Postcranial remains of basal typotherian notoungulates from the Eocene of northwestern Argentina

ARMELLA, MATÍAS; DERACO, VIRGINIA; BERTELLI, SARA; BABOT, MARÍA; SAADE, LUIS; GARCÍA-LÓPEZ, DANIEL; HERRERA, CLAUDIA

ACTA PALAEONTOLOGICA POLONICA

INST PALEOBIOLOGII PAN

Lugar: Polonia; Año: 2020 vol. 65 p. 1 - 17

0567-7920

Notoungulates represent the most taxonomically diverse and temporally and geographically widespread group amongSouth American native ungulates. Here, we analyze anatomical and systematic aspects of proximal tarsal bones recoveredfrom the Lower and Upper Lumbrera formations (middle and late middle Eocene) in northwestern Argentina. We providedetailed descriptions, comparisons, and infer foot stances and range of movements for the taxa implicated. Materialstudied includes astragali belonging to the oldfieldthomasiid Colbertia lumbrerense (Lower Lumbrera Formation), a setof proximal tarsals referred as Typotheria indet. (Lower Lumbrera Formation), and tarsals (also including navicular andcuboid) of the informal taxon ?Campanorco inauguralis? (Upper Lumbrera Formation). The comparison of the tarsalsof Colbertia lumbrerense (middle Eocene of Argentina) with Colbertia magellanica (early Eocene of Brazil) revealsseveral differences including variations on the development and arrangement of articular facets, and the size of the dorsalastragalar foramen in the Argentinean species. The specimen of Typotheria indet. shows morphological affinities withbasal interatheriid taxa. However, its larger size contrasting with the overall small body sizes of Eocene interatheriidsprecludes an indisputable taxonomic assignment. Concerning ?Campanorco inauguralis?, our observations indicate thatthere is no morphological evidence for a close phylogenetic relationship with Mesotheriidae. It presents a ?reversed alternatingtarsus? condition, which is also observed in Leontiniidae, ?Notohippidae?, Toxodontidae, and some typotherians.However, the spectrum of singularities exhibited by this form precludes the assessment of its relationships in the contextof the Paleogene radiation of Typotheria and it is necessary to extend the comparison to Eocene notoungulates. Finally,in a morphofunctional context a plantigrade foot posture is inferred for the specimens here reported. These observationshave the potential to provide functional proxies for paleoecological reconstructions to be applied to the study of the earlyradiation of these notoungulate faunas.