EXPLORATORY EVALUATION OF ABNORMAL EROSIVE STRUCTURES IN PACHYCEPHALOSAURID CRANIA

The frontoparietal domes of pachycephalosaurids (Ornithischia: Marginocephalia) have been hypothesized as functioning structures for elaborate display rather than agonistic behavior, which is the traditional functional hypothesis. The display hypothesis is based, in part, on a reported lack of identified pathologies on the dorsal surface of frontoparietal domes. Abnormal surface features that have been reported on domes have received casual mention and attributed to taphonomic alteration. Identifying the potential etiologies of these features is problematic; erosive structures can be caused by a variety of biological processes such as pathologies due to injury or disease, and taphonomic processes such as scavenging, insect modification, weathering, and erosion.

To establish a quantified evaluation of frontoparietal abnormalities, pachycephalosaur domes from the vertebrate paleontology collections at the Burpee Museum of Natural History (BMRP) in Rockford, IL, University of Alberta (ALVP) in Edmonton, Alberta, and the Tyrell Museum of Paleontology (TMP) in Drumheller, Alberta were compared and recorded for any abnormal surface feature, regardless of cause. A classification of lesions was constructed, composed of five categories based on depth, width, and morphology of the feature. A total of 16 specimens were observed for this preliminary comparison, and the BMRP specimen was also CT-scanned to observe internal characteristics associated with erosive cranial structures.

The preliminary results of this study indicate a similar assemblage of abnormal surface features on frontoparietal domes present throughout the pachycephalosaur clade. The similarity of these features suggests a potential suite of common etiologies resulting in erosive pitting on the dorsal surface of pachycephalosaur domes. Future evaluations of frontoparietal dome taphonomy will likely bring better understanding of the potential etiologies of abnormal surface features on pachycephalosaurid crania, and will contribute to investigations regarding the function of frontoparietal domes.