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Book Chapter

Morphology and diversity of the mandibular symphysis of archosauriforms

By
Casey M. Holliday
Casey M. Holliday
Department of Pathology and Anatomical Sciences, School of Medicine, University of Missouri, Columbia, MO, USA
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Sterling J. Nesbitt
Sterling J. Nesbitt
Department of Biology, University of Washington, Seattle, WA 98145, USA
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Published:
January 01, 2013

Abstract

Archosauromorphs radiated into numerous trophic niches during the Mesozoic, many of which were accommodated by particular suites of cranial adaptations and feeding behaviours. The mandibular symphysis, the joint linking the mandibles, is a poorly understood craniomandibular joint that may offer significant insight into skull function and feeding ecology. Using comparative data from extant amniotes, we investigated the skeletal anatomy and osteological correlates of relevant soft tissues in a survey of archosauromorph mandibular symphyses. Characters were identified and their evolution mapped using a current phylogeny of archosauriforms with the addition of non-archosauriform archosauromorphs. Extinct taxa with the simple Class I condition (e.g. proterochampsids, ‘rauisuchians’), rugose Class II (aetosaurs, protosuchians, silesaurids) and interdigitating Class III symphyses (e.g. phytosaurs, crocodyliforms) and finally fused Class IV (avians) build the joints in expected ways, although they differ in the contributions of bony elements and Meckel’s cartilage. Optimization of the different classes of symphyses across archosauromorph clades indicates that major iterative transitions from plesiomorphic Class I to derived, rigid Class II–IV symphyses occurred along the lines to phytosaurs, aetosaurs, a subset of poposauroids, crocodyliformes, pterosaurs and birds. These transitions in symphyseal morphology also appear to track changes in dentition and potentially diet.

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Geological Society, London, Special Publications

Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin

S. J. Nesbitt
S. J. Nesbitt
University of Washington, USA
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J. B. Desojo
J. B. Desojo
Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’, Argentina
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R. B. Irmis
R. B. Irmis
Natural History Museum of Utah, USA
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Geological Society of London
Volume
379
ISBN electronic:
9781862396395
Publication date:
January 01, 2013

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