| Polymorphis | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | † Litopterna |
| Family: | † Macraucheniidae |
| Subfamily: | † Cramaucheniinae |
| Genus: | † Polymorphis Roth, 1899 |
| Type species | |
| †Polymorphis lechei Roth, 1899 | |
| Synonyms | |
| |
Polymorphis is an extinct genus of litopterns belonging to the family Macraucheniidae. It lived during the Middle Eocene of Argentina.
The type species of Polymorphis is Polymorphis lechei. Both the genus and the species were named by Santiago Roth in 1899. The lectotype of P. lechei is the left half of a mandible with teeth. [1]
Two other species, Megacrodon planus and "Lambdaconus" alius, have been previously assigned to Polymorphis, [2] but are poorly known and may not belong to the genus. [3] [4]
Megacrodon, Polyacrodon (which has the junior objective synonym Oroacrodon), Decaconus, and Periacrodon have been considered synonyms of Polymorphis. [5]
Polymorphis is the most basal member of Macraucheniidae. [6] [7] It is considered to be either part of the paraphyletic subfamily Cramaucheniinae, [4] [8] or in a monotypic subfamily of its own, Polymorphinae. [9] [5]
Polymorphis is known from the Eocene of Argentina, belonging to the Mustersan South American land mammal age, and is the earliest known macraucheniid. [10]
This animal is only known from fossils of teeth and a mandible, and it is therefore impossible to faithfully restore its appearance. Polymorphis was a small to medium sized litoptern, probably with a rather slender build. The mandible was characterized by a still primitive complete dentition ; on the molars, the trigonid was complete ; the paraconid and the metaconid were nearly of equal size and separated by a narrow groove.
In 1899, Santiago Roth described several new genera and species of mammal from Patagonia. These taxa included Polymorphis and its type species P. lechei, Megacrodon and its species M. prolixus and M. planus, and Polyacrodon and its species P. lanciformis and P. ligatus. [11] Polymorphis and Megacrodon were both based on lower jaws with teeth, whereas Polyacrodon was based on upper molars. Roth did not specifically comment on the affinities of Polymorphis or Megacrodon, [12] but suggested that Polyacrodon may have been a predecessor of the toxodonts. [13]
Florentino Ameghino believed that the name Polyacrodon was preoccupied by Polyacrodus , a hybodont shark genus named ten years earlier by Otto Jaekel, and proposed the replacement name Oroacrodon in 1904, [14] viewing P. ligatus as the type species. In the same paper, he established a separate genus, Periacrodon, for Polyacrodon lanciformis. Ameghino classified both Oroacrodon and Periacrodon as phenacodontid condylarths, but noted the similarity between Oroacrodon and macraucheniids, and suggested it was close to the origins of the latter group. [15]
In 1936, George Gaylord Simpson noted that Polyacrodon was not preoccupied by Polyacrodus, making Oroacrodon an unnecessary synonym of it. [16] He also synonymized Periacrodon with Decaconus. In 1948, as part of a review of South American mammal taxonomy, Simpson synonymized Megacrodon and Polymorphis, selecting Polymorphis, which was based on a better type specimen, as the valid name. [17] However, he kept the type species separate as Polymorphis lechei and Polymorphis planus, as he felt he lacked sufficient evidence to synonymize them. [2] Simpson synonymized Trigonostylops wortmani with P. lechei and Didolodus multicuspis with P. planus. [18] He also assigned Lambdaconus alius to Polymorphis as a third species. [2] Simpson suspected that Polyacrodon was synonymous with Polymorphis, but did not formally synonymize the two genera. [19] Simpson classified Polymorphis and Polyacrodon as members of Proterotheriidae. [20]
In 1982 and 1983, Miguel Soria and Richard Cifelli independently concluded that Polymorphis was a macraucheniid, the most basal member of the clade. [6] [21] Cifelli synonymized Polyacrodon and Polymorphis and selected Polymorphis as the valid name, but regarded their type species as probably distinct. [22] Cifelli regarded Polyacrodon planus and Polyacrodon alius as inadequately characterized, [3] but accepted Decaconus as synonymous with Polymorphis. [23] In 1997, McKenna and Bell listed Polyacrodon, Megacrodon, Decaconus, and Periacrodon as synonyms of Polymorphis. [5] In research by Soria posthumously published in 2001, he viewed Megacrodon and Decaconus as didolodontids and Polymorphis as a cramaucheniine macraucheniid. [4]
Litopterna is an extinct order of South American native ungulates that lived from the Paleocene to the end of the Pleistocene-early Holocene around 63 million-12,000 years ago, and were also present in Antarctica during the Eocene. They represent the second most diverse group of South American ungulates after Notoungulata. It is divided into nine families, with Proterotheriidae and Macraucheniidae being the most diverse and last surviving families.
