Theropod Dinosaur Ichnogenus Hispanosauropus Identified from the Morrison Formation (Upper Jurassic), Western North America

摘要

Redescription of a trackway from the Salt Wash Member of the Morrison Formation (Upper Jurassic) in eastern Utah and comparisons with other tracks known from the Jurassic and Cretaceous of the region and the Late Jurassic globally indicate that the large theropod ichnogenus Hispanosauropus Mensink and Mertmann, 1984, previously known only from Europe, occurs also in the Morrison Formation. Hispanosauropus is distinct from Megalosauripus and most likely was made by an allosauroid theropod, although the possibility that it was made by a spinosauroid (torvosaurid) or a ceratosauroid cannot be ruled out. Close geographic and stratigraphic association of Hispanosauropus with the large theropod body fossil taxa Allosaurus, Torvosaurus, and Ceratosaurus in both North America and the Iberian Peninsula strengthens the case for the track's having been made by one of these genera. Megalosauripus appears to dominate large theropod track samples from the Entrada Sandstone through the base of the Morrison Formation (Tidwell Member); Hispanosauropus and similar tracks are most common in the Salt Wash Member and its equivalents, suggesting taxonomic turnover in the large theropod faunas during the early part of Morrison Formation deposition.