Abstract

REGUERO, Marcelo A.  and  CASTRO, Paula V.. A new Trachytheriinae (Mammalia, ^†Notoungulata) from the Deseadan (Late Oligocene) of Patagonia, Argentina: phylogeny, biogeography, and biostratigraphy of the Mesotheriidae Family. Rev. geol. Chile [online]. 2004, vol.31, n.1, pp.45-64. ISSN 0716-0208.  http://dx.doi.org/10.4067/S0716-02082004000100003.

An incomplete mandible of Trachytheriinae collected by Carlos Ameghino in Cabeza Blanca, Chubut Province, Argentina, is regarded here as Anatrachytherus soriai gen. et sp. nov of Deseadan age. It was previously referred by Florentino Ameghino as Trachytherus spegezzianus Ameghino, a taxon characteristic of Deseadan Age (Late Oligocene) of Argentina and Bolivia. This new taxon is more primitive than the Deseadan species T. spegazzinianus in the following characters: shortened mandibular body; i1-2 less procumbent, more complete dental formula; short diastema between i2 and canine, and m3 shorter than m2. A phylogenetic analysis based on 39 cranial and dental characters supports monophyly of this species, with only one synapomorphy, and a close sister group relationship with Trachytherus. The parsimony analysis also suggests the monophyly of the Mesotheriidae, which is here defined as the clade containing the most recent common ancestor of Trachytherus? mendocensis, Anatrachytherus and Trachytherus and all of its descendants including Mesotheriinae. The absence of mesotheriids during the Colhuehuapian and Santacrucian SALMAs (South American land Mammal Age) in Patagonia, the stratigraphic and phylogenetic relationships of the Mesotheriidae suggest that the Altiplano of Chile and Bolivia may have served as a biogeographic center of origin and dispersal for Mesotheriinae (hypselodont clade). Here the authors define the parachron of Trachytherus spegazzinianus Ameghino, the sister species of A. soriai, between 27,6 (Pico Truncado, Argentina) and 24,8 Ma (Salla, Bolivia); and consequently it is recommended the use of this species to characterize the Oligocene fauna assigned to the Deseadan SALMA in Patagonia and Bolivia

Keywords : Mesotheriidae; Systematic; Late Oligocene; Deseadan age; Patagonia; Biostratigraphy; Phylogenetic analysis; Argentina.