Perissodactyla is an order of ungulates. The order includes about 17 living species divided into three families: Equidae, Rhinocerotidae (rhinoceroses), and Tapiridae (tapirs). They typically have reduced the weight-bearing toes to three or one of the five original toes, though tapirs retain four toes on their front feet. The nonweight-bearing toes are either present, absent, vestigial, or positioned posteriorly. By contrast, artiodactyls bear most of their weight equally on four or two of the five toes: their third and fourth toes. Another difference between the two is that perissodactyls digest plant cellulose in their intestines, rather than in one or more stomach chambers as artiodactyls, with the exception of Suina, do.
Ungulates are members of the diverse clade Euungulata which primarily consists of large mammals with hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined to be a polyphyletic and thereby invalid clade based on molecular data. As a result, true ungulates had since been reclassified to the newer clade Euungulata in 2001 within the clade Laurasiatheria while Paenungulata has been reclassified to a distant clade Afrotheria. Living ungulates are divided into two orders: Perissodactyla including equines, rhinoceroses, and tapirs; and Artiodactyla including cattle, antelope, pigs, giraffes, camels, sheep, deer, and hippopotamuses, among others. Cetaceans such as whales, dolphins, and porpoises are also classified as artiodactyls, although they do not have hooves. Most terrestrial ungulates use the hoofed tips of their toes to support their body weight while standing or moving. Two other orders of ungulates, Notoungulata and Litopterna, both native to South America, became extinct at the end of the Pleistocene, around 12,000 years ago.
Propalaeotherium was an early genus of perissodactyl endemic to Europe and Asia during the early Eocene. There are currently six recognised species within the genus, with P. isselanum as the type species.
Chalicotheriidae is an extinct family of herbivorous, odd-toed ungulate (perissodactyl) mammals that lived in North America, Eurasia, and Africa from the Middle Eocene until the Early Pleistocene, existing from 48.6 to 1.806 mya. They are often called chalicotheres, a term which is also applied to the broader grouping of Chalicotherioidea. They are noted for their unusual morphology compared to other ungulates, such as their elongated clawed forelimbs. They are thought to have been browsers.
Hyrachyus is an extinct genus of perissodactyl mammal that lived in Eocene Europe, North America, and Asia. Its remains have also been found in Jamaica. It is closely related to Lophiodon.
The evolution of the horse, a mammal of the family Equidae, occurred over a geologic time scale of 50 million years, transforming the small, dog-sized, forest-dwelling Eohippus into the modern horse. Paleozoologists have been able to piece together a more complete outline of the evolutionary lineage of the modern horse than of any other animal. Much of this evolution took place in North America, where horses originated but became extinct about 10,000 years ago, before being reintroduced in the 15th century.
Palaeotheriidae is an extinct family of herbivorous perissodactyl mammals that inhabited Europe, with less abundant remains also known from Asia, from the mid-Eocene to the early Oligocene. They are classified in Equoidea, along with the living family Equidae.
Amynodontidae is a family of extinct perissodactyls related to true rhinoceroses. They are commonly portrayed as semiaquatic hippo-like rhinos but this description only fits members of the Metamynodontini; other groups of amynodonts like the cadurcodontines had more typical ungulate proportions and convergently evolved a tapir-like proboscis.
Anoplotherium is the type genus of the extinct Palaeogene artiodactyl family Anoplotheriidae, which was endemic to western Europe. It lived from the late Eocene to the earliest Oligocene. It was the fourth fossil mammal genus 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 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, there are four known species.
Schizotheriines are one of the two subfamilies of the extinct family Chalicotheriidae, a group of herbivorous odd-toed ungulate (perissodactyl) mammals that lived from the Eocene to the Pleistocene. The other clade is the Chalicotheriinae. Both clades had claws rather than hooves on their front feet, an adaptation understood as related to feeding. Schizotheriines also had claws on their hind feet. The fossils of both groups are found in environments that had trees and shrubs. While chalicotheriines developed very derived body forms, schizotheriines remained basically similar in shape to other perissodactyls such as horses and tapirs. Like most forest-dwelling ungulates, they had long necks and forelimbs longer than their hindlimbs. Schizotheriines had longer, higher-crowned cheek teeth than chalicotheriines, which indicates they typically fed on tougher vegetation. The sediments where their fossils are found show they also lived in a wider range of environments, from moist forests to drier woodland or savannah-like environments with trees. Perhaps for this reason, they became more widely distributed than chalicotheriines. Though chalicotheres likely evolved in Asia, schizotheriine fossils are also found in Africa and North America, which they reached by the Bering land bridge. The best-known schizotheriine genus is Moropus. The last survivor of the group was traditionally thought to be Nestoritherium, but it was found to actually be a member of Chalicotheriinae.
