Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla, are animals—ungulates—who have reduced the weight-bearing toes to three or one of the five original toes. The non-weight-bearing toes are either present, absent, vestigial, or positioned posteriorly. By contrast, the even-toed ungulates 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 odd-toed ungulates digest plant cellulose in their intestines, rather than in one or more stomach chambers as even-toed ungulates, with the exception of Suina, do.
Mesonychia is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely when the last genus, Mongolestes, became extinct in the early Oligocene. In Asia, the record of their history suggests they grew gradually larger and more predatory over time, then shifted to scavenging and bone-crushing lifestyles before the group became extinct.
Eosimias is a genus of early primates, first discovered and identified in 1999 from fossils collected in the Shanghuang fissure-fillings of Liyang, the southern city of Jiangsu Province, China. It is a part of the family Eosimiidae, and includes three known species: Eosimias sinensis, Eosimias centennicus, and Eosimias dawsonae. It provides us with a glimpse of a primate skeleton similar to that of the common ancestor of the Haplorhini. The name Eosimias is designed to mean "dawn monkey", from Greek eos "dawn" and Latin simius "monkey".
Chalicotheres are an extinct clade 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 one of the five major radiations of perissodactyls, with three groups living, and two extinct.
Pakotitanops is a genus of poorly known brontothere represented only by a few tooth fragments. Its fossil dates from the middle Eocene Kuldana Formation, in the Ganda Kas area of Pakistan. Because this species is known only from a few tooth fragments it is difficult to compare it to other species to determine if it is indeed a distinct species and to what other species it is mostly closely related.
Eotitanops is an extinct genus of brontothere native to North America and Asia.
Megacerops is an extinct genus of the prehistoric odd-toed ungulate family Brontotheriidae, an extinct group of rhinoceros-like browsers related to horses. It was endemic to North America during the Late Eocene epoch, existing for approximately 4.1 million years.
Paroodectes is an extinct genus of placental mammals from clade Carnivoraformes, that lived in Europe during middle Eocene.
Mesonychidae is an extinct family of small to large-sized omnivorous-carnivorous mammals. They were endemic to North America and Eurasia during the Early Paleocene to the Early Oligocene, and were the earliest group of large carnivorous mammals in Asia. They are not closely related to any living mammals. Mesonychid taxonomy has long been disputed and they have captured popular imagination as "wolves on hooves," animals that combine features of both ungulates and carnivores. Skulls and teeth have similar features to early whales, and the family was long thought to be the ancestors of cetaceans. Recent fossil discoveries have overturned this idea; the consensus is that whales are highly derived artiodactyls. Some researchers now consider the family a sister group either to whales or to artiodactyls, close relatives rather than direct ancestors. Other studies define Mesonychia as basal to all ungulates, occupying a position between Perissodactyla and Ferae. In this case, the resemblances to early whales would be due to convergent evolution among ungulate-like herbivores that developed adaptations related to hunting or eating meat.
Brachydiastematherium transylvanicum is the westernmost species of brontothere, with the first fossils of it being found in Transylvania, Romania. In comparison with other brontothere fossils, it is suggested that B. transylvanicum would have had an elongated head, not unlike Dolichorhinus, and be about 2 meters at the withers.
Cormohipparion is an extinct genus of horse belonging to the tribe Hipparionini that lived in North America during the late Miocene to Pliocene. This ancient species of horse grew up to 3 feet long.
Xinyuictis is an extinct genus of placental mammals from clade Carnivoraformes, that lived in Asia from early to late Eocene.
Telmatherium is a genus of a North American Brontothere. It stood 1.25 metres (4.1 ft) tall. It lived during the Eocene epoch.
Dawsonicyon is an extinct genus of placental mammals from clade Carnivoraformes, that lived in North America from early to middle Eocene. Fossils of type species Dawsonicyon isami are known from the ‘Bridger B’, site of Black’s Fork member of the Bridger Formation in Wyoming, and includes an almost complete skeleton.
Brontotheriidae is a family of extinct mammals belonging to the order Perissodactyla, the order that includes horses, rhinoceroses, and tapirs. Superficially, they looked rather like rhinos, although they were actually more closely related to horses; Equidae and Brontotheriidae make up the suborder Hippomorpha. They lived around 56–34 million years ago, until the very close of the Eocene.
Diplacodon is a genus of prehistoric odd-toed ungulates in the family Brontotheriidae. It was the size of a rhinoceros, with the last two upper premolars molar-like.
The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene, or Clarkforkian, Wasatchian and Bridgerian in the NALMA classification.
The Santiago Formation is a geologic formation in Orange and northwestern San Diego County, California. The siltstones, mudstones and sandstones of the formation preserve fossils of Walshina esmaraldensis and Diegoaelurus vanvalkenburghae, dating back to the Late Eocene to Late Oligocene periods.
Sivaladapis is a genus of adapiform primate that lived in Asia during the middle Miocene.
Limnocyon is an extinct paraphyletic genus of limnocyonid hyaenodonts that lived in North America during the middle Eocene. Fossils of this animal have been found in California, Utah and Wyoming.
