Beyond extinction: Uncovering morphological aspects of the last typotherid population (Mesotherium cristatum) and the unexpected body mass decrease

Abstract

We present a detailed analysis of the craniomandibular and dental remains of Mesotherium cristatum, the quaternary mesotheriid typotherid notoungulate, from Corralito, Santa María Department, Cordoba Province. This population represents the final lineage of Typotheria during middle Pleistocene, Post-Ensenadan Age (>220 ± 13 ka). We compared these new craniomandibular and postcranial samples from Corralito with those from Toscas del Río de La Plata, as well as other localities in the province of Buenos Aires dating to the Ensenadan Age 1.98–0.4 Ma). Our investigation reveals a substantial decline in the size and body mass of the last known population of M. cristatum during the Bonaeran Age period, before its extinction. This occurrence, hitherto unrecorded in any prior South American Land Mammal Age leading up to extinction, might be attributed to the climatic and abiotic changes of the Pleistocene. These changes notably caused a marked reduction in the paleobiogeographical distribution area ofM. cristatum during the Middle Pleistocene. This size and body mass reduction, possibly an outcome of compelled reproductive isolation, is situated against the context of global cooling and heightened predatory pressures. Moreover, our analysis unveiled distinctive taxonomic attributes specific to this taxon, we compare dental size and find a preliminary evidence of an accelerated tooth replacement pattern. Furthermore, we have effectively updated the faunal composition information of the Corralito deposit, elucidating previous biostratigraphic inferences that had led to the belief of Corralito being an Ensenadan Age site. This adjustment impacts the first appearance datum (FAD) of the Neolicaphrium recens proterotheriid litoptern, younger than previously estimated and revised Bonaerian-Lujanian. Finally, this study provides insights into the biological analysis of the iconic species M. cristatum, prevalent in the South American quaternary of the Pampean region. It unreveils new faunal features specific to the Pampean region, shedding light particularly on the lesser-explored western area. These findinngs provide crucial insight into the ever-evolving ecosystem dynamics during the Middle Pleistocene.