| Helohyidae Temporal range: | |
|---|---|
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| Reconstruction of the skull of Achaenodon | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Family: | † Helohyidae Marshall, 1877 |
| Species | |
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Helohyidae were a group of artiodactyl mammals. [1] [2] They were most prominent in the mid-to-upper Eocene (~50 to 39 million years ago).
Helohyidae share vague similarities to present-day pigs, though were slimmer in build. They possessed prominent canines and molars with bunodont cusps, bulging dental wreaths, and wrinkled enamel. Their upper molars were usually squared, due to the enlargement and displacement of the metaconule, but there was also a small hypocone and hypoconule. The paraconule was reduced and there was no mesostyle. Their lower molars increased in size as they proceeded to the bottom of the jaw, and the paraconid was small or absent. Some forms (e.g. Gobiohyus) possessed small diastemas that separated the premolars from each other. The snout was usually elongated (e.g. in Helohyus), but in some forms ascribed to this family ( Achaenodon ), it was very short. Compared to other primitive artiodactyls such as dichobunids, they possessed higher sagittal ridges; the genus Achaenodon, in particular, possessed a large sagittal crest and its size was much larger than those of other helohyids. [3]
The family Helohyidae was established by Marshall in 1877 to accommodate some forms of early artiodactyl mammals of the American Eocene. In addition to the genus Helohyus, the North American Parahyus and Achaenodon were later ascribed to this family. Other forms come from the Upper-Middle-East Eocene of Asia (Gobiohyus [4] of Inner Mongolia, Pakkokuhyus of Burma and Progenitohyus [5] of Thailand. The latter form may be close to the origin of the family of hippo-like anthracotheres. The artiodactyl Simojovelhyus was once thought to be an unusually late-surviving genus of helohyid from the Upper Oligocene (extending the families temporal range by around 10 million years), [6] however recent studies consider it a peccary. [7]
Helohyids have been variously classified as relatives of archaic dichobunids or as close to the origin of anthracotheres. Some authors consider them close relatives of dichobunids, [8] while other have considered at least some members of the family as close relatives of the entelodonts as part of Cetancodontamorpha. [9]
Entelodontidae is an extinct family of pig-like artiodactyls which inhabited the Northern Hemisphere from the late Eocene to the Middle Miocene epochs, about 38-19 million years ago. Their large heads, low snouts, narrow gait, and proposed omnivorous diet inspires comparisons to suids and tayassuids (peccaries), and historically they have been considered closely related to these families purely on a morphological basis. However, studies which combine morphological and molecular (genetic) data on artiodactyls instead suggest that entelodonts are cetancodontamorphs, more closely related to hippos and cetaceans through their resemblance to Pakicetus, than to basal pigs like Kubanochoerus and other ungulates.
Entelodon, formerly called Elotherium, is an extinct genus of entelodont artiodactyl endemic to Eurasia. Fossils of species are found in Paleogene strata ranging in age from the Houldjinian until the Rupelian epoch of the early Oligocene.
Anthracotherium is an extinct genus of artiodactyls characterized by having 44 teeth, with five semi-crescentic cusps on the crowns of the upper molars. The genus ranged from the middle Eocene period until the early Miocene, having a distribution throughout Eurasia. Material subjectively assigned to Anthracotherium from Pakistan suggests the last species died out soon after the start of the Miocene.
Archaeotherium is an extinct genus of entelodont artiodactyl endemic to North America during the Eocene and Oligocene epochs (35—28 mya), existing for approximately 9.1 million years. Archaeotherium fossils are most common in the White River Formation of the Great Plains, but it has also been found in the John Day Basin of Oregon and the Trans-Pecos area of Texas.
Elomeryx is an extinct genus of artiodactyl ungulate, and is among the earliest known anthracotheres. The genus was extremely widespread, first being found in Asia in the middle Eocene, in Europe during the latest Eocene, and having spread to North America by the early Oligocene. The closest living relatives of the Elomeryx are bovids, suids, and cetaceans.
Anthracothema was a genus of extinct artiodactyl ungulate mammals that lived in Myanmar during the late Eocene.
Anthracokeryx is a genus of extinct artiodactyl ungulate mammal belonging to Anthracotheriidae that lived in Asia during the middle to late Eocene.
Anthracohyus was a genus of extinct artiodactyl ungulate mammal belonging to Anthracotheriidae that lived in Asia during the middle to late Eocene.
Anoplotherium is the type genus of the extinct Paleogene artiodactyl family Anoplotheriidae, which was endemic to western Europe. It lived from the late Eocene to the earliest Oligocene. The fossil mammal genus was the 4th to be described with official taxonomic authority, with a history extending back to 1804 when its fossils from Montmartre in Paris, France were first described by the famous French naturalist Georges Cuvier. Discoveries of incomplete skeletons of A. commune in 1807 led Cuvier to thoroughly describe unusual features for which there are no modern analogues. His drawn skeletal and muscle reconstructions of A. commune in 1812 were amongst the first instances of anatomical reconstructions based on fossil evidence. Cuvier's contributions to palaeontology based on his works on the genus were revolutionary for the field, not only proving the developing ideas of extinction and ecological succession but also paving the way for subfields such as palaeoneurology. Today, it has four known species, although A. pompeckji is similar to A. laurillardi and not as well-defined in distinction.
