New records of bioerosive traces associated with Quaternary vertebrate remains in the Toropí/Yupoí Formation (Corrientes, Argentina)

Abstract

Within the fossil record, bioerosions on bone substrates are relatively rare; however, they have an important ecological value, as they allow characterizing the environmental conditions at the time they were produced and the behavior of the producing organisms. Bones constitute an important substrate on which various organisms, in particular insects representing several orders (e.g., Dermestidae, Tenebrionidae, Calliphoridae, Tineidae, and Termitidae), produce modifications as a result of different activities such as feeding, locomotion, fixation, pupation, refuge, among other behaviors. In this study we analyze the fossil traces found in a skull of the sloth Catonyx tarijensis (CTES-PZ7151; Colección Paleontológica "Dr. Rafael Herbst" of the Universidad Nacional del Nordeste, Corrientes) collected from the Lower Member of the Toropí/Yupoí Formation (Late Pleistocene) exposed in the vicinity of Lavalle, Corrientes. The description of the traces was carried out following the methodology proposed by Pirrone and her colleagues in 2014. The material under study is in a good state of preservation, which allowed us to recognize the presence, on the left side of the skull, of a set of bioerosive traces. These are in the form of chambers, some with crescent shape, with an average maximum length of 14.72 mm in its widest part and 6.84 mm in the narrowest, while others have an oval shape, with an average length of 10.68 mm in the widest section and 5.36 mm in the narrowest. All of them have no bioglyphs or active filling, and are limited to the cortical bone. The best-preserved chambers have a flat bottom parallel to the bone surface and an acute angle between the bottom and the walls, characteristics that allow us to assign it to Cubiculum cooperi, a trace interpreted opportunely as corresponding to insect pupation (Pupichnia), probably dermestid beetles, which would be associated with the final stages of decomposition of the remains of this sloth. However, since two distinct morphologies have been identified, it is likely that more than one agent was responsible for the creation of these traces, or that they correspond to different stages of larval development of the same taxon. The presence of these perforations suggests that the animal carcasses remained on the soil surface for long periods before being buried, allowing scavenging invertebrates to take advantage of the dry bones. This new record improves our knowledge about the behavior of the cadaveric entomofauna associated with the Quaternary vertebrate remains of the Northeastern Region of Argentina.