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

Interatheres (Interatheriinae; Notoungulata) from the Cerro Boleadoras Formation, north-west of Santa Cruz Province (Argentina) are described here for the first time. <i>Boleatherium praeludium</i> 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 p2 − 4 and m2 − 3), 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 Boleadoras fauna, we also recognize <i>Protypotherium</i> aff. <i>colloncurensis</i> (upper and lower dentition, and limb bones), Interatheriinae gen. sp. A (lower molars) comparable to <i>P</i>. cf. <i>P</i>. <i>endiadys</i>, and Interatheriinae gen. sp. B (tarsal bones) comparable to <i>P</i>. <i>colloncurensis</i>. The configuration of tarsal bones of <i>B</i>. <i>praeludium</i> and <i>Protypotherium</i> aff. <i>colloncurensis</i> reveals an intermediate evolutionary stage between the foot of early Miocene representatives (e.g. <i>P</i>. <i>australe</i>) and the foot of late Miocene members (e.g. <i>Miocochilius anomopodus</i>). In terms of phylogenetic relationships, <i>B</i>. <i>praeludium</i> forms a polytomy with <i>Caenophilus tripartitus</i>, <i>Juchuysillu arenalesensis</i>, <i>Protypotherium sinclairi</i> and <i>Miocochilius federicoi</i>, 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 to the distinctive endemicity of the Cerro Boleadoras fauna with the recognition of a new taxon; (3) supports a Burdigalian − Langhian 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. http://zoobank.org/urn:lsid:zoobank.org:pub:71EBFBAC-CC67-48F9-8DF2-D075921CA1FC