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Book Chapter

A new aetosaur from the Upper Triassic Chinle Formation of the Eagle Basin, Colorado, USA

By
Bryan J. Small
Bryan J. Small
Museum of Texas Tech University, 3301 4th St., Lubbock, TX 79409-3191, USA
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Jeffrey W. Martz
Jeffrey W. Martz
Department of Earth Sciences, Denver Museum of Nature and Science, 2001, Colorado Blvd, Denver, CO 80205, USA
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Published:
January 01, 2013

Abstract

A small aetosaur skull and skeleton and referred material from the Chinle Formation, Eagle Basin of Colorado, USA, is described as a new taxon, Stenomyti huangae gen. et sp. nov, distinguished from other aetosaurs by the following autapomorphies: three premaxillary teeth; four palpebrals; pronounced midline ridge on frontals and parietals; paired ridges flanking midline ridge on parietal and frontal; exclusion of quadratojugal from ventral margin of skull by contact between jugal and quadrate; exclusion of postorbital from infratemporal fenestra; infratemporal fenestra a horizontally oriented oval that embays the posterior edge of the jugal; retroarticular process longer than distance between articular glenoid and posterior edge of external mandibular fenestra; oval to irregularly shaped ventral osteoderms that do not contact each other. Paramedian and lateral osteoderms of S. huangae are nearly identical to those of Aetosaurus ferratus, and other shared cranial characters suggest that these taxa are closely related and lie outside the clade Typothoracisinae + Desmatosuchinae. This discovery indicates that other reports of Aetosaurus across Laurasia based on osteoderms should be reassessed. Similar confusion with the osteoderms of other non-typothoracisine/desmatosuchine aetosaurs such as Aetosauroides, Stagonolepis and Calyptosuchus suggests that osteoderms are not always reliable taxonomic indicators.

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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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