Congrats to Dr. Kirstin Brink!
Kirstin Brink successfully defended her Ph.D. in the Department of Ecology and Evolutionary Biology at the University of Toronto this past Monday. Here thesis is entitled “Phylogenetics and Dental Evolution in Sphenacodontidae (Synapsida)”. Her thesis explores the importance of dental histology for identifying tooth characters for phylogenetic analyses, as well as understanding feeding ecology changes through time in the oldest terrestrial apex predator, the iconic sail-backed Dimetrodon. ABSTRACT: Paleozoic sphenacodontid synapsids are the oldest known fully terrestrial apex predators, distinguished by strong heterodonty, massive skulls, and well-developed labio-lingually compressed, recurved teeth with mesial and distal cutting edges (carinae). Dimetrodon is an Early Permian (295–272 Ma) sphenacodontid known from southern USA, Canada, and Germany. Dimetrodon is of exceptional importance as it is the most abundant and speciose sphenacodontid, providing valuable information on issues related to the origin of therapsids. Thirteen species of Dimetrodon are currently recognized from hundreds of specimens, but many of these taxa are primarily identified on the basis of size, stratigraphic, and geographic locations. Therefore, little is known about the relationships among species of Dimetrodon or the role they and other sphenacodontids played as apex predators in shaping Early Permian ecosystems. A robust, species-level phylogeny of sphenacodontids will allow for the examination of evolutionary patterns within the clade. The first in-depth description, including histological analyses of several species of Dimetrodon, reveals that the dentition is diverse and bears species-specific morphology. Tooth morphology includes simple carinae with smooth cutting edges and elaborate enamel features, including the first occurrence of cusps and true denticles (ziphodonty) in the fossil record, and the first description of plicidentine in synapsids. The first species-level time calibrated phylogenetic analysis for sphenacodontids, including the enigmatic Bathygnathus borealis, indicates that significant changes within the clade are related to the dental apparatus. This suggests that the morphological changes in sphenacodontids are associated with changes in feeding style and trophic interactions in these ecosystems. The results presented in this thesis are the first steps towards a more comprehensive understanding of evolutionary changes within sphenacodontids and highlights innovations in the group, including the first adaptations towards hypercarnivory.
Congrats to Kirstin on completing her degree. I also want to thank her for her help setting up and running the palaeohistology lab at the ROM. Kirstin is moving on to a prestigious Killam Postdoctoral Fellowship at the University of British Columbia, working with Dr. Joy Richmond, starting in September.