Padrões ecológicos de tubarões (Superordem: Selachimorpha) fósseis e recentes obtidos a partir de isótopos estáveis e suas considerações para manejo e conservação

Abstract

Sharks populations are declining drastically in many parts of the world, demanding new complementary approaches for the comprehension of biological characteristics. Amplifying the temporal range of investigation to the Miocene past (23 Ma), this research had as objective interpret ecological features from extant and fossil sharks by the way of stable isotopes measurements of carbon and oxygen, looking to generate intellectual basis for management and conservation plans. In total, 46 teeth of several localities were utilized, most are from the coastal region of eastern Amazonia, but also from proto-Caribbean fossiliferous deposits. Isotopic analysis were employed in the distinct bioapatites structures: carbonate and phosphate, where the enameloid was preferentially uptaken in the samples to reduce possibilities of collect unoriginal chemical signatures. A tooth file analyzed from extant specimens exhibited strong correlations among the involved variables (carbon and oxygen), potentially signaling an isotopic fractionation effect in the carbonate structure varying in accordance with tooth development. Oxygen in phosphate results ranged between 18,9‰ to 21.4 ‰, indicating paleotemperatures where these animals lived around 21,6°C to 30,6°C. Statistical tests were performed in the observed values, allowing the discrimination of three groups: Pirabas group (fossil sharks of Pirabas Formation) Recent group (extant sharks of the Amazon coastal region) and non-Pirabas group (fossil sharks of proto-Caribbean deposits). Global, regional and biological environmental considerations about these individuals were revised to understand their distinct chemical signatures. Oceanographic influences and changes in planetary patterns seem to justify some peculiarities of the measures found in non-Pirabas group. On the other hand, the ecological stability verified comparing the paleotemperatures of the Pirabas group with the Recent group suggests resilience on the part of these sharks, by maintaining similar ecological niches during geological time in the Amazon region. However, it also implies a biological preference for swimming in specific conditions for a better physiological performance. The ecological pattern of activity proposed for the sharks of the northern Brazil (23°C-30°C), in addition to paleointerferences about the group here realized should be incorporated in future plans of management and conservation of elasmobranchs, as they reinforce the existing scientific knowledge concerning this táxon.