Palimpsest of micromammal deposits in an archaeological rockshelter (Álvarez 4) from Northwestern Patagonia. Taphonomy, palaeoenvironments and human subsistence

FERNANDO J. FERNÁNDEZ; AILÍN GUILLERMO; CLAUDIA MONTALVO

Terragona

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

Microvertebrate Working Group (ICAZ)

This study provided a taphonomic and paleoenvironmental analysis of the micromammal (˂1 kg)accumulations from the archaeological site of Álvarez 4, a rockshelter located in the middle basinof the Limay river (40º48?38.8? S, 70º27?12.9?W), Northwestern Patagonia. The subsistence ofthe hunter-gatherers that inhabited the rockshelter throughout the last 1100 years was based mainly on Lama guanicoe, and complemented with medium-sized animals. The archaeological sequence was divided into five units: 1) Period I (PI; 1100±7014C BP); 2) Period II (PII; 210±9014C BP); 3) a disturbed square ?S3?; 4) a discrete fossil ?pellet? accumulation, immediately below the 5)Surface unit. The micromammal remains [Number of identified specimens (NISP) = 400] were evaluated using taphonomic categories (including anatomical representation, breakage and digestion) and palaeoenvironmental (presence/absence of certain species) methodologies. The most frequent rodent remains in the stratigraphic units correspond to Ctenomyidae [Minimum number of Elements (MNE) = 65] and Caviidae (MNE = 118). Two tibias of Caviidae from PII and ?S3? presented partially thermoaltered distal portions, which is a typical pattern indicating humanconsumption. Two species of Caviidae were identified (Microcavia australis and Galealeucoblephara) in the stratigraphic units. This low-ranking resource may have complemented theotherwise high-ranking animals (L. guanicoe) found in Álvarez 4, suggesting significant dietbreadth as is frequently seen from several archaeological sites in the area. In fossil ?pellets?accumulation, Sigmodontinae (MNE = 98) are the most abundant taxa. The average of relativeabundances of elements from units PI, PII and ?S3? were lower compared to the ?pellets?accumulation and Surface unit. In all units, taphonomic indices show better representation ofcranial elements than postcranial, and distal elements than proximal of limb bones. In stratigraphicunits PI, PII and ?S3?, remains without evidence of digestion dominated the assemblages followedby those exhibiting light modification.The presence of several remains with light digestion could indicate the action of strigiforms in these levels. In fossil ?pellets?, the proportion of cranial and postcranial elements present was similar, with several complete specimens and others highly fragmented. These accumulations have remains with digestive corrosion embracing all categories, including extreme, which suggests the action of a predator that cause heavy modification such as accipitriforms or falconiforms. The sigmodontines Phyllotis xanthopygus and Reithrodon auritus were found in all units. Other sigmodontines including Eligmodontia sp., Akodon iniscatus, Euneomys chinchilloides, Loxodontomys micropus, Abrothrix hirta and Calomys musculinus, and the marsupial Lestodelphys halli were only recorded in PI, PII and S3.These micromammal assemblages point out the development of open areas of shrubby-grassy Patagonian steppe and large rocky outcrops. In addition, the aforementioned taxa are also found in modern pellets yielded by different raptor species (Tyto alba, Bubo virginianus and Geranoaetus melanoleucus) occurring within a ~40-km radius of the rockshelter, suggesting fairly stable ecological conditions for the last 1100 years. Some minor change could be indicated by Galea leucoblephara, which is known to inhabit the Monte desert, and found in the stratigraphic units of Álvarez 4, but not within in the nearest modern samples to the rockshelter.