It was widely distributed across North America, with most of its remains being discovered in the White River Group of the Great Plains, though the John Day Beds of Oregon and the Cypress Hills Formation in Saskatchewan also represent important fossil sites.

[2] Two decades after the description of D. vetus, the smaller D. hartshornianus was named by Edward Drinker Cope on the basis of fossils he discovered in Cedar Creek, Colorado.

This is partly a result of the plesiomorphic and homoplastic traits of early members of the family, as well as the poor fossil record of Middle Eocene Asia.

The 2016 description of Angelarctocyon and Gustafsonia includes a review of the earliest Amphicyonidae, and a phylogenetic analysis that recovers Daphoenus as more derived than the aforementioned taxa, as well as the Eurasian Cynodictis.

While Middle Eocene remains of Cynodoctis have been mentioned in faunal lists of the Lushi Basin and the Ulan Shireh Formation, which would make them the earliest known bear dogs, as well as a possible tooth of similar age from Myanmar, the validity of the assignment of these fossils to the Amphicyonidae could not be verified.

The lack of amphicyonid fossils from the late Uintan and early Duchesnean faunas west of the Rocky Mountains further supports this hypothesis, as they include some of the oldest known reports of other North American immigrants of Eurasian origin.

It is likely that Daphoenus was ancestral to the later daphoenines of North America, such as Daphoenictis, Paradaphoenus, and Daphoenodon, whereas Cynodictis gave rise to the diversity of Old World bear dogs.

[8] It is more primitive than other species of the genus, as shown by the well-developed buccal shelf on its M1, a feature typical of miacids, as well as the less open trigonid of M1 and the greater development of the paraconid on M2.

Even though it is similar to D. hartshornianus in its size, frontal inflation less pronounced than in D. vetus, and a narrow snout, it differs in its more sectorial dentition, which is reminiscent of Oligocene canids.

The first is known from a single cranium, discovered in the uppermost White River Group of Wildcat Ridge, located in western Nebraska, dating to 28.6 Ma, with a 24 cm long skull.

Furthermore, a large maxilla with unusually big teeth (JODA 1411) is known from Fremd's Unit C from the Blue Basin, correlating with the earliest Arikareean, indicating that a third species of Daphoenus was present in the John Day beds.

[4] The postcranial skeleton of Daphoenus was gracile, with an anatomy possibly suggesting a scansorial animal, and even the earliest members of the genus show subcursorial adaptions, possessing a paraxonic digitigrade to subdigitigrade gate and the ability to evert and invert their hindfoot.

However, fossils of male Daphoenus vetus are remarkable for the presence of enormous bone spurs, which developed on both sides on the inner edge of its distal radii, and increase in size with age.

[19][20][21][22] Due to its unspecialized teeth, Daphoenus has been recovered as omnivore, with one study suggesting that no food item dominated, but small mammals, hard-shelled invertebrates, and fruits were consumed frequently, indicating that their diet was similar to modern binturongs and golden jackals.

[23][24] Orellan coprolites, which include the remains of didelphimorphs, camelids, canids, lagomorphs, oreodonts, leptomerycids, and hypertragulids have been discovered, and were likely produced by a predator similar in size and diet to a coyote, presumably Daphoenus vetus.

It is associated with a sharp drop of temperature of perhaps 10°C in the mid-latitudes of North America by circa 40 Ma, with evidence of similar cooling being found from all across the globe.

[28] Among the larger predators, the archaic oxyaenids also disappear after the Uintan, whereas the last mesonychians survive into the Duchesnean, which also saw the first appearance of nimravids like Pangurban in North America, showing a major restructuring of the continent's carnivore guild.

[31] Badwater Locality 20, where the oldest known fossils of Daphoenodus demilo were discovered, is notable for its diverse assemblage of microvertebrates, similar to the one seen in modern rainforest biomes.

These include various rodents from the families Ischyromyidae, Eomyidae, Sciuravidae & Cylindrodontidae, a variety of insectivores, the marsupial relative Herpethotherium, and the multituberculate Ectypodus.

[32] By the late Duchesnean, at least four genera of amphicyonids (Angelarctocyon, Daphoenictis, Daphoenus, and Gustafsonia) were distributed across North America, and two more (Brachyrhynchocyon and Daphoenocyon) appear during the following epoch.

This association of hyaenodonts, nimravids and daphoenines would continue to dominate the carnivoran fauna of North America until the early Arikareean, when all three disappear in rapid succession.

Ungulates are represented by a wide variety of genera, including the equid Mesohippus, the hornless rhinoceros-relative Hyracodon, the camelid Poebrotherium, the anthracothere Bothriodon, several leptomerycids and protoceratids, and the oreodont Merycoidodon.

The paleosols of White River group also show the replacement of dense woodlands, with annual precipitation of over 1000 mm, with more arid, open woodland-grassland mosaics, that received less than half that amount of rainfall.

[38] Despite this, the mammal associations of the continent saw only minor changes, most notably the extinction of Hemipsalodon, the brontotheres, oromerycids, and cylindrodont rodents, unlike in Europe, where the Grande Coupure transformed the mammalian fauna.

[14][39] In the White River faunas of the Orellan, D. vetus and D. hartshornianus coexisted, and likely avoided competition due to size difference, despite their similar morphology.

[3] Other survivors from the late Eocene carnivoran assemblage include Hyaenodon, Hesperocyon, Dinictis, and Hoplophoneus, whereas the canid Osbornodon newly emerged during this epoch.

Common herbivores include the equids Mesohippus and Miohippus, the tapir Colodon, Archaeotherium, Poebrotherium and Paratylopus among the camelids, and a variety of rhinoceros relatives and oreodonts.

[38] An analysis of the trophic diversity of Orellan carnivorans recovers both White River species of Daphoenus as well as the early canid Mesocyon as mesocarnivores, whereas the large nimravids and Hyaenodon were found to be hypercarnivores.