e s d e r i v e d f o r Carcharodon carcharias and Carcharhinus leucas (51.16 and 56.80, r e s p e c t i v e l y ) may a t f i r s t seem s u r p r i s i n g . I n t u i t i v e l y , t e e t h i n opposing jaws which are out of phase w i t h each o t h e r ( i . e . , having c l o s e l y r e l a t e d MLDs) w i l l impede the c l o s i n g of the jaws. One e x p l a n a t i o n f o r t h i s might be t h a t , w i t h an out-of-phase alignment of the t e e t h and the l o o s e a s s o c i a t i o n of the jaws w i t h the s k e l e t o n , the jaws are a b l e t o s h i f t l a t e r a l l y i n t o phase when r e s i s t a n c e i s encountered i n the a c t of b i t i n g . F u n c t i o n a l l y , t h i s f l e x i b i l i t y might be thought of as a l a t e r a l e q u i v a l e n t t o the a b i l i t y of the t e e t h t o f l e x s l i g h t l y i n the l i v i n g a n imal. Whether l o c a l i z e d r e s i s t a n c e t o jaw c l o s u r e i s encountered l a t e r a l l y or l o n g i t u d i n a l l y , f l e x u r e of the jaw apparatus may occur t o permit a more e f f e c t i v e c l o s i n g of the jaws, and thus a more e f f e c t i v e purchase on the prey item. Teeth more c l o s e l y i n phase w i l l shear a g a i n s t each o t h e r as the jaws are c l o s e d . The h i g h p e r c e n t of phase v a l u e c a l c u l a t e d f o r Lamna ditropis (89.93) i n d i c a t e s a g r e a t e r p o t e n t i a l f o r t h i s s h e a r i n g e f f e c t by r e d u c i n g the d i s t a n c e between t e e t h of s i m i l a r m i d l i n e displacement i n opposing jaws. T h i s may be viewed i n two ways: e i t h e r the g r e a t e r s h e a r i n g e f f e c t i n L. ditropis i s a compensation f o r n o n - s e r r a t e d t e e t h , o r the r e l a t i v e l y l a r g e r i n t e r d e n t a l spaces i n Carcharodon carcharias and Carcharhinus leucas are a compromise t o reduce the b i n d i n g of s e r r a t e d t e e t h i n prey items (see F r a z z e t t a , 1988). The t e e t h of male specimens i n a l l t h r e e s p e c i e s demonstrated l e s s v a r i a b i l i t y i n p o s i t i o n , as w e l l as a l a r g e r average h e i g h t and width. T h i s has been g e n e r a l l y observed, and may r e l a t e t o s o c i a l b e h a v i o r . S o c i a l l y , the male b i t e s onto the female d u r i n g c o p u l a t i o n i n o r d e r t o h o l d the p a i r t o g e t h e r . P o s s i b l e a i d s t o t h i s means of i n t e r c o u r s e are the l o n g e r t e e t h of males, and the t h i c k e r integument of females (Stevens, 1987). In summary, the r e s u l t s of t h i s p o r t i o n of the study have shown t h a t t h e r e i s l e s s v a r i a t i o n i n the p o s i t i o n of the f u n c t i o n a l shark t e e t h w i t h i n 30^ of the m i d l i n e . Tooth p o s i t i o n i s not unique i n any s e c t i o n of the mouth, but s l i g h t v a r i a t i o n s i n t o o t h s i z e and p o s i t i o n may be used t o p l o t t o o t h maps f o r the purpose of s p e c i e s i d e n t i f i c a t i o n . D e f i n i n g more d e f i n i t e p a t t e r n s or commonalities i n t o o t h p o s i t i o n would r e q u i r e the use of a l a r g e r d a t a s e t than used here, but p r o p e r l y p repared museum specimens have been shown u s e f u l i n t h i s r e g a r d . 65 CHAPTER 3: FEEDING DYNAMICS 3.1; INTRODUCTION The p r i n c i p a l muscles i n v o l v e d i n the a c t i o n of the jaws are d i v i d e d by Moss (1977) i n t o t h r e e groups: 1) the q u a d r a t o m a n d i b u l a r i s , which a c t s t o c l o s e the jaws; 2) the p r e o r b i t a l i s ; and 3) the l e v a t o r hyoidea and l e v a t o r p a l a t o q u a d r a t i i , which a c t t o p u l l the jaw complex forward ( F i g u r e 1-3). The l o o s e a s s o c i a t i o n of the upper jaw w i t h the b r a i n c a s e a f f o r d s the f e e d i n g apparatus much movement, both l a t e r a l l y and a n t e r o - v e n t r a l l y . With a p r o t r u s i v e jaw apparatus, s u c t i o n c u r r e n t s may be d i r e c t e d up from the benthos i n t o the mouth, food may be more p r e c i s e l y grasped, and the upper jaw may p e n e t r a t e more deeply i n f e e d i n g (Moss, 1977). P r o t r a c t i o n of the upper jaw i s commonly noted i n f e e d i n g among C a r c h a r h i n i d s and Lamnids and d e s c r i b e s a gouging f e e d i n g mechanism. Moss (1977) a l s o d e s c r i b e s s u c t i o n , c r u s h i n g , c u t t i n g , and f i l t e r f e e d i n g mechanisms. A n a t o m i c a l l y , jaw p r o t r u s i o n (or p r o t r a c t i o n ) i s p e r m i t t e d i n most C a r c h a r h i n o i d s and Lamnoids by l o n g h y o i d arches and elongated ethmopalatine ligaments a t t a c h e d t o r e l a t i v e l y s h o r t o r b i t a l p r o c e s s e s . The r e v e r s e c o n d i t i o n , (shortened h y o i d e a l arches and e l o n g a t e d o r b i t a l p r o c e s s e s ) , i s found i n s p e c i e s such as Squalus and i s b e t t e r s u i t e d f o r a c u t t i n g f e e d i n g method (Moss, 1977). In a d d i t i o n t o the l o o s e a s s o c i a t i o n w i t h the b r a i n c a s e , the jaw complex i s a l s o a t t a c h e d t o the h y o i d a r c h . In the a c t of b i t i n g , the widening of the h y o i d arches on e i t h e r s i d e of the i aws e f f e c t i v e l y moves the p o i n t of jaw a r t i c u l a t i o n down, forward, and outward. T h i s s p r e a d i n g a c t s t o widen the base of support a f f o r d e d the jaws, maximizes v e r t i c a l opening, and braces the jaws a g a i n s t the s i d e of the head (Moss, 1977). The upper jaw i s then r o t a t e d downward as the gape i s c l o s e d ( F i g u r e 3-1). The a b i l i t y t o p r o t r a c t the jaw i s o f t e n a s s i s t e d by a v i o l e n t s i d e - t o - s i d e shaking of the head, and sometimes a corkscrew t u r n i n g of the body i n C a r c h a r h i n i d s ( G i l b e r t , 1962; Moss, 1962). The upper t e e t h are p e r m i t t e d t o take an a c t i v e r o l e i n the f e e d i n g p r o c e s s — g o u g i n g deeply i n t o the prey item, which i s h e l d i n p l a c e by the lower t e e t h . (Moss, 1972b, 1977). 67 FIGURE 3-1: P r o t r a c t i o n of the upper jaw i n the white shark, d i v i d e d i n t o 4 p r i n c i p a l components. A = P o s i t i o n p r i o r t o f e e d i n g . B = Snout l i f t w i t h lower jaw drop. C = P a l a t o q u a d r a t e r o t a t i o n downward, upward and forward movement of lower jaw. D = Snout drop. SOURCE: T r i c a s and McCosker, 1984 69 T r i c a s and McCosker (1984) d e s c r i b e i n d e t a i l the sequence of events i n jaw p r o t r u s i o n of the g r e a t white. These events i n c l u d e : 1) snout l i f t and lower jaw drop, 2) p a l a t o q u a d r a t e p r o t r u s i o n , 3) lower jaw l i f t , and 4) snout drop (see F i g u r e 3-1). T r i c a s and McCosker suggest t h a t the h y o s t y l i c jaw suspension a l l o w s a more r a p i d c l o s i n g of the jaws ( s i n c e the weight of the e n t i r e head need not be p u l l e d along) and thus p r o v i d e s the p r e d a t o r w i t h a 'second chance' o p p o r t u n i t y t o c a p t u r e e s c a p i n g prey. The r o t a t i o n of the jaws may a l s o h e l p t o d i r e c t food items i n t o the mouth, r a t h e r than having them knocked away by a d i r e c t l y c l o s e d mandible ( F r a z z e t t a and Prange, 1987). T h e o r i e s of a p l u c k i n g or g r a s p i n g f u n c t i o n of p r o t r a c t i o n are a l s o extant (e.g., S p r i n g e r , 1961) and supported by o b s e r v a t i o n s of jaw p r o t r u s i o n d u r i n g f e e d i n g on p a s s i v e prey items ( T r i c a s , 1985) . T h i s author suggests another f u n c t i o n f o r jaw p r o t r u s i o n by analogy w i t h some t e l e o s t f i s h e s , where p r o t r u s i o n i s used t o accentuate s u c t i o n f e e d i n g by r a p i d l y r e d u c i n g the p r e d a t o r - p r e y d i s t a n c e (e.g., G o s l i n e , 1961; Alexander, 1967; Liem, 1978). E f f e c t i v e s u c t i o n s t r i k e ranges are d e s c r i b e d i n these s t u d i e s as b e i n g o n l y about 1/4 the l e n g t h of the p r e d a t o r ' s head. A d d i t i o n a l l y , the r a p i d i n c r e a s e i n the s i z e of the p r e d a t o r ' s head may a s s i s t the i n f l o w of water i n t o the mouth by d i f f e r e n t i a l p r e s s u r e . Although t h i s i s d o u b t f u l l y the p r i n c i p a l f u n c t i o n i n l a r g e 70 p e l a g i c sharks, jaw p r o t r u s i o n may w e l l a c t t o q u i c k l y reduce the d i s t a n c e of the t e e t h from the prey item by r a p i d l y extending the jaws. Although remarkably simple i n i t s anatomical d e s i g n , the dynamics of the shark f e e d i n g apparatus can become q u i t e i n v o l v e d . The c a r t i l a g i n o u s s k e l e t a l elements and chondrocranium r e a d i l y f l e x and d i s t o r t i n animation. The l o o s e attachment of the jaws a f f o r d s them a g r e a t d e a l of l a t e r a l and forward motion. The jaws may be d i s l o c a t e d , and t h i n f i l a m e n t o u s c o n n e c t i o n s a t the m i d l i n e of the jaw permit an i n t e r m i t t a n t r o t a t i o n of e i t h e r s i d e of the l o n g i t u d i n a l a x i s ( F r a z z e t t a and Prange, 1987). The weak anchorage of the t e e t h may permit sources of p o i n t b i n d i n g t o be broken o r t o f l e x out of the way, p e r m i t t i n g the r e s t of the jaw t o c l o s e (G. Naylor, p e r s . comm.) C l e a r l y , anatomical measurements taken from shark specimens alone h o l d l i t t l e r e l e v a n c e u n l e s s some account i s taken f o r the a c t i v i t y of the f e e d i n g apparatus i n the l i v i n g a nimal. For t h i s reason, high-speed v i d e o t a p e footage of f e e d i n g sharks has been i n c o r p o r a t e d i n t o t h i s study t o g a i n an a p p r e c i a t i o n f o r the dynamics of f e e d i n g events, and i t s e f f e c t s on the r e l a t i v e p o s i t i o n of the a n t e r i o r b u c c a l c a v i t y s t r u c t u r e s . 