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The evolution of branchiostegal rays in teleostome fishes McAllister, Don Evan

Abstract

The origin, function and evolution of the branchiostegal rays, the related opercular and gular bones and associated hyoid elements were investigated in teleostome fishes. Alizarin, skeletal or alcoholic specimens of over half the living families (over 240) and all the living orders of teleostome fishes with branchiostegals were examined. Literature provided data for most of line remaining living and fossil families and orders. Several evolutionary trends became apparent; a tendency for number of branchiostegals to decrease, following Williston's Law; increasing separation of mandibular and hyoid arches; and an increase in number and complexity of hyoid elements. In the development of hyoid elements, but not of branchiostegal rays, the ontogenetic sequence paralleled the phylogenetic sequence. Examination of the unusual adult hyoid relationships in the neotenic Schindleria showed it to resemble the larval condition of normal fishes. The condition in the tiny goby, Mistichthys, is similar. The structure of the branchiostegal series and hyoid elements proved valuable in tracing the relationships of fishes. Major findings include: Hiodontidae were found not be be closely related to the Notopteridae; the Notopteridae and osteoglossoid families to be related to the mormyriforms; the Neoscopelidae and Myctophidae to differ from other myctophiforms; the ophidioids to require ordinal separation from the Perciformes and placement near the Gadiformes and Ateleopiformes; the Amblyopsidae to belong in the Percopsiformes; the Anabantoidei and Ophicephaloidei to be closely related suborders of common ancestry deserving placement in the same order; the Beloniformes to differ from most other orders in the loss of the interhyal and upper hypohyal; and the Echeneiformes to differ from most Perciformes in the possession of 8-11 branchiostegals. The number of branchiostegals was found to be influenced by posterior extension of the jaws, small body length, feeding habits, gill membrane attachment and deepsea existence.

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