A new poposaurid from the Upper Triassic of Argentina

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Abstract
The Poposauridae are a group of Middle to Late Triassic rauisuchian archosaurs that are the sister-group of the Crocodylomorpha. A new specimen from the Ischigualasto Formation (Carnian) of Argentina (PVSJ-85) is the first clear record of this group from Gondwana, and is designated the holotype of a new genus and species, Sillosuchus longicervix. The specimen consists of most of the vertebral column, both femora, pubes, and ischia, a partial right ilium, and a single paramedian plate. A distinctive feature shared with Chatterjeea, a poposaurid known from the Dockum Formation of Texas, is the presence of elongate cervical vertebrae with deep, dorsoventrally foreshortened excavations in the sides of the centra. The ilium of Sillosuchus has a prominent overhang that makes the upper surface of the acetabulum concave and partially encloses its dorsolateral edge. The pubes are elongate and narrow with a modest distal expansion forming a small foot. At least four and possibly as many as six sacral vertebrae are present. A number of other poposaurids are known from North America and Europe, although all are currently represented by fragmentary material. Sillosuchus has derived characters (e.g., increased number of sacral vertebrae, cervical morphology, acetabular shape) in common with more derived poposaurids such as Poposaurus and Chatterjeea.