The last record of the last typotherid (Notoungulata, Mesotheriidae, Mesotherium cristatum) for the middle Pleistocene of the western Pampean region, Córdoba Province, Argentina, and its biostratigraphic implications

Abstract

We document a new Last Appearance Datum of the mesotheriine notoungulate Mesotherium cristatum in 220 ± 13 ka, Middle Pleistocene of the west Pampean Region of the Province of Cordoba, Corralito, Santa María Department, Argentina. We increase the previous LAD of this taxon into ca. 530 ka compared to its latest occurrence in Ensenadan Age (ca. 1.95–0.4 Ma; Early-Middle Pleistocene) sediments from the east Pampean Region. Our detailed literature review of the traditional biostratigraphic support (“Mesotherium cristatum Biozone”) of the Ensenadan Age for the east Pampean Region, and our new temporal record of M. cristatum for the western region of the Pampean Region, .allows us to draw the following conclusions that affect the biostratigraphic model considered so far extensive in South America: (1) M. cristatum should no longer be considered as the guide taxon of the Ensenadan Age; (2) “M. cristatum Biozone” no longer constitutes the biostratigraphic support of the Ensenadan Age as it is also present in sediments of Bonaerian Age; (3) Distinct biostratigraphic units (“M. cristatum Biozone” and “Megatherium americanum Biozone”) overlap in their temporal ranges. In application of the International Stratography Code, we proclaim that the models of chronostratigraphic and biostratigraphic units, established for the Pampean Region, need a strong and consolidated biostratigraphic support, whose temporal limits must be defined by the presence of fossils and not by the temporal limits of the chronostratigraphic units. This study proclaims the biostratigraphic importance of the western Pampean Region near the Sierras Pampeanas (Córdoba Province) which due to its differential paleoecological conditions and its altitudinal diferenciation with respect to the eastern regions of the Pampean Region could have acted as a faunal reservoir during the Pleistocene.