3.2: MATERIALS AND METHODS Infor m a t i o n on the f e e d i n g a c t i v i t y of Carcharodon carcharias was o b t a i n e d from v i d e o t a p e d footage p r o v i d e d by Ocean Images, Oakland, C a l i f o r n i a . The footage was taken at Dangerous Reef, South A u s t r a l i a , January 1-7, 1983, u s i n g a Photosonic A c t i o n M a s t e r 500 v i d e o camera (tape speed 200 frames s e c " ^ ) . Footage was o b t a i n e d both a t the s u r f a c e , from the deck of the t r a w l e r Nenad, and below the s u r f a c e from a shark cage. The cage frame was c o n s t r u c t e d from 1-inch s t e e l t u b i n g and covered w i t h 6-inch mesh wi r e f e n c i n g . Wherever p o s s i b l e , these known dimensions were used t o d e r i v e approximate d i s t a n c e s and displacements of the f i l m e d animals. The 3/4-inch v i d e o tapes were an a l y z e d a t the f a c i l i t i e s of Ocean Images i n June, 1989, u s i n g a Sony RM 440 automatic e d i t i n g c o n t r o l VCR (playback speed 2 frames s e c ~ l ) and a Panasonic CT-110MA h i g h - r e s o l u t i o n c o l o r monitor. Movements of the animals were taken from the monitors w i t h t r a c i n g paper ( T r i c a s and McCosker, 1984; F r a z z e t t a and Prange, 1987). Relevant anatomical ( t o o t h p o s i t i o n , jaw and c r a n i a l f l e x u r e ) and d i r e c t i o n a l movements 72 were noted on the paper t o permit measurement and i n t e r p r e t a t i o n of the f e e d i n g dynamics. The footage was d i v i d e d i n t o 4 sequences, w i t h each sequence c o r r e s p o n d i n g t o a p a r t i c u l a r gape o r i e n t a t i o n . Sequence 1 i n c l u d e d footage of white shark f e e d i n g i n a v e r t i c a l o r i e n t a t i o n a t the s u r f a c e ; Sequences 2 and 3 i n c l u d e d v a r i o u s o r i e n t a t i o n s of r i g h t and l e f t p r o f i l e , r e s p e c t i v e l y ; and Sequence 4 i n c l u d e d footage of f e e d i n g d i r e c t e d s t r a i g h t a t the camera. I t c o u l d not be determined from the footage how many d i f f e r e n t sharks were r e p r e s e n t e d , so each segment was assumed t o be of one animal w i t h a d i f f e r e n t animal r e p r e s e n t e d by each sequence. These sharks w i l l be r e f e r r e d t o as F l ( f o r Filmed, sequence 1) through F4. S e l e c t e d t r a c i n g s of the sequences are p r o v i d e d i n the F i g u r e s of Appendix B. In each sequence, the p o s i t i o n of the f u n c t i o n a l t e e t h were c h a r t e d as the jaws were c l o s e d i n the a c t of b i t i n g . In keeping w i t h the measures taken by the dentometer, changes i n t o o t h p o s i t i o n were measured as the degree of e r e c t i o n r e l a t i v e t o a r e f e r e n c e plane extending 73 from the t i p of the tooth to the point of jaw a r t i c u l a t i o n (see sect ion 2 .2) . For comparative a n a l y s i s , t h i s was l i m i t e d to the teeth of the upper, middle jaw. Cut t ing angle changes were measured for as many teeth as poss ib le during each b i t i n g event ( i . e . , jaw c losure from maximum to minimum observed gape for each f i lmed sequence, with ECAs measured at the extremit ies of t h i s range) . The values for a l l teeth of a given b i t e were then averaged to give the 13 b i t i n g events of Table 3-1. Averaging was necessary to accurate ly assess the movement of sec t ion 2 (the upper, middle jaw), s ince the palatoquadrate c a r t i l a g e s forming the jaw may rotate independently about the midl ine symphysis (see sect ion 3 .1 ) . I d e a l l y , these measures should have been taken from d i r e c t p r o f i l e views of the animal's b i t e for comparabi l i ty with dentometer measurements, but footage at these angles was scant and poor i n q u a l i t y . Footage of animals at angles other than perpendicular to the camera was in t erpre ted by taking r e l a t i v e measurements from stock footage of a set of Carcharodon carcharias jaws set on a r o t a t i n g turntable (see Figure B - l ) . Tooth angles could be approximated wi th in 5 degrees by t h i s method. The r e s u l t s of t h i s ana lys i s are summarized i n sect ion 3 .3 . 74 3.3: RESULTS The r e s u l t s of the f i l m a n a l y s i s are summarized i n Ta b l e 3-1 and F i g u r e s 3-2 and 3-3, and s e l e c t e d t r a c i n g s of the f i l m s are g i v e n i n Appendix B. The t e e t h of s e c t i o n 2 (middle, upper jaw) were noted t o i n c r e a s e t h e i r c u t t i n g angle w i t h r e s p e c t t o the p o i n t of jaw a r t i c u l a t i o n f o r gape c l o s u r e s of 0 t o 35 degrees. The average i n c r e a s e was 8.7° f o r t h i s i n t e r v a l t e e t h (n= 6 b i t e s ; 15 t e e t h c h a r t e d ) . For jaw c l o s u r e s of 35 t o 90 degrees, the c u t t i n g angle of the s e c t i o n 2 t e e t h decreased an average of 15.7° (n=6 b i t i n g events; 19 t e e t h charted) r e l a t i v e t o t h e i r p o s i t i o n w i t h the jaws maximally opened. T h i s i s a s t a t i s t i c a l l y s i g n i f i c a n t decrease (.0025 > p > .001, see Tabl e 3-2) i n s e c t i o n 2 t e e t h ECAs w i t h gape c l o s u r e (n = 13 b i t i n g e v e n t s ) . For gape angles of l e s s than 20°, the t e e t h became obscured by the l a b i a l f o l d s or the prey item, and measurement of t o o t h p o s i t i o n was not p o s s i b l e . The change i n ECA w i t h jaw movement i s i l l u s t r a t e d i n F i g u r e s 3-2 and 3-3. Although not d i r e c t l y measured, the t o o t h bed was not observed t o s h i f t o r r o l l over the jaw margin i n the a c t of b i t i n g . As a r e s u l t , the t e e t h remained i n p l a c e (with r e s p e c t t o t h e i r i n i t i a l p o s i t i o n on the jaw margin) f o r a l l b i t i n g events. 75 TABLE 3-1: Summary of Feeding A n a l y s i s . EVENT = b i t i n g event, d e f i n e d as one gape c l o s u r e from maximaum gape t o l a s t v i s i b l e p o i n t of c l o s u r e ; GA^ = gape angle at i n i t i a t i o n of b i t e ; GA^ = gape angle at end of b i t e ; n = number of middle, upper jaw ( s e c t i o n 2) t e e t h c h a r t e d and averaged t o d e r i v e c u t t i n g angle (ECA) v a l u e s ; ECA^ = mean c u t t i n g angle a t i n i t i a t i o n of b i t e ; ECAf = mean c u t t i n g angle a t end of b i t e ; G A ^ j , E C A ^ f _ ^ j = change i n gape / c u t t i n g angle d u r i n g event. RANGE (eca) = range of values averaged t o c a l c u l a t e mean t o o t h angle (ECA), t a b u l a t e d as lowest v a l u e , h i g h e s t v a l u e . Since any number of intermediary p o s i t i o n s are p o s s i b l e d u r i n g jaw p r o t r a c t i o n , o n l y i n i t i a l and f i n a l t o o t h angles were measured. A l l t o o t h angles were measured from p o i n t of jaw a r t i c u l a t i o n (see t e x t ) . 76 TABLE 3-1: Summary of Feeding A n a l y s i s VERTICAL GAPE (sequence 1) EVENT GA, GAg GA,*!) 1 2 80 100 50 45 -30 -55 n 2 3 EC ( 85 75 95 63 + 10 -12 RANGE (eca) 10, 10 - 5,-15 RIGHT PROFILE (sequence 2) EVENT GAi GA, # ( ^ G A ( g - i ) n EC. ( RANGE (eca) 3 90 60 -30 2 50 58 + 8 5, 4 95 25 -70 3 135 100 -35 -30, 5 60 35 -25 2 73 88 + 15 15, 6 85 60 -25 2 38 43 + 8 5, LEFT PROFILE (sequence 3) EVENT GAi GAg GA,*.;, # ( e) ( e) r B ) n EC ( 7 85 35 -50 4 83 65 -18 8 110 30 -80 3 90 77 -13 9 54 50 - 4 4 69 79 +10 RANGE (eca) -10,-30 -10,-20 5, 15 STRAIGHT ATTACK (sequence 4) EVENT GAi GAg GA (g_ ± ) „ EC. 10 40 25 -15 2 85 85 0 11 70 15 -55 3 72 63 - 8 12 70 35 -35 1 70 80 +10 13 110 20 -90 3 83 76 - 8 RANGE (eca) 0, 0 0,-15 -5,-10 77 TABLE 3-2: R e s u l t s of l i n e a r r e g r e s s i o n and Pearson's c o r r e l a t i o n a n a l y s i s of f e e d i n g footage, u s i n g a l l ( i . e . , unaveraged) f i l m a n a l y s i s data from Table 3-1. 78 TABLE 3-2: REGRESSION ANALYSIS OF FEEDING FILM RESULTS CHANGE IN ECA VERSUS CHANGE IN GAPE ANGLE SOURCE SS T o t a l Regression R e s i d u a l s F = 21.345 F 7847.06 3139.81 4707.25 r 2 = 0.4001 = 4.17 0.05(1)1,32 Reject H 0 (Beta = 0) EST DF 33 1 32 p « . 