Andrewsarchus, meaning "Andrews' ruler", is an extinct genus of artiodactyl that lived during the Middle Eocene in what is now China. The genus was first described by Henry Fairfield Osborn in 1924 with the type species A. mongoliensis based on a largely complete cranium. A second species, A. crassum, was described in 1977 based on teeth. A mandible, formerly described as Paratriisodon, does probably belong to Andrewsarchus as well. The genus has been historically placed in the families Mesonychidae or Arctocyonidae, or was considered to be a close relative of whales. It is now regarded as the sole member of its own family, Andrewsarchidae, and may have been related to entelodonts. Fossils of Andrewsarchus have been recovered from the Middle Eocene Irdin Manha, Lushi, and Dongjun Formations of Inner Mongolia, each dated to the Irdinmanhan Asian land mammal age.
Creodonta is a former order of extinct carnivorous placental mammals that lived from the early Paleocene to the late Miocene epochs in North America, Europe, Asia and Africa. Originally thought to be a single group of animals ancestral to the modern Carnivora, this order is now usually considered a polyphyletic assemblage of two different groups, the oxyaenids and the hyaenodonts, not a natural group. Oxyaenids are first known from the Palaeocene of North America, while hyaenodonts hail from the Palaeocene of Africa.
Mesonychia is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. Mesonychians 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.
Paraceratherium is an extinct genus of hornless rhinocerotoids belonging to the family Paraceratheriidae. It is one of the largest terrestrial mammals that has ever existed and lived from the early to late Oligocene epoch. The first fossils were discovered in what is now Pakistan, and remains have been found across Eurasia between China and the Balkans. Paraceratherium means "near the hornless beast", in reference to Aceratherium, the genus in which the type species P. bugtiense was originally placed.
Chalicotheriidae is an extinct family of herbivorous, odd-toed ungulate (perissodactyl) mammals that lived in North America, Eurasia, and Africa from the Middle Eocene to the Early Pleistocene. 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 clawed forelimbs. Members of the subfamily Chalicotheriinae developed elongate gorilla-like forelimbs that are thought to have been used to grasp vegetation. They are thought to have been browsers on foliage as well as possibly bark and fruit.
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.
Pakicetus is an extinct genus of amphibious cetacean of the family Pakicetidae, which was endemic to Indian Subcontinent during the Ypresian period, about 50 million years ago. It was a wolf-like mammal, about 1–2 m long, and lived in and around water where it ate fish and other animals. The name Pakicetus comes from the fact that the first fossils of this extinct amphibious whale were discovered in Pakistan. The vast majority of paleontologists regard it as the most basal whale, representing a transitional stage between land mammals and whales. It belongs to the even-toed ungulates with the closest living non-cetacean relative being the hippopotamus.
Archaeotherium is an extinct genus of entelodont artiodactyl endemic to North America during the Eocene and Oligocene epochs. Archaeotherium fossils are most common in the White River Formation of the Great Plains, but they have also been found in the John Day Basin of Oregon and the Trans-Pecos area of Texas. Archaeotherium's fossils come from North America, between the Priabonian and Rupelian stages of the Eocene and Oligocene. Up to fifteen species of Archaeotherium have been identified, which are divided into three subgenera. One contains the type species, A. mortoni, among others; another contains very large taxa formerly named Megachoerus and Pelonax; and the last contains A. calkinsi.
Dissacus is a genus of extinct carnivorous jackal to coyote-sized mammals within the family Mesonychidae, an early group of hoofed mammals that evolved into hunters and omnivores. Their fossils in Paleocene to Early Eocene aged strata in France, Asia and southwest North America, from 66 to 50.3 mya, existed for approximately 15.7 million years.
