Protypotherium

Source: Wikipedia, the free encyclopedia.

Protypotherium
Temporal range:
Ma
Fossil of P. australe. Exhibit in the National Museum of Nature and Science, Tokyo, Japan
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: †Notoungulata
Family: †Interatheriidae
Subfamily: †Interatheriinae
Genus: †Protypotherium
Ameghino 1882
Type species
†Protypotherium antiquum
Moreno 1882
Species

See text

Synonyms
  • Toxodontophanus Moreno 1882

Protypotherium is an extinct genus of

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

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.[1][2][3][4] The oldest occurrence of Protypotherium dates back to the Late Oligocene (Deseadan) Fray Bentos Formation of Uruguay.[5]

Cranium of Protypotherium praerutilum

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,[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. A species from Chile, P. concepcionensis was described in 2019.[8]

Mandible of Protypotherium australe

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.[9]

Interatheriinae

Eopachyrucos pliciferus

Santiagorothia chiliensis

Federicoanaya sallaensis

Brucemacfaddenia boliviensis

Archaeophylus patrius

Progaleopithecus tournoueri

Argyrohyrax proavus

Protypotherium australe

Protypotherium endiadys

Protypotherium distinctum

Protypotherium sinclairi

Miocochilius federicoi

Miocochilius anamopodus

Protypotherium minutum

Protypotherium colloncurensis

Species

The following species of Protypotherium have been described:[10]

  • P. altum Ameghino 1891
  • P. antiquum Ameghino 1882
  • P. attenuatum Ameghino 1887
  • P. australe Moreno 1882
  • P. claudum Ameghino 1889
  • P. colloncurensis Vera et al. 2017[9]
  • P. diastematum Ameghino 1891
  • P. distinctum Cabrera & Kraglievich 1931
  • P. endiadys Roth 1898
  • P. minutum Cabrera & Kraglievich 1931
  • P. praerutilum Ameghino 1887
  • P. sinclairi Kramarz et al. 2015[7]
  • P. concepcionensis Solórzano et al. 2019

Description

Stegotherium tesselatum

Protypotherium was slightly larger than a rabbit, measuring about 40 centimetres (1.3 ft) 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.[11] 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.[12]

Skull and dentition

Lower dentition of Protypotherium endiadys
Lower and upper dentition of Protypotherium colloncurensis

The skull of Protypotherium was about halfway up the cranial vault, was slightly descending in the anterior part; the posterior part, on the other hand, lowered abruptly, in contrast to similar forms such as

spongy tissue. The epitympanic sinus was of medium size. The two branches of the mandible
were firmly joined in the anterior part; the posterior part of the mandible was very elevated.

Skull and upper dentition of Protypotherium endiadys

The

hyraxes
. The teeth were partially overlapping: one molar covered the posterior-external margin of the previous molar. An opposite outer and inner groove divided the molars into two lobes; the posterior lobe was shorter. A slight anterior-internal groove disappeared over time as tooth wear progressed.

Dentition detail of Protypotherium endiadys

The upper incisors of Protypotherium are characterized by a three-layered schmelzmuster represented by outer radial enamel. The prism diameter is ~6 μm. The Hunter-Schreger bands are thin (20–50 μm thick) and oblique. The interprismatic matrix forms closed coats near the outer enamel service and interrow sheets near the enamel dentine junction, and is intermediate to modified in the Hunter-Schreger bands. Lower incisors of Protypotherium are characterized by a one-layered schmelzmuster with Hunter-Schreger bands. Prism diameter is ~6 μm. Hunter-Schreger Bands are generally oblique and steady, even if they present a low decussation on both sections and are less discernible on some transverse sections. The interprismatic matrix forms closed coats in the entire thickness, but it is also slightly anastomosing near the enamel dentine junction. The thickness of its dentition suggest that it was a grazer, eating mainly grass.[14]

Protypotherium has euhypsodont (well high-crowned) premolars and molars, and

trigonid. The third and fourth premolars are relatively smaller than the first and second molars. The first and third molars have sub-triangular trigonids, while the first and second molars have longer talonids than the trigonids.[15]

Mandibular fragment of Protypotherium sinclairi

Compared with the related Interatherium and Cochilius, Protypotherium had well-differentiated third and fourth premolars compared to molars, and numerous other dental features. In contrast to Miocochilius, moreover, Protypotherium possessed the canine-shaped lower first premolar and shorter lower third molar.[9]

