Systematic revision of the species of Protypotherium (Notoungulata: Interatheriidae) from the Santa Cruz Formation (Early-Middle Miocene), Argentinian Patagonia: a new phylogenetic hypothesis for the Interatheriidae

Protypotherium is one of the main genera of the Interatheriidae due to its species richness, abundance, and wide distribution from southern to middle latitudes of Argentina, Bolivia, Uruguay, and Chile. This genus is better known from the species founded by Florentino Ameghino during late 19(th) century from the prolific Santa Cruz Formation (Santacrucian South American Land Mammal Age (SALMA); Burdigalian-Early Langhian), Santa Cruz Province (Argentina). This contribution provides the taxonomic revision of the Santacrucian species of Protypotherium and the species erected by Florentino within this genus. We conclude that among the initial 21 species, Protypotherium antiquum, Protypotherium australe, Protypotherium praerutilum, Protypotherium compressidens, and Protypotherium claudum are valid, whereas Protypotherium obstructum is a Hegetotheriidae indet. We present a phylogenetic analysis that does not recover Protypotherium as a clade, due to the nesting of Juchuysillu and Caenophilus, and this assemblage appears as the sister taxon of the clade Progaleopithecus plus Archaeophylus. Finally, the interatheriines from the Santa Cruz Formation do not allow a subdivision of this unit, due to their wide geographic and temporal distribution, thus rejecting the biozones preliminary proposed by other authors. The Atlantic coast (east) and Rio Santa Cruz (central) regions are similar in their interatheriine content, but both differ from the western area.