Taphonomic analysis of a late Pleistocene vertebrate accumulation from Lage Grande Paleontological Site, Pernambuco State, northeastern Brazil: New remarks on preservational aspects of tank deposits

摘要

Biological, stratigraphic, and temporal processes act on the origin of fossil concentrations. The influence of these phenomena on fossil vertebrate accumulations from tank deposits recently began to be analyzed in detail. This paper documents taphonomic patterns recognized in the late Pleistocene fossil vertebrate accumulation from a tank deposit of Lage Grande Paleontological Site (LGPS), Pernambuco State, northeastern Brazil. The preservation observed in LGPS differs strongly from the expected for tank accumulations and, given the high quality of preservation and the low rate of time-averaging inferred (indicated by the low degrees of surface bone modifications), it seems reasonable that LGPS accumulation reflects nearly non-biased biocenotic patterns. Under this hypothesis, Eremotherium laurillardi was the most abundant species in the region of Lage Grande during the late Pleistocene, similarly to other areas with tank deposits. Surprisingly, cingulates were rare or absent. Non-mammalian vertebrates and Glossotherium were rare in that area. Taphonomic signatures indicate that the thanatocoenosis of Lage Grande experienced a short time span of subaerial exposure prior to burial and short transport to inside the tanks by debris-flows. Thus, LGPS accumulation can be classified as parautochthonous. Besides the inferred rapid burial of the LGPS assemblage, when compared to other tank accumulations, another feature that may had generated the peculiar taphonomic setting of LGPS accumulation is the uncommon pond-like morphology of this deposit. Morphology of the tanks may be one additional factor responsible for differential preservation of vertebrates in this kind of deposit.