''Rhizocyon'' ("root dog") is an early member of the subfamily

Borophaginae The extinct Borophaginae form one of three subfamilies found within the canid family. The other two canid subfamilies are the extinct Hesperocyoninae and extant Caninae. Borophaginae, called "bone-crushing dogs", were endemic to North America du ...

, an extinct subgroup of canids that were endemic to western

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

during the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

epoch, living from ~31—24.5 Ma., existing for approximately . ''Rhizocyon'' was similar to a contemporary species, '' Archaeocyon leptodus'', from the

Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, an ...

, but it shows a few subtle differences in the structure of the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

and

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolo ...

that indicate that ''Rhizocyon'' may be close to the ancestry of later borophagines. Only a single species, ''R. oregonensis'', is known and all fossils come from the

John Day Formation The John Day Formation is a series of rock strata exposed in the Picture Gorge district of the John Day River basin and elsewhere in north-central Oregon in the United States. The Picture Gorge exposure lies east of the Blue Mountain uplift, whi ...

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

References

* Wang, Xiaoming., 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. * Balisi, Mairin and B. Van Valkenburgh. 2020
Iterative evolution of large-bodied hypercarnivory in canids benefits species but not clades
Communications Biology 3(461). Borophagines Oligocene canids Aquitanian genus extinctions Oligocene mammals of North America Prehistoric carnivoran genera Rupelian genus first appearances Taxa named by Xiaoming Wang {{canid-stub