Abstract

A new kannemeyeriiform dicynodont is described from the Upper Triassic Tecovas Formation (Dockum Group) of west Texas, U.S.A. The taxon, Argodicynodon boreni gen. et sp. nov., is diagnosed by numerous cranial characters including: squamosal-interparietal sutural contact broad and interdigitating; tall, narrow intertemporal region formed by the parietals with long postorbitals forming the lateral face of the dorsal platform; interparietal forms knobby, bilobed exostoses that wedge between the parietals to form a W-shaped outline in dorsal view; basioccipital and exoccipital contributions to the occipital condyle are distinct, and the dorsal fossa separating the exoccipitals is deeply incised and dorsoventrally deep; caniniform process of the maxilla is dorsoventrally deep and well developed; and an elongated tab-like medial process of the articular exceeds the width of the quadrate roller. A phylogenetic analysis based on 23 continuous and 176 discrete (numeric) morphological characters and 120 taxa finds Argodicynodon conservatively to be a placeriine near the Placerias + Moghreberia group, representing the oldest placeriine in the southwestern U.S.A. and the first named dicynodont genus from the Dockum Group of Texas. A review of Euramerican dicynodont records exposes their hidden diversity and abundance in Laurasia during the Late Triassic. The records of Argodicynodon and other previously undescribed dicynodont fossils from nearby localities underscores the diversity of non-Placerias dicynodonts in the North American Upper Triassic.