Histologia óssea e diagênese fóssil de smilodon populator e puma concolor (carnivora: felidae) do pleistoceno do Brasil equatorial

Abstract

Large felids have been one of the groups most impacted by climate change over the last 50,000 years. By comparing palaeobiological aspects of extinct species with those of living species, it is possible to identify possible reasons for extinction selectivity and even describe how species were affected by environmental changes in the past. Understanding these issues is fundamental to understanding the risk that current species face in the face of ongoing climate change. In this study, the femur histology of Smilodon populator (MCC-868V) and a fossil specimen of Puma concolor (MCC-991V) were sampled, both from Quaternary deposits in Rio Grande do Norte, northeastern Brazil, one from a tank and the other from a cave. In addition, estimates of body mass were made for the specimens analysed to compare with bone compactness, and the diagenetic signatures of both specimens were analysed. The presence of EFS (External Fundamental System), generations of secondary osteons and remodeled bone tissue suggest that the individuals analysed were sexually mature, although MCC-868V was a young adult at the time of death and MCC-991V a senescent adult. P. concolor showed slightly greater bone compactness, which may be related to its more advanced ontogenetic stage. The estimated mass for the P. concolor (62 kg) is within the limits observed for the species. However, the estimated mass for S. populator (157 kg) is lower than expected, even though the specimen analysed was an adult with closed growth. There is no histological evidence that the specimen in question was restricted during its growth, suggesting a naturally smaller individual, a trait that may have been selected in a local population due to the specific environmental and ecological conditions of the region and/or the presence of competition with other carnivore(s). Both specimens analysed showed growth with intense secondary remodelling, which differs from what is known for most tetrapods. The extinction of Smilodon is likely more related to ecological aspects, such as a reduction in prey availability or preferred habitat than physiological aspects. Finally, MCC-868V shows diagenetic fractures filled with oxides that break up histological structures and the presence of quartz grains in the bone trabeculae. MCC-991V, on the other hand, shows evidence of recent weathering and the presence of oxide precipitates. The diagenesis of the specimens analysed is very similar to that found in other fossils from the same deposits, which adds to the understanding of the fossilization processes involved in tank and cave deposits in equatorial regions.