Abstract
Many explanations for Eocene climate change focus on the Southern Ocean—where tectonics influenced oceanic gateways, ocean circulation reduced heat transport, and greenhouse gas declines prompted glaciation. To date, few studies focus on marine vertebrates at high latitudes to discern paleoecological and paleoenvironmental impacts of this climate transition. The Tertiary Eocene La Meseta (TELM) Formation has a rich fossil assemblage to characterize these impacts; Striatolamia macrota, an extinct (†) sand tiger shark, is abundant throughout the La Meseta Formation. Body size is often tracked to characterize and integrate across multiple ecological dimensions. †S. macrota body size distributions indicate limited changes during TELMs 2–5 based on anterior tooth crown height (n = 450, mean = 19.6 ± 6.4 mm). Similarly, environmental conditions remained stable through this period based on δ18OPO4 values from tooth enameloid (n = 42; 21.5 ± 1.6‰), which corresponds to a mean temperature of 22.0 ± 4.0°C. Our preliminary ε Nd (n = 4) results indicate an early Drake Passage opening with Pacific inputs during TELM 2–3 (45–43 Ma) based on single unit variation with an overall radiogenic trend. Two possible hypotheses to explain these observations are (1) †S. macrota modified its migration behavior to ameliorate environmental changes related to the Drake Passage opening, or (2) the local climate change was small and gateway opening had little impact. While we cannot rule out an ecological explanation, a comparison with climate model results suggests that increased CO2 produces warm conditions that also parsimoniously explain the observations.
Highlights
The Eocene marked a period of climate vastly different from today with temperate ecosystems at high latitudes (i.e., Douglas et al, 2014; Eberle & Greenwood, 2012)
We delve into the paleoecology of the ancient sand tiger shark, †Striatolamia macrota (Agassiz), an extinct, cosmopolitan species found in Eocene nearshore deposits that span from the Arctic (Padilla et al, 2014) to Antarctica (Welton & Zinsmeister, 1980), including midlatitude sites in both hemispheres (Cappetta, 2012)
Teeth were sampled from collections at the University of California Museum of Paleontology (UCMP; Berkeley, CA, USA), which were described in Long (1992), and the Zinsmeister collection at the Paleontological Research Institute (PRI; Ithaca, NY, USA), which were described in Stilwell and Zinsmeister (1992)
Summary
The Eocene marked a period of climate vastly different from today with temperate ecosystems at high latitudes (i.e., Douglas et al, 2014; Eberle & Greenwood, 2012). During this time, climate transitioned from greenhouse to icehouse conditions (Zachos et al, 2008) and impacted the evolutionary history of flora and fauna (Gingerich, 2006; Jocque et al, 2010; Krug et al, 2010; Millar, 1993; Scheibner et al, 2005). We refer to the extinct Eocene †S. macrota and extant C. taurus collectively as “sand tiger” sharks
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