New Mexico Geological Society Annual Spring Meeting — Abstracts

In 1988, Hunt (New Mexico Geology, 10: 65) claimed the oldest prosauropod dinosaur from the Upper Triassic of the western United States was based on teeth from the Bull Canyon Formation of the Chinle Group in east-central New Mexico. However, he later reassigned these teeth to the ornithischian dinosaur Revueltosaurus. An isolated tooth from the Tecovas Member of the Dockum Formation near Kalgary, Crosby County, Texas, represents the oldest definitive record of a prosauropod dinosaur from the western United States. Its age is Adamanian (late Carnian, about 225 Ma) based on vertebrate biostratigraphy, palynostratigraphy and other data.

The tooth is tall, bilaterally compressed and spatulate. Height = 7 mm, basal crown width = 1 mm, and basal crown length = 4 mm. In lingual or labial view, the tooth is symmetrical with as many as 33 serrations on each margin, all of which are inclined about 450 to the crown edges. On both the lingual and labial surfaces, a median ridge extends from the apex to the base of the crown and gradually widens to form a shallow, triangular concavity on the basal half of the tooth. These concavities may represent abrasion of the relatively prominent basal ridge surfaces. Mesio-distally, the tooth is straight and narrow. The crown base shows slight constriction.

The Kalgary tooth thus displays the following features, which in combination are dental synapomorphies of the Prosauropoda: (1) spatulate shape; (2) symmetrical crown; (3) numerous, obliquely-angled marginal serrations; (4) poorly developed "neck"; and (5) straight and narrow shape in mesio-distal views. These features clearly distinguish the specimen from the numerous ornithischian teeth also collected at the Kalgary locality. With the addition of this tooth, prosauropods are known nearly to the base of the Chinle Group.