| Mesotheriidae Temporal range: | |
|---|---|
 | |
| Mesotherium cristatum | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | † Notoungulata |
| Suborder: | † Typotheria |
| Family: | † Mesotheriidae Alston, 1876 |
| Subfamilies & genera [2] | |
Mesotheriidae ("Middle Beasts") is an extinct family of notoungulate mammals known from the Oligocene through the Pleistocene of South America. Mesotheriids were small to medium-sized herbivorous mammals adapted for digging.
Mesotheriids were small to medium-sized notoungulates; larger forms were approximately the size of a sheep. [3] Additionally, the family is characterized by specializations of the teeth and skeleton. In the dentition, all mesotheriids have ever-growing incisors with enamel restricted to the anterior surface, a condition termed gliriform, as it also occurs in Glires (rodents and lagomorphs). The cheek teeth (premolars and molars) of mesotheriids are high-crowned (hypsodont) and in advanced members of the family, the cheek teeth are also ever-growing. [3] Mesotheriid skeletons are heavily built and show features associated with digging in living mammals. In particular, fossorial characteristics of mesotheriids include deeply fissured claws, presence of a sesamoid bone in the elbow and reinforcement of the pelvic girdle by addition of vertebrae to the sacrum and fusion of the sacrum and innominate. [3]
A biomechanical study of the skeleton of three mesotheriid genera ( Trachytherus , Plesiotypotherium , and Mesotherium ) spanning the temporal range of the family indicates that most or all mesotheriids were adapted for digging. Mesotheriids likely dug for roots and tubers and were most similar in their diet and behavior to living wombats, although no living group is perfectly analogous. [3] Extensive burrowing was considered possible but unlikely given the relatively large size of most mesotheriids.
As with almost all other notoungulates, mesotheriids are known only from the Cenozoic of South America. [4] Unlike some other families, mesotheriid fossils are not found across the continent. Instead, mesotheriids are most abundant and diverse in faunas from middle latitudes in Bolivia and Chile, particularly the Altiplano. [5] Mesotheriid fossils are rare in high latitude Patagonian faunas and absent entirely from tropical faunas in northern South America.
The earliest secure records of the family come from the late Oligocene, when the family is represented by the genus Trachytherus from Argentina and Bolivia. [6] The family reached its greatest diversity in the Miocene, [5] and mesotheriids persisted into the middle Pleistocene, in the form of the type genus, Mesotherium . [4] Mesotheriidae was one of only three notoungulate families to persist into the Quaternary, the others being Hegetotheriidae and Toxodontidae.
Within the order Notoungulata, Mesotheriidae is placed in the suborder Typotheria. [7] In fact, Typotheria is named for the genus Typotherium , a synonym of Mesotherium. [3] In addition to Mesotheriidae, Typotheria traditionally includes other small bodied notoungulates in the families Oldfieldthomasiidae, Interatheriidae, and Archaeopithecidae. [8] [4] Recent opinion, however, favors inclusion of two additional families in Typotheria, Archaeohyracidae and Hegetotheriidae. [9] These families have traditionally been placed in a separate suborder, Hegetotheria, but phylogenetic studies indicate that their exclusion would render Typotheria paraphyletic. [7] [10] Within Typotheria, mesotheriids are more closely related to archaeohyracids and hegetotheriids than to the remaining typotherian families. In fact, both Mesotheriidae and Hegetotheriidae may have originated from within Archaeohyracidae. [10]
McKenna and Bell recognized three subfamilies within Mesotheriidae: Fiandraiinae, Mesotheriinae, and Trachytheriinae. However, Flynn et al. suggested that Fiandraia , the only known fiandraiine, is not a mesotheriid and may represent a toxodontid instead. [5] Of the remaining subfamilies, Trachytheriinae includes only Trachytherus and may be paraphyletic with respect to Mesotheriinae, which includes more derived genera from the Miocene and later. [6]
Classification of Mesotheriidae: [11]
Family †Mesotheriidae
Notoungulata is an extinct order of mammalian ungulates that inhabited South America from the early Paleocene to the Holocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms resembling animals as disparate as rabbits and rhinoceroses. Notoungulata are the largest group of South American native ungulates, with over 150 genera in 14 families having been described, divided into two major subgroupings, Typotheria and Toxodontia. Notoungulates first diversified during the Eocene. Their diversity declined during the Late Neogene, with only the large toxodontids persisting until the end of the Pleistocene. Collagen analysis suggests that notoungulates are closely related to litopterns, another group of South American ungulates, and their closest living relatives being perissodactyls, including rhinoceroses, tapirs and equines. but their relationships to other South American ungulates are uncertain. Several groups of notoungulates separately evolved ever growing teeth like rodents and lagomorphs, a distinction among ungulates only shared with Elasmotherium.
