PhD Defense - Laura Bento Da Costa

Palaeobiology and palaeoenvironments during the Lower Miocene : the study of rodents for the correlations in Subsaharan Africa

Thèse de doctorat sous la direction de Loïc Ségalen et de Brigitte Senut.

Composition du jury:

• M. Pablo Pelaez-Campomanes, Senior Researcher MNCN-CSIC, rapporteur
• M. Christophe Snoeck, Research Professor, rapporteur
• M. François Baudin, Pr Sorbonne Université, examinateur
• Mme Sophie Montuire, DE EPHE, examinatrice
• M. Romain Amiot, CR CNRS, examinateur
• M. Loïc Ségalen, Pr Sorbonne Université, co-directeur
• Mme Brigitte Senut, Pr MNHN, co-directrice

Abstract :

For several years, rodents have been actively studied because of their ecological diversity, showing various locomotor adaptations ranging from fossorial to gliding species. This diversity is represented in the fossil record by abundant remains found in the lower Miocene sites of Napak (Karamoja, Uganda) and Grillental, Elisabethfeld and Langental (Sperrgebiet, Namibia). This study focusses on several species from these sites: Paranomalurus bishopi, Paranomalurus walkeri (Anomaluridae), Nonanomalurus soniae (Nonanomaluridae) and Renefossor songhorensis (Renefossoridae) found in the Ugandan sites, and the Namibian species Bathyergoides neotertiarius, and Diamantomys luederitzi (Diamantomyidae) the latter of which is represented in both areas. After updating the systematics of these species, discriminant morphometric analyses allowed prediction of their locomotor behaviour, linked to clear adaptations in the skull, humerus, ulna and femur ensuring stabilization or increase of mobility of the limbs: the arboreals privilege the mobility of their movements in the trees or when gliding, while the terrestrials and fossorials favour stabilization of the limbs. Thus, these analyses highlight specialist species, such as those of the genus Paranomalurus predicted as gliders, Nonanomalurus soniae principally arboreal and Bathyergoides neotertiarius showing fossorial adaptations. In contrast, Diamantomys luederitzi shows a variety of locomotor repertoires, and is considered to be a generalist. The locomotor variability indicates environmental heterogeneity in Uganda and Namibia, highlighted also by the δ13C and δ18O analyses carried out on their dental enamel. Indeed, the analysis of the carbonates shows an open environment with a C3-plant dominated vegetation, with the presence of woodland patches, characterizing a wooded savannah in both areas. These isotopic ratios, when coupled with the comparisons isotope ratios of large mammals, indicate a more humid and/or cooler environment in the Ugandan and Namibian sites than occurs in these countries today, with the Namibian being less humid and/or having a higher temperature than the East African during the lower Miocene.