摘要:

This study investigates the origin of jaws by re‐assessing homologies between the oropharyngeal regions of Agnatha and Chondrichthyes. In accordance with classical theory, jaws are interpreted as the most anterior arches of the ventilatory branchial basket. It is proposed that jaws first enlarged for a ventilatory function, i.e. closing the jaws prevented reflux of water through the mouth during forceful expiration. Next, they enlarged further to grasp prey in feeding. As they enlarged, the jaws tilted forward, squeezing the ancestral oral cavity in front of them (‘old mouth’) into a slit between the jaws and lips. Simultaneously, the anterior part of the pharynx behind the jaws was pulled forward and became a ‘new mouth’ (the buccal part of the buccopharyngeal cavity of gnathostomes). During the transition to gnamostomes, the premandibular cheeks and lips of the old mouth remained in place, and are represented in ammocoete lampreys, chimaeroids, and sharks. The stages in the evolution of gnathostomes, driven by selection for increasing activity, are modelled as: ancestral vertebrate (with unjointed branchial arches) to early pre‐gnathostome (jointed internal arches and stronger ventilation) to late pre‐gnadiostome (with mouth‐closing, ventilatory ‘jaws’) to early gnathos

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb01658.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A monotypic new genus,Coleicarpus, is proposed forCastericystis? sprinkleiUbaghs&Robison 1988, the only solute known to be attached when adult.Coleicarpus sprinkleiwas fixed by the tip of its stele or tail to trilobite exoskeletal fragments which themselves adhered to the sea bed. The tail ofC. sprinkleiis uniformly circular in cross‐section and made of small non‐imbricating plates which form imprecise transverse rings and longitudinal rows. The tail ofC. sprinkleiis not divided into discrete regions as are the tails of other solutes.C. sprinkleiis probably the most primitive known solute because of its attachment and lack of tail regions. These features of its tail are consistent with the theory of the descent of solutes from aCephalodiscus‐like ancestor and also the phylogenetic placement ofC. sprinkleiin the stem group of the Dexiothetica, the monophyletic group which comprises the echinoderms and chordates exclus

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb01659.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Book reviewed in this article:Towards Stability in the Names of Animals. A History of the International Commission on Zoological Nomenclature 1895–1995, by Richard J. Melville.The Biology of Lemmings, edited by N.C. Stenste

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1996.tb01660.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY