THE TETRAPOD FAUNA OF THE LATE TRIASSIC REDONDA FORMATION OF EAST-CENTRAL NEW MEXICO: THE MOST SIGNIFICANT LATEST TRIASSIC NONMARINE FAUNA IN NORTH AMERICA

Latest Triassic tetrapod faunas are rare in North America. The best faunas are both known from New Mexico and are the restricted fauna of the Rock Point Formation at the Whitaker quarry in Rio Arriba County and the more diverse fauna of the Redonda Formation in east-central New Mexico. The Redonda fauna is still being developed but it provides diverse elements from a variety of taphofacies. The Redonda fauna occurs in a series of facies in a lacustrine-palustrine basin and includes aquatic through terrestrial components. Tetrapods occur in beach through fluvial settings. A large ichnofauna from the lake margin facies includes Brachychirotherium, “Pseudotetrasauropus,” “Tetrasauropus,” Grallator and two ichnospecies of Rhynchosauroides. The bone record is dominated by phytosaurs, which include several morphotypes that represent Redondasaurus gregorii and at least one other species. Aetosaurs include Redondasuchus reseri and a Typothorax-like form. The metoposaur Apachesaurus gregorii is locally common. Other larger tetrapods include the sphenosuchian Redondavenator, the enigmatic Vancleavea, a small theropod and a large archosaur. Smaller tetrapods include a possible cynodont, a sphenodontid and a procolophonid. The fauna is notable for a number of reasons: (1) several taxa (phytosaur, aetosaur, sphenosuchian) are of very large body size; (2) the fauna has the overall aspect of Carnian-Norian faunas in being dominated by phytosaurs, metoposaurs and aetosaurs in contrast to broadly contemporaneous faunas in South America, South Africa and Europe that are dinosaur dominated; (3) this is the only Late Triassic tetrapod body-fossil fauna associated with a large ichnofauna; (4) the body fossil fauna is not accurately reflected in the associated ichnofauna; and (5) the Redonda is unusual in preserving Late Triassic vertebrate fossils in a range of taphofacies from shallow water lacustrine to paleosol.