Regarding the species Protypotherium sinclairi, it can be distinguished from other species of Protypotherium by its dentition, with all teeth having a thick cementum covering. The third and fourth premolar both have a shorter anteroposterior diameter of the talonid than the trigonid, while the first and second premolars are short and non-molariform. The teeth of this species are smaller than those of P. australe, but larger than those of P. praerutilum and P. attenuatum, all of which are Santacrucian in age. The posterior lower premolars show proportionally larger buccolingual diameter of the talonid than those in the Santacrucian species.[2]

Postcranial skeleton

Reconstructed skeleton

The skeleton of Protypotherium is well known, especially regarding the species Protypotherium australe. Fifteen dorsal

vertebrae
, seven lumbar vertebrae and five sacral vertebrae were probably present. The tail was long, with at least eighteen vertebrae.

The

hamate, and laterally it was in contact with the cuneiform bone via a large surface. The joints of the first phalanges were limited to the plantar and distal surfaces. The phalanges
nail joints were laterally compressed and provided with a small incision at the end.

Post-cranial bones of P. endiadys

The

navicular bone and had a large facet for the fibula. The phalanges possessed the same structure as those of the hand, but were larger. It is likely that at least the feet of Protypotherium were digitigrade.[9]

Paleobiology

Protypotherium was mainly a herbivore, but it is possible that Protypotherium fed occasionally on carrion as well. The legs clearly show robust nail phalanges, thanks to which the animal could dig burrows or modify those abandoned by other animals.[12]

A 2021 study concerning numerous fossils of the teeth of various species of Protypotherium showed that there is a trend in the preservation of tooth pattern, increase in size and decrease in number of species over time. This could be correlated with a global trend of cooling temperatures, indicating a deterioration of paleoenvironmental conditions during the Miocene. There also appears to have been a latitude shift in the distributional range of these animals: from Lower Miocene Patagonia to northern areas of South America towards the end of the Miocene.[4]

Paleoenvironment

Fossils of Protypotherium have been found in various fossiliferous stratigraphic units in South America. Several specimens come from the

Austral Basin in southern Patagonia, Argentina,[16][17] with other finds from the Cerro Azul,[18] Cerro Boleadoras,[15] Ituzaingó,[19] Cerro Bandera,[2][7] Chichinales,[1] Collón Curá Formations, and the Sarmiento Formations of the Colorado, Austral, Paraná, Neuquén, Cañadón Asfalto, and Golfo San Jorge Basins, as well as the Aisol and Salicas Formations of the same country.[20][21] Furthermore, fossil finds of Protypotherium have been found in other countries, such as the Fray Bentos Formation of Uruguay, also in the Paraná Basin, the Muyu Huasi Formation of the Muyu Huasi Basin in Bolivia, the Nazareno Formation in the same country, of the Tupiza Basin,[22] and the Cura-Mallín Formation of the Cura Mallín Basin of Argentina and Chile and the Río Frías Formation of the Magallanes Basin in Chile.[23]

In the Chichinales Formation, which is known for its local mammal fauna, Protypotherium would have coexisted with

wading bird, Opisthodactylus horacioperezi, a species of rhea, and Patagorhacos, a phorusrhacid. During the Miocene the area likely consisted of open but wooded environment with temperate climate and a proximity to freshwater.[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.[49][50][51] The late-surviving meridiolestidan Necrolestes was also present.[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. During the Miocene, the climate was similar to those of the coasts of Chile with semi-temperate forests and oceanic winds. Grasslands began spreading into Argentina during the Miocene, though much of inner Patagonia was still arid with small rainforests in between. 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.[58][59][60] Both mammalian and avian carnivores inhabited the area, the largest being the phorusrhacid Phorusrhacos. Marsupials also lived in the region, including the large carnivorous sparassodonts Borhyaena and the smaller sparassodonts Acyon, Cladosictis, and Sipalocyon. 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.[66] There were also primates found in the formation, such as Carlocebus and Homunculus.[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

Middle Miocene Climate Transition, a global cooling event which had a drying effect on continents.[70]

The Collón Curá Formation of Argentina has provided a wide assemblage of mammals, including at least 24 taxa such as the

amphibians, and fish.[69]

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External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Protypotherium&oldid=1203561885"