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Palate and braincase of Whatcheeria deltae Lombard & Bolt, 1995

Published online by Cambridge University Press:  18 December 2018

John R. BOLT  and
R. Eric LOMBARD
John R. BOLT
Affiliation:
Department of Geology, Field Museum of Natural History, 1400 S Lake Shore Drive, Chicago, IL 60605, USA.
R. Eric LOMBARD*
Affiliation:
Department of Organismal Biology and Anatomy, The University of Chicago, 1027 E 57th Street, Chicago, IL 60637, USA. Email: elombard@uchicago.edu
*
*Corresponding author
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Abstract

The reconstructed palate of Whatcheeria deltae indicates a skull that was unusually narrow: at least 2.2 times longer than wide if the pterygoids are conservatively placed in the horizontal plane. This maximum width is narrower than any other early tetrapod reconstructed so far. Rotating the pterygoids to produce a vaulted palate would produce an even narrower skull. Primitive palatal features include very narrow interpterygoid vacuities and a vomer, palatine, and ectopterygoid with fang-sized replacement pairs. It is derived in that there is no anterior palatal fenestra and the premaxilla has a substantial palatal shelf – a combination of characters shared only with Proterogyrinus among early tetrapods. There is a possible septomaxilla in one specimen. Whatcheeria differs from and is more derived than Pederpes, its likely sister taxon, in that only the pterygoid is covered with denticles, the vomer, palatine, and ectopterygoid containing labyrinthine teeth only. Reconstructed dental occlusion indicates that the large choana apparently accommodated the large dentary fangs; this would be a unique feature among early tetrapods. The palatal ramus of the pterygoid is longer than the quadrate ramus, which does not have a descending flange. Like Meckel's cartilage in the lower jaw, the palatoquadrate is fully ossified in larger specimens, such that in a posterior view of the skull the pterygoid is mostly hidden from sight by the epipterygoid. The ossified neurocranium consists of the basiparasphenoid and basioccipital; no ossified sphenethmoid has been found. Remains of otic capsules are partial, crushed, and smeared, so no useful morphology is available. The stapes appears to be more columnar and less plate-like than in many other primitive, early tetrapods.

Keywords

AsbianchoanafossilMississippianocclusionskulltetrapodswhatcheeriids
Type
Articles
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 109 , Issue 1-2: Fossils, Function and Phylogeny: Papers on Early Vertebrate Evolution in Honour of Professor Jennifer A. Clack , March 2018 , pp. 177 - 200
Copyright
Copyright © The Royal Society of Edinburgh 2018 

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