CAMPANIAN-MAASTRICHTIAN ANKYLOSAURS OF WEST TEXAS

The Ankylosauria are a well known clade of armored dinosaurs from the Late Cretaceous of North America . Taxa such as Euoplocephalus tutus and Edmontonia longiceps have been found in Late Creataceous formations in Wyoming, Montana, New Mexico and Alberta. However, there is one area of North America were Ankylosaurs are only known from fragmentary specimens. The Big Bend region of West Texas has yielded ankylosaur specimens since the early 20^thcentury, however little work has been done to properly classify these fossils. In this study histologic and osteological methods were used to identify and compare ankylosaur fossils from Big Bend to known North American taxa from the Late Cretaceous. The most common element of ankylosaurs that are found are their dermal armor plates, commonly referred to as osteoderms. Due to this, this study has primarily focused on classifying ankylosaurs using their osteoderms. In the past this method of classifying ankylosaur was thought to be unsound, however studies from Scheyer and Sander (2014), Currie and Burns (2004), and Hayashi et al., (2010) have proved that ankylosaur osteoderms have unique textural and internal osteological features, which can be used to classify ankylosaur at the familial and taxon level. In most previous studies thin sections of the osteoderms were used to study osteological features, which in turn destroyed the specimen for further study. However, in this study microCT scanning and 3-D imaging software have been used as an alternative to destructive testing. The results show a highly detailed 3-D model of the specimens which can be manipulated to external and internal structures. This allows us to view the type of bone that makes up the osteoderms, as well as their relative thickness, and the arrangement of structural fiber bundles. These characteristics can be used to identify families and taxa without destroying the fossil. By using these methods it is possible to further build our understanding of ankylosaur diversity during the end of the Cretaceous.