Basal notoungulates (Henricosborniidae, Notostylopidae)

The basal notoungulate families Henricosborniidae and Notostylopidae are generally restricted to early Tertiary faunas of South America (?Tiupampan through Mustersan SALMAs).   Acamana, an enigmatic fragmentary fossil taxon from the Divisadero Largo Formation (Divisaderan), and a similar form from the Deseadan, may represent henricosborniids, extending their range into the Oligocene.  The Tinguiririca Fauna of Chile (early Oligocene) contains a notostylopid, considerably extending that family's range as well.

Skull of Notostylops murinus in lateral view (from Simpson, 1948) and reconstruction of Notostylops (from Dixon et al., 1988).

Henricosborniids are small animals with a generalized dentition (i.e., they have a complete, low-crowned dentition, typical of early herbivores).  Their postcranial characteristics are unknown.       Notostylopids are better known than henricosborniids and are represented by both skulls and postcranial specimens.  Notostylops itself is especially common in Casamayoran strata, so much so that these layers were referred to as the "Notostylops beds" by early paleontologists.  As occurred in some later typotheres, notostylopids evolved a somewhat rodent-like dentition; the first pair of incisors are enlarged, the second and third and the canine are very reduced, and a diastema (space in the dental arcade) is present between the canine and the second premolar.  The lower incisors are not recurved as they are in rodents but are more procumbant, similar to the lower incisors of hyraxes.   Simpson (1980) describes them as being designed for "nipping" instead of gnawing. Representative Taxa   Order Notoungulata       Family Henricosborniidae:  Henricosbornia , Othnielmarshia, Simpsonotus, ?Acamana       Family Notostylopidae:  Homalostylops, Notostylops, Otronia, Boreastylops