WEATHERING

The Salado River Depression was inhabited during the Late Holocene (2400-400 14C YBP) by pottery-maker societies with a hunting-gathering-fishing lifeway. The archaeological remains are deposited in the A horizon of the modern soil, which constitutes a "biomantle" as pedogenetic formation processes predominate. These include an intense biological activity produced by the action of roots and edaphic fauna that promote displacements of objects and their sinking to different depths. Hence the archaeological sites of this microregion are shallow. In order to broaden the knowledge about the action of earthworms in these sites, an actualistic taphonomy experiment was designed. The goal was to observe the activity of these invertebrates and to evaluate their possible incidence as a disturbing agent on small bones deposited on a soil. The aim of this paper is to introduce the methodological design of this experimentation and present the preliminary results. For this purpose, two containers with sediment containing humus and earthworms were placed in the open air. Some selected bones of Dasypus hybridus and Gallus gallus were deposited in each container. The activity of earthworms was observed along one year with a weekly record and was detected as deep as 16 cm. Other features associated -such as burrows- were documented, especially in autumn and winter. No modifications were identified on bone cortical surfaces, though vertical movement of some elements through the sediment is highlighted.

This work analyzes a modern bone concentration at Cueva 7, in Los Toldos archaeological locality, as part of the taphonomic studies that we have carried out in the northeast of the Central Plateau of Santa Cruz province (Argentina). The goal of this work is to identify the actualistic taphonomic patterns that can contribute to a better interpretation of the archaeological sites in caves or rock shelters where piles or dense bone concentrations were registered in the study region. From the identification of different taxonomic, anatomic, mortality, and bone modification patterns in this highly-dense accumulation, we evaluate the possible causes of its formation, and produce actualistic information which may be of use to learn about the different processes that accumulate and scatter zooarchaeological remains in the cave environments of the study area. The results show a monospecific assemblage integrated by no less than 43 Ovis aries individuals whose death was natural. The accumulation is characterized by a natural disarticulation pattern, which appears to be more accelerated in appendicular elements, a homogenous weathering profile with minor differences that may be associated with the microenvironments recorded inside the cave, and the very low incidence of natural agents, where trampling was the highest. This work thus provides valuable actualistic information that can be used as a parameter in the determination of possible natural contamination in archaeological contexts.

A mass stranding of 181 false killer whales (Pseudorca crassidens) occurred in March 1989 on both sides of the Strait of Magellan. Fifteen years later, taphonomic observations were made on this concentration and the results are presented in this article. In the coast of Bahía Lomas, Tierra del Fuego (Chile), frequencies of articulated elements were quantified following Hill (1979a, 1979b), and a ranking of natural bone disarticulation for whales was proposed. This ranking was made on the basis of skeletons from one species but, given the morphological similarities of Cetaceae, it is possible to suggest that it applies to similarly-sized Odontoceti. Together with other useful taphonomic criteria (weathering and bone preservation), these results can be used to disentangle the origin of whale bone accumulations at coastal archaeological sites in different parts of the world and to estimate the time of burial of zooarchaeological assemblages. In this way, the role of whales in human diet can be discussed in greater detail.

In this study we evaluate modern accumulation, dispersion and preservation patterns of guanaco bones (Lama guanicoe) and discuss their implications for the zooarchaeological record of coastal Tierra del Fuego in southern South America. We surveyed four environmental units: the supra-tidal zone, forests, grasslands, and peat bogs. The guanaco assemblages consist of both disarticulated and articulated bones, most represented by limbs and heads (only two nearly complete carcasses were recorded). Natural processes such as marine abrasion largely affected the preservation of specimens, while weathering is a conspicuous effect observed on bones from the forest. Age and sex profiles, as well as variability in preservation, reflect attritional deaths in different time periods. The guanaco seems to be found regularly along the southeast coasts, being an available resource for coastal and marine hunter-gatherers with relatively narrow foraging ranges. The presence of guanaco is higher during autumn and winter. Bone remains are subject to vertical migration in peat bogs, grasslands and other soft substrates, allowing time-averaging of faunal assemblage formations.

The main objective of this paper is to characterize the pattern of thermal alteration in a sample of modern bones collected after a natural grassland fire in the Pampas region (Argentina). A total of 917 bone remains were recovered, including a variety of different body size taxa. Results suggest that natural grassland fires affect bone remains in a more severe way than previously documented. In general, a high proportion of bones with thermal alteration (70%) was recorded for the different body size categories, with calcined bones dominating the sample. Some differences in relation to the size classes were found; specifically, a higher extension of burning was recorded for the smaller-sized taxa. For the small animals, the homogeneous distribution of the burning damage in long bones and mandibles could help to differentiate a natural grassland fire from cooking, in which the burning pattern would be more heterogeneous.

Results of the taphonomic analysis of small mammal bone accumulations generated by the accipitriforms Geranoaetus melanoleucus and Geranoaetus polyosoma in several areas from Central Western Argentina (Mendoza Province) are presented here. In order to identify the role that these predators had in the formation of zooarchaeological assemblages, the anatomical representation, bone breakage patterns, and degrees of digestive corrosion were evaluated. According to these taphonomic variables, both G. melanoleucus and G. polyosoma may be placed in the Category 4 (heavy) of modification of prey bones. The results presented here were used as an analytical model for the interpretation of the micromammal fossil record from three archaeological sites in Mendoza Province. This comparison suggests that the skeletal remains recovered from one archaeological site are very close to those produced by G. polyosoma. However, accumulations from the other sites had intermediate values between those of G. polyosoma and G. melanoleucus.

In many southern Patagonia archaeological bone assemblages deposited in open-air settings, a remarkable difference in preservation between shafts and epiphyses of guanaco (Lama guanicoe) long bones, leading to an overrepresentation of the latter, has been found. It has been suggested that, in dynamic sedimentary deposits like those investigated in this region, the observed pattern is mainly related to subaerial weathering or to a combination of weathering and abrasion preferentially affecting long bone shafts, processes that may have little relationship with bone mineral density (BMD). In order to investigate in more detail the relationship between weathering and bone mineral density (BMD) and cortical thickness in guanaco long bones, a microscopic (low magnification) metrical analysis of partial cross-sections from a sample of modern radii-ulnae with a various degrees of weathering was performed. Overall, the obtained results suggest that subaerial weathering can suffice to explain the observed archaeological pattern of differential intraosseous preservation, although this inference should be further supported with data from a larger sample including other long bones as well as a more complete record of the weathering sequence.

Based on a bibliographic survey, this paper reviews the state of the art of actualistic taphonomic information of different autochthonous mammalian carnivores in the southern Neotropics. The characteristics of this corpus of data and its implications for the fossil record are analysed. The paper focuses on identifying and discussing those areas of research that are robustly reflected by existing studies. Synthetic discussion of the results of research on the most studied carnivore taxa, types of bone assemblages, actualistic approaches, and ecological zones in the region are presented. While the field of actualistic taphonomic research is well-developed in the region, there are several gaps that require more attention for the future investigation.