| dc.description.abstract | Caenagnathidae is a clade of derived oviraptorosaurian theropods that existed in both Asia and North America during the late Cretaceous, forming the sister clade to Oviraptoridae. While the oviraptorids are known from many well-preserved fossils including brooding specimens and with preserved feathers, the caenagnathid record is less spectacular, particularly from North America. Here, specimens of caenagnathids are rare and fragmentary. The largest North America caenagnathid, Anzu wyliei, from the end-Maastrichtian Hell Creek Formation, is the most complete caenagnathid from North America, and is the only one currently described from that time period. However, the question remains whether or not Anzu wyliei was the only caenagnathid of its time. Here, I describe a new, much smaller caenagnathid specimen from the Hell Creek Formation consisting of several hindlimb elements. A histological analysis was conducted to determine approximate age at the time of death and for comparison to the much larger Anzu wyliei. Based on several histological and osteological traits, I found that this new specimen was not a juvenile Anzu wyliei, but instead a subadult of a second, undescribed species of caenagnathid from the Hell Creek formation, more closely related to Elmisaurus rarus and Citipes elegans than to A. wyliei. The ability to accurately and reliably estimate body mass of extinct taxa is a vital tool for interpreting the physiology and even behavior of long-dead animals. For this reason, paleontologists have experimented with many possible methods of estimating the body mass of extinct animals, with varying degrees of success. These methods can be divided into two main categories: volumetric mass estimation and extant scaling methods. Each has advantages and disadvantages, which is why, when possible, it is best to perform both, and compare the results to determine what is best within reason. Here I employ volumetric mass estimation (VME) to calculate an approximate body mass for previously described specimens of Anzu wyliei from the Carnegie Museum of Natural History. I also use extant scaling methods to try to obtain a reliable mass estimate for this taxon. In addition, I present the first digital life restoration and convex hull of the dinosaur Anzu wyliei used for mass estimation purposes. I found that the volumetric mass estimation using my digital model was 216 - 280kg, which falls within the range predicted by extant scaling techniques, while the mass estimate using minimum convex hulls was below the predicted range, between 159 - 199kg. The VME method for Anzu wyliei strongly affirms the predictive utility of extant-based scaling. However, volumetric mass estimates are likely more precise because the models are based on comprehensive specimen anatomy rather than regressions of a phylogenetically comprehensive but disparate sample. | |
