Geochemical characterization of late cretaceous marine reptiles and fish from Antarctica and Patagonia

Abstract

Mosasaur, plesiosaur and Enchodus fish remains from Antarctica (Isla Marambio – López de Bertodano Fm., late Maastrichthian), as well as mosasaur and shark teeth from Patagonia, Argentina (Los Bajos de Trapalco and Santa Rosa, Río Negro – Jagüel Fm., late Maastrichthian) have been 18OPO4 13CCO3 18OCO3) and trace element compositions in order to trace possible ecological and taphonomical information of their bioapatite. Enamel18OPO4 values of the fishes from Antarctica are 1 ‰ higher on average than the Patagonian population, which could reflect expected latitudinal seawater temperature differences between the two regions during the Late Cretaceous (paleolatitude of 64°S versus 45°S, respectively). In contrast, the marine reptiles have a higher 18OPO4 values and average isotopic compositions 3 to 4 ‰ lower than those of the fishes. This result is compatible with earlier studies and collectively suggests that these reptiles were able to maintain higher body 13CCO3 values are also different between fishes and reptiles with higher values for the fishes. Both mosasaurs and plesiosaurs have very low 13CCO3 values (–11.2 ± 2.2 ‰, n=12 and 11.8± 0.9 ‰, n=5, respectively), which cannot only be explained by their trophic level (i.e., diet) but are also linked to their respiratory physiology relating to their diving habits. The two oxygen isotopic values 18OPO4 and 18OCO3, derived from enamel/enameloid correlate for the Antarctica samples (R2=0.79), which may be taken as a sign of good preservation. Complete isotopic re-equilibration between the two oxygen bearing phases is highly unlikely in the view of preserved ecological differences between fishes and 18OPO4 13CCO3 18OCO3 can be overprinted in the structural carbonate of the apatite, which is probably the case for the Patagonian samples. In view of the trace element content, especially the early diagenetic rare earth elements (REE) and uranium (U), all samples may have had a complex diagenetic history, indicated by their large variation in REE concentrations and distributions. Enamel/enameloid seems to be better preserved and reflect early depositional conditions, while in some cases dentine probably affected further by late trace element exchange maybe even during weathering processes.