Dicynodonts More Diverse In Norian Triassic North America

On the Validity and Phylogenetic Position of Eubrachiosaurus browni, a Kannemeyeriiform Dicynodont (Anomodontia) from Triassic North America

Authors:

1. Christian F. Kammerer (a)
2. Jörg Fröbisch (a)
3. Kenneth D. Angielczyk (b)

Affiliations:

a. Museum für Naturkunde, Leibniz Institute for Research on Evolution and Biodiversity, Berlin, Germany

b. Department of Geology, Field Museum of Natural History, Chicago, Illinois, United States of America

Abstract:

The large dicynodont Eubrachiosaurus browni from the Upper Triassic Popo Agie Formation of Wyoming is redescribed. Eubrachiosaurus is a valid taxon that differs from Placerias hesternus, with which it was previously synonymized, by greater anteroposterior expansion of the scapula dorsally and a very large, nearly rectangular humeral ectepicondyle with a broad supinator process. Inclusion of Eubrachiosaurus in a revised phylogenetic analysis of anomodont therapsids indicates that it is a stahleckeriid closely related to the South American genera Ischigualastia and Jachaleria. The recognition of Eubrachiosaurus as a distinct lineage of North American dicynodonts, combined with other recent discoveries in the eastern USA and Europe, alters our perception of Late Triassic dicynodont diversity in the northern hemisphere. Rather than being isolated relicts in previously therapsid-dominated regions, Late Triassic stahleckeriid dicynodonts were continuing to disperse and diversify, even in areas like western North America that were otherwise uninhabited by coeval therapsids (i.e., cynodonts).