Micromammal Assemblages from Gcwihaba caves, Botswana: First insights on the taphonomy and paleoenvironments

Ongoing excavation missions at the Gcwihaba caves are continuing to identify new areas that are rich in archaeological and paleontological deposits. This includes the recent uncovering of new fossil micromammal assemblages from four distinct units within the cave —three stratified levels, likely of Holocene age, from the Deep Chamber and one unit of probable Pleistocene age from the Corridor area. The study of these remains provides an opportunity for a diachronic comparison of the faunal composition and taphonomic signature of the bones pending further absolute dating. This presentation offers first insights from the examination of these micromammal remains with the aim of understanding the site formation processes and tracing the past environmental and climatic changes over time in the northwest region of Botswana.

The study of fossil micromammals accumulated in cave sites has increasingly been used to reconstruct past landscapes and climatic changes over time. Because of their diversity, short lifespans, small home ranges, relatively precise habitats, and sensitivity to fluctuations in climate and vegetation, they are considered key indicator taxa. However, despite all this significance, the remains of this faunal group are still very little studied in Botswana.

We first performed a taphonomic investigation of the fossils in order to understand the processes responsible for the accumulation and preservation of the remains. We did this by assessing and analysing the relative abundance of skeletal elements, breakage patterns, and digestion modifications on each of the assemblages. We compared our results with patterns quantified on a modern barn owl bone accumulation collected from the cave. This step allowed us to ascertain which predator/(s) had been responsible for the accumulation of this fossil assemblage. The preliminary comparison of taphonomic results indicated some similarities in terms of the accumulating agent.

Following this, we performed taxonomic identification of the cranio-dental remains to assess and classify the species present in the samples. Both the fossil and modern assemblages show the presence of taxa belonging to at least four mammalian orders: Rodentia (rodents), Eulipoptyphla (shrews), Macroscelidea (elephant shrews), and Chiroptera (bats). The presence of taxa associated with specific habitat types can provide preliminary paleoenvironmental indications under the principle of actualism. Thus, the species variations observed over time can be interpreted in terms of climate and environmental changes. Considering this, the subsequent phase will be the application of a range of paleoecological methods to investigate the evolution of the environments surrounding the cave from the Pleistocene to the present.