''Hyopsodus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

early

ungulate Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, ...

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

of the family

Hyopsodontidae Hyopsodontidae is an extinct family of primitive mammals from the order Condylarthra, living from the Paleocene to the Eocene in North America and Eurasia. Condylarthra is now thought to be a wastebasket taxon; hyopsodontids have occasionally be ...

, a group associated with or basal to the Perissodactyla.

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s of this genus have been found in the Eocene of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

, especially the Bighorn Basin region of the United States. It has also been found in Eurasia.

Taxonomy

Eighteen species of Hyopsodus have been described from North America, four from Asia, and two from Europe. The exact number and identity of species has been contested, as is common when taxa are erected based on fragmentary materials. However, there is broad agreement that multiple species in the genus lived in the Wasatchian, Uintan, and Bridgerian North American Land Mammal Ages, and they have been used both to reconstruct paleoenvironments and to study evolutionary change.

Appearance and habits

Members of the genus had a long spinal column with short limbs and tail, making them one of the few genera of Paleogene mammal with a common name: "tube-sheep" Reconstructing their appearance in life was originally difficult, as remains are common but often consist only of fragmentary jaws or skulls and teeth. (In ''H. paulus'', this preservation has been observed in predator coprolites, along with lizard scutes.) However, several whole individuals in the genus have been found beautifully preserved in life positions in langerstatten in fossil lakes. They show ''Hyopsodus'' individuals had an arched back with a posture similar to a

hyrax Hyraxes (), also called dassies, are small, thickset, herbivorous mammals in the order Hyracoidea. Hyraxes are well-furred, rotund animals with short tails. Typically, they measure between long and weigh between . They are superficially simila ...

, rather than a weasel-like tube-shaped body. Study of the limbs in ''H. lepidus'' has shown these animals were not adapted either for life as underground diggers like

moles Moles can refer to: * Moles de Xert, a mountain range in the Baix Maestrat comarca, Valencian Community, Spain * The Moles (Australian band) *The Moles, alter ego of Scottish band Simon Dupree and the Big Sound People *Abraham Moles, French engin ...

and

groundhogs The groundhog (''Marmota monax''), also known as a woodchuck, is a rodent of the family Sciuridae, belonging to the group of large ground squirrels known as marmots. The groundhog is a lowland creature of North America; it is found through mu ...

, or for life in the trees. However, they would have moved quickly on the ground, and could have dug for food or shelter as

pigs The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus s ...

and

bandicoots Bandicoots are a group of more than 20 species of small to medium-sized, terrestrial, largely nocturnal marsupial omnivores in the order Peramelemorphia. They are endemic to the Australia–New Guinea region, including the Bismarck Archipelago t ...

do. An endocast of the brain of ''H. lepidus'' has shown it had an excellent sense of smell and an expanded ability to process sounds. Though they did not have a sophisticated echolocation system like

bats Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...

, they may have had basic terrestrial echolocation to help them avoid or find objects in the dark, like modern

shrews Shrews (family Soricidae) are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to different ...

and

tenrecs A tenrec is any species of mammal within the afrotherian family Tenrecidae endemic to Madagascar. Tenrecs are wildly diverse; as a result of convergent evolution some resemble hedgehogs, shrews, opossums, rats, and mice. They occupy aquatic ...

. It is likely ''H. lepidus'' was a nocturnal ground-dweller in damp closed forests and by the edges of lakes. ''H. wortmani'' had strong chest muscles and could have dug burrows or swum. The teeth of all species show they were

omnivores An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutri ...

; at least one species, ''H. lovei,'' had a battery of procumbent incisors worn by chewing, and likely had a specialized diet. In their heyday, ''Hyopsodus'' species may have occupied a variety of niches later taken by other flexible forest feeders such as

rats Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' (pack rats), ''Bandicota'' (bandicoot ...

, small early

perissodactyls Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla (, ), are animals—ungulates—who have reduced the weight-bearing toes to three (rhinoceroses and tapirs, with tapirs still using four toes on the front legs) o ...

, and hypocarnivores like

raccoons The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of . ...

References

Condylarths Eocene mammals of North America Eocene mammals of Asia Eocene mammals of Europe Fossil taxa described in 1870 Prehistoric placental genera {{paleo-oddtoedungulate-stub