A NEW POPOSAURID FROM THE UPPER TRIASSIC OF ARGENTINA

The Poposauridae are a group of Middle to Late Triassic rauisuchian ar chosaurs that are the sister-group of the Crocodylomorpha. A new speci men from the Ischigualasto Formation (Carnian) of Argentina (PVSJ-85) is the first clear record of this group from Gondwana, and is designat ed the holotype of a new genus and species, Sillosuchus longicervix. T he specimen consists of most of the vertebral column, both femora, pub es, 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 v ertebrae with deep, dorsoventrally foreshortened excavations in the si des of the centra. The ilium of Sillosuchus has a prominent overhang t hat makes the upper surface of the acetabulum concave and partially en closes its dorsolateral edge. The pubes are elongate and narrow with a modest distal expansion forming a small foot. At least four and possi bly as many as six sacral vertebrae are present. A number of other pop osaurids are known from North America and Europe, although all are cur rently represented by fragmentary material. Sillosuchus has derived ch aracters (e.g., increased number of sacral vertebrae, cervical morphol ogy, acetabular shape) in common with more derived poposaurids such as Poposaurus and Chatterjeea.