NEW GENUS OF SPHENODONTIA FROM THE MORRISON FORMATION (LATE JURASSIC, UTAH) WITH IMPLICATIONS ON MIGRATION PATTERNS AND DIVERSITY

Two nearly complete mandibles of an herbivorous adult Opisthodontia (Sphenodonta, i.e. tuatara) were collected from the Aaron Scott Quarry (Morrison Formation, Jurassic, Utah) - CMC VP 11237 and 11238. The Opisthidontia are represented by eight genera from the Triassic to the Cretaceous, with most genera represented by fewer than five specimens. Previously, only Opisthias and Eilenodon were known from the Jurassic in the United States and only from the Morrison Formation. The specimens from the Aaron Scott Quarry differ significantly from Eilenodontia and are more similar to the Triassic Fraserosphenodon of Europe. Cladistic analysis suggests these specimens with Fraserosphenodon are less derived than Opisthodontia. The relationships of Fraserosphenodon and the Aaron Scott specimens remains unresolved but may indicate 1) a common ancestor for all Opisthodontia or 2) two different ancestors for the clade including Fraserosphenodon, the new specimens and Eilenodontia. Distribution of these specimens indicates two migration paths into North America, with Fraserosphenodon and the new specimens migrating from Europe and the Eilenodontia migrating from South America.