A new Interatheriinae (Mammalia, Notoungulata) from the Cerro Boleadoras Formation (Santa Cruz, Argentina) and the evolution of the tarsus within the lineage during the Miocene

Abstract

Interatheres (Interatheriinae; Notoungulata) from the Cerro Boleadoras Formation, north-west of Santa Cruz Province (Argentina) are described here for the first time. Boleatherium praeludium gen. et sp. nov. is described from a partial skeleton and is characterized by a singular combination of exclusive characters (p1 longer than p2, p3 and p4; lingual trigonid?talonid contact in p24 and m23), ancestral features (p2 longer than the p3 and p4, with well-developed talonid), and derived traits (triangular talonid, short trigonid?talonid contact in lower molars). In the Cerro Boleadorasfauna, we also recognize Protypotherium aff. colloncurensis (upper and lower dentition, and limb bones), Interatheriinae gen. sp. A (lower molars) comparable to P. cf. P. endiadys, and Interatheriinae gen. sp. B (tarsal bones) comparable to P. colloncurensis. The configuration of tarsal bones of B. praeludium and Protypotherium aff. colloncurensis reveals an intermediate evolutionary stage between the foot of early Miocene representatives (e.g. P. australe) and the foot of late Miocene members (e.g. Miocochilius anomopodus). In terms of phylogenetic relationships, B. praeludium forms a polytomy with Caenophilus tripartitus, Juchuysillu arenalesensis, Protypotherium sinclairi and Miocochilius federicoi, which is supported by three synapomorphies. The interathere assemblage described from the Cerro Boleadoras Formation: (1) increases the known diversity of Interatheriinae for the Miocene of southern Patagonia; (2) contributes tothe distinctive endemicity of the Cerro Boleadoras fauna with the recognition of a new taxon; (3) supports a BurdigalianLanghian age for the Cerro Boleadoras fauna based on its taxonomic composition and published dating near the base of the formation; and (4) illuminates the evolutionary changes related to foot into the Interatheriinae lineage during the Miocene.