Stable Isotope Analysis of Late Cretaceous (Maastrichtian) Shark Teeth (Serratolamna serrata; Carcharias holmdelensis) from the Western Interior Seaway

• Main Author: Lisle, Rachel
• Other Authors: Davis, Edward, Tate-Jones, Kellum, Munger, Lisa
• Format: Thesis
• Language: English
• Published: University of Oregon 2022
• Subjects: paleoecology; shark; paleontology; stable isotope; cretaceous; Arctic; Arctic Ocean
• Online Access: https://scholarsbank.uoregon.edu/xmlui/handle/1794/27367

The Western Interior Seaway was a Late Cretaceous (100.5-66 Mya) inland sea that, at its largest, stretched north to south from the modern-day Arctic Ocean to the Gulf of Mexico. Research concerning this 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. I sampled fossilized teeth from two species of sharks (Serratolamna serrata; Carcharias holmdelensis) collected from an Arkansas site located in the Late Maastrichtian of the Western Interior Seaway. I used laser ablation techniques to do stable isotope analysis on 10 teeth from S. serrata and 8 teeth from C. holmdelensis. The mean 18O (VSMOW) isotopic value for S. serrata (22.2‰) and C. holmdelensis (22.3‰) indicate no significant difference in primary habitat. The mean reconstructed paleotemperature was 19.5 C, putting this locality at within the upper parameters of a warm temperate climate. The mean 13C (VBDP) isotopic value for S. serrata (-7.23‰) and C. holmdelensis (-9.58‰) indicate a difference in dietary habits or preferences. I hypothesize that these differences are attributed to significant size differences between S. serrata and C. holmdelensis. These size differences would have enabled them to fill slightly different ecological niches which would result in somewhat differing prey sources. Future research is needed to expand upon the paleoecology of Late Cretaceous sharks and the Maastrichtian Western Interior Seaway.