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Book Chapter

Early Crocodylomorpha

By
Randall B. Irmis
Randall B. Irmis
Natural History Museum of Utah, 301 Wakara Way, Salt Lake City, UT 84108-1214, USADepartment of Geology & Geophysics, University of Utah, Salt Lake City, UT 84112-0102, USA
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Sterling J. Nesbitt
Sterling J. Nesbitt
Department of Biology, University of Washington, Seattle, WA 98195-1800, USADivision of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA
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Hans-Dieter Sues
Hans-Dieter Sues
Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, NHB MRC 121, P.O. Box 37012, Washington, DC 20013-7012, USA
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Published:
January 01, 2013

Abstract

Non-crocodyliform crocodylomorphs, often called ‘sphenosuchians’, were the earliest-diverging lineages of Crocodylomorpha, and document the stepwise acquisition of many of the features that characterize extant crocodylians. The first crocodylomorph fossils are approximately 230 million years old (upper Carnian, Late Triassic), and at least one of these early lineages persisted until at least 150 million years ago (Late Jurassic). These taxa occupied a wide variety of terrestrial environments from equatorial regions to high-paleolatitudes during the early Mesozoic. Despite a quarter-century of quantitative phylogenetic work, the interrelationships of early crocodylomorphs remain in a state of flux, though recent studies suggest that these lineages are paraphyletic with respect to Crocodyliformes, rather than forming a monophyletic early offshoot of Crocodylomorpha as some previously hypothesized. Nearly all early crocodylomorphs were upright quadrupedal small-bodied taxa, but lumping them all together as small cursorial faunivores masks ecological and morphological disparity in diet and limb functional morphology. With the accelerated pace of recent discovery of new specimens and taxa, future consensus on early crocodylomorph phylogeny will provide a solid framework for understanding their change in diversity and disparity through time, potential biogeographic patterns, and the morphological transformation leading to Crocodyliformes.

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Contents

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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