0 0 0 5 MS 3139.81 147.10 SE 95% Confidence U Beta .3686 Alpha 11.565 .0798 4.200 .2061 3.007 .532 20.123 PEARSON'S CORRELATION ANALYSIS OF FEEDING FILM RESULTS CHANGE IN ECA VERSUS CHANGE IN GAPE ANGLE Pearson's C o r r e l a t i o n C o e f f i c i e n t = .6326 SE of r = .1369 t - S t a t i s t i c =4.62 DF = 32 :0.05(2)32 .339 t0.05(2)32 - 2 ' 0 4 Reject H Q (p =0), p « .005 79 FIGURE 3-2: Change i n ECA ( t o o t h c u t t i n g angle) of upper, middle jaw t e e t h (mean f o r a l l t e e t h c h a r t e d i n each b i t i n g event) v e r s u s a b s o l u t e change i n Gape angle f o r f e e d i n g a n a l y s i s . V a r i a t i o n on end p o i n t s i n d i c a t e s observed range of f i n a l t o o t h angles (ECAs) b e f o r e a v e r a g i n g , (see T a b l e 3-1). [1] = V e r t i c a l gape (sequence 1) [2] = R i g h t p r o f i l e (sequence 2) [3] = L e f t p r o f i l e (sequence 3) [4] = S t r a i g h t a t t a c k (sequence 4) 80 140' 120 • 100-801 60 20 | | | I I I I I I I I 110 90 70 50 30 10 GAPE ANGLE (degrees) LEGEND: sequence # -* 1 change in ECA range of change in ECA (unaveraged) change in_$ gape 81 FIGURE 3-3: Change i n ECA ( t o o t h c u t t i n g angle) v e r s u s r e l a t i v e change i n Gape angle f o r f e e d i n g a n a l y s i s . Unaveraged ECA v a l u e s are p l o t t e d (see RANGE of Table 3-1). Time (sec) taken from T r i c a s and McCosker (1984) i s mean time of gape c l o s u r e (mandible e l e v a t i o n t o snout drop) f o r n = 11 c o n s e c u t i v e b i t i n g events. R e g r e s s i o n l i n e e q u a t i o n : Y = 11.565 + .369 X r 2 = 0.400 CHANGE IN GAPE ANGLE (degrees) 83 3.4 DISCUSSION During the f e e d i n g a n a l y s i s , the f u n c t i o n a l t e e t h d i d not v i s i b l y move as a r e s u l t of t o o t h bed movement on or over the jaw margin. T h i s was a n t i c i p a t e d , both from p r e v i o u s o b s e r v a t i o n s and the knowledge t h a t the t e e t h are anchored o n l y t o the t o o t h bed and not d i r e c t l y t o the jaw c a r t i l a g e s . The t o o t h bed p r o v i d e s the p r i n c i p a l means of t o o t h support and must h o l d the t e e t h i n p l a c e on the jaw i f any support of the t o o t h r o o t i s t o occur . The t e e t h were expected t o change t h e i r p o s i t i o n on the jaws o n l y over long term measurement (as by growth of the t o o t h bed), and t h i s was one r a t i o n a l e f o r measuring t o o t h angles r e l a t i v e t o a n o n - s k e l e t a l r e f e r e n c e plane extending back t o the jaw j o i n t s . The noted changes i n t o o t h ECA d u r i n g b i t i n g events i s t h e r e f o r e suggested t o be p r i n c i p a l l y the r e s u l t of jaw and c r a n i a l f l e x u r e . With the opening of the jaws and i n i t i a t i o n of jaw p r o t r a c t i o n , the hy o i d arches swing outward, b r i n g i n g the p o i n t of jaw a r t i c u l a t i o n down and forward. I f the jaw i s a c o n s i d e r e d t o be a r i g i d s t r u c t u r e , the ECA of the frontmost t e e t h ( s e c t i o n 2) w i l l not be changed, s i n c e the t o o t h angle r e l a t i v e t o the jaw j o i n t s w i l l not be d i f f e r e n t . I t i s f o r t h i s reason t h a t the dentometer method i s s a i d t o be s e n s i t i v e t o f l e x u r e of the jaws, and why t o o t h angle was not measured d i r e c t l y a t the p o i n t o f attachment t o the 84 t o o t h bed w i t h a standard p r o t r a c t o r . In the next stage of the b i t e , the p r e o r b i t a l i s muscles c o n t r a c t , drawing the jaw complex forward and p r o t r a c t i n g the p a l a t o q u a d r a t e . S i n c e the upper jaw i s p u l l e d d i r e c t l y forward, the ECAs of the middle, upper jaw ( s e c t i o n 2) should not change as they are o n l y d i s p l a c e d a n t e r i o r l y from the p o i n t of jaw a r t i c u l a t i o n . Once a g a i n , a r i g i d jaw i s assumed. Note t h a t , w i t h jaw p r o t r a c t i o n , the t e e t h of s e c t i o n 2 are moved outward r e l a t i v e l y more; s e c t i o n 5 t e e t h , i n the middle, lower jaw, are not d i s p l a c e d as f a r forward, and the t e e t h of the l a t e r a l s e c t i o n s are o n l y moved sideways r e l a t i v e t o t h e i r i n i t i a l p o s i t i o n . As the jaws are c l o s e d , the p a l a t o q u a d r a t e i s r o t a t e d downwards as the h y o i d arches swing back and r e t r a c t the r e a r of the f e e d i n g apparatus. Moss (1962) and T r i c a s and McCosker (1984) note t h i s jaw r o t a t i o n , but make no mention of the r e l a t i v e motion of the t e e t h . For gape angle c l o s u r e s of 35° or l e s s , an 8.7° (average) i n c r e a s e i n ECA was noted i n t h i s study. From Tabl e 3-1, these s m a l l e r gape c l o s u r e s corresponded t o s h o r t e r b i t i n g events (1,5,6,9,10, and 12). I t i s suggested t h a t the i n c r e a s e i n ECA w i t h i n i t i a l jaw c l o s u r e may be due t o a f l e x u r e of the p a l a t o q u a d r a t e i n a ' r e a c h i n g ' type of a c t i o n (see F i g u r e 3-4 C ) . During s m a l l e r or p a r t i a l gape c l o s u r e s , a simultaneous c o n t r a c t i o n of the quadratomandibularis and the p r e o r b i t a l i s muscles may bend 85 the upper jaw upwards, and a s s i s t i n the g r a s p i n g o r p l u c k i n g o f s m a l l e r prey items (see T r i c a s , 1985), o r move the t e e t h around l a r g e prey items. With the jaws opened and the p a l a t o q u a d r a t e p r o t r a c t e d , the s k u l l would not impede such a f l e x u r e of the upper jaw. As the gape i s c l o s e d through a l a r g e r a r c ( i . e . , i n b i t i n g events w i t h a g r e a t e r net change i n gape a n g l e ) , a bending f o r c e i s a p p l i e d t o the moment arms of the l e v e r system o f the jaws by the adductor muscles. Given the f l e x i b l e nature of the jaw c a r t i l a g e s , the jaws may f l e x s l i g h t l y inward, towards the p o i n t of jaw a r t i c u l a t i o n (see F i g u r e 3-4 D). T h i s f l e x u r e decreases the t o o t h ECA (to the p o i n t where the upper jaw i s r e s t r a i n e d by the ethmopalatine ligaments) r e l a t i v e t o the jaw j o i n t s as the p a l a t o q u a d r a t e i s r e t r a c t e d and the jaws are c l o s e d . With gape c l o s u r e , the upper jaw t e e t h are r o t a t e d downwards and inwards, r e s u l t i n g i n a f i n a l ECA 15.7 degrees l e s s than t h e i r p o s i t i o n a t the maximum gape of the b i t i n g event. T h i s i s not t o say t h a t the p o s i t i o n of the t e e t h i s a b s o l u t e l y d i f f e r e n t from t h e i r p o s i t i o n p r i o r t o b i t e i n i t i a t i o n , but r a t h e r t h a t i n the a c t of b i t i n g , the t e e t h of the middle jaw are r o t a t e d f i r s t outwards, then p u l l e d s l i g h t l y inwards w i t h jaw f l e x u r e (see F i g u r e s 3-2, 3-3 and 86 FIGURE 3-4: Change i n tooth c u t t i n g angle with jaw f l exure . A Resting p o s i t i o n : h = hyoid attachment to jaws. pq = palatoquadrate; t = tooth; ga = gape angle; DRP = dentometer reference plane. B With hyoid movement of jaw symphysis up (gape closure) or down (gape opening) ECA (tooth c u t t i n g angle) does not change i f jaws remain r i g i d . C Antagonis t ic ac t ion of p r e o r b i t a l i s (preorb) and quadratomandibularis (qm) may create upward f lexure of jaw for short b i t i n g events, e l = ethmopalatine ligaments ( s l ack ) . ECA (tooth c u t t i n g angle) increased. D Jaw r e t r a c t i o n (hyoid swinging in) and quadratomandibularis contract ion combine to create jaw f lexure for long b i t i n g events, reducing tooth c u t t i n g angle (ECA) u n t i l r e s t ra ined by taut ligaments ( e l ) . 87 88 Although the use of image t r a c i n g was s u i t a b l e f o r t h i s study, two drawbacks t o t h i s use of the f e e d i n g f i l m s are noted: F i r s t l y , the degree of accuracy i s l i m i t e d i n the use of f i l m e d images. Even w i t h the use of h i g h - r e s o l u t i o n monitors, the r e l a t i v e p o s i t i o n of the t e e t h c o u l d o n l y be es t i m a t e d w i t h i n 5 degrees. T h i s l e v e l of accuracy may not be s u f f i c i e n t f o r some a n a l y s e s , and c e r t a i n l y i s not as d e s i r a b l e as d i r e c t measurement of the b u c c a l c a v i t y . Secondly, although the method of a n a l y s i s used on the f i l m s was chosen t o make use of the same plane of r e f e r e n c e employed by the dentometer (see s e c t i o n 2.2), the sideways component of the f e e d i n g event was not accounted f o r . In the a c t of jaw p r o t r a c t i o n , t h i s i s o n l y a s l i g h t movement, as the pa l a t o q u a d r a t e i s extended d i r e c t l y forward. In the a n a l y s i s of s t r e s s e s imposed on the t e e t h , however, e x c l u s i o n of l a t e r a l f o r c e s i s u n r e a l i s t i c . T w i s t i n g o r corkscrewing the body i s o f t e n employed by f e e d i n g sharks t o apply t o r s i o n t o the f e e d i n g apparatus and t w i s t chunks out of the prey item ( G i l b e r t , 1962; Moss, 1962). Indeed, t h i s r e s i s t a n c e t o l a t e r a l s t r a i n i s one su g g e s t i o n f o r the broad base of the upper jaw t e e t h of Carcharodon carcharias and s i m i l a r s p e c i e s . Although important i n deter m i n i n g a l l s t r e s s e s on the t e e t h , the 89 measurement of f e e d i n g events i n p r o f i l e o n l y i s s u f f i c i e n t t o t e s t the second premise of t h i s study: whether the t e e t h change p o s i t i o n d u r i n g f e e d i n g . The r e s u l t s i n d i c a t e t h a t a change i n p o s i t i o n does occur, however whether o r not t h i s c o n t r i b u t e s t o the f u n c t i o n a l i t y of the t e e t h by making them harder t o remove remains t o be determined. 