From Eocene Greenhouse to Icehouse: Probing environmental and palaeoecological processes on sharks and their relatives from Seymour Island, Antarctica

Autor(en)

Gabriele Larocca Conte, Ashley Liao, Jürgen Kriwet, Thomas Mörs, Sora L. Kim

Abstrakt

The Eocene Epoch (56 – 33.7 Ma) was a geological age when Earth experienced a wide climatic transition from a greenhouse to an icehouse world. Such climatic variability was prompted by the opening of oceanic seaways around Antarctica and/or a drop in atmospheric CO2 levels. Central to this question is the effect of this climatic transition on marine predators like elasmobranchs (i.e., sharks and rays), which may reveal how they survived, declined, or adapted across the natural course of events.

Here, we measure oxygen stable isotopes preserved in shark tooth bioapatite (δ18Op; n = 161) to investigate environmental conditions and paleoecology of the rich and diverse elasmobranch fossil record in the Tertiary La Meseta Formation (TELM 2 to 7, middle to late Eocene) from Seymour Island (Antarctic Peninsula, West Antarctica). We found high variability within TELMs and no significant change in environmental conditions across TELMs (mean δ18Op = 22.0 ± 1.4‰) except from TELM 5 to 6, where δ18Op values increased from 21.7 ± 1.5‰ to 22.5 ± 0.6‰. Across the same units, δ18Op values of benthic sharks increased from 22.0 ± 1.2‰ to 22.7 ± 0.3‰, while pelagic sharks do not show significant changes between TELMs. Among them, the pelagic sand tiger sharks Striatolamia macrota, Brachycarcharias lerichei, and Carcharias sp. are the most abundant representatives in our dataset (n = 119), with S. macrota showing lower δ18Op values in comparison to its relatives only during TELM 4 (middle Eocene; S. macrota δ18Op = 21.2 ± 0.8‰, B. lerichei δ18Op = 22.9 ± 0.5‰, and Carcharias sp. δ18Op = 22.2 ± 1.7‰).

This preliminary dataset indicates that changes to a colder climate occurred toward the late Eocene. The high variability in δ18Op values may reflect seasonal salinity changes in Seymour Island, which was likely an estuarine environment. Alternatively, such variation may reflect regional signals due to the ability of sharks to migrate to deeper or warmer conditions in order to cope with environmental changes and prevent competition between taxa. Further investigations on benthic taxa will elucidate whether they inhabited colder and deeper environments toward the late Eocene in order to constrain the opening of the Drake Passage and the formation of bottom currents around Antarctica.

Organisation(en)

Institut für Paläontologie

Externe Organisation(en)

University of California, Merced, Swedish Museum of Natural History

Anzahl der Seiten

1

Publikationsdatum

2023

Peer-reviewed

Ja

ÖFOS 2012

105118 Paläontologie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/7cb34c3b-88b5-43e3-bcd1-09dda6040775