Decoding the microvertebrate record in Los Viscos (Catamarca, Argentina): a taphonomic investigation of the surface bone assemblage.

M.C. MOREANO ; P.E. ORTIZ ; M. MONDINI; M.C. MADOZZO-JAÉN ; C.I. MONTALVO ; M.F. ARIAS

Simposio; 3rd Meeting of the ICAZ Microvertebrate Working Group; 2020

Alero Los Viscos is an archaeological site located in El Bolsón Valley (Catamarca, Argentina), an arid region of the South-Central Andes, at 2470 m.a.s.l. It is a 380 m2 rockshelter containing stonewalled structures, which was occupied since ca. 1220 BP. The faunal record includes many microvertebrate remains, especially on the modern surface and in the upper stratigraphic layers (dated to ca. 600-400 BP), where they may be intrusive. Use of the rockshelter by predator birds and, to a lesser extent, carnivores is indicated by the presence of perches over the rocky walls and pellets and scats on the modern surface. Surface bones of rodents, birds, didelphids, armadillos, and anurans, accumulated over the last 600 years at the most, display clear digestive traces. To help disentangle the complex formation history of the most recent faunal record of the site and assess the actors involved, we performed a taphonomic analysis of 243 micromammal skeletal elements collected from the site modern surface over different field seasons. We evaluated taxonomic and anatomical representation, relative abundance, and degree of breakage and digestion of the remains. Most bones belong to rodents of the genera Ctenomys, Abrocoma, Microcavia, Andinomys, Calomys, and Phyllotis, and a few to the didelphid Thylamys, ranging 15-300g weight. All the taxa are known currently from the study area, although distributed in different habitats (grasslands, shrubs, and rocky areas). Relative abundance was 31.75% average, and cranial elements and femora were frequent. While several skulls, mandibles and postcranial elements were complete, remains with various categories of breakage were abundant. Light to no evidence of digestion was found in 58.71% remains, and several had moderate (16.07%) and extreme digestive modification (6.67%). While breakage may be partly explained by trampling and other processes, digestion traces are more sensitive to the accumulating agent. The fact that light digestion is dominant suggests a Strigiform as the main accumulating actor. Yet, the presence of more intense digestion points to diurnal raptors and/or mammalian carnivores, and suggests that the formation of the assemblage is complex and involves several agents. The modal involvement of a nocturnal raptor is in agreement with the findings in a nearby rockshelter, Cueva de las Máscaras, where a dense natural accumulation of digested skeletal elements was interpreted to be an owl pellet accumulation, possibly by Tyto furcata. By adding to our knowledge of the taphonomic signature of Strigiformes in this Andean area, our study will help unravel the complex taphonomic history of archaeological sites in the El Bolsón Valley, particularly of Alero Los Viscos, where more than half of the zooarchaeological material recovered from the upper layers are microvertebrates.