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Topic

Investigating the diversity and palaeobiogeography of ankylosaurian dinosaurs using tooth morphometrics

School of Earth and Ocean Sciences

Date & location

• Friday, July 26, 2024
• 1:00 P.M.
• Clearihue Building, Room A127

Examining Committee

Supervisory Committee

• Dr. Victoria Arbour, School of Earth and Ocean Sciences, ·¬ÇÑÉçÇø (Co-Supervisor)
• Dr. Andy Fraass, School of Earth and Ocean Sciences, UVic (Co-Supervisor)
• Dr. Blake Dyer, School of Earth and Ocean Sciences, UVic (Outside Member)

External Examiner

• Dr. Michael Burns, Department of Biology, Jacksonville State University

Chair of Oral Examination

• Dr. Michael McGuire, Department of Electrical and Computer Engineering, UVic

Abstract

The presence of a basal cingulum, fluting, and overall size have been used to differentiate nodosaurid and ankylosaurid teeth for decades. However, the taxonomic utility of tooth morphology in ankylosaurs has not yet been quantitatively tested. Additionally, new phylogenetic hypotheses recognize four ankylosaur families (Panoplosauridae, Polacanthidae, Struthiosauridae, and Ankylosauridae), rather than the traditional nodosaurid-ankylosaurid dichotomy. Understanding ankylosaur tooth variation could better help identify taxa with ambiguous phylogenetic affinities or allow isolated teeth to test palaeoecological questions like the potential extirpation of mid Cretaceous ankylosaurids from Laramidia. I analyzed a large sample of ankylosaur teeth from the Cretaceous of Laramidia using traditional and 2D outline geometric morphometrics and investigated the utility of size and the presence or absence of a cingulum and fluting for differentiating ankylosaur teeth. Morphometric analyses show that ‘nodosaurids’ had the greatest variation in tooth shape and size. Panoplosauridae accounts for a large amount of ‘nodosaurid’ variation, whereas basal ankylosaurs, Polacanthidae, and Ankylosauridae share a similar restricted morphospace. Previously, small teeth were identified as ankylosaurid and large teeth as nodosaurid; teeth with a crown base length or height over 10 mm are only found in panoplosaurids and Peloroplites, traditionally considered a nodosaurid but recently recovered as a polacanthid, but smaller sizes are found in all clades. A basal cingulum and fluting are associated with Ankylosauridae and Panoplosauridae, but not with other ankylosaur families. Linear discriminant analyses could only accurately identify between 50-75% of the teeth in our sample. LDAs should therefore be used in conjunction with size and discrete traits to identify isolated teeth as panoplosaurids. As such, caution should be used when attempting to use isolated ankylosaur teeth in broader palaeoecological questions.