90 CHAPTER 4: STRUCTURAL INTEGRITY  4.1; INTRODUCTION " I t i s ax i o m a t i c i n mechanical e n g i n e e r i n g t h a t a w e l l designed machine w i l l a u t o m a t i c a l l y r e v e a l i t s f u n c t i o n through the a n a l y s i s of i t s s t r u c t u r e . " (Parke, 1975). These words denote the importance of r e l a t i n g the observed morphology of the f e e d i n g apparatus t o some i n d i c a t o r of r e l a t i v e performance i n t h i s b i o l o g i c a l machine. The jaws of the shark are f i r m l y b u t t r e s s e d by the musculature, which a l s o reduces the s t r e s s imposed on the j o i n t s ( L i s s e a u , 1977). The jaws are supported f u r t h e r s t i l l d u r i n g b i t i n g as the hy o i d arches brace themselves on the s i d e s of the head. The a p a t i t e / p r o t e i n composite s t r u c t u r e of the t e e t h compares t o the s t r o n g e s t of man-made m a t e r i a l s ( L i s s e a u , 1977). Given t h i s , the weakest l i n k of t h i s system may be the p o i n t of attachment of the t e e t h t o the c o l l a g e n o u s t o o t h bed, and the l e v e l a t which t o e v a l u a t e the e f f e c t i v e n e s s of the f e e d i n g apparatus. The t o o t h bed not o n l y anchors the t e e t h , but i s r e s p o n s i b l e f o r the r o t a t i o n of the t e e t h t o a f u n c t i o n a l p o s t u r e . In f r e s h specimens, the t e e t h may be f l e x e d back and f o r t h a t t h i s p o i n t of attachment, w i t h the t o o t h t i p d e s c r i b i n g an a r c e q u i v a l e n t t o the h e i g h t of the t o o t h (Powlik, unpub. o b s . ) . An i n v e s t i g a t i o n of the r e l a t i v e f o r c e s r e q u i r e d t o remove 91 t e e t h from the t o o t h bed may h e l p e x p l a i n the observed f u n c t i o n a l t o o t h arrangements. 4.2; MATERIALS AND METHODS T e s t i n g of the s t r u c t u r a l i n t e g r i t y of v a r i o u s t o o t h p o s i t i o n s was performed on a T e n s i l e T e s t i n g Apparatus, ( I n s t r o n Model 1122) ( F i g u r e 4-1). F r e s h white shark specimens were p r o v i d e d by the N a t a l Sharks Board, Umhlanga Rocks, RSA. Captured animals were d e c a p i t a t e d past the f i r s t g i l l a r c h (to m a i n t a i n the i n t e g r i t y of the f e e d i n g apparatus) and promptly f r o z e n . The heads were kept a t -20^C, then thawed f o r 36 hours p r i o r t o t e s t i n g . One white shark head was r e f r i g e r a t e d a f u r t h e r 36 hours a t 4^C d u r i n g e x p e r i m e n t a t i o n t o await instrument r e p a i r . Each head weighed approximately 30 kg, w i t h Head 1 (specimen Hi) and H2 having gape widths of 250 mm and 238 mm r e s p e c t i v e l y , as measured by the dentometer. The remainder of the b u c c a l c a v i t y dimensions are g i v e n i n T a b l e s A - l and A-2. The s i z e of the heads used was l i m i t e d by the s i z e of the t e s t i n g apparatus stage, which measured 400 mm a c r o s s . The l a b i a l f o l d s were c u t from the thawed heads t o expose the t e e t h , w i t h c a r e taken not t o damage the t o o t h bed beneath. The heads were then p l a c e d i n a c o l l e c t i n g 92 FIGURE 4-1: Set up of t e n s i l e t e s t i n g apparatus, showing attachment to the specimen. CB = c o l l e c t i n g bucket; RB = r e s t r a i n i n g b i t to hold specimen i n p lace; W = weights to add a d d i t i o n a l load . INSET: P r o f i l e view of tooth attachment to the Instron T= tooth; TB = tooth bed; A = a r t i c u l a t o r arm; S = 4-40 s ta in l e s s s t ee l screw; N = nut; WA = washer. During experimentation, each tooth attached to the Instron was p u l l e d upwards ( i . e . , d i r e c t l y outward from the mouth) to simulate a forward d i s lodg ing force experienced during feeding. 9 3 94 bucket w i t h a c r o s s b a r r e s t r a i n i n g the movement of the head * a t the p o i n t of jaw a r t i c u l a t i o n . The c r o s s b a r p r o v i d e d a f i r m r e s t r a i n t , w h i l e s t i l l p e r m i t t i n g r e p o s i t i o n i n g of the head t o d i f f e r e n t o r i e n t a t i o n s by i n s e r t i n g wood shims under the c o l l e c t i n g bucket. Because the f o r c e r e q u i r e d t o p u l l the t e e t h o f t e n exceeded the combined weight of the head and bucket, the ends of the c r o s s b a r were loaded w i t h 50kg l e a d weights t o prevent movement of the head (see F i g u r e 4-1). F u n c t i o n a l t e e t h were removed by a p p l y i n g f o r c e d i r e c t l y outward from the b u c c a l c a v i t y . Although the p r i n c i p a l l o a d i n g of the t e e t h would be compressional ( d i r e c t l y downward from the t i p ) , gouging f e e d e r s such as the white shark a l s o s t r e s s the t e e t h outward i n removing chunks of f l e s h from the prey item. P u l l i n g the t e e t h outward from the mouth intended t o s i m u l a t e the f o r c e a p p l i e d t o the t e e t h by an e s c a p i n g prey item, or the forward d i s l o d g i n g f o r c e imposed on the t o o t h f o l l o w i n g b i n d i n g i n the f l e s h of a prey item. U n l i k e the prepared museum specimens, the t e e t h of the f r e s h specimens were observed t o f l e x s l i g h t l y a t the p o i n t of attachment t o the t o o t h bed, w i t h the t i p of the t o o t h d e s c r i b i n g an a r c l e n g t h approximately equal t o the h e i g h t of the t o o t h ( i . e . , the t i p of a 20 mm t o o t h c o u l d be moved back and f o r t h a d i s t a n c e of 20 mm). For c o n s i s t e n c y , the ECA v a l u e s of the t e e t h were taken a t the p o i n t of maximum outward f l e x u r e , and the f o r c e a p p l i e d from t h i s 95 p o i n t . (N.B.: ECA v a l u e s r e c o r d e d f o r these specimens are those of maximal outward f l e x u r e ) . Each t o o t h was a t t a c h e d t o the l o a d c e l l by d r i l l i n g a 3/16" h o l e through the t o o t h j u s t above the p o i n t of attachment t o the t o o t h bed. Then a 4-40 s t a i n l e s s s t e e l screw was f a s t e n e d t o the t o o t h by washers and nuts on e i t h e r s i d e of the t o o t h . F i n a l l y , the screw was threaded i n t o an aluminum a c t u a t o r arm t h a t was then a t t a c h e d t o a 500 kg l o a d c e l l on the t e n s i l e t e s t i n g apparatus (see i n s e t of F i g u r e 4-1). The apparatus a p p l i e d an upward f o r c e on the t o o t h b e i n g t e s t e d by r a i s i n g the crosshead a t 50 mm min~^ w i t h a f u l l s c a l e l o a d s e t a t 100kg. Tooth removal was d e f i n e d as the p o i n t where the t o o t h p u l l e d f r e e from the t o o t h bed, or where the t o o t h broke, r e l e a s i n g the a r t i c u l a t o r arm. R e s u l t s of the experiments are summarized i n Table 4-1. The a p p l i e d l o a d r e q u i r e d t o remove or f r a c t u r e each t o o t h was p l o t t e d a g a i n s t the i n i t i a l c u t t i n g angle (ECA) of the t o o t h t o d e r i v e F i g u r e s 4-2 and 4-3. Other r e s u l t s are d i s c u s s e d i n s e c t i o n 4.3. 4.3: RESULTS A t o t a l of 23 t e e t h were removed from the two white shark heads (Hi = 10 t e e t h ; H2 = 13). Of these, 12 r e s u l t e d i n f a i l u r e of the t o o t h , w h i l e the remaining 11 96 TABLE 4-1: R e s u l t s of a p p l i e d l o a d on the t e e t h of Carcharodon carcharias. R e s u l t s are c l a s s i f i e d a c c o r d i n g t o Tooth Breakage o r Tooth Removal, a c c o r d i n g t o the p o i n t of f a i l u r e ( t o o t h o r t o o t h bed, r e s p e c t i v e l y ) as the t o o t h was p u l l e d d i r e c t l y outward from the mouth. TABLE 4-1: Summary of T e n s i l e T e s t i n g Experiments HEAD #1 TOOTH # MLD ECA LOAD COMMENT (deg) (deg) (kg) 1-2A 3 35 46 Tooth broke 1-4A 20 30 55 Tooth broke 1-6A 31 68 30 Tooth broke 1-7A 34 90 15 Tooth removal 1-8A 49 72 40 Tooth broke 1-1B 5 110 12 Tooth removal 1-2B 10 138 30 Tooth removal 1-4B 30 100 46 Tooth removal 1-7B 72 90 13 Tooth removal 1-9B 85 102 48 Tooth removal HEAD 1 TOOTH # MLD ECA LOAD COMMENT (deg) (deg) (kg) 1-1A 45 70 65 Tooth broke 1-2A 45 60 58 Tooth broke 1-3A 52 81 58 Tooth removal 1-4A 58 59 70 Tooth removal 1-8A 70 70 50 Tooth removal 1-10A 83 81 50 Tooth broke 1-12A 87 90 56 Tooth removal 1-1B 8 170 50 Tooth removal 1-2B 10 150 22 Tooth broke 1-3B 52 175 40 Tooth broke 2-2B 10 64 51 Tooth broke 1-4B 48 131 50 Tooth broke 2-4B 48 45 53 Tooth broke 98 TABLE 4-2: R e s u l t s o f l i n e a r r e g r e s s i o n a n a l y s i s o f removal l o a d v e r s u s t o o t h p o s i t i o n (MLD) and c u t t i n g ang le ( E C A ) . C a l c u l a t i o n from v a l u e s o b t a i n e d f o r t o o t h removal o n l y (Table 4 - 1 ) . 