Theosodon is an extinct genus of litoptern mammal from the Early to Middle Miocene of South America.
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.
Cramauchenia is an extinct genus of litoptern South American ungulate. Cramauchenia was named by Florentino Ameghino. The name has no literal translation. Instead, it is an anagram of the name of a related genus Macrauchenia. This genus was initially discovered in the Sarmiento Formation in the Chubut Province, in Argentina, and later it was found in the Chichinales Formation in the Río Negro Province and the Cerro Bandera Formation in Neuquén, also in Argentina, in sediments assigned to the SALMA Colhuehuapian, as well as the Agua de la Piedra Formation in Mendoza, in sediments dated to the Deseadan. In 1981 Soria made C. insolita a junior synonym of C. normalis. A specimen of C. normalis was described in 2010 from Cabeza Blanca in the Sarmiento Formation, in sediments assigned to the Deseadan SALMA.
Proterotherium is an extinct genus of litoptern mammal of the family Proterotheriidae that lived during the Late Miocene of Argentina and Chile. Fossils of this genus have been found in the Ituzaingó Formation of Argentina, and the Galera Formation of Chile.
Promacrauchenia is an extinct genus of macraucheniids that lived during the Late Miocene to Late Pliocene epochs of what is now Argentina and Bolivia. It belongs to the subfamily Macraucheniinae, which also includes Huayqueriana, Macrauchenia, and Xenorhinotherium. Fossils of this genus have been found in the Ituzaingó, Andalhuala, and Cerro Azul Formations of Argentina.
Ernestokokenia is an extinct genus of mammal, belonging to the Didolodontidae. It lived during the Early Eocene and the Middle Eocene, and its fossils were discovered in South America.
Paulogervaisia is an extinct genus of mammal, belonging to the family Didolodontidae. Its fossilized remains have been found in South America.
Sparnotheriodontidae is an enigmatic extinct family of litopterns known primarily from teeth. Sparnotheriodontids are one of two South American native ungulate clades known to have reached Antarctica, the other being astrapotheres.
Proadiantus(Ameghino, 1897) is an extinct genus of adianthid litoptern. It lived during the Late Oligocene, in what is today South America. It consists of only 1 species, Proadiantus excavatus.
Anisolambda is an extinct genus of litoptern. It lived from the Late Paleocene to the Middle Eocene in what is now Argentina.
Proectocion is an extinct genus of adianthid litoptern. It lived during the Early Eocene, in what is now South America.
Protheosodon is an extinct genus of proterotheriid litoptern. It lived from the Late Oligocene to the Early Miocene in what is now Argentina and Colombia.
Xesmodon is an extinct genus of mammal. It lived from the Middle to the Late Eocene, in what is today South America.
Prolicaphrium is an extinct genus of proterotheriid litoptern that lived during the Early Miocene, in what is now Argentina. Fossils have been found in the Sarmiento Formation of Argentina.
Tetramerorhinus is an extinct genus of proterotheriid litoptern that lived during the Early and Middle Miocene in what is now Argentina and Peru.
The Sarmiento Formation, in older literature described as the Casamayor Formation, is a geological formation in Chubut Province, Argentina, in central Patagonia, which spans around 30 million years from the mid-Eocene to the early Miocene. It predominantly consists of pyroclastic deposits, which were deposited in a semi-arid environment. It is divided up into a number of members. The diverse fauna of the Sarmiento Formation, including a variety of birds, crocodilians, turtles and snakes, also includes many mammals such as South American native ungulates as well as armadillos, and caviomorph rodents.
Pternoconius is an extinct genus of macraucheniid litoptern from the Late Oligocene and Early Miocene of Argentina. Fossils of this genus have been found in the Sarmiento Formation of Argentina.
Guilielmofloweria is an extinct genus of proterotheriid litoptern that lived from the Middle to Late Eocene of what is now Argentina. Fossils have been found in the Sarmiento Formation of Argentina.
Adianthidae is an extinct family of litopterns that existed from the Middle Eocene (Mustersan) to the Early Miocene (Santacrucian).
