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.
Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates. It is now largely considered to be a wastebasket taxon, having served as a dumping ground for classifying ungulates which had not been clearly established as part of either Perissodactyla or Artiodactyla, being composed thus of several unrelated lineages.
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.
Panperissodactyla is a clade of ungulates containing living order Perissodactyla and all extinct ungulates more closely related to Perissodactyla than to Artiodactyla.
Birbalomys is an extinct genus of rodent from Asia.
Anthracobunidae is an extinct family of stem perissodactyls that lived in the early to middle Eocene period. They were originally considered to be a paraphyletic family of primitive proboscideans possibly ancestral to the Moeritheriidae and the desmostylians. The family has also thought to be ancestral to the Sirenia.
Anthracobune is an extinct genus of stem perissodactyl from the middle Eocene of the Upper Kuldana Formation of Kohat, Punjab, Pakistan.
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.
Indobune is an extinct genus of ungulate endemic to Asia during the Eocene from 55.8—48.6 Ma, living for approximately 7.2 million years.
Phenacodontidae is an extinct family of large herbivorous mammals traditionally placed in the “wastebasket taxon” Condylarthra, which may instead represent early-stage perissodactyls. They lived from the late early Paleocene to early middle Eocene and their fossil remains have been found in North America and Europe. The only unequivocal Asian phenacodontid is Lophocion asiaticus.
Eobarbourula delfinoi is an extinct toad which existed in what is now Gujarat, India, during the Middle Ypresian age of the early Eocene. It was described by Annelise Folie, Rajendra S. Rana, Kenneth D. Rose, Ashok Sahni, Kishor Kumar, Lachham Singh and Thierry Smith in 2012, and is the only species in the genus Eobarbourula. The name of the genus is a combination of "Eo", referring to the epoch in which the animal existed, and Barbourula, the generic name of the jungle toads, while the specific epithet refers to Massimo Delfino, an Italian paleontologist.
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.
The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene, or Clarkforkian, Wasatchian and Bridgerian in the NALMA classification.
Olbitherium is an extinct mammal of the order Perissodactyla from the early Eocene epoch of Shandong, China.
Asiadapis is a genus of adapiform primate that lived in India's Cambay Shale Formation during the early Eocene (Ypresian). It has two known species, Asiadapis cambayensis and Asiadapis tapiensis.
Hassianycteris is an extinct genus of Early Eocene (Ypresian) to Middle Eocene (Lutetian) bats from the Hassianycterididae with four or five known species: the type, H. magna, and H. revilliodi, all found in the Messel pit, Germany, H. kumari, found in the Cambay Shale Formation, India, and the possible fifth species "H." joeli, found in the Kortijk Clay Formation, Belgium, which may instead belong to Onychonycteridae. The Messel bats Palaeochiropteryx and Hassianycteris are the first fossil mammals whose colouration has been discovered: both were reddish-brown when alive.
Cambaytheriidae is a family of primitive four or five-toed ungulates native to the Indian subcontinent. They lived during the Early Eocene epoch and are distinguished by the presence of bunodont teeth suitable for eating tough vegetation. They are related to, but distinct from, the early perissodactyls, and may also be closely related to the anthracobunids as a sister group to the Perissodactyla.
Indohyaenodontidae is an extinct family of placental mammals from extinct order Hyaenodonta. Fossil remains of these mammals are known from early to late Eocene deposits in Asia.
The Cambay Shale Formation is geologic formation in the Cambay Basin, India. It is of lower Eocene age. It varies in thickness from a few meters on the margins of the basin to more than 2,500m in the depressions. It directly overlies the Olpad Formation and is, in turn, overlain by the Anklesvar Formation in the southern part of the basin and by Kalol Formation in the northern part of the basin. Further north, the Cambay Shale, in its lower part, is gradually replaced by tongues of paralic-deltaic Kadi Formation and finally by Tharad Formation.
