South African barn owls, star witnesses of the climate over two million years ago

The Wonderwerk cave in South Africa is home to an outstanding fossil collection of small mammals from 2 million years ago in the Lower Palaeolithic era. For the first time, Universidad Complutense de Madrid (UCM) and the Spanish National Museum of Natural Sciences (MNCN-CSIC) have, following an analysis of the processes that gave rise to these formations, demonstrated that the dominant predator throughout this lengthy period remained constant: the barn owl (Tyto alba). 

The information obtained and published in Quaternary International is of great significance. "Given the absence of changes of predator over the sequence, we can confirm that any possible changes in the composition of the assemblage of micro-mammals are not the result of a predator's preferences, but environmental changes", explains Sara García Morato, a researcher at the Department of Geodynamics, Stratigraphy and Palaeontology at UCM and MNCN.

Micro-mammals are seen as good environmental and climatic indicators, as they respond swiftly to changes in their surroundings. Prior to conducting a paleo-environmental study, a taphonomic analysis is first required so as to confirm the origin and agent or agents giving rise to the fossil assemblage. 

According to García Morato, "In the case of the South African deposit, this lengthy continuation of the same type of predator guarantees that paleo-ecological interpretations of the site are providing us with reliable paleo-environmental results over the course of almost 2 million years, which is quite outstanding".

To conduct the work, the researchers study the different skeletal elements of the micro-mammals, the degree of breakage and the damage caused to the bone tissue in the digestion process. 

These results are compared with patterns from different predators, in this case nocturnal and diurnal birds of prey and carnivorous mammals, which could give rise to assemblages of micro-mammals. "Each predator produces its distinctive signature on the prey that it ingests", indicates Yolanda Fernández Jalvo, a researcher at MNCN. 

"In this study, the fossils obtained revealed few modifications, which is typically associated with the presence of barn owls," continues Marin Monfort, the lead author of the study and a researcher at the museum.

Tendency towards aridity

Aside from changes in predator, taphonomic studies serve to confirm or rule out the presence of such other processes as transportation, acidic corrosion or the formation of manganese deposits, all of which have implications for paleo-environmental, paleo-ecological and paleo-climatic interpretations. 

In the case of Wonderwerk, manganese oxides can be found, typically deposited on the surface of bones when the atmosphere is humid. "The presence of manganese oxides declines the more modern the era that the fossils correspond to, allowing us to confirm a climatic trend towards greater aridity in the region," adds Fernández Jalvo.

Aside from UCM and MNCN, the study also involved the University of Valencia, the Natural History Museum in London, the University of Toronto, the University of Witswatersrand in South Africa, and other institutions.