Much More Than It Was Expected: Preservational Differences of Diaphysis and Epiphyseal Ends of Guanaco (Lama guanicoe) Long Bones in Southern Patagonia (Argentina)

Abstract

In archeofaunal assemblages from different parts of the world there is a predominance of diaphysis over articular ends. This differential proportion of diaphysis over epiphysis also characterizes a considerable proportion of the faunal samples from Patagonia, especially those from caves and rockshelters. However, the assemblages recovered from open-air contexts in south Patagonia shows an inverse pattern: a predominance of the epiphysis over the diaphysis of guanaco (Lama guanicoe) long bones, contrary to the expectations derived from their respective bone mineral density (BMD) values. The archeofaunal information obtained from six open-air sites is presented and the pattern is evaluated and compared considering the diaphyseal and epiphyseal long bone structure, the densitometric values obtained by Stahl (1999) for South American camelids, the environmental characteristics related with the substrates (lacustrine clay and sand dunes) of the sites and the regional taphonomic information. It is proposed that in dynamic environments such as those here considered, the observed pattern is related to weathering/abrasion, acting differentially on the types and position of the tissues that form the diaphysis and epiphysis. When the diaphysis begins to open and fragment the fracture stops in the epiphysis. Such process would be accelerated in cultural contexts as a result of obtaining nutrients from long bones -considered of low processing cost (sensu Marean & Cleghorn, 2003)- and blanks for artifacts, causes bone to be fractured. Besides, the lack of large carnivores in Patagonia is another important factor that would affect the differential representation on epiphysis over diaphysis. Similar results obtained on different substrates can sustain the expression of the pattern on a regional scale while indicating that it corresponds to openair site contexts in general. Thus, the correlation between present elements and BMD would result in a partial tool to evaluate the integrity of archaeofaunas from Southern Patagonia open-air sites.