99 TABLE 4-2: REGRESSION ANALYSIS OF INSTRON RESULTS APPLIED LOAD VERSUS MLD OF REMOVED TEETH SOURCE SS T o t a l Regression R e s i d u a l s F = 1.4623 F0.05(1)1,9 4012.182 560.778 3451.404 5.12 0.1398 Accept H Q (Beta = 0) p » .25 DF 10 1 9 EST SE 95% Confidence MS 560.778 383.489 U Beta .2436 Alpha 29.413 .2014 11.064 -.2122 4.377 .6993 54.447 APPLIED LOAD VERSUS ECA OF REMOVED TEETH SOURCE SS T o t a l Regression R e s i d u a l s F = 0.5191 F0.05(1)1,9 4012.182 218.778 3793.407 r 2 = 0.0545 - 5.12 Accept HQ (Beta EST DF 10 1 9 0) p » .25 SE 95% Confidence Beta -.1503 Alpha 55.753 .2086 21.76 MS 218.778 421.490 -.622 6.526 U .3217 104.98 100 FIGURE 4-2: Force of removal versus tooth p o s i t i o n (MLD) f o r fresh frozen Carcharodon carcharias material. Crosses denote points of tooth breakage; dots denote points of tooth removal. Regression l i n e ( s o l i d l i n e ) and 95% confidence i n t e r v a l s (dotted l i n e s ) drawn for points of tooth removal only (see Table 4-1). Regression l i n e equation: Y «= 29.413 + .2436X r 2 = 0.140 101 102 FIGURE 4-3: C u t t i n g angle (ECA) ve r s u s f o r c e o f removal f o r f r e s h f r o z e n Carcharodon carcharias m a t e r i a l . Crosses denote p o i n t s of t o o t h breakage; dots denote p o i n t s of t o o t h removal. R e g r e s s i o n l i n e ( s o l i d l i n e ) and 95% c o n f i d e n c e i n t e r v a l s ( d o t t e d l i n e s ) drawn f o r data on t o o t h removal o n l y (see Tab l e 4-1). Reg r e s s i o n l i n e e q u a t i o n : Y = 55.753 - .1503X r 2 = 0.055 t r i a l s re su l t ed i n successful removal of the i n t a c t tooth from the tooth bed. Referr ing to Table 4-1 and Figure 4-2, there i s no s i g n i f i c a n t increase i n the force required to remove teeth from any p a r t i c u l a r mouth sect ion (r = .140, see Table 3-10). S i m i l a r l y , Figure 2-3 shows no s i g n i f i c a n t increase i n the required load needed to remove teeth of lower ECA values ( r 2 = 0.055). The highest load required for tooth removal was 70 kg (for tooth 1-4A, H2). The lowest required load was 12 kg ( for tooth 1-1B, H i ) . On averaging between Hi and H2 for a l l t ee th , there appears to be no s i g n i f i c a n t r e l a t i o n s h i p between force of removal and p o s i t i o n along the jaw margin. The consequences of t h i s are discussed i n the next s ec t ion . 4.4: DISCUSSION From the t e n s i l e t e s t i n g r e s u l t s , there i s no apparent increase i n the required force of removal with increased distance from the mid l ine , or enhanced c u t t i n g angle . Assuming that there i s l i t t l e d i f f erence i n the s tructure of the tee th , or the co l lagen f i b e r s i n the tooth bed, a tooth should be supported by s i m i l a r mater ia l regardless of i t s p o s i t i o n on the jaw margin. The res i s tance to i t s removal w i l l depend on the proport ion of the tooth a c t u a l l y embedded i n the tooth bed. 105 F i g u r e 4-3 might b e t t e r e x p l a i n c o n d i t i o n s a s s i s t i n g the l a t e r a l components of f e e d i n g a c t i v i t y . Once the jaws have f u l l y b i t t e n i n t o a prey item, c l o s i n g the gape as much as p o s s i b l e , the l a t e r a l t e e t h are s t r e s s e d i n a b a c k - a n d - f o r t h ( i n and out) d i r e c t i o n when the head i s shaken from s i d e t o s i d e . The t e e t h of the c e n t r a l s e c t i o n are then s t r e s s e d l a t e r a l l y , a g a i n s t the r e l a t i v e l y s t r o n g e r support of the lo n g a x i s of the t o o t h ' s base. The r e s u l t s d i d not r e v e a l an i n c r e a s e i n f o r c e of removal f o r t e e t h l o c a t e d f u r t h e r from the m i d l i n e . The t e e t h a t the g r e a t e s t s MLDs were not t e s t e d , s i n c e they were q u i t e s m a l l (2-3 mm t o o t h h e i g h t ) , and c o u l d not be p r o p e r l y a t t a c h e d t o the apparatus. I t i s suggested, however, t h a t the s m a l l e r mean s i z e of the l a t e r a l t e e t h may a s s i s t t h e i r r e t e n t i o n by having reduced l e v e r a g e on them due t o the l e n g t h o f the t o o t h , and thus reduce t h e i r s u s c e p t i b i l i t y t o f r a c t u r e . In a d d i t i o n t o a l l o w i n g b e t t e r c l o s i n g of the jaws, s m a l l e r t e e t h a t the h i g h e s t MLD p o s i t i o n s have a g r e a t e r p r o p o r t i o n of t h e i r s u r f a c e embedded i n the t o o t h bed. The l a t e r a l t e e t h are then p o s s i b l y strengthened by emulating the c r u s h i n g type o f t o o t h found i n ground sharks and Hexanchoids. Loads a p p l i e d t o t e e t h of v a r i o u s ECAs p a r a l l e l t o the m i d l i n e s i m u l a t e the s t r e s s e s on the t e e t h d u r i n g jaw p r o t r a c t i o n and addu c t i o n . Here, the l a t e r a l t e e t h are 106 supported by t h e i r broad axis, and the front teeth are pulled back-and-forth. With regard to the teeth of the middle jaw, one would i n t u i t i v e l y expect teeth of a lower ECA to require greater loads for removal when forced i n a d i r e c t i o n d i r e c t l y outwards from the mouth. In a back-slanted p o s i t i o n , the collagen f i b r e s of the tooth bed have a greater area of the tooth root to attach to, and the lever provided by the length of the tooth i s shorter. The f a i l u r e to observe t h i s i n t h i s study i s l i k e l y the f a u l t of two shortcomings i n the method used. The objective for t h i s stage of the study was to te s t the r e l a t i v e s u i t a b i l i t y of various observed functional tooth positions, with 'better' s u i t a b i l i t y defined as a greater resistance to removal. Testing t h i s would require the a p p l i c a t i o n of forces i n a va r i e t y of di r e c t i o n s on a tooth of f i x e d p o s i t i o n (a given ECA i n t h i s case). This would require many r e p l i c a t e measures on mandible sections (or analogous models) for each tooth p o s i t i o n to be tested. Resources were not available to attempt t h i s methodology at the time of the study. What was act u a l l y done i n t h i s study was the app l i c a t i o n of a force i n one d i r e c t i o n on a va r i e t y of tooth positions (the ECAs found i n the fresh specimens). 107 T h i s method a c t u a l l y t e s t e d the r e l a t i v e s t r e n g t h of the t o o t h bed i n each i n s t a n c e . Given the d i r e c t i o n of l o a d i n g , o n l y the c o l l a g e n f i b r e s on the i n s i d e of the t o o t h were loaded. As the t e e t h were loaded, a l l r o t a t e d t o a more or l e s s f u l l y e r e c t p o s i t i o n (90° or more) b e f o r e b e i n g p u l l e d out, r e g a r d l e s s of i n i t i a l p o s i t i o n . D i f f e r e n c e s i n the f o r c e of removal may have r e s u l t e d from the t e a r i n g of a d d i t i o n a l , or fewer, con n e c t i o n s t o the t o o t h bed. In a d d i t i o n , removal loads may have been a f f e c t e d by p o s s i b l e p r e - s t r e s s i n g or damaging the t o o t h bed d u r i n g removal of a d j a c e n t t e e t h . A second shortcoming t o the method of s e c t i o n 4.2 was the way i n which the t e e t h were a t t a c h e d t o the t e n s i l e t e s t i n g apparatus. With the screw a c t i n g as a f i x e d and r i g i d body a t t a c h e d t o the t o o t h , the a c t u a l f o r c e a p p l i e d t o the t e e t h was l i k e l y much more c o m p l i c a t e d than i s assumed here. Indeed, the l e v e r a g e a p p l i e d by the screw w i t h i n the h o l e was o f t e n r e s p o n s i b l e f o r b r e a k i n g the t e e t h . D e t a i l e d examination of the nature of t h i s l e v e r a g e system would r e q u i r e e x t e n s i v e analyses thought t o be beyond the scope of the c u r r e n t work. The r e g r e s s i o n c o e f f i c i e n t (r ) v a l u e s c a l c u l a t e d i n the r e g r e s s i o n a n a l y s i s f o r F i g u r e s 4-2 and 4-3 (0.140 and 0.055, r e s p e c t i v e l y ) are not o n l y i n s i g n i f i c a n t a t P = 0.05, but i n b e i n g f a r below 0.5 a l s o i n d i c a t e a t h a t a l a r g e amount of the t o t a l v a r i a t i o n i s not e x p l a i n e d by the 108 r e g r e s s i o n (Zar, 1984). The primary sources of t h i s v a r i a t i o n are suggested t o be the v a r i a b i l i t y of the t o o t h bed's compo s i t i o n and the le v e r a g e e f f e c t of a r i g i d attachment on the f o r c e a p p l i e d t o the t e e t h t e s t e d . A means of p u l l i n g on the t o o t h which a r t i c u l a t e s t o accommodate the t o o t h ' s displacement as i t i s loaded would c l e a r l y be p r e f e r r e d . A f i s h hook i s an example of such a d e v i c e , however any hooks which were s m a l l enough t o f i t t he h o l e s capably d r i l l e d through the t e e t h were r e a d i l y s t r a i g h t e n e d by the loads a p p l i e d . A p o s s i b l e s o l u t i o n t o both the problem of an a r t i c u l a t i n g attachment and the s t r e s s i n g of the t o o t h by d r i l l i n g a h o l e would be t o glu e a p l a t e attachment t o the t o o t h s u r f a c e . The a r t i c u l a t o r arm c o u l d then be a t t a c h e d t o the p l a t e , r a t h e r than the t o o t h . The d e s i g n of such a p l a t e was not undertaken d u r i n g the experimental d e s i g n . With the f l e x i b l e nature of the t o o t h ' s attachment t o the bed, g l u i n g the t o o t h t o the a r t i c u l a t o r arm would a l s o serve o n l y t o t e s t the f i b r e s of the t o o t h bed, and would not be as e f f e c t i v e as the t e s t i n g of a t o o t h of f i x e d p o s i t i o n d i s c u s s e d above. The loads of up t o 70 kg r e q u i r e d t o remove a s i n g l e one of these t e e t h have done much t o r e f u t e the i n i t i a l e x p e c t a t i o n t h a t the p o i n t of t o o t h attachment i s a p o i n t of weakness i n t h i s system, and t h a t shark t e e t h are r e a d i l y expended i n l i g h t of t h i s . 