Henricosborniidae is a family of extinct notoungulate mammals known from the Paleocene and early Eocene of Argentina and Brazil. The name honors U.S. paleontologist Henry Fairfield Osborn. Henricosborniidae is a group of primitive notoungulates assigned to the suborder Notioprogonia together with Notostylopidae, not because these two families share any derived features, but because they do not clearly belong to any other clade. The henricosborniids are only known from the late Paleocene and early Eocene (Itaboraian-Casamayoran SALMA, 59 to 48 million years ago), making them slightly older and more primitive than the notostylopids. The henricosborniid dentition is the most generalized and primitive of all notoungulates, and they are believed to be near the source of all notoungulates. They