Pachyaena was a genus of heavily built, relatively short-legged mesonychids, early Cenozoic mammals that evolved before the origin of either modern hoofed animals or carnivores, and combined characteristics similar to both. The genus likely originated from Asia and spread to Europe, and from there to North America across a land bridge in what is now the North Atlantic ocean. Various described species of Pachyaena ranged in size from a coyote to a bear. However, a 2007 paper suggests that Pachyaena may be paraphyletic, with P. ossifraga being closer to Synoplotherium, Harpagolestes and Mesonyx than to P. gigantea.
Ankalagon saurognathus is an extinct carnivorous mammal of the family Mesonychidae, endemic to North America during the Paleocene epoch, existing for approximately 3.1 million years.
Tillodontia is an extinct suborder of eutherian mammals known from the Early Paleocene to Late Eocene of China, the Late Paleocene to Middle Eocene of North America where they display their maximum species diversity, the Middle Eocene of Pakistan, and the Early Eocene of Europe. Leaving no descendants, they are most closely related to the pantodonts, another extinct group. The tillodonts were medium- to large-sized animals that probably fed on roots and tubers in temperate to subtropical habitats.
Georgiacetus is an extinct genus of ancient whale known from the Eocene period of the United States. Fossils are known from Georgia, Alabama, and Mississippi and protocetid fossils from the right time frame, but not yet confirmed as Georgiacetus, have been found in Texas and South Carolina.
Archaeohippus is an extinct three toed member of the family Equidae known from fossils of early Oligocene to middle Miocene age. The genus is noted for several distinct skeletal features. The skull possesses deeply pocketed fossa in a notably long preorbital region. The genus is considered an example of phyletic dwarfism with adults estimated at being on average 20 kilograms in weight. This is in contrast to the most common equid of the period, Miohippus. Characters of the teeth show a mix of both primitive and advanced traits. The advanced traits are very similar to those shown in the genus Parahippus. The noted similarities of Archaeohippus and Parahippus show them to be descended from a common ancestor. They are considered sister species.
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.
Asiatosuchus is an extinct genus of crocodyloid crocodilians that lived in Eurasia during the Paleogene. Many Paleogene crocodilians from Europe and Asia have been attributed to Asiatosuchus since the genus was named in 1940. These species have a generalized crocodilian morphology typified by flat, triangular skulls. The feature that traditionally united these species under the genus Asiatosuchus is a broad connection or symphysis between the two halves of the lower jaw. Recent studies of the evolutionary relationships of early crocodilians along with closer examinations of the morphology of fossil specimens suggest that only the first named species of Asiatosuchus, A. grangeri from the Eocene of Mongolia, belongs in the genus. Most species are now regarded as nomina dubia or "dubious names", meaning that their type specimens lack the unique anatomical features necessary to justify their classification as distinct species. Other species such as "A." germanicus and "A." depressifrons are still considered valid species, but they do not form an evolutionary grouping with A. grangeri that would warrant them being placed together in the genus Asiatosuchus.
Afrasia djijidae is a fossil primate that lived in Myanmar approximately 37 million years ago, during the late middle Eocene. The only species in the genus Afrasia, it was a small primate, estimated to weigh around 100 grams (3.5 oz). Despite the significant geographic distance between them, Afrasia is thought to be closely related to Afrotarsius, an enigmatic fossil found in Libya and Egypt that dates to 38–39 million years ago. If this relationship is correct, it suggests that early simians dispersed from Asia to Africa during the middle Eocene and would add further support to the hypothesis that the first simians evolved in Asia, not Africa. Neither Afrasia nor Afrotarsius, which together form the family Afrotarsiidae, is considered ancestral to living simians, but they are part of a side branch or stem group known as eosimiiforms. Because they did not give rise to the stem simians that are known from the same deposits in Africa, early Asian simians are thought to have dispersed from Asia to Africa more than once prior to the late middle Eocene. Such dispersals from Asia to Africa also were seen around the same time in other mammalian groups, including hystricognathous rodents and anthracotheres.
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.
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.
Hemipsalodon is an extinct genus of hyainailourid hyaenodonts from the subfamily Hyainailourinae that lived in North America during the middle to late Eocene.
