LAUSR

ABSTRACT During the recovery from the end-Permian extinctions in the Middle Triassic, small reptiles (<50 cm) are exceptionally rare, and this gap in the fossil record inhibits our understanding of small reptile ecology and evolution during such a critical transition in Earth history. Here, we fully describe two fragments of left and right hemimandibles of a small sauropsid (UMZC T1162) that likely belonged to the same individual. The specimen bears anteriorly enlarged dentary teeth and labiolingually expanded crown bases, two character states unique to Ruhuhuaria reiszi (Procolophonoidea: Owenettidae), a taxon recently described from the same locality. From this, we tentatively assign UMZC T1162 to Ruhuhuaria reiszi. Micro-computed tomography (CT) and scanning electron microscopy (SEM) were employed to fully examine the morphology of the new specimen and illuminate details of the teeth not available in the holotype. The dentition of UMZC T1162 is better preserved than that of the holotype and shows that the more posterior teeth of this animal were chisel-shaped rather than pointed, that at least some of the teeth were transversely expanded at the base, and that tooth implantation is acrodont in the posterior portion and pleurodont in the anterior portion of the dentary. This potential second specimen of Ruhuhuaria reiszi complicates the previously hypothesized relationships of the taxon and further illustrates the difficulties in assigning small sauropsids to various clades in the Triassic Period. If UMZC T1162 does represent another specimen of Ruhuhuaria reiszi, it would show that small Triassic sauropsids had more variation in their tooth implantation and tooth disparity than previously appreciated.