Tag: Kellum Tate-Jones

Stable Isotope Analysis of Fossil Shark Teeth from the Late Cretaceous Western Interior Seaway

Presenter: Rachel Lisle − Earth Sciences

Faculty Mentor(s): Edward Davis, Kellum Tate-Jones

Session: (In-Person) Poster Presentation

The Western Interior Seaway was a Late Cretaceous (100.5-66 mya) inland sea that, at it’s largest, stretched north to south, from the modern-day Arctic Ocean to the Gulf of Mexico. Research concerning the seaway has revealed that there was likely a significant temperature gradient present, with cooler temperate waters to the north and warmer subtropical waters to the south. Using fossilized teeth from two species of sharks collected from an Arkansas site associated with the Western Interior Seaway, I seek to use carbon and oxygen isotopes to interpret the paleoecological conditions present in the southern province of the seaway during the Late Cretaceous. I also seek to identify what conditions made it suitable for these sharks to live in this province. Using stable isotope analysis by way of laser ablation, as well as conducting a literature review on relevant sources, I have found that these sharks likely preferred the subtropical temperatures over cooler temperate waters. Mirroring this is a similar pattern in salinity, wherein these species likely preferred water with a higher salinity than the more brackish water up north. This research is essential in understanding what conditions made the seaway favorable for shark species and how extinct marine vertebrates interacted with and reacted to their environment.

Lobodon carcinophaga: Evolutionary constraints on the spatial variability of crabeater seal postcanine teeth for successful filter-feeding foraging strategies

Presenter(s): Megan Pollak—Earth Sciences—Paleontology

Faculty Mentor(s): Kellum Tate-Jones

Session 6: The Earth, Sky & Everything In Between

Pinnipeds, the group that includes true seals, eared seals, and walruses, generally display highly variable tooth spacing . Previous studies have credited this variability to the typical pinniped feeding mechanism, a combination of suction feeding and pierce feeding known as the “grab-and-gulp” method, which does not require precise dental occlusion . However, the crabeater seal (i .e ., Lobodon carcinophaga) is unique among pinnipeds as a filter-feeder . The distinct sieve-like postcanine tooth processes such as high-cuspation and intricate trellis-like morphology allow the crabeater seal to effectively strain small krill from the water . I hypothesize that individuals in this group with unevenly spaced teeth are unlikely to survive ecological pressures and are thus removed from the population by natural selection, leading to lesser variation in crabeater seal tooth spacing than in grab-and-gulp feeders . I test this hypothesis by assessing whether the distinctive feeding method of the crabeater seal constrains tooth spacing by comparing the variability in tooth gaps of crabeater seals to that of bearded seals (i .e ., Erignathus barbatus) . I measured the tooth gaps between the postcanine teeth of 21 specimens of L . carcinophaga and 11 specimens of E . barbatus . I then performed an F test of equal variance on these two datasets . I found that crabeater seal tooth gaps are significantly less variable in spacing than those of bearded seals . This result supports my hypothesis that natural selective processes have generated evolutionary constraints for lower variability in tooth spacing in the filter- feeder, L . carcinophaga, than in grab-and-gulp feeders such as E . barbatus .