Tafonomia e paleoicnologia em vertebrados quaternários de cavernas do Lajedo da Escada, Baraúna, Rio Grande do Norte

Abstract

In the Brazilian Intertropical Region, caves concentrate a large amount of Quaternary mammalian fossils, however studies related to the preservational modes of their fossil assemblages are still scarce. The caves of Lajedo da Escada (LES; Baraúna, Rio Grande do Norte; 5° 11.114'S, 37° 43.424'W) had their fossils only studied from taxonomic and paleopathological points of view. The aim of this dissertation is to reveal the taphonomic history of Quaternary vertebrates preserved in LES caves from the identification and interpretation of taphonomic signatures. The LES consists of an outcrop of limestone from the Jandaíra Formation (Upper Cretaceous, Potiguar Basin) with two karst floors, in which five Quaternary caves are inserted. The analyzed material consists of 547 attributed to mammals and reptiles. There were evaluated: (i) taxonomic composition; (ii) ontogenetic stages; (iii) degree of articulation; (iv) fragmentation and bone representativeness; (v) hydraulic equivalence; (vi) transportability indices; (vii) breaking patterns; (viii) weathering marks; (ix) corrosion marks; (x) abrasion marks; (xi) trample marks; (xii) tooth marks; (xiii) insect marks; (xiv) root marks; (xv) color patterns; (xvi) permineralization; (xvii) mineral overgrowth; (xvi) deformation; and (xvii) pathological alterations. There are at least 17 distinct taxa, Eremotherium laurillardi being the most abundant (53.75%, monodominant multitaxic assemblage). All specimens are disarticulated. About 45.52% of the bones are fragments and 97.80% of the breaks are biostratinomic. Approximately 81% of the specimens do not present weathering features, indicating shortly subaerial exposure. About 53.93% of the sample does not present corrosion, reflecting low humidity inside the cave and/or high availability of carbonates associated with terrigenous sediments. Approximately 52.29% of the specimens are not abraded, suggesting little transport. About 7.86% have biogenic marks, reflecting paleoecological interactions in the biocoenosis/thanatocoenosis. Approximately 2.38% have pathological alterations. The large number of specimens of adult individuals (71.12%) point to a selective death in the formation of thanatocoenosis. There is no hydraulic equivalence between the size of the bones and the granulometry of the sediments. In addition, the FTI analyzes indicate a peripheral assemblage. Unexpectedly, there are many articulated individuals of Pachyarmatherium brasiliense, suggesting in situ-preserved assemblage. Finally, the co-occurrence between typical features of wet periods (corrosion) and arid periods (desiccation) reveals temporal mixing in the LES assemblage. In addition, the presence of in-situ and peripheral preserved assemblages indicates spatially-mixed accumulations. Comparatively, the LES caves have similar preservational modes to another Brazilian Quaternary caves but differ from those of South Africa and France