1990 NMGS Spring Meeting: Abstract-2079

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TETRAPOD FAUNA OF THE REDONDA FORMATION (UPPER TRIASSIC), EAS'RCENTRAL NEW MEXICO Adrian P. Hunt New Mexico Museum of Natural History, P.O. Box 7010, Albuquerque, NM, 87194-7010 The Upper Triassic Redonda Formation is widely exposed in Quay and Guadalupe Counties in east-central New Mexico in the Tucumcari basin. The Redonda is the youngest Triassic unit in this area. The Redonda is dominantly of lacustrine origin and is sparsely fossiliferous. However, fluvial and beach facies in eastern Quay County have yielded a diverse tetrapod fauna. Phytosaurs are the most common element of this fauna, represented by a complete skull, a fragmentary skull and numerous postcranial elements and teeth. The skull and ilia represent a new taxon characterized by very wide postorbital-squamosal bars, supratemporal fenestrae that are concealed in dorsal view and a distinct morphology of the ilium; other specimens are indeterminate. Another common taxon is a small new metoposaurid characterized by elongate intercentra, a lacrimal excluded from the orbit and shallow otic notches. A new sphenosuchian is represented by a cervical vertebra and numerous osteoscutes. This sphenosuchian is distinguished from Hesperosuchus by having shorter anterior cervicals with horizontal ventral margins and paramedian osteoscutes that are smooth with very slender anterior processes. An aetosaur similar to Typothorax coccinarum is represented by numerous paramedian osteoscutes. This aetosaur differs from Typothorax in being much smaller with a very narrow carapace and in having paramedian osteoscutes whose length is half their width and which are strongly curved in anterior view. The Redonda aetosaur is similar to Typothorax in having paramedian osteoscutes with a simple pitted pattern and a strong ventral keel. Another new animal is a ?cynodont represented by three teeth. These teeth are thecodont (they thus do not represent a trilophosaur as suggested previously) with a single prominent cusp and prominent cingulae with accessory cusps. Teeth of a large rauisuchian, similar to Postosuchus are common at one locality. P. Murry (Tarleton state) has found a sphenodontid and a ?procolophonid in Redonda microvertebrate samples. Tetrapod trace fossils include coprolites and the ichnotaxa Grallator and Brachychirotherium. The Redonda Formation is a correlative of the Rock Point Member of the Chinle Formation on the Colorado Plateau. Thus, the Redonda fauna is equivalent in age to the dinosaur-dominated fauna of the Ghost Ranch (Coelophysis) quarry in northwestern New Mexico. These faunas are of middle or late Norian age. The Redonda fauna has a typical Late Triassic phytosaur/metoposaur fauna in a time interval dominated by dinosaur faunas in the Rock Point Member and in European stratigraphic units (e.g., Stubensandstein) and thus is important in interpreting faunal change during the later Norian. pp. 40 1990 New Mexico Geological Society Annual Spring Meeting April 6, 1990, Macey Center.

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