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 dentalremains of Mesotherium cristatum, a mesotheriid notoungulate, from Corralito,Santa María Department, Cordoba Province. This population represents the final lineageof Typotheria during middle Pleistocene, Post-Ensenadan Age (>220± 13 ka). Wecompared these new craniomandibular and postcranial samples from Corralito withthose from Toscas del Río de La Plata, as well as other localities in BuenosAires dating to the Ensenadan Age 1.98-0.4 Ma). Our investigation reveals asubstantial decline in the body mass of the ultimate populationwithin the M. cristatumduring the Bonaeran Age period, before its extinction. This occurrence,hitherto unrecorded in any prior South American Land Mammal Age leading up toextinction, might be attributed to a marked reduction in the species´paleobiogeographical range. This body mass reduction, possibly an outcome ofcompelled reproductive isolation, is situated against the context of globalcooling and heightened predatory pressures. Moreover, our analysis unveiled distinctivetaxonomic attributes specific to this taxon, we compare dental size and find apreliminary evidence of an accelerated tooth replacement pattern. Furthermore,we have effectively updated the faunal composition information of the Corralitodeposit, elucidating previous biostratigraphic inferences that had led to thebelief of Corralito being an Ensenadan Age site. This adjustment impacts thefirst appearance datum (FAD) of the Neolicaphrium recens proterotheriid,younger than previously estimated and revisedBonaerian-Lujanian. Finally, this studyprovides insights into the biological analysis of one of the most iconicspecies (M. cristatum) of the South American Quaternary,revealing new characteristics for the Pampean region within the ever-changingecosystem during the Middle Pleistocene epoch.