FLUVIAL AND LACUSTRINE ENVIRONMENTS

The aim of this paper is to present and discuss methodological criteria that may be of use in exploring the role of water in the formation of the faunal record in fluvial and lacustrine environments. As such, the dispersion potential of the bones of adult and neonate guanaco (Lama guanicoe) skeletons in an aquatic environment with very low hydraulic energy is evaluated through experimentation. Results of the experiments are integrated with other, complementary criteria and applied to the bone assemblage recovered at Paso Otero 1 site, situated on the margin of the ancient flood plain of the Quequén Grande River (Buenos Aires Province, Argentina). The results of this study indicate that water was the main agent responsible for guanaco bone accumulation at the site. It is proposed that some of the skeletal parts, which belong to guanaco carcasses that were processed and exploited by hunter-gatherers in areas close to the site, were added to those from animals that died naturally. This resulted in a mixture of material of both natural and anthropic origin.

Preliminary taphonomic studies were conducted on three different early hominid Chadian sites aged between 5 Ma and 3 Ma (KB, KL, KT fossil areas). Specific excavations and taphonomic sampling protocols were established. Research of the various alterations and the origins of bone modifications were carried out. All fossil assemblages bear traces of carnivore tooth marks as well as weathering and wind/water polishing. Digestion is present on bones from the KB & KL sites. Rootmark traces were found only on bones from the KB and KT sites. All three sites display various polishing patterns among which much of the abrasion results from wind polishing on the top surface, on the exposed face of large flat bones difficult to move. By contrast water action works on all faces of polished bones. KL seems to show more water transport influence than the two other sites. Weathering stages are light to heavy (stages 2-4) and the presence of gnawing, and traces of roots plus tooth marks indicates that bones stayed sometimes on the soil surface and that the assemblages may be of attritional origin. But the low density of bones and the presence of a very thin fossil layer are very exceptional and it is not clear weather the fossil sites have been condensed during the past or if this is the result of present day extreme desert conditions. More detailed work on other Djourab sites should allow to refine the taphonomic history concerning these early hominid accumulations and formation.

This study documents the occurrence of brachiopod shells (Bouchardia rosea) in wrack-lines from backshore deposits of a tropical beach (Itamambuca beach), in the northern coast (Ubatuba County) of the state of São Paulo, Brazil. The main goals are: (a) to analyze the provenance and sorting of the brachiopod shells; (b) to provide the taphonomic signatures of the shells, which may favor the recognizance, description and diagnoses of similar shell concentrations in ancient rocks, and (c) to discuss the taphonomic meaning of these detrital accumulations. Sampling transects were done at the reflective and dissipative sectors of the Itamambuca beach. For this project, two thousand brachiopod shells were collected and examined. In general, shells are minute, pale in color, and extremely rounded with reduced shell micro-relieves. Abrasion is the main taphonomic signature recorded. Abraded shells are characterized by V-shaped scars on the external surface, exposing the secondary fibrous layer of the shell microstructure. In some cases, holes produced by abrasion (facets) are recorded in the most convex portion of the shells. A pronounced bias in favor of ventral valve is also noted, and the size frequency distribution of shells is shaped by taphonomy. Finally, shells show intense taphonomic overprinting, but the taphonomic signatures recorded on those shells are worth to provide valuable clues about the taphonomic pathways and spatial transportation of each bioclast.