South American native ungulates, commonly abbreviated as SANUs, are extinct ungulate-like mammals of controversial affinities that were indigenous to South America prior to the Great American Biotic Interchange. They comprise five major groups conventionally ranked as orders—Astrapotheria, Litopterna, Notoungulata, Pyrotheria, and Xenungulata—as well as some other taxa, such as Didolodontidae and Kollpaniidae. It has been proposed that some or all of the members of this group form a clade, named Meridiungulata, though the relationships of South American ungulates remain largely unresolved. The two largest groups of South American ungulates, the notoungulates and the litopterns, were the only groups to persist beyond the mid Miocene. Only a few of the largest species of notoungulates and litopterns survived until the end-Pleistocene extinctions.
Leontiniidae is an extinct family comprising eighteen genera of notoungulate mammals known from the Middle Eocene (Mustersan) to Late Miocene (Huayquerian) of South America.
Toxodontidae is an extinct family of notoungulate mammals, known from the Oligocene to the Holocene of South America, with one genus, Mixotoxodon, also known from the Pleistocene of Central America and southwestern North America (Texas). They somewhat resembled rhinoceroses, and had teeth with high crowns and open roots, suggesting that they often fed on tough pampas grass. However, isotopic analyses have led to the conclusion that the most recent forms were grazing and browsing generalists.
Nesodon is a genus of Miocene mammal belonging to the extinct order Notoungulata which inhabited southern South America during the Late Oligocene to Miocene living from 29.0 to 16.3 Ma and existed for approximately 12.7 million years. It had a relatively large size, weighing up to 554 kg (1221 lbs) and reaching 1.5 m in height.
Mesotherium is an extinct genus of mesotheriid notoungulates, a long-lasting family of superficially rodent-like, burrowing notoungulates from South America. It was first named by Étienne Serres in 1867, and through further finds now contains four species, M. cristatum, M. hystatum, M. maendrum, and M. pachygnathum. Fossils have been found in the Miramar and Vorohué Formations of Argentina.
The South American land mammal ages (SALMA) establish a geologic timescale for prehistoric South American fauna beginning 64.5 Ma during the Paleocene and continuing through to the Late Pleistocene. These periods are referred to as ages, stages, or intervals and were established using geographic place names where fossil materials where obtained.
The Divisaderan age is a South American land mammal age, covering a period of geologic time within the Middle and Late Eocene epochs of the Paleogene. It follows the Mustersan age and is followed by the Tinguirirican age.
The Deseadan age is a period of geologic time within the Oligocene epoch of the Paleogene to the Early Miocene epoch of the Neogene, used more specifically within the SALMA classification of South America. It follows the Tinguirirican and precedes the Colhuehuapian age.
The Agua de la Piedra Formation is a Late Oligocene geologic formation of the Malargüe Group that crops out in the southernmost Precordillera and northernmost Neuquén Basin in southern Mendoza Province, Argentina.
Typotheriopsis is an extinct genus of Notoungulate, belonging to the family Mesotheriidae, which included several small sized Meridiungulates specialized in digging. It is considered as the sister taxon of the clade including Mesotherium and Pseudotypotherium. Its fossils are known from the Chasicoan and the Huayquerian periods, notably among Late Miocene rocks from the Arroyo Chasicó Formation and the Cerro Azul Formation of Argentina.
Fiandraia is an extinct monotypic genus of notoungulate that lived in Uruguay during the Oligocene and the Early Miocene. It was found in the Fray Bentos Formation, in rocks dated back from the Deseadan period.
Prosotherium is an extinct genus of hegetotheriid notoungulate. It lived during the Late Oligocene, and its fossilized remains were found in South America.
Ethegotherium is an extinct genus of Notoungulates, belonging to the suborder Typotheria. It lived from the Lower to the Middle Miocene, and its fossilized remains were discovered in South America. It might be a synonym of the genus Prohegetotherium.
Trachytherus is an extinct genus of mesotheriid notoungulate that lived from the Late Oligocene to the Early Miocene in what is now South America.
Pseudotypotherium is an extinct genus of Notoungulates, belonging to the suborder Typotheria. It lived from the Late Miocene to the Late Pliocene, and its fossilized remains were discovered in South America.
Plesiotypotherium is an extinct genus of Notoungulate, belonging to the suborder Typotheria. It lived from the Middle to the Late Miocene, and its fossilized remains were discovered in South America.
Sallatherium is an extinct genus of Notoungulate, belonging to the suborder Typotheria; It lived during the Late Oligocene, and its fossilized remains were discovered in South America.
Eopachyrucos is an extinct genus of interatheriid notoungulates that lived from the Middle Eocene to the Late Oligocene of Argentina and Uruguay. Fossils of this genus have been found in the Sarmiento Formation of Argentina and the Fray Bentos Formation of Uruguay.
Rosendo is an extinct genus of notohippid notoungulates that lived during the Early Oligocene in what is now Argentina and Chile. Fossils of this genus have been found in the Sarmiento Formation and the Abanico Formations of Argentina and Chile.
