New Mexico Geological Society Annual Spring Meeting — Abstracts

In 1986, field parties from the New Mexico Museum of Natural History (NMMNH) collected an extensive vertebrate fauna form the Upper Triassic (Revueltian lvf: early Norian) Bull Canyon Formation of east-central New Mexico. These included teeth assigned to Revueltosauruscallenderi, then considered to represent an ?ornithischian dinosaur. Localities that yielded Revueltosaurus also yielded diverse skeletal remains. These specimens included a partial skeleton (NMMNH P-16932), and numerous more incomplete remains, of an undescribed, armored crurotarsan. Preparation of dentulous cranial fragments of NMMH P-16932 has shown that this animal is Revueltosaurus and that it is not ornithischian dinosaur.

Revueltosaurus is a crurotarsan distinguished by: wide, rectangular paramedian osteoderms with an irregular pattern of deep pits, lack of lateral osteoderms, a wide tarsus that has a small astragalar medial process and corresponding medial calcaneal concavity and teeth that are remarkably convergent on those of ornithischians. Numerous partial osteoderms and one complete osteoderm are in the NMMNH collection. The complete osteoderm is rectangular and is 64 mm long, 33 mm wide and 5 mm thick. The dorsal surface is covered by an irregular pattern of deep, rounded pits. The medial end of the osteoderm is thickened. The osteoderm thins at its lateral and anterior margins. A smooth lappet runs along the anterior margin and broadens near the lateral margin.

The taxon is a crurotarsan because it processes: (1) a hemicylindrical calcaneal condyle for the fibula; (2) a flexed tibial facet on astragalus; (3) a singular articulation between astragalus and calcaneum; and (4) a single paramedian osteoderm per vertebra. Furthermore, it is assignable to a clade containing derived crurotarsans on the basis of possession of an advanced “crocodile-normal” tarsus. Revueltosaurus this is another unique archosaurmorph of the Chinle Group fossil vertebrate fauna.