109 The p r i n c i p a l l o a d i n g on a t o o t h i n the a c t of f e e d i n g would presumably be s t r a i g h t down ( i . e . , a p p l i e d from the t o o t h t i p towards the t o o t h b a s e ) . The f o r c e r e q u i r e d t o break the t o o t h a t t h i s o r i e n t a t i o n would be q u i t e l a r g e , and i n f a c t the arrangement of a p a t i t e c r y s t a l s w i t h i n the t o o t h a c t t o d i s t r i b u t e loads a p p l i e d a t t h i s p o i n t (R. Lund, p e r s . comm.). A p p l i c a t i o n of a r e s i s t i v e f o r c e d i r e c t l y outward from the mouth, as was done here, might t h e r e f o r e seem i r r e l e v a n t . However, w i t h the gouging type of f e e d i n g employed by Carcharodon carcharias, and the removal o f chunks from prey items l a r g e r than the p r e d a t o r ' s jaws, t h e r e i s an i n c r e a s e d l i k l i h o o d of the f u n c t i o n a l t e e t h b e i n g p u l l e d i n t h i s d i r e c t i o n as the prey's f l e s h i s removed, o r r e s i s t s removal. During f e e d i n g , the c e n t e r jaw t e e t h are l i k e l y embedded i n the prey item by the time the jaws are f u l l y c l o s e d and r e t r a c t e d , and probably e x p e r i e n c e l i t t l e subsequent s t r a i n . As torque i s a p p l i e d t o the jaws by t w i s t i n g o r shaking the body, the l a t e r a l t e e t h assume most of t he l o a d i n g f o r the a c t u a l removal of f l e s h w h i l e the c e n t r a l t e e t h are s t r e s s e d p a r a l l e l t o the broader a x i s of t h e i r base. I f the f r o n t t e e t h are a b l e t o g a i n purchase i n the f l e s h , the f e e d i n g apparatus becomes i n c r e a s i n g l y supported by the musculature as the gape i s drawn c l o s e d . 110 The r e s u l t s suggest s l i g h t v a r i a t i o n s i n t o o t h removal loads between specimens of comparable s i z e (HI and H2). The a d d i t i o n a l 36 hours of r e f r i g e r a t i o n of Hi due t o instrument break-down was of i n i t i a l concern t o the author. As the f r e s h m a t e r i a l began t o decompose, the t e e t h would presumably become e a s i e r t o remove. Although the v a l u e s o b t a i n e d f o r Hi are g e n e r a l l y lower than those of H2, t h e r e i s no i n d i c a t i o n of h i g h e r v a l u e s f o r the Hi t e e t h removed immediately a f t e r thawing (4A, 7A, 2B, 7B) when compared t o the t e e t h removed a f t e r r e f r i g e r a t i o n (6A, 8A, IB, 4B, 9B). The d e l a y d i d not appear t o compromise the i n t e g r i t y of the m a t e r i a l . I t i s s p e c u l a t e d t h a t v a r i a t i o n s i n removal loads between i n d i v i d u a l s may i n d i c a t e d i s c r e p a n c i e s i n the r e l a t i v e q u a l i t y o r n u t r i t i o n of the t o o t h bed. I l l CHAPTER 5t GENERAL DISCUSSION AND CONCLUSIONS  THE POSITION OF SHARK TEETH F r a z z e t t a (1988) suggests t h a t the c h a r a c t e r i s t i c o u t - t u r n i n g of the t o o t h t i p i n many C a r c h a r h i n i d s p e c i e s f a c i l i t a t e s the c apture of prey by i n c r e a s i n g the l i k e l i h o o d of the prey c o n t a c t i n g the p o i n t of the t o o t h . The back-s l a n t e d t e e t h of Carcharodon carcharias are e q u a l l y w e l l s u i t e d t o impale prey items p u l l i n g forward from w i t h i n the mouth. Although the t o o t h t i p s of Lamna ditropis are s l i g h t l y o u t -turned, n e i t h e r Carcharodon carcharias nor Carcharhinus leucas express t h i s t r a i t markedly. Adduction of the jaws from a wide gape reduces the angle of the frontmost t e e t h , p o i n t i n g them more d i r e c t l y towards the g u l l e t . The i n i t i a l h y p o t h e s i s , t h a t the t e e t h are r e p o s i t i o n e d by jaw p r o t r a c t i o n i n such a way as t o make them f u n c t i o n a l l y s u p e r i o r , was o n l y p a r t i a l l y supported by t h i s study. I t was found t h a t p r o t r a c t e d t e e t h assume a lower degree of e r e c t i o n than r e t r a c t e d t e e t h , but whether t h i s c o n t r i b u t e s t o f u n c t i o n a l i t y , as d e f i n e d , remains t o be determined by more complex an a l y s e s on the f o r c e s r e q u i r e d t o d i s l o d g e the t e e t h . The f e e d i n g apparatus of the white shark i s a h i g h l y s p e c i a l i z e d s t r u c t u r e . In the a c t of f e e d i n g , the 112 jaws are not simply f l u n g out and snapped c l o s e d . Rather, the sequence of events i s h i g h l y v a r i a b l e , and c o n t i n u a l l y a d j u s t s t o compensate f o r the nature of the prey item. P r o t r a c t i o n of the jaw a s s i s t s prey purchase, and i n i t i a l l y ' t e s t s ' the food item. As the jaws are drawn c l o s e d , f l e x u r e of the t e e t h a l l o w s removal of p o i n t b i n d i n g t o a s s i s t c l o s i n g of the e n t i r e jaw. As the jaws are f u l l y c l o s e d , the jaws s h i f t l a t e r a l l y , p e r m i t t i n g a b e t t e r meshing of the t e e t h i n t o a more e f f e c t i v e c u t t i n g s u r f a c e . As the apparatus i s r e t r a c t e d , the c a r t i l a g i n o u s jaws are f l e x e d by the a c t i o n of the adductor muscles. T h i s f l e x u r e a d j u s t s the t e e t h t o a lower ECA and p o i n t s them f u r t h e r inward. As the h y o i d arches are drawn i n , the jaws are f l e x e d m e d i a l l y , p o s s i b l y d e c r e a s i n g the c u t t i n g a ngless of the l a t e r a l t e e t h (Powlik, unpub. o b s . ) . F i n a l l y , shaking the head or t w i s t i n g of the body f a c i l i t a t e s t e a r i n g , of the prey i t e m by the s t r o n g e r t e e t h of the l a t e r a l s e c t i o n s , w h i l e the c e n t r a l t e e t h are supported by the broad a x i s of t h e i r base (see F i g u r e 5-1). Taken t o g e t h e r , t h i s r e s e a r c h has p r o v i d e d a r a t i o n a l e f o r the o r i e n t a t i o n of the f u n c t i o n a l t e e t h , and p r o t a c t i o n of a f l e x i b l e jaw. APPLICATIONS AND FUTURE RESEARCH In d e t e r m i n i n g the f i n e - s c a l e r e l a t i o n s h i p s of t o o t h p o s i t i o n between s p e c i e s or f e e d i n g groups, a number 113 FIGURE 5-1: Summary of p o s s i b l e sequence of events i n v o l v e d i n shark f e e d i n g , as d e s c r i b e d i n the t e x t . STAGE I = prey s e l e c t i o n ( s p e c u l a t i v e ) , a d e c i s i o n i s made t o b i t e , and whether t o p r o t r a c t the jaw; STAGE I I = mechanical responses t o jaw c l o s u r e , as suggested i n t h i s study. The f l e x i b i l i t y of the jaws and t o o t h attachment permits t o o t h e r e c t i o n (ECA) t o be decreased and reduces l o c a l i z e d b i n d i n g ; STAGE I I I = s p e c u l a t i o n of events i n c l u d i n g l a t e r a l r o t a t i o n of the f e e d i n g apparatus. C l e n c h i n g of the jaws may decrease gape width w i t h inswing of h y o i d arches, d e c r e a s i n g the e r e c t i o n of l a t e r a l s e c t i o n s . Body shaking and t w i s t i n g a s s i s t f l e s h removal, o r a new purchase i s taken ( d o t t e d l i n e ) . BEHAVIORAL MECHANICS III. 3 - D DYNAMICS t PREY ENCOUNTERED * • —*> BITE NO-•feeding not initiated YES mouth opens * ] 1 JAW PROTRACTION YES N 0 4 - P R E Y PURCHASE < 1 YES mouth closure initiated • TOOTH POINT BINDING— NO jaws bent inwards by adductor muscles central ECA reduced LATERAL RESISTANCE YES jaw 'shear'. mouth closure completed I —»> FLESH REMOVED — i gape width reduced/ lateral ECA decreased L_L • HEAD SHAKING & BODY TWISTING • Y E S -tooth socket flexure/ tooth loss YES PREY CAPTURED 115 of u s e f u l a p p l i c a t i o n s become r e a d i l y apparent, both i n terms of f e e d i n g dynamics and m o r p h o l o g i c a l study. Although c o n c l u s i v e evidence f o r many such a p p l i c a t i o n s are beyond the scope of t h i s t h e s i s , hypotheses and s u g g e s t i o n s f o r f u t u r e r e s e a r c h i n t h i s area w i l l now be d i s c u s s e d . One a p p l i c a t i o n i s the p r o v i s i o n of d a t a i n r e t r o s p e c t i v e i n v e s t i g a t i o n of shark a t t a c k on humans or oceanographic equipment. Knowledge of t o o t h p o s i t i o n i n a l a r g e and v a r i e d number of specimens c o u l d p r o v i d e evidence f o r the s p e c i e s , sex, and s i z e of the animal r e s p o n s i b l e f o r a shark a t t a c k . An example of t h i s p r e d i c t i v e power was r e v e a l e d i n the course of t h i s study. I n i t i a l examination of the f r e s h white shark heads was performed without knowledge of the sex or dimensions of the o r i g i n a l animals. Measurement of the b u c c a l c a v i t y dimensions and X comparison w i t h the N museum specimens, however, r e v e a l e d the b e s t g o o d n e s s - o f - f i t w i t h specimens 6 and 11 (see Table 2-5). T h i s ' p r e d i c t e d ' t h a t the two heads came from male specimens of approximately 2.5 meters l e n g t h and 250 kg weight (and t h e r e f o r e probably immature, by t h i s s m a l l s i z e ) . Correspondence w i t h the N a t a l Sharks Board r e v e a l e d an a c t u a l s i z e of 2204 and 2407mm ( t o t a l length) f o r the two specimens, which were both immature males. 