See text Protypotherium is an extinct genus of notoungulate mammals native to South America during the Oligocene and Miocene epochs.

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.

Protypotherium was a typical representative of the Interatheriidae, a group of typotherian notoungulates with rodent-like appearances, usually with slender forms.

Fossils assigned to Protypotherium have been found in numerous localities in Argentina, Bolivia, Chile, and Uruguay.

[1][2][3][4] The oldest occurrence of Protypotherium dates back to the Late Oligocene (Deseadan) Fray Bentos Formation of Uruguay.

[5] 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.

Another well-known species is P. australe, also from the Santa Cruz Formation,[6] 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,[7] all found in various localities in Argentina in Lower and Middle Miocene deposits.

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 interprismatic matrix forms closed coats in the entire thickness, but it is also slightly anastomosing near the enamel dentine junction.

The third and fourth premolars have a sub-triangular shape, with the mesio-distal length shorter than the labio-lingual breadth and a smaller size than the first and second molars.

The posterior lower premolars show proportionally larger buccolingual diameter of the talonid than those in the Santacrucian species.

The humerus was very stout in the proximal region, with two low tuberosities; the distal end was enlarged, with the entepicondyle developed and provided with a large foramen.

The hand was tetradactylous, as opposed to the related Miocochilius, which had only three fingers, two of which were functional, with an alternating structure of the carpus and relationships between the metacarpals.

[23] In the Chichinales Formation, which is known for its local mammal fauna, Protypotherium would have coexisted with astrapotheres, the notoungulates Cochilius volvens, Colpodon, Hegetotheriopsis sulcatus and Hegetotherium,[24] the litoptern Cramauchenia, the rodents Australoprocta, Caviocricetus, Eoviscaccia, and Willidewu esteparius,[25] the armadillos Proeutatus and Stenotatus, and the sparassodont Cladosictis.

[1] The Sarmiento Formation has provided a wide assemblage of mammals, consisting of pyroclastic deposits in an arid desert environment.

[26] Among these mammals were the astrapotheres Astrapotherium and Parastrapotherium,[27] the fellow notoungulates Argyrohippus,[28] Cochilius, Colpodon,[29] Interatherium and Pachyrukhos,[3] the litopterns Cramauchenia,[30] Lambdaconus, Paramacrauchenia, Proheptaconus,[31] Prolicaphrium,[32] Pternoconius,[33][34][35] Tetramerorhinus[3] and Theosodon,[36] the xenarthrans Hapaloides, Holomegalonyx, Nematherium, Peltephilus, Proeutatus, Proschismotherium, Prozaedyus, Stegotherium, and Stenotatus,[37] the metatherians Acyon, Acrocyon, Arctodictis, Borhyaena, Cladosictis, Palaeothentes, and Sipalocyon,[38] the rodents Acarechimys[25] Acaremys,[39] Caviocricetus,[40] Eosteiromys, Eoviscaccia,[41] Hypsosteiromys, Neoreomys,[42] Paradelphomys,[40] Parasteiromys, Perimys, Prospaniomys, Prostichomys, Protacaremys, Protadelphomys, Sarremys and Soriamys,[43][44][45][46][47][48] and the primates Homunculus, Mazzonicebus and Tremacebus.

[38] Multiple species of Protypotherium lived during the Early Miocene in the Santa Cruz Formation of Argentina, which preserves mostly a coastal environment, but also forested and grassland regions.

[52] The area had little rainfall, so forests developed around lakes and rivers, giving Santa Cruz a diverse environment.

Large, herbivorous, South American ungulates such as the astrapothere Astrapotherium, the toxodont notoungulates Adinotherium, Homalodotherium and Nesodon shared the niche of low browsers, along with the litopterns Adianthus,[31] Anisolophus, Diadiaphorus, Tetramerorhinus, Theosodon, and Thoatherium,[53][54][55][16][56][57] with the rabbit-like interatheres such as Interatherium and the hegetotheres Hegetotherium and Pachyrukhos being frugivorous.

Xenarthrans in the Santa Cruz Formation were fairly common, such as the ground sloths Analcimorphus, Analcitherium, Eucholoeops,[61] Hapalops, Hyperleptus, Nematherium, Megalonychotherium, Planops, Prepotherium, Schismotherium, Trematherium, and Xyophorus,[62][63] and the armadillos Cochlops, Eucinepeltus, Proeutatus, Propalaehoplophorus, Prozaedyus, Stegotherium, and Stenotatus.

[64][16] In addition, fossils of rodents, such as Acarechimys, Acaremys, Adelphomys, Eocardia, Neoreomys, Perimys, Pliolagostomus, Prolagostomus,[65] Schistomys, Scleromys, Spaniomys, and Stichomys are also known.

[67][68] The Collón Curá Formation and the Colloncuran age of South America represent a time when more open environments with reduced plant covering predominated, similar to semiarid and temperate to warm, dry woodlands or bushlands.

[70] The Collón Curá Formation of Argentina has provided a wide assemblage of mammals, including at least 24 taxa such as the xenarthrans Megathericulus, Prepotherium, Prozaedyus, and Paraeucinepeltus, the notoungulates Hegetotherium, Interatherium, and Pachyrukhos, the astrapothere Astrapotherium, the sparassodonts Patagosmilus and Cladosictis, the marsupial Abderites, the primate Proteropithecia, and rodents such as Maruchito, Protacaremys, Neoreomys, and Prolagostomus.

[71][72][73][74] In addition to the mammals that characterize sediments of this age, there are also a few fossils of birds, reptiles, amphibians, and fish.