| Amphicyon Temporal range: Aquitanian–Tortonian |
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| A. ingens, American Museum of Natural History | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Family: | †Amphicyonidae |
| Subfamily: | †Amphicyoninae |
| Genus: | †Amphicyon |
| Species | |
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| Range of Amphicyon based on fossil evidence | |
Amphicyon ("ambiguous dog") is an extinct genus of large carnivorous bone-crushing mammals, known as bear-dogs, of the family Amphicyonidae, subfamily Amphicyoninae, from the Aquitanian Epoch until the Tortonian. They ranged over North America, Europe, Asia, and Africa from 20.6—9 Ma ago, existing approximately 11.6 million years.[1]
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Amphicyon was the typical bear-dog amphicyonid with morphology similar to both bears and dogs. With its robust build and maximum length of 2.5 m (8 ft), the largest species looked more like a bear than a dog. It had a large heavy tail, thick neck, robust limbs and teeth like a wolf. It was probably an omnivore with a lifestyle comparable to that of the brown bear.
A single specimen was examined by Legendre and Roth and estimated to have a body mass of 84.2 kg (190 lb),[2] roughly half that of Ischyrocyon and twice that of Epicyon which shared its time period and habitat. A. ingens was much bigger: Sorkin (2008) estimated the largest known specimen (AM 68108) to weigh 600 kg,[3] making it the largest amphicyonid and one of the largest known carnivorous land mammals.
The earliest occurrences of Amphicyon in North America are from the early to mid-Miocene, found in the Runningwater Formation in Sioux County, Nebraska, and from the lower part of the Troublesome Formation, Colorado (A. galushai, A. frendens, and A. ingens). Although other large amphicyonids from the Miocene of North America have been placed in Amphicyon, many of these carnivores are now placed in other amphicyonid genera. The Amphicyon lineage in the New World is restricted to the above three species (18.8–14.2 Ma). Particularly rich samples of the large North American species of Amphicyon have been found in the Sheep Creek Formation (A. frendens) and Olcott Formation (A. ingens) of central Sioux County, northwest Nebraska.[4] Amphicyon has also been found in France, Spain[5] and Germany in Europe.
Amphicyon frendens lived from 20.16–13.6 Ma, approximately 6.56 million years.[6] The species was originally described by W. Matthew in 1924 from specimens found in the middle member of the Sheep Creek Formation, Sioux County, Nebraska.[7] A. frendens specimens have since been found at sites in Harney and Malheur Counties, Oregon.[6] A specimen examined by S. Legendre and C. Roth in 1988 yielded an estimated body mass of 135.6 kg (300 lb),[2] similar to that of Ischyrocyon, Amphicyon galushai and its borophagine competitor Epicyon, which it coexisted with.
Amphicyon galushai lived from 20.6–16.3 Ma, approximately 4.3 million years.[8] A. galushai was described by R. Hunt in 2003 based on the type specimen F:AM 25406, found in the Dunlap Camel Quarry, Runningwater Formation, Dawes County, Nebraska [4] Specimens assigned to this species have since been found at several sites in Nebraska and one site in Colorado.[8]
Amphicyon giganteus lived from 16.8–7.2 Ma, approximately 9.7 million years,[9] in what is now Europe[9][10] and Namibia.[11] The species was first described in 1884 by Kaup.[12] A specimen of Iberotherium rexmanueli zbyszewskii with teeth marks from A. giganteus was found in Portugal. It is unknown if he young Iberotherium was attacked or the carcass found and scavenged. The find was described by paleontologists Antunesa et al. in 2006.[13]
Amphicyon ingens lived from 20.06–13.6 Ma, approximately 6.46 million years.[14] The species was originally described by W. Matthew in 1924 from specimens found in the Olcott Formation, Sioux County, Nebraska.[7] Specimens attributed to this species have since been found in California, Colorado, and New Mexico.
Amphicyon major lived from 16.9–9.0 Ma, approximately 7.9 million years.[15] Specimens have been found in across Europe and in western Turkey.[15] The species was named by De Blainville in 1841.[15]