116 V e r i f i c a t i o n of specimen s i z e from an a c t u a l head i s not d i f f i c u l t , however the example i l l u s t r a t e s how an o f f e n d i n g animal might be i d e n t i f i e d from measurement of b i t e marks on human v i c t i m s , prey items, o r marine sampling equipment. In t h i s way, museum specimens have a l s o demonstrated t h e i r u t i l i t y i n a s s i s t i n g the c o m p i l a t i o n of dat a on the p o s i t i o n of t e e t h i n a v a r i e t y of s p e c i e s (see s e c t i o n 2.4). A p p l i c a t i o n s of r e s e a r c h on shark t o o t h r e t e n t i o n might a l s o be found i n the improvement of human d e n t a l i n s e r t s and p r o s t h e s e s . R e l a t i n g the p o s i t i o n of the f u n c t i o n a l t e e t h i n these animals, and the way i n which the p o s i t i o n i s changed w i t h the a c t i o n of the jaws may p r o v i d e c l u e s on improving t o o t h r e t e n t i o n , m a t e r i a l r e s i l i e n c y , and c r a n i o f a c i a l s u r g i c a l t echniques i n human systems. I f t h i s methodology i s t o be extended t o the examination of f r e s h l y k i l l e d and l i v i n g animals on a l a r g e s c a l e , i t must be r e v i s e d . I n f o r m a t i o n on t o o t h p o s i t i o n and c u t t i n g angle of the t e e t h can be determined from photographing the open mouth of f r e s h l y dead or a n a e s t h e t i s e d animals, u s i n g the i n t e r p r e t a t i o n of image appearance s i m i l a r t o the method of a n a l y s i s used f o r the f e e d i n g dynamics i n t h i s study. At some expense i n accuracy, comparison of f u n c t i o n a l t o o t h p o s i t i o n i n many more and d i v e r s e specimens than examined here would be p o s s i b l e through photographic a n a l y s e s . 117 A f i n e r - s c a l e of a n a l y s i s i s a l s o necessary i n the e l u c i d a t i o n of the f o r c e s a c t i n g on the t e e t h . E l e c t r o n microscopy of the t o o t h base and the s u r r ounding c o l l a g e n f i b r e s may p r o v i d e an e x p l a n a t i o n f o r the r e l a t i v e f o r c e s r e q u i r e d f o r t o o t h removal, and methods of improving t o o t h r e t e n t i o n i n human systems. By a p p l y i n g computer s i m u l a t i o n s and a n a l y s e s , the biomechanical p r o p e r t i e s of the composite m a t e r i a l s of the f e e d i n g apparatus can be t r a n s l a t e d t o a c l e a r e r understanding of the dynamics of the e n t i r e s t r u c t u r e . CONCLUSIONS Although e m p i r i c a l methods were used t o d e r i v e and t e s t the r e s u l t s of t h i s study, i t must be s t r e s s e d t h a t the u n d e r l y i n g premise of t h i s t h e s i s remains l a r g e l y t h e o r e t i c a l . T h i s i s not t o downplay the r e l e v a n c e of these f i n d i n g s , but r a t h e r t o suggest the l i g h t i n which they should be examined. The s i g n i f i c a n t f i n d i n g s of t h i s study a r e : 1) The p o s i t i o n of the f u n c t i o n a l t e e t h i n Carcharodon carcharias, Carcharhinus leucas, and Lamna ditropis are not d i s s i m i l a r w i t h r e s p e c t t o t h e i r displacement from the m i d l i n e , o r degree of e r e c t i o n . W i t h i n specimens, t h e r e i s no s t a t i s t i c a l d i f f e r e n c e i n the p o s i t i o n of the t e e t h i n any p a r t i c u l a r s e c t i o n of the mouth, however t h e r e are s l i g h t commonalities i n t o o t h s i z e and reduced v a r i a t i o n i n c e r t a i n r e g i o n s of the mouth which may have a p p l i c a t i o n i n 118 d e s c r i b i n g animals on the b a s i s of t h e i r b i t e . The t e e t h of male specimens, Carcharhinus leucas, and those w i t h i n 30° of the m i d l i n e demonstrate lower v a r i a t i o n i n p o s i t i o n than o t h e r n a t u r a l groups, which pr o b a b l y r e l a t e s t o d i e t and s o c i a l b e h a v i o r . 2) In the a c t of jaw p r o t r a c t i o n the t e e t h of the c e n t r a l jaw are r o t a t e d outwards as the jaws are f l e x e d . As the gape i s c l o s e d , the e r e c t i o n o f the frontmost t e e t h i s decreased r e l a t i v e t o the g u l l e t by the a c t i o n of the adductor muscles and p o i n t of a r t i c u l a t i o n w i t h the h y o i d . 3) The loads r e q u i r e d f o r t o o t h removal are not s i g n i f i c a n t l y i n c r e a s e d among t e e t h of lower degrees of e r e c t i o n . 4) The f e e d i n g apparatus of Carcharodon carcharias i s seen t o be a h i g h l y - s p e c i a l i z e d and s e l e c t i v e system. The p o s i t i o n o f the t e e t h and f l e x i b i l i t y of the jaws prevent p o i n t b i n d i n g , and a l l o w the jaws t o c l o s e more co m p l e t e l y . The c l o s e d , supported s t r u c t u r e then a c t s i n c o n j u n c t i o n w i t h wrenching of the body t o gouge chunks out of the prey item. 5) The s i m i l a r i t y i n t o o t h p o s i t i o n , and they way i n which the f u n c t i o n a l t e e t h are r e p o s i t i o n e d r e l a t i v e t o the g u l l e t by jaw f l e x u r e suggests a mechanical r a t i o n a l e f o r the shape, s i z e , and p o s i t i o n of the f u n c t i o n a l t e e t h , as w e l l as the p r o t r a c t i o n and f l e x i b i l i t y of the jaws. LITERATURE CITED; 119 Alexander, R. McN. 1967. The f u n c t i o n s and mechanisms of the p r o t r u s i b l e upper jaws of some Acanthopterygian f i s h . J . Z o o l . Lond. 151:43-64. Applegate, S.P. 1965. 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Modulatory m u l t i p l i c i t y i n the f u n c t i o n a l r e p e r t o i r e of the f e e d i n g mechanism i n c i c h l i d f i s h e s . J . Morph. 158: 323-360. LeRiche, M. 1905. Les poissons Eocene de la Belgique, memoires du Musee Royal Histoire Naturelle Belgique Bruxilles, T. I l l , pp. 49-228, p i s . IV-XII, 1 s e r i e s , Mem. No. 11. 122 1910. Les poissons oligocene de la Belgique, Memoires du Musee Royal Histoire Naturelle Belgique Bruxelles, T.V., pp 231-363, f i g s 65-159, p i s X I I I -XXVII. 1926. Les poissons Neogene de la Belgique, Memoires du Musee Royal Histoire Naturelle Belgique Bruxelles, Memoire 32, 1926, pp 368-472, p i s XXVIII-XLI, t e x t f i g s 161-228. L i g h t o l l e r , G.H.S. 1939. Probable homologues. A study of the comparative anatomy of the mandibular and h y o i d arches and t h e i r musculature. Trans. Z o o l . Soc. London. 24:349-444. L i s s e a u , S. 1977. Jaws of "Jaws". Oceanus, November 1977. Luthor, A.F. 1909. Untersuchungen uber die vom N. t r i g e r m i n u s innervierte Musculatur der Selachier (Haie and Rochon) unter Berucksichtigung ihrer Beziehunger zu benachbarten Organen. A c t a Soc. S c i . Fenn. 36: 1-176. Maisey, J.D. 1980. An e v a l u a t i o n of the jaw suspension i n sharks. Amer. Mus. N o v i t a t . (2706): 17pp. Moss, S.A. 1962. The mechanisms of upper jaw p r o t r u s i o n i n sharks. Amer. Z o o l . , v o l . 2 , p.542. 1967. Tooth replacement i n the lemon shark (Negaprion brevirostris) IN: Sharks, Skates, and Rays, eds. P.W. G i l b e r t , R.F. Mathewson, and D.P. R a i l . B a l t i m o r e — t h e Johns Hopkins P r e s s : 319-329. 123 1972a. Tooth replacement and body growth r a t e s i n the smooth d o g f i s h , Mustelus canis ( M i t c h i l l ) Copeia ( 4 ) : 808-811 1972b. The f e e d i n g mechanism of the sharks of the f a m i l y C a r c h a r h i n i d a e . J . Z o o l . (London) 167 (1972), pp423-436. 1977. Feeding mechanisms i n sharks. Amer. 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Mathewson, and D.P. R a i l . B a l t i m o r e — t h e Johns Hopkins P r e s s : 331-337. S p r i n g e r , S. 1961. Dynamics of the f e e d i n g mechanisms i n l a r g e g a l e o i d sharks. American Z o o l o g i s t , 1(1961) pp. 183-185. 1967. S o c i a l o r g a n i z a t i o n of shark p o p u l a t i o n s . IN: Sharks, Skates, and Rays. eds. P.W. G i l b e r t , R.F. Mathewson, and D.P. R a i l . B a l t i m o r e — t h e Johns Hopkins P r e s s , pp 149-174. Stevens, J.D. 1987. The B i o l o g y of Sharks. IN: JD Stevens (ed.) Sharks. F a c t s on F i l e P u b l i c a t i o n s , New York. S t r a s b u r g , D.W. 1963. The d i e t and d e n t i t i o n of Isistius brasiliensis w i t h remarks on t o o t h replacement i n o t h e r sharks. Copeia; 33-40. T a y l o r , V. 1981. A n t i - s h a r k armor t h a t works. S k i n D i v e r , October 1981, pp 23-27. T r i c a s , T.C. and J.E. McCosker 1984. P r e d a t o r y b e h a v i o r of the white shark (Carcharodon carcharias) w i t h notes on i t s b i o l o g y . Proc. C a l . Acad. S c i . 43(14) 221-238. T r i c a s , T.C. 1985. Feeding e t h o l o g y of the white shark (Carcharodon carcharias). Mem. Sou. C a l . Acad. S c i . , v o l 9, pp 81-91. Wass, R.C. 1973. S i z e , growth, and r e p r o d u c t i o n of the sandbar shark, Carcharhinus milberti, i n Hawaii Pac. S c i . 