The extinct Borophaginae form one of three subfamilies found within the

canid Canidae (; from Latin, ''canis'', "dog") is a family (biology), biological family of caniform carnivorans, constituting a clade. A member of this family is also called a canid (). The family includes three subfamily, subfamilies: the Caninae, a ...

family. The other two canid subfamilies are the extinct Hesperocyoninae and extant

Caninae Caninae (whose members are known as canines () is the only living subfamily within Canidae, alongside the extinct Borophaginae and Hesperocyoninae. They first appeared in North America, during the Oligocene around 35 million years ago, subsequent ...

. Borophaginae, called "bone-crushing dogs", were

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

during the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Hesperocyoninae. The earliest and most primitive borophagine is the genus '' Archaeocyon'', which is a small fox-sized animal mostly found in the fossil beds in western North America. The borophagines soon diversified into several major groups. They evolved to become considerably larger than their predecessors, and filled a wide range of niches in late

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

North America, from small omnivores to powerful,

bear Bears are carnivoran mammals of the family (biology), family Ursidae (). They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats ...

-sized carnivores, such as '' Epicyon''.

Species

There are 66 identified borophagine species, including 18 newly identified species that range from the Orellan to

Blancan The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years BP, a period of .phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis of the species was conducted using

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

methods, with Hesperocyoninae as an archaic group of canids, as the outgroup. Aside from some transitional forms, Borophaginae can be organized into four major clades: Phlaocyonini, Cynarctina, Aelurodontina, and Borophagina (all erected as new tribes or subtribes). The Borophaginae begins with a group of small fox-sized genera, such as '' Archaeocyon'', '' Oxetocyon'', '' Otarocyon'', and '' Rhizocyon'', in the Orellan through early Arikareean stages. These canids reached their maximum diversity of species around 28 million years ago. Often generically referred to as "bone-crushing dogs" for their powerful

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

and jaws, and hyena-like features (although their

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-physiology ...

was more primitive than that of hyenas), their

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s are abundant and widespread; in all likelihood, they were probably one of the top predators of their

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

s. Their good fossil record has also allowed a detailed reconstruction of their

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

, showing that the group was highly diverse in its heyday. All Borophaginae had a small fifth toe on their rear feet (similar to the toes that bear dew claws on the front feet), where as all modern

have only four toes normally. Noteworthy genera in this group are '' Aelurodon'', '' Epicyon'', and '' Borophagus'' (='' Osteoborus''). According to Xiaoming Wang, the Borophaginae played broad ecological roles that are performed by at least three living carnivoran families, Canidae (which they were a part of), Hyaenidae, and Procyonidae. Wang Borophagine Construct

Classification

Borophagine taxonomy, following Wang et al. (million years=in existence) *Family

Canidae Canidae (; from Latin, ''canis'', "dog") is a family (biology), biological family of caniform carnivorans, constituting a clade. A member of this family is also called a canid (). The family includes three subfamily, subfamilies: the Caninae, a ...

**Subfamily †Borophaginae ***†'' Archaeocyon'' 33—26 Ma, existing ***†'' Oxetocyon'' 33—28 Ma, existing ***†'' Otarocyon'' 34—30 Ma, existing ***†'' Rhizocyon'' 33—26 Ma, existing ***Tribe † Phlaocyonini 33—13 Ma, existing ****†'' Cynarctoides'' 30—18 Ma, existing ****†'' Phlaocyon'' 30—19 Ma, ***Tribe † Borophagini 30—3 Ma, existing ****†'' Cormocyon'' 30—20 Ma, existing ****†'' Desmocyon'' 25—16 Ma, existing ****†'' Metatomarctus'' 19—16 Ma, existing ****†'' Euoplocyon'' 18—16 Ma, existing ****†'' Psalidocyon'' 16—13 Ma, existing ****†'' Microtomarctus'' 21—13 Ma, existing ****†'' Protomarctus'' 20—16 Ma, existing ****†'' Tephrocyon'' 16—14 Ma, existing ****Subtribe † Cynarctina 20—10 Ma, existing *****†'' Paracynarctus'' 19—16 Ma, existing *****†'' Cynarctus'' 16—12 Ma, existing ****Subtribe † Aelurodontina 20—5 Ma, existing *****†'' Tomarctus'' 23—16 Ma, existing *****†'' Aelurodon'' 16—12 Ma, existing ****Subtribe † Borophagina *****†'' Paratomarctus'' 16—5 Ma, existing *****†'' Carpocyon'' 16—5 Ma, existing *****†'' Protepicyon'' 16—12 Ma, existing *****†'' Epicyon'' 12—10 Ma, existing *****†'' Borophagus'' (='' Osteoborus'') 12—5 Ma, existing Cladogram showing borophagine interrelationships, following Wang et al., figure 141:

Extinction

According to an analysis of the fossil record of North American fossil

carnivora Carnivora ( ) is an order of placental mammals specialized primarily in eating flesh, whose members are formally referred to as carnivorans. The order Carnivora is the sixth largest order of mammals, comprising at least 279 species. Carnivor ...

ns, the decline of borophagines from a diversity of about 30 species 15 million years ago to extinction was largely driven by competition with

felid Felidae ( ) is the Family (biology), family of mammals in the Order (biology), order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ). The 41 extant taxon, extant Felidae species exhibit the gre ...

s and canines. Felids invaded the continent from Eurasia about 20 million years ago and were better ambush predators, in part