Chriacus
Chriacus is an extinct genus of placental mammals that lived in what is now North America from the Paleocene and early Eocene epochs. In life, members of the genus may have looked something like a kinkajou or binturong, though they were not closely related to any living mammal. Like many early Cenozoic mammals, its relationships are uncertain, with possible affinities to ungulates or Ferae.
Paleobiology
Chriacus were probably omnivores, eating fruit, eggs, insects and small mammals.Climbing adaptations
Chriacus has better-preserved fossils than most other Paleocene mammals. The most complete skeleton belongs to an uncertain species from the Willwood Formation of Wyoming. In life, it would have measured around long, including a long, robust tail, which may or may not have been prehensile. Other features include a light build, weighing approximately, and many adaptations typical of animals that live in trees. These include the ability to walk on the soles of their five-toed feet, as well as claws which are long, curved, and compressed. The powerfully-built limbs have flexible joints, especially the ankles, an adaptation that allows an animal to turn its hind feet behind it, like modern tree squirrels, in order to climb downward.Senses
Analysis of casts of the brain and inner ear from C. 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 had a range of 0.12–0.41 and the neocortex was less developed than later mammals. By the standards of modern mammals, Chriacus 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, suggesting the genus may be close to the origin of ungulates, though it is too different in form to be a direct ancestor.Classification
At least nine species are currently recognized in the genus, though it is unknown whether all of these species share exclusive ancestry with each other. Variation within the genus is unusually high. Some Chriacus fossils point towards a slow, climbing lifestyle. Others are oddly similar to the fleet-footed early artiodactyl Diacodexis.Like most early placental mammals, the classification of Chriacus in relation to other groups is disputed. Halliday et al. consider it a member of the family Oxyclaenidae, a sister group to palaeoryctids and creodonts, while Tabuce et al. classify it as an arctocyonid, most closely related to Loxolophus, then Arctocyon, and allied to the Mesonychia.
This difference mirrors the history of the mammals classified as arctocyonids. They were first considered creodonts, and then "condylarths". Modern studies suggest the confusion is due to the fact that ungulates, carnivorans, 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.