27(4), pp305-318. 125 Zar, J.A. 1984. B i o s t a t i s t i c a l A n a l y s i s (2nd e d . ) . P r e n t i c e - H a l l / New J e r s e y 718pp. APPENDIX A: SPECIMEN COLLECTION AND DIMENSIONS 126 TABLE A - l : Study specimen c o l l e c t i o n . SPECIMEN # = number as tagged i n museum; TL = t o t a l l e n g t h ; PC = precaudal l e n g t h . 127 TABLE A - l : Study Specimen C o l l e c t i o n STUDY #/ MEANS OF SPECIMEN # SPECIMEN PRESERVATION COLLECTION P l / BCPM 983-1731 P2/ BCPM unnumbered P3/ BCPM 988-1723 P4/ BCPM 983-1731 P5/ BCPM 987-208 P6/ BCPM 984-700 P7/ BCPM 987-210 P8/ BCPM 980-298 P.glauca female 800 mm PC P.glauca female 1553mm PC L . d i t r o p i s male 783 mm PC L . d i t r o p i s male 1053mm PC L . d i t r o p i s female 770 mm PC L . d i t r o p i s female 813 mm PC L . d i t r o p i s male 720 mm PC H.griseus female 1292mm PC whole a lcohol vat whole a lcohol vat whole alcohol vat whole alcohol vat whole alcohol vat whole alcohol vat whole alcohol vat whole alcohol vat J u l 23,1983 4 9 ° 2 3 . 5 ' N 1 3 3 ° 5 9 . 8 ' W 1980 Stat ion P Aug 24,1983 5 2 ° 2 8 . 4 ' N 1 3 5 ° 5 9 . 1 ' W J u l 23,1983 4 9 ° 2 8 . 5 ' N 1 1 3 ° 5 7 . 8 ' W Jun 8,1987 3 8 ° 1 5 . 8 ' N 1 6 2 ° 8 . 7 ' W g i l l net Aug 31,1984 Tof ino , Chst'man beach Jup 9,1987 3 8 ° 7 . 7 ' N 1 6 2 ° 2 5 . 9 ' W Georgia S t r a i t 128 TABLE A - l (con 't) 1/ H.griseus d r i e d N/A CAS upper jaw 55477 2/ C . c a r c h a r i a s d r i e d J u l 12,1959 CAS female jaw s e t Go l e t a P o i n t 26361 2518mm TL 3/ C . c a r c h a r i a s d r i e d J u l 2,1960 CAS female jaw s e t Tomales Bay 26781 2990mm TL (sans teeth) 4/ C . c a r c h a r i a s d r i e d N/A CAS N/A jaw set 27014 N/A 5/ C . c a r c h a r i a s d r i e d Aug 28,1959 CAS male jaw set Palm Beach 26378 1908mm TL 6/ C. c a r c h a r i a s d r i e d Aug 10,1959 CAS male jaw s e t Soquel P o i n t 26376 1949mm TL 7/ C . c a r c h a r i a s d r i e d Boat Harbour CAS female jaw s e t g i l l n e t 55435 1467mm TL 8/ C. c a r c h a r i a s d r i e d N/A CAS female jaw s e t unnumbered 1473mm TL 9/ C . c a r c h a r i a s d r i e d Aug 29,1959 CAS male jaw s e t Sunset Beach 26683 2071mm TL 10/ C . c a r c h a r i a s d r i e d J u l y 31,1959 CAS female jaw set Sel v a Beach 26370 3683 11/ C . c a r c h a r i a s d r i e d J u l y 25,1959 CAS male jaw set Tomles Bay 26363 3148mm TL 12/ C . c a r c h a r i a s d r i e d N/A CAS N/A jaw s e t 48413 N/A 13/ C . c a r c h a r i a s d r i e d Nov 9?,1959 ACC N/A jaw s e t St i n s o n Beach 1951x1:15 N/A 129 TABLE A - l ( c o n ' t l 14/ C . c a r c h a r i a s d r i e d J u l 28, 1959 CAS male jaw s e t Tomales Bay 26363 N/A 15/ C . c a r c h a r i a s d r i e d N/A CAS N/A jaw s e t 26695 N/A 16/ C . c a r c h a r i a s d r i e d N/A CAS N/A jaw s e t 55467 N/A 17/ L . d i t r o p i s d r i e d N/A CAS N/A jaw s e t 55476 N/A 18/ L . d i t r o p i s d r i e d N/A CAS N/A jaw s e t 55496 N/A 19/ L . d i t r o p i s whole Dec 31,1984 CAS male a l c o h o l v a t S't Maria Beach 56966 921mm TL washed ashore 20/ L . d i t r o p i s whole N/A CAS female a l c o h o l v a t 53202 1130mmTL 21/ C.leucas d r i e d N/A CAS N/A jaw set 55482 N/A 22/ C.leucas d r i e d Dec 7,1957 CAS N/A jaw set Bur i e Bay, unnumbered N/A T h a i l a n d 23/ C.leucas d r i e d N/A CAS N/A jaw set 55483 N/A 24/ C.leucas d r i e d Chesapeake CAS N/A jaw set Bay 55484 N/A HI/ C . c a r c h a r i a s fresh,whole Aug 7, 1989 NSB male head Umhlanga Rocks 1 2075 mm PC RSA H2/ C . c a r c h a r i a s fresh,whole Umhlanga Rocks NSB N/A head RSA 2 N/A 130 TABLE A-2: A n t e r i o r b u c c a l c a v i t y dimensions f o r a l l specimens. GA = gape angle; GW = gape width; PQL = palatoquadrate l e n g t h (upper d e n t a l a r c l e n g t h ) ; MCL = Meckel's c a r t i l a g e l e n g t h (lower d e n t a l arc l e n g t h ) ; AREA = t o t a l i n s i d e area of both jaws, assuming each jaw margin t o be a h a l f - e l l i p s e (see t e x t , Chapter 2). TABLE A-2: Specimen Buccal C a v i t y Dimensions # GA GW PPL MCL AREA (deg) (mm) (mm) (mm) (mnr) P l 54 60 40 30 2592 P2 0 120 82 71 7210 P3 0 70 60 53 3106 P4 31 95 63 54 4365 P5 5 87 54 59 3861 P6 0 82 72 60 4251 P7 10 71 58 52 3067 P8 20 160 115 70 11 624 1 na 80 112 na na 2 155 220 220 180 34 558 3 160 320 230 160 49 009 4 126 230 200 140 30 709 5 153 205 140 100 19 320 6 121 215 150 95 20 686 7 51 125 120 117 20 941 8 22 128 90 79 10 702 9 170 na 135 120 na 10 130 215 290 215 42 637 11 135 292 210 163 42 771 12 102 na na na na 13 140 240 160 120 26 389 14 117 237 138 110 22 887 15 125 284 205 115 40 171 16 107 165 180 140 20 734 17 75 79 115 105 6408 18 85 95 155 132 10 707 19 42 82 67 58 4025 20 31 89 90 76 5802 21 118 280 185 140 35 736 22 103 227 150 134 25 317 23 130 250 160 115 26 998 24 na 240 155 115 25 447 HI 25 250 140 100 23 562 H2 20 238 190 150 31 777 132 TABLE A-3: Summary of Midline Displacement (MLD) values, n denotes the number of teeth in each mouth section used to derive the average MLD value. Negative values denote positions left of the midline. Specimens P l , P2, P8, 1, and 3 were omitted from analysis due to a lack of measurable teeth (see text). 133 TABLE A-3: Summary of M i d l i n e Displacement Values SPECIMEN MOUTH SECTION # 1 2 3 4 5 6 P3 MLD 43.9 -2.8 -49.3 2.9 -38.2 n 1 4 2 4 2 P4 60.0 -2.8 -56.8 74.2 -2.5 -71.0 5 4 7 6 2 6 P5 53.5 -2.3 -59.0 40.0 4.7 -53.7 4 2 3 3 4 4 P6 32.7 4.9 -54.4 56.7 2.2 -49.8 2 5 6 4 4 4 P7 41.7 -1.3 -52.0 58.5 4.1 -65.6 6 5 3 5 3 5 2 32.8 5.3 -37.9 36.6 0.0 -37.0 2 8 5 2 4 1 4 34.9 2.8 -30.5 30.4 -0.7 3 8 2 1 5 5 35.0 2.6 -31.4 31.5 3.2 1 7 2 2 4 6 36.9 -2.0 -31.5 35.8 1.8 -32.5 3 9 3 3 5 2 7 47.0 6.0 -43.1 44.8 10.0 -42.8 4 5 5 3 1 2 8 36.3 -1.4 -39.7 55.0 15.0 -36.7 2 3 1 2 2 1 9 -1.1 -33.0 31.8 3.9 8 2 2 4 10 44.0 -3.5 -31.8 40.6 3.6 1 1 4 1 3 -11 33.5 1.5 -36.4 37.7 -1.0 -35.0 2 7 2 4 5 1 12 35.1 4.8 -32.4 -9.3 -32.7 3 4 3 4 3 13 42.9 -33.5 2 1 14 -0.2 34.9 3.5 -34.9 11 3 4 3 15 2.8 -37.3 43.1 5.2 -30.0 1 1 5 3 4 16 30.9 1.1 34.8 3.0 -32.0 3 6 8 8 2 17 46.9 1.6 -49.1 51.3 -8.2 -46.1 5 5 4 5 3 5 18 50.4 3.9 -51.0 53.7 0.9 -47.0 6 4 5 5 2 3 19 36.7 3.3 -40.4 36.8 2.6 -37.0 4 8 3 4 7 2 134 T A B L E A-3 ( c o n ' t ) : 20 48.4 4.9 -48.4 39.5 2.3 -40.9 3 6 3 3 4 4 21 40.1 4.3 -36.3 40.4 3.6 -34.1 4 10 3 5 5 5 22 34.0 -3.6 39.0 0.1 -37.1 6 4 4 4 4 23 40.4 4.2 -33.3 34.7 0.1 5 8 5 4 10 24 35.6 1.4 -30.0 37.8 1.9 -34.1 7 7 6 4 2 6 HI 65.1 1.9 -55.0 68.5 2.3 -69.1 3 7 1 3 4 3 H2 77.1 2.3 75.9 0.0 -86.5 3 4 2 4 2 135 TABLE A-4: Tooth Cutting Angles (ECAs) for a l l specimens, n = number of teeth i n each mouth section. 136 TABLE A-4: E f f e c t i v e C u t t i n g Angle (ECA) Measurements SPECIMEN MOUTH SEGMENT # 1 2 3 4 5 6 P3 ECA 60.31 69.77 n 4 4 P4 85.00 59.99 90.00 62.81 57.25 88.19 5 4 7 6 2 6 P5 67.76 76.43 87.98 75.74 70.90 83.52 4 2 3 3 4 4 P6 71.57 72.55 68.57 80.34 60.84 83.83 2 5 6 4 4 4 P7 90.00 80.11 90.00 70.52 50.56 81.64 6 5 3 5 3 5 2 14.04 90.00 12.21 49.16 63.39 72.50 2 8 5 2 4 1 4 37.37 125.0 58.76 64.59 129.0 104.92 3 8 2 1 5 1 5 40.00 75.36 85.00 21.45 60.80 72.50 1 7 2 2 4 2 6 73.33 87.49 45.00 54.23 79.19 77.09 3 9 3 3 5 2 7 36.73 85.98 14.01 25.56 100.0 88.75 4 5 5 3 2 2 8 85.00 77.50 51.60 32.08 81.36 87.50 2 3 1 2 3 1 9 55.00 62.36 89.97 73.65 95.00 8 2 2 4 2 10 68.77 71.20 85.00 4 1 1 11 50.00 77.49 9.90 31.38 81.01 48.14 2 7 2 4 5 1 12 82.52 86.77 5.00 95.00 83.36 77.88 3 4 3 4 4 3 13 86.67 14 63.08 21.86 61.51 79.79 72.09 11 2 3 4 3 15 95.00 90.00 90.00 73.97 1 5 3 4 16 82.50 90.00 80.00 85.33 82.51 90.00 3 6 2 3 8 2 17 85.00 90.00 51.98 67.41 110.0 83.33 5 5 4 5 3 5 18 83.38 82.10 68.74 76.58 90.00 86.67 6 4 5 5 2 3 19 50.59 80.08 56.34 40.00 85.42 4 8 3 4 7 137 TABLE A-4 (con't) 20 83.36 90.00 85.04 48.47 78.76 81.26 3 6 3 3 4 4 21 90.00 46.99 90.00 81.55 42.93 33.66 4 10 3 5 5 5 22 62.30 43.75 73.99 27.40 6 4 4 4 23 80.00 47.49 90.00 81.04 66.53 75.14 5 8 5 4 10 5 24 83.33 45.26 79.20 74.54 73.61 70.91 7 7 6 4 2 6 HI 59.31 49.58 80.00 59.31 61.25 77.12 3 7 1 3 4 3 H2 77.12 66.08 68.61 157.56 58.92 3 4 2 4 2 APPENDIX B: SELECTED FEEDING FILM TRACINGS 138 FIGURE B - l : R o t a t i o n t r a c i n g s o f r e f e r e n c e jaws . S e l e c t e d p o s i t i o n s a r e shown here were used t o e s t i m a t e changes i n t o o t h p o s i t i o n from footage o f a n i m a l s not p e r p e n d i c u l a r t o the camera . Diagrams 75% o f t r a c e d image. 140 FIGURE B-2: T r a c i n g s of V e r t i c a l A t t a c k (sequence 1). S e l e c t e d i l l u s t r a t i o n s showing the r e l a t i v e p o s i t i o n s of the t e e t h i n a v e r t i c a l gape c l o s u r e . Diagrams 75% of t r a c e d image. 143 FIGURE B-3: T r a c i n g s of Angle A t t a c k (sequence 2 ) . S e l e c t e d i l l u s t r a t i o n s showing the change i n jaw and t o o t h p o s t i o n i n r i g h t p r o f i l e . Diagrams 75% of t r a c e d image. 146 FIGURE B-4: T r a c i n g s of Angle A t t a c k (sequence 3 ) . S e l e c t e d i l l u s t r a t i o n s showing the change i n jaw and t o o t h p o s i t i o n s i n l e f t p r o f i l e approach. Diagrams 75% of t r a c e d image. B 149 FIGURE B-5: T r a c i n g s of S t r a i g h t A t t a c k (sequence 4 ) . S e l e c t e d i l l u s t r a t i o n s of r e l a t i v e jaw and t o o t h p o s i t i o n changes i n a t t a c k s p a r a l l e l t o the camera. Diagrams 75% of t r a c e d image. S C A L E : 1:4 

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