Chalicotheriines are one of the two subfamilies of the extinct family Chalicotheriidae, a group of herbivorous, odd-toed ungulate (perissodactyl) mammals that lived from the Eocene to the Pleistocene. The other subfamily is the Schizotheriinae. Chalcotheriines evolved unique characteristics for ungulates, with very long forelimbs, short hindlimbs, and a relatively gorilla-like physique, including knuckle-walking on their flexible forelimbs, which bore long curved claws. Members of this subfamily possessed some of the longest forelimbs and shortest hindlimbs in relation to each other out of all extinct animals. Analysis of dental wear implies that most chalicotheriines fed on seeds and fruit. Their claws were likely used in a hook-like manner to pull down branches, suggesting they lived as bipedal browsers.
Pterodon is an extinct genus of hyaenodont in the family Hyainailouridae, containing five species. The type species Pterodon dasyuroides is known exclusively from the late Eocene to the earliest Oligocene of western Europe. The genus was first erected by the French zoologist Henri Marie Ducrotay de Blainville in 1839, who said that Georges Cuvier presented one of its fossils to a conference in 1828 but died before he could make a formal description of it. It was the second hyaenodont genus with taxonomic validity after Hyaenodon, but this resulted in taxonomic confusion over the validities of the two genera by other taxonomists. Although the taxonomic status of Pterodon was revised during the late 19th and early 20th centuries, it became a wastebasket taxon for other hyaenodont species found in Africa and Asia. Today, only the type species is recognized as belonging to the genus while four others are pending reassessment to other genera.
The Bouldnor Formation is a geological formation in the Hampshire Basin of southern England. It is the youngest formation of the Solent Group and was deposited during the uppermost Eocene and lower Oligocene.
Xiphodon is the type genus of the extinct Palaeogene artiodactyl family Xiphodontidae. It, like other xiphodonts, was endemic to western Europe and lived from the middle Eocene up to the earliest Oligocene. Fossils from Montmartre in Paris, France that belonged to X. gracilis were first described by the French naturalist Georges Cuvier in 1804. Although he designated the species to Anoplotherium, he recognized that it differed from A. commune by its dentition and limb bones, later designating it to its own subgenus in 1822. Xiphodon was promoted to genus rank by other naturalists in later decades. It is today defined by the type species X. gracilis and two other species X. castrensis and X. intermedium.
Homogalax is an extinct genus of tapir-like odd-toed ungulate. It was described on the basis of several fossil finds from the northwest of the United States, whereby the majority of the remains come from the state of Wyoming. The finds date to the Lower Eocene between 56 and 48 million years ago. In general, Homogalax was very small, only reaching the weight of today's peccaries, with a maximum of 15 kg. Phylogenetic analysis suggests the genus to be a basal member of the clade that includes today's rhinoceros and tapirs. In contrast to these, Homogalax was adapted to fast locomotion.
Urtinotherium is an extinct genus of paracerathere mammals. It was a large animal that was closely related to Paraceratherium, and found in rocks dating from the Late Eocene to Early Oligocene period. The remains were first discovered in the Urtyn Obo region in Inner Mongolia, which the name Urtinotherium is based upon. Other referred specimens are from northern China.
Ronzotherium is an extinct genus of perissodactyl mammal from the family Rhinocerotidae. The name derives from the hill of 'Ronzon', the French locality near Le Puy-en-Velay at which it was first discovered, and the Greek suffix 'therium' meaning 'beast'. At present 5 species have been identified from several localities in Europe and Asia, spanning the Late Eocene to Upper Oligocene.
Tonsala is an extinct genus of Plotopteridae, a family of flightless seabird similar in biology with penguins, but more closely related to modern cormorants. The genus is known from terrains dated from the Late Oligocene of the State of Washington and Japan.
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 based on fossil remains found in the Quercy Phosphorites Formation. Bachitherium curtum was defined the type species, and another species called 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.
Diplobune is an extinct genus of Palaeogene artiodactyls belonging to the family Anoplotheriidae. It was endemic to Europe and lived from the late Eocene to the early Oligocene. The genus was first erected as a subgenus of Dichobune by Ludwig Rütimeyer in 1862 based on his hypothesis of the taxon being a transitional form between "Anoplotherium" secundaria, previously erected by Georges Cuvier in 1822, and Dichobune. He based the genus etymology off of the two-pointed pillarlike shapes of the lower molars, which had since been a diagnosis of it. However, in 1870, Diplobune was elevated to genus rank by Oscar Fraas, who recognized that Diplobune was a distinct genus related to Anoplotherium and not Dichobune. After several revisions of the anoplotheriids, there are currently four known species of which D. minor is the type species.
