Protypotherium is an extinct genus of notoungulate mammals native to South America during the Oligocene and Miocene epochs. A number of closely related animals date back further, to the Eocene. Fossils of Protypotherium have been found in the Deseadan Fray Bentos Formation of Uruguay, Muyu Huasi and Nazareno Formations of Bolivia, Cura-Mallín and Río Frías Formations of Chile, and Santa Cruz, Salicas, Ituzaingó, Aisol, Cerro Azul, Cerro Bandera, Cerro Boleadoras, Chichinales, Sarmiento and Collón Curá Formations of Argentina.
The taxonomy of the genus and the species within has a long and complicated history. Other genera of interatheriids such as Epipatriarchus, Eudiastatus, and Toxdontophanus, have been named, but no complete specimens exist, making comparison and classification difficult. Most modern scientists consider these genera to be junior synonyms of Protypotherium, and it is thought to contain the following species; P. australe, P. praerutilum, P. antiquum, P. altum, P. attenuatum, P. claudum, P. colloncurensis, P. diastematum, P. distinctum, P. minutum, P. endiadys, P. sinclairi, and P. concepcionensis. The most completely-known species is P. australe, so most reconstructions of the genus are based on it.
Taxonomy
Protypotherium was a typical representative of the Interatheriidae, a group of typotherian notoungulates with rodent-like appearances, usually with slender forms. The genus has a wide stratigraphic and geographic distribution, around 29 million years. Fossils assigned to Protypotherium have been found in numerous localities in Argentina, Bolivia, Chile, and Uruguay. The oldest occurrence of Protypotherium dates back to the Late Oligocene (Deseadan) Fray Bentos Formation of Uruguay.
The genus Protypotherium was first described in 1882 by Florentino Ameghino, based on fossil remains found in the Ituzaingó Formation in Entre Ríos Province, Argentina, in soils dating from the Late Miocene. The type species is Protypotherium antiquum. Another well-known species is P. australe, also from the Santa Cruz Formation, but several other species have been attributed to this genus, such as P. altum, P. attenuatum, P. claudum, P. colloncurensis, P. diastematum, P. distinctum, P. endiadys, P. minutum, P. praerutilum, and P. sinclairi, all found in various localities in Argentina in Lower and Middle Miocene deposits. A species from Chile, P. concepcionensis was described in 2019.
Protypotherium was a rather specialized member of the interatheriids, akin to the bizarre Miocochilius; these two forms, according to a 2017 study, formed a monophyletic derived clade within the family Interatheriidae. In the same study, it is indicated that the species P. australe would be the most basal known species of the genus and may be ancestral to the other species of Protypotherium and the genus Miocochilius. In spite of its name, Protypotherium was not an ancestor of "Typotherium", a genus that is now considered to be a synonym of Mesotherium, another notoungulate belonging to another family, the Mesotheriidae.
The following cladogram of the Interatheriinae is based on Vera et al. 2017, showing the position of Protypotherium.
Species
The following species of Protypotherium have been described:
P. altum
P. antiquum
P. attenuatum
P. australe
P. claudum
P. colloncurensis
P. diastematum
P. distinctum
P. endiadys
P. minutum
P. praerutilum
P. sinclairi
P. concepcionensis
Description
Protypotherium was slightly larger than a rabbit, measuring about in length. The body and legs as well as the tail of this animal were relatively long, while its neck was short. It probably resembled a rodent, possessing slender limbs with four, digitigrade clawed feet. Its rat-like skull contained a set of 44 unspecialized teeth.
From the shape of its claws, Protypotherium would have been adept at digging and likely took over the burrows of other animals.