Archaeopithecidae encompasses small Eocene notoungulates defined by Ameghino and characterized by an incipient trend towards hypsodonty. Although their remains are very abundant in early Eocene outcrops from Patagonia, their taxonomic diversity is poor, and very few species had been recognized. Teratopithecus elpidophoros gen. et sp. nov. from the early Eocene levels of Paso del Sapo, Las Violetas, and Cañadón Vaca is here described. It has a stylar cusp labial to the ectoloph, which is a novel feature not previously identified in notoungulates. We also describe other archaeopithecid remains from the Paso del Sapo area that are referred to Archaeopithecus cf. A. rogeri and discuss the biochron of the family. The study of previous collections made by Feruglio, Brandmayr, Simpson, and Pisano during the first half of the XX century allows confirmation of the presence of Archaeopithecidae in the Itaboraian, Riochican, and Mustersan Mammal Ages as well as in the Sapoan fauna.