Dacentrurine Stegosaurs in North America: New Occurrences from the Upper Jurassic of USA (Morrison Formation)

Dacentrurinae is a subclade within the iconic dinosaur group Stegosauria, first discovered in the late 19th century and characteristic of Late Jurassic Europe. The taxon “Alcovasaurus” longispinus (Wyoming, USA) has been recombined as the dacentrurine Miragaia longispinus, after comparisons with Miragaia longicollum (Portugal) found it closer to the latter than to the cohabiting Stegosaurus. This demonstrated that dacentrurines were also present in Late Jurassic North America and opened the possibility of more occurrences being found. After first-hand examination of various paleontological collections from the USA and reviews of the literature, at least five more occurrences of dacentrurines were identified, including four in the genus Miragaia. The material reviewed comprises one cervical plate, one dorsal vertebra, and three caudal spines from the Upper Jurassic Morrison Formation of Wyoming or Utah. The existing holotype material of M. longispinus was also analyzed here. These findings further support the theorized dinosaur faunal interchange between Europe and North America during the Late Jurassic and suggest that the presence of dacentrurine stegosaurs in Late Jurassic North America was not a rare accidental occurrence; rather, they were an established part of that ecosystem, likely more diverse and widespread than can currently be determined.