During the Eocene, the Earth climate system transitioned from greenhouse to icehouse conditions. Central to many explanations is the Southern Ocean—where tectonic configurations influenced oceanic gateways, ocean circulation reduced heat transport, and/or greenhouse gas declines prompted glaciation. To date, few studies have explored the implications of this climate transition on high latitude, marine vertebrates. Seymour Island near the Antarctic Peninsula preserves a rich, diverse fossil assemblage in the Tertiary Eocene La Meseta (TELM) Formation (Fm). We examine teeth of Striatolamia macrota, an extinct (†) sand tiger shark that is abundant throughout the La Meseta Fm. to discern ecological and environmental characteristics. Body size is an integrative ecological trait often tracked through time and space. †Striatolamia macrota body size distributions indicate no shifts during TELMs 2-5 based on anterior tooth crown height (n=450, mean=19.6 ± 6.4 mm, total body length 88-389 cm). Similarly, environmental conditions seem to remain stable through this period based on †S. macrota enameloid with mean d¹⁸O_PO4 value of 21.5 ± 1.6‰ (n=39) and mean temperature estimates of 22.2 ± 5.4°C. This ecological and environmental stasis is intriguing given changes in ocean circulation as tracked by neodymium isotope composition. Our preliminary e_Nd (n=4) results indicate an early Drake Passage opening with Pacific inputs as early as TELM 2 based on 1 unit variation with an overall radiogenic trend, similar to previous results from deep ocean localities. We hypothesize that †S. macrota modified its migration behavior to preclude environmental changes related to the Drake Passage opening. Our results shed important light on paleoceanographic conditions and indicate paleoecological responses to climate change.

see methods in Kim, S. L., Zeichner, S. S., Colman, A. S., Scher, H. D., Kriwet, J., Mörs, T., & Huber, M. (2020). Probing the ecology and climate of the Eocene Southern Ocean with sand tiger sharks Striatolamia macrota. Paleoceanography and Paleoclimatology, 35, e2020PA003997. https://doi.org/10.1029/2020PA003997

DS01.csv contains anterior tooth crown height measurements from extint Striatolamia macrota teeth found in TELMs 2, 3, 4, and 5 from the Eocene La Meseta Fm. of Seymour Island. Also included are total lengths for extant sand tigers Carcharias taurus caught by Dr. Dewayne Fox's research group in the Delaware Bay and the estimated anterior tooth crown heights for those individuals.

Supp_Table1_20-1112.csv includes the specimen IDs, collection, TELM, anterior tooth crown height (ATCH), oxygen isotope composition (from phosphate) and estimated temperature for data included in Kim & Zeichner et al., 2020.

Supp_Table2_20-1112.csv is clumped isotope and oxygen isotope composition (from carbonate) data as well as estimated temperatures and oxygen isotope composition of seawater from Douglas et al., 2014. Kim & Zeichner et al., (2020) applied a different clumped isotope temperature calibration to this previously generated dataset to evaluate the effect on estimated temperature and oxygen isotope composition of seawater. The two values from cement that were interpreted as altered by Douglas et al. (2014) were not included in our analysis.

Supp_Table3_20-1112.pdf compiles the Eoocene paleoceanography and paleoclimateology studies Kim & Zeichner et al. (2020) took into consideration in evaluating their results. This literature review was quite comprehensie and includes both modeling and empirical datasets published from 1991 to 2020. The region, time period, temperature estimate for the Southern Ocean, model vs. indicator (i.e., proxy), and implications are noted.