Brachyhyops is an extinct genus of entelodont artiodactyl mammal that lived during the Eocene Epoch of western North America and southeastern Asia. The first fossil remains of Brachyhyops are recorded from the late Eocene deposits of Beaver Divide in central Wyoming and discovered by paleontology crews from the Carnegie Museum of Natural History during the early 20th century. The type species, Brachyhyops wyomingensis, is based on a single skull and was named by E.H. Colbert in 1937, but was not officially described until 1938. During the latter half of the 20th century, additional specimens from North America have been recorded from Saskatchewan and as far south as Texas, indicating that Brachyhyops had a broad distribution and was well-dispersed throughout western North America.
Paraentelodon is an extinct entelodont from the Late Oligocene and Oligocene-Miocene boundary of Asia. The fossils of the type species P. intermedium were found in Georgia, Kazakhstan and China. An indeterminate species represents in Bugti Hills which is the late Oligocene of Pakistan.
The Irdin Manha Formation is a geological formation from the Eocene located in Inner Mongolia, China, a few kilometres south of the Mongolian border.
Microbunodon was a genus of extinct artiodactyl mammals in the family Anthracotheriidae. It lived between the upper Eocene and the lower Pliocene. Its fossil remains have been found in Europe and Asia.
Varavudh Suteethorn, or Warawut Suteethorn is a Thai palaeontologist and geologist. He is the current director of the Palaeontological Research and Education Centre, Mahasarakham University. He is best known for his work on vertebrate paleontology in northeastern Thailand, having contributed to the discovery of many fossil taxa and dig sites in the Khorat Plateau, as a part of a long-standing collaboration between Thai and French scientists.
Achaenodon is an extinct artiodactyl mammal, possibly belonging to the family Helohyidae. It lived in the mid-late Eocene and its fossil remains have been found in North America.
The bothriodontines are a paraphyletic assemblage of anthracotheres that originated from Eurasia in the late middle Eocene (Bartonian). The group can be distinguished from other anthracothere lineages by their upper molars with the mesostyle that is occupied by the transverse valley, selenodont cusps, ventrally concave symphysis, elongated muzzles, with presence of a diastema between the canine and first premolar. The size range of the group ranged from small, basal forms to larger and more derived forms. During their evolution, the bothriodontines undergone a trend from evolving from small basal forms such as Qatraniodon into larger taxa such as Libycosaurus and Merycopotamus. Some genera the snouts became even more elongated and teeth specialized in a folivorous diet, while others like Merycopotamus became wide, heavy and shallow muzzles with teeth more adapted for grazing.
The microbunodontines were an extinct subfamily of anthracotheres that were predominately a Paleogene group of Eurasian artiodactyls. The group died out at the end of the Late Miocene. It comprised the genera Anthracokeryx, Geniokeryx, Microbunodon, and possibly Etruscotherium. They are different from the other anthracothere lineages by their smaller size, slenderer limbs and male specimens having laterally compressed, longer canines. They were originally classified as members of the other subfamily of anthracotheres, Anthracotheriinae but recent phylogenetic studies have found them to be their own clade sister to Bothriodontinae.
The anthracotheriines are an extinct subfamily of anthracotheres that comprised Paleogene to early Neogene North American and Eurasian artiodactyls. The group contained the genera Anthracotherium, Heptacodon, and Paenanthracotherium, as well as possibly Myaingtherium and Siamotherium. They were small to large sized anthracotheres, and when compared to the other two subfamilies, Microbunodontinae and Bothriodontinae, anthracotheriines are found to occupy a primitive, basal position in the family.
Ancodonta is an infraorder of semiaquatic artiodactyl ungulates including modern hippopotamus and all mammals closer to hippos than to cetaceans (whales). Ancodonts first appeared in the Middle Eocene, with some of the earliest representatives found in fossil deposits in Southeast Asia. Throughout their evolutionary history they have occupied different browsing and grazing niches in North America, Eurasia and Africa. The last continent is notable as they were among the first laurasiatherian mammals to have migrated to Africa from Europe, where they competed with the native afrothere herbivores for the same niches. Of the nearly 50 genera that have existed, only two of them are extant – Choeropsis and Hippopotamus. The interrelationships within the ancodonts has been contended. The traditional notion is that there at minimum two families Anthracotheriidae and Hippopotamidae and were merely sister taxa. However many detailed research of the dentition among ancodonts, as well as how some anthracotheres were similar to hippos in appearance, lead the current consensus where Anthracotheriidae is paraphyletic to Hippopotamidae. Among the anthracotheres members of Bothriodontinae are among the closest to the ancestry of hippos, with the Oligocene aged Epirigenys from Lokon, Turkana, Kenya being the sister taxon to hippos. In response of this many similar clade names have been used for this clade.
Bachitherium is an extinct genus of Paleogene ruminants that lived in Europe from the late Eocene to the late Oligocene. The genus was erected in 1882 by Henri Filhol for Bachitherium curtum, the type species, and B. insigne; five more species have since been named although one, B. sardus, is currently pending reassessment. The genus name derives from "Bach", the French locality where its first fossils were found, and the Greek θήρ/therium meaning "beast". Bachitherium has historically been assigned to various families within the ruminant infrorder Tragulina, but was reclassified to its own monotypic family Bachitheriidae by Christine Janis in 1987.