Post mortem modifications (Pseudopaleopathologies) in middle- late pleistocene mammal fossils from Southern Brazil

Abstract

Here are described post mortem modifications (pseudopaleopathologies) in 762 specimens of extinct mammals from three middle to late Pleistocene assemblages (Campanha, Chuí Creek and continental shelf) of the state of Rio Grande do Sul, southern Brazil. These assemblages include mostly large-sized herbivores preserved in fluvial facies, although the assemblage from the shelf consist of remains that were reworked several times by sea-level oscillations. Although some patterns of modification are similar between the assemblages (e.g. post-fossilization plain fractures), others such as the grade of abrasion or weathering varies according to the depositional setting. The scarcity of modifications that could be attributed to predators or scavengers indicate that carnivory was not a major process driving the formation of the assemblages. Most of the fossils from the Campanha are complete, but a relatively high proportion of them exhibits advanced stage of weathering, whereas those from Chuí Creek and the continental shelf are mostly unweathered. Most of the remains from the Campanha and Chuí Creek are unabraded, whereas all fossils from the shelf were subject to abrasion. Few fossils exhibit signs of modification by organisms such as plants and insects. Fossils from the continental shelf have crusts of beach rock, and some specimens from the Campanha and Chuí Creek have crusts of calcium carbonate or iron oxide. Besides the abrasion, the main difference between fossils from the continental and marine assemblages is the dark color and higher mechanical resistance of the latter. This difference is related to post depositional geochemical processes in the marine environment. The chemical composition of fossils from Chuí Creek and continental shelf was qualitatively analyzed using energy dispersive X-ray spectrometry (EDX) and compared with recent bones. The results show the presence in the fossils of several elements not found in recent bones, incorporated through diagenetic processes controlled by specific conditions of each depositional environment.