Differentiating ankylosaur species in the Upper Jurassic Morrison Formation in light of newly recovered skeletal elements of Mymoorapelta maysi from its type locality

Abstract

Since the first Jurassic ankylosaur from North America, Mymoorapelta maysi, was described in 1994, considerably more material has been recovered from the type locality in western Colorado. This taxon is the most complete ankylosaur from the Morrison Formation and is completely distinct from Gargoyleosaurus. The new material from this and 11 other known Morrison ankylosaur localities justify a new description of the available fossils to better characterize these two Morrison dinosaur genera and better resolve their distribution through the extent of the Morrison Formation. Mymoorapelta is restricted to the upper Morrison Formation in Utah, Colorado, and southern Wyoming, whereas Gargoyleosaurus is found near the base of the Morrison and up section into the upper Morrison. Gargoyleosaurus may well be represented by more than one species through its stratigraphic range.