Revisiting the Dicynodonts of Western North America

Kammerer, C. F., Fröbisch, J., and Angielczyk, K. D. 2013. On the validity and phylogenetic position of Eubrachiosaurus browni, a kannemeyeriiform dicynodont (Anomodontia) from Triassic North America. PLoS ONE 8(5): e64203. doi:10.1371/journal.pone.0064203

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).

Redescription of a Lower Triassic Synapsid and a Reappraissal of Lower Triassic Therocephalian Biostratigraphy

Botha-Brink, J., and S. P. Modesto. 2011. A new skeleton of the Therocephalian synapsid Olivierosuchus parringtoni from the Lower Triassic South African Karoo Basin. Palaeontology Early View. DOI: 10.1111/j.1475-4983.2011.01048.x

Abstract - We provide a redescription of the therocephalian therapsid Olivierosuchus parringtoni based on a new specimen recovered from the Lower Triassic Lystrosaurus Assemblage Zone of South Africa and discuss the biostratigraphic implications of Lower Triassic South African therocephalians. The new specimen comprises a skull and articulated anterior portion of the postcranial skeleton. Olivierosuchus parringtoni can be distinguished from its akidnognathid relatives, Promoschorhynchus and Moschorhinus, by the presence of a relatively slender snout. Features that further distinguish Olivierosuchus from Promoschorhynchus include fewer upper postcanines, an obtuse angle of the transverse process of the pterygoid and an oblique alignment of the suborbital fenestra margin of the palatine. Features that further distinguish Olivierosuchus from Moschorhinus include the presence of a sharp rather than blunt crista choanalis, a spatulate posterior portion of the ectopterygoid instead of a narrow shaft, the presence of prominent pterygoid tuberosities and a narrow, elongated tabular. A reappraisal of Lower Triassic therocephalian biostratigraphy reveals that most of these taxa are restricted to the lowermost part of the Lystrosaurus Assemblage Zone revealing a high diversity, whereafter the diversity decreases dramatically in the middle of the zone. However, despite their scarcity in the middle and upper Lystrosaurus Assemblage Zone, therocephalians in the Karoo Basin remain the most diverse therapsid clade in the lowermost Triassic, which suggests that they were able to recover relatively quickly from the end-Permian extinction event and form an important part of the postextinction earliest Triassic recovery.

First Record of Cynodonts from the Late Triassic of Northern Italy

Renesto, S., and S.G. Lucas. 2009. Cynodont teeth from the Carnian (Late Triassic) of northern Italy. Acta Palaeontologica Polonica 54: 357-360. doi:10.4202/app.2008.0055

Abstract - A jaw fragment with three teeth preserved, collected from the Gorno Formation (Carnian, Upper Triassic) of Lombardy (Italy) is described. The teeth are transversely elongated, three-cusped and bear anterior and posterior cingula. Their overall morphology supports their identification as postcanines of a gomphodont cynodont. The unique tooth morphology of the new specimen supports its attribution to a new genus and species, while at the same time precluding positive assignment to already known gomphodont families. There is a fairly small record of gomphodont cynodonts in Europe, so that the described specimen adds to the knowledge of the distribution and diversity of European gomphodonts and it also represents the first ever collected in Italy.

The authors acknowledge that these teeth are remarkably similar to those of pycnodont fishes; however, they argue strongly for synapsid affinities instead although they admit that the morphology is unique for that group. Indeed, the overall morphology of the teeth is extremely similar to that of pycnodonts (compare Figure 2a in Renesto and Lucas (2009) to a toothplate of Coelodus stantoni pictured here), but I am not familiar enough with synapsids or pycnodonts to make a determination either way. Even though the pycnodonts pictured at the Oceans of Kansas Site are from the Cretaceous, pycnodonts are known from the Late Triassic of the Tethyan Region (including Italy). Furthermore, the formation in which the specimen was recovered (the Gorno Formation) has been interpreted as lagoonal deposits and thus could support either interpretation.

The new taxon erected for these teeth is Gornogomphodon caffii.