Temporal range: Early Oligocene–Late Oligocene
|Skull of Archaeocyon leptodus|
Wang, Tedford, & Taylor, 1999
|Range of Archaeocyon based on fossil distribution|
Archaeocyon ("beginning dog") is a small extinct genus of the Borophaginae within the family Canidae (terrestrial canine) which inhabited most of North America during the Whitneyan stage through Geringian stage of the Oligocene epoch 33.3—26.3 Ma  Archaeocyon existed for approximately .
Species of Archaeocyon are among the earliest known borophagines, although a species of Otarocyon has a slightly earlier first appearance.
Archaeocyon was a comparatively small and unspecialized dog. Its dentition (teeth) suggests a slightly more hypocarnivorous (omnivorous) diet than the otherwise similar Hesperocyon. The skeleton is also generalized, lacking specializations for running and retaining a plantigrade foot posture.
A few derived features of the dentition support a relationship to Borophaginae and Caninae (the subfamily that includes living canids), rather than to the basal canid subfamily Hesperocyoninae. The temporal position of Archaeocyon suggests an affinity to borophagines because the first members of Caninae appear substantially earlier.
Fossil specimens of two individuals' body mass were examined by Legendre and Roth. The first specimen was estimated to weigh 1.43 kg (3.15 lbs). The second specimen was estimated to weigh 1.49 kg (3.28 lbs).
Three species of Archaeocyon have been described. The two earlier species, A. pavidus and A. leptodus, differ primarily in size, with A. leptodus being larger. The third species, A. falkenbachi, is the size of A. leptodus and differs from other Archaeocyon species in having a shorter, broader skull.
- Kew Quarry, Sespe Formation, Ventura County, California.
- North Blue Basin Site, John Day Formation, Grant County, Oregon.
- Canyon Ferry Reservoir, Lewis and Clark County, Montana.
- Roundhouse Rock, Brule Formation, Morrill County, Nebraska and other Nebraska sites.
- White Butte Site, Killdeer Formation, Slope County, North Dakota.
- PaleoBiology Database: Archaeocyon Taxonomy, Species
- Wang, X., R.H. Tedford, and B.E. Taylor. 1999. Phylogenetic systematics of the Borophaginae (Carnivora, Canidae). Bulletin of the American Museum of Natural History, 243:1-391.
- S. Legendre and C. Roth. 1988. Correlation of carnassial tooth size and body weight in recent carnivores (Mammalia). Historical Biology