Latest Maastrichtian middle- and high-latitude mosasaurs and fish isotopic composition: carbon source, thermoregulation strategy, and thermal latitudinal gradient

LEUZINGER ;L.; KOCSIS, L. ; ULYANOV, A. ; FERNÁNDEZ, M.S.

PALEOBIOLOGY

PALEONTOLOGICAL SOC INC

Lugar: Lawrence; Año: 2023

0094-8373

Here we report high-latitude stable isotope compositions of Maastrichtian fossil fish and marine reptiles (mainly mosasaurs) from Antarctica (64°S paleolatitude) and compare them with midpaleolatitude samples from Argentine Patagonia (45°S). Disparities between the δC values of bony fish and marine reptiles correspond to differences in the foraging ground (distance from the shore and depth), while dramatically higher δ 13 C values (by 18‰) in shark enameloid cannot be explained through ecology and are here imputed to biomineralization. Comparison with extant vertebrates suggests that the diet alone can explain the offset observed between bony fish and mosasaurs; however, breath holding due to a diving behavior in mosasaurs may have had some impact on their δ 13 C values, as previously suggested. The δ 18 O values of the remains confirm a relatively stable, elevated body temperature for marine reptiles, meaning that they were thermoregulators. We calculated a water temperature of ∼8°C for Antarctica from the fish δPO4 18 O values, warmer than present-day temperatures and consistent with the absence of polar ice sheets during the latest Maastrichtian. Our fish data greatly extend the latitudinal range of Late Cretaceous fish δ 18 PO4 O values and result in a thermal gradient of 0.4°C/1° of latitude whencombined with literature data.