''Chriacus'' is an extinct genus of placental mammals that lived in what is now North America during the

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

epoch and died out after the early Eocene. In life, members of the genus would have looked something like a

kinkajou The kinkajou ( /ˈkɪŋkədʒuː/ ''KING-kə-joo''; ''Potos flavus'') is a tropical rainforest mammal of the family Procyonidae related to olingos, coatis, raccoons, and the ringtail and cacomistle. It is the only member of the genus ''Poto ...

binturong The binturong (''Arctictis binturong'') (, ), also known as the bearcat, is a viverrid native to South and Southeast Asia. It is uncommon in much of its range, and has been assessed as Vulnerable on the IUCN Red List because of a declining po ...

, though they were not closely related to any living mammal. Well preserved fossils allow clear information on what they looked like. They were about long including a long, robust tail, which may or may not have been

prehensile Prehensility is the quality of an appendage or organ that has adapted for grasping or holding. The word is derived from the Latin term ''prehendere'', meaning "to grasp". The ability to grasp is likely derived from a number of different origi ...

. Other features include a light build, weighing approximately 7 kg (15 lb), and many adaptations typical of animals that live in trees. These include walking on the soles of their five-toed feet, and having long, curved, compressed

claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tars ...

s. The powerfully built limbs had flexible joints, especially the ankles, an adaptation that allows an animal to turn its hind feet behind it, like modern tree

squirrels Squirrels are members of the family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels, ground squirrels (including chipmunks and prairie dogs, among others), and flying squirrels. ...

, in order to climb downward. They were probably

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 nut ...

, eating fruit, eggs, insects and small mammals. Analysis of casts of the brain and inner ear from ''Chriacus pelvidens'' and ''C. baldwini'' suggest these animals depended more on their sense of smell than sight, may have been able to hear about as well as a modern aardvark, and were slow-moving to moderately agile. The encephalization quotient (EQ) had a range of 0.12–0.41 (1.0=average brain size compared with modern mammals of a similar body size) and the neocortex was less developed than later mammals. By the standards of modern mammals, they would have been neither especially quick nor intelligent, but their brains were comparable to many mammals of their time. Derived features of the inner ear were shared with fossils that are assigned to

Euungulata 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, c ...

(artiodactyls+perissodactyls), suggesting the genus may be close to the origin of ungulates, though it is too different in form to be a direct ancestor.

Classification

There are nine species currently recognized in the genus. Like most early placental mammals, the classification of ''Chriacus'' in relation to other groups is disputed. Halliday et al. (2015) consider it a member of the family Oxyclaenidae, a sister group to Palaeoryctids and

Creodonts Creodonta ("meat teeth") 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 an ...

, while Tabuce et al. (2011) classify it as an arctocyonid, most closely related to ''Loxolophus,'' then ''

Arctocyon ''Arctocyon'' ('bear dog') is an extinct genus of ungulate mammals. ''Arctocyon'' was a "ground dwelling omnivore", that lived from 61.3-56.8 Ma. Synonyms of ''Arctocyon'' include ''Claenodon'', and ''Neoclaenodon''. ''Arctocyon'' was likely plant ...

'', and allied to the

mesonychids Mesonychia ("middle claws") 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 ...

. This difference mirrors the history of the mammals classified as arctocyonids. They were first considered creodonts (imagined to be the ancestors of modern carnivores), and then "condylarths," (imagined to be the ancestors of hoofed mammals). Modern studies suggest the confusion is due to the fact that ungulates, carnivores, and creodonts are related groups, and flesh-eating lineages and adaptations evolved within each of them. ''Chriacus'' lies somewhere within the range of their early relatives.

References

Article on Paleocene mammals

Technical information in the Paleobiology database

External links

Picture of a ''Chriacus'' reconstructed from skeletons
{{Taxonbar, from=Q2398857 Condylarths Paleocene mammals of North America Eocene mammals of North America Fossil taxa described in 1883 Prehistoric placental genera Taxa named by Edward Drinker Cope