Paleoecologia isotópica de mastodontes (Mammalia: Proboscidea) para o Pleistoceno de Minas Gerais, Brasil

Abstract

Proboscidea is a group of large mammals present in the Brazilian fossil record, represented by the species Notiomastodon platensis (Ameghino, 1888). In contribution to all studies seeking to understand the taxonomy, chronology, and diet, including annual variations, as well as the paleoenvironmental aspects of the habitats in which the species lived, a morphological description, absolute dating, and analysis of stable isotopes of carbon and oxygen (δ13C and δ18O) were performed for the mastodon fossils from the North and Triângulo mesoregions of the Minas Gerais State, Brazil. The material includes isolated teeth, mandibular portions, and post-cranial bones in different levels of fragmentation, associated with at least eight adult individuals and one juvenile. The only individual from Campina Verde was dated at 27,715-27,903 Cal yr BP. It presented a mixed diet based on C4 plants (piC4 = 90 %; δ13C = +0.5 ‰), which implies the occupation of an open environment, mostly pasture. The region was relatively humid (δ18O = +24.7 ‰), which is supported by the existence of humidity corridors from the Amazon region. A similar phytophysiognomy was interpreted for the North Region between at least 21,966-22,279 Cal yr BP and 18,944-19,157 Cal yr BP. However, one specimen presented a δ13C value that differed from the others (piC3= 0.87 %; δ13C = –10.2 ‰), occupying a transitional environment between low-density forest and arboreal savannah, probably at a different moment favorable to the expansion of trees and shrubs. The region underwent a climate change, from relatively humid conditions (δ18O = +25.6±0.2 ‰) to expressively dry (δ18O = +34.6 ‰) between the dated periods, a change corroborated by some palynological data. The multiannual paleoecological analysis, based on sequential sampling of three dentin layers of an incisor, indicated the relative stability of vegetation and climate. The perceived disassociation between vegetation dynamics and local hydrology corroborates the idea that other factors may act as more important modulators than precipitation in the Cerrado regions.