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A survey of skeletal elements in the orbit of Pseudosuchia and the origin of the crocodylian palpebral

Published online by Cambridge University Press:  07 October 2013

Sterling J. Nesbitt ,
Alan H. Turner  and
Jonathan C. Weinbaum
Sterling J. Nesbitt*
Affiliation:
Burke Museum and Department of Biology, University of Washington, Seattle, WA 98195, USA
Alan H. Turner
Affiliation:
Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY 11794-8081, USA
Jonathan C. Weinbaum
Affiliation:
Biology Department, Southern Connecticut State University, New Haven, CT 06515, USA
*
Email: sjn@gmail.com
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Abstract

Ossified skeletal elements within the orbit, such as scleral ossicles, palpebrals, supraorbitals and sesamoids, are widespread across Reptilia, including extant members of Crocodylia, Aves, Squamata and Chelonia. Extant crocodylians lack scleral ossicles, but have a unique palpebral that has recently been shown, through developmental studies, to be an osteoderm in the upper eyelid. Here, we examine the diversity and disparity of the crocodylian palpebral in extant members of Crocodylia and, through the fossil record, trace the origin and evolutionary history of the element throughout Pseudosuchia (all archosaurs more closely related to crocodylians than avians). We show that the crocodylian palpebral originated outside of Crocodylomorpha in early pseudosuchian groups (e.g. Aetosauria, Loricata) and that scleral ossicles are lost in nearly all groups of pseudosuchians, but appear in poposauroids, at least one early crocodylomorph, and some partially or fully marine Crocodyliformes (e.g. thalattosuchians). The morphology and number of palpebrals differs across Crocodyliformes; the presence of two palpebrals is plesiomorphic, but this is reduced to one by Crocodylia. We further recommend the restriction of the term palpebral to the structure in crocodylians and their homologues, but not to the structure in ornithischian dinosaurs.

Keywords

Aetosaurus ferratusArchosauriaCrocodylomorphaevolutionnoveltyPostosuchus kirkpatrickiSaurosuchus galileisupraorbital
Type
Articles
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 103 , Issue 3-4: The Full Profession: A Celebration of the Life and Career of Wann Langston, Jr., Quintessential Vertebrate Palaeontologist , September 2012 , pp. 365 - 381
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Copyright © The Royal Society of Edinburgh 2013 

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