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.
The Desmostylia are an extinct order of aquatic mammals native to the North Pacific from the early Oligocene (Rupelian) to the late Miocene (Tortonian). Desmostylians are the only known extinct order of marine mammals.
Afrotheria is a superorder of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews, otter shrews, tenrecs, aardvarks, hyraxes, elephants, sea cows, and several extinct clades. Most groups of afrotheres share little or no superficial resemblance, and their similarities have only become known in recent times because of genetics and molecular studies. Many afrothere groups are found mostly or exclusively in Africa, reflecting the fact that Africa was an island continent from the Cretaceous until the early Miocene around 20 million years ago, when Afro-Arabia collided with Eurasia.
Paenungulata is a clade of "sub-ungulates", which groups three extant mammal orders: Proboscidea, Sirenia, and Hyracoidea (hyraxes). At least two more possible orders are known only as fossils, namely Embrithopoda and Desmostylia.
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.
Phenacodus is an extinct genus of mammals from the late Paleocene through middle Eocene, about 55 million years ago. It is one of the earliest and most primitive of the ungulates, typifying the family Phenacodontidae and the order Perissodactyla.
Tethytheria is a clade of mammals that includes the sirenians and proboscideans, as well as the extinct order Embrithopoda.
Panperissodactyla is a clade of ungulates containing living order Perissodactyla and all extinct ungulates more closely related to Perissodactyla than to Artiodactyla.
Jozaria is an extinct genus of stem perissodactyl from the Early to Middle Eocene of the Kuldana Formation of Kohat, Pakistan. It and other anthracobunids were formerly classified with proboscideans.
Anthracobune is an extinct genus of stem perissodactyl from the middle Eocene of the Upper Kuldana Formation of Kohat, Punjab, Pakistan.
Ishatherium is an extinct genus of ungulate from the early Eocene of the Subathu formation in northwestern India.
Lammidhania is an extinct genus of anthracobunids, which lived from the early to middle Eocene period. Its fossil remains were discovered in 1940 in the Chorlakki locality of the Punjab province of Pakistan.
Nakusia is an extinct genus of ungulate from the early Eocene epoch, described in 1999 in the Ghazij formation of Baluchistan, Pakistan. It was classified as an anthracobunid in 1999 but was suggested in a 2014 cladistic analysis to be more likely to belong to Quettacyonidae or Cambaytheriidae.
Hsanotherium is an extinct genus of early ungulate from the middle Eocene, described in 2000 in the Pondaung Formation, Myanmar.
Meniscotherium is an extinct genus of dog-sized mammal which lived 54–38 million years ago. It was a herbivore and had hooves. Fossils have been found in Utah, New Mexico. and Colorado. Many individuals have been found together, indicating that it lived in groups.
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.
Altungulata or Pantomesaxonia is an invalid clade (mirorder) of ungulate mammals comprising the perissodactyls, hyracoids, and tethytheres.
Ocepeia is an extinct genus of afrotherian mammal that lived in present-day Morocco during the middle Paleocene epoch, approximately 60 million years ago. First named and described in 2001, the type species is O. daouiensis from the Selandian stage of Morocco's Ouled Abdoun Basin. A second, larger species, O. grandis, is known from the Thanetian, a slightly younger stage in the same area. In life, the two species are estimated to have weighed about 3.5 kg (7.7 lb) and 10 kg (22 lb), respectively, and are believed to have been specialized leaf-eaters. The fossil skulls of Ocepeia are the oldest known afrotherian skulls, and the best-known of any Paleocene mammal in Africa.
Cambaytherium is an extinct genus of placental mammals in the family Cambaytheriidae whose fossils were found in an open pit coal mine located in Gujarat, India. The mine was a treasure trove full of teeth and bones, over 200 of which were identified as belonging to Cambaytherium thewissi. The fossils were dated to the Early Eocene, 54.5 million years ago, making them slightly younger than the oldest known fossils belonging to the order Perissodactyla.
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.
