Tomarctus is a canine

Canidae

Canidae is the biological family of carnivorous and omnivorous mammals that includes wolves, foxes, jackals, coyotes, and domestic dogs. A member of this family is called a canid . The Canidae family is divided into two tribes: Canini and Vulpini...

 of the extinct subfamily Borophaginae

Borophaginae

The subfamily Borophaginae is an extinct group of canids called "bone crushing dogs" that were endemic to North America during the Oligocene to Pliocene and lived roughly 36—2.5 million years ago and existing for approximately .-Origin:...

 which inhabited most of North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 during the late Early Miocene

Early Miocene

The Early Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages....

 to the Early Barstovian

Barstovian

The Barstovian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology , typically set from 16,300,000 to 13,600,000 years BP, a period of . It is usually considered to overlap the Langhian and Serravallian...

 age of the Middle Miocene

Middle Miocene

The Middle Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene....

 (23—16 mya). Tomarctus existed for approximately .

Tomarctus evolved from the earlier genus Nothocyon

Nothocyon

Nothocyon is an extinct genus of carnivoran which inhabited North America during the late Oligocene. At one time, many species of the dog family Canidae were placed in Nothocyon, but new fossils showed that the type species of Nothocyon, N. geismarianus, is more closely related to bears...

. This animal shared a period of time and ecology with a variety of other bear dog

Bear dog

Amphicyonidae is an extinct family of large terrestrial carnivores belonging to the suborder Caniformia and which inhabited North America, Europe, Asia, and Africa from the Middle Eocene subepoch to the Pleistocene epoch 46.2—1.8 Mya, existing for approximately .-Taxonomy:Amphicyonidae was named...

s like the giant mustelid genus of bone-crushing canidae, Cynarctoides

Cynarctoides

Cynarctoides is an extinct genus of terrestrial canine of the family Borophaginae and tribe Phlaocyonini which inhabited most of North America during the Whitneyan stage of the Early Oligocene to the Barstovian stage of the Middle Miocene 33.3—13.6 Mya existing approximately .-Origin:Cynarctoides...

. As the bear dogs and giant mustelids became extinct, Tomarctus further radiated to fill a line of dog

Dog

The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...

s which filled the hyena

Hyena

Hyenas or Hyaenas are the animals of the family Hyaenidae of suborder feliforms of the Carnivora. It is the fourth smallest biological family in the Carnivora , and one of the smallest in the mammalia...

-like fruit eating and bone-crushing niches.

Species

The genus currently contains two accepted species, Tomarctus brevirostris and Tomarctus hippophaga.

Tomarctus brevirostris, synomymous with Aelurodon francisi, was named by Edward Drinker Cope

Edward Drinker Cope

Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...

 in 1873. Fossil specimens have been found as far south as Panama

Panama

Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...

, east to Plum Point, Maryland

Maryland

Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

, west to California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

, and north to Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

.

Tomarctus hippophaga was first described by Matthew and Cook in 1909 from the Trojan Quarry, Olcott Formation, Nebraska

Nebraska

Nebraska is a state on the Great Plains of the Midwestern United States. The state's capital is Lincoln and its largest city is Omaha, on the Missouri River....

. Specimens have since been found as far west as California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 and as far north as the Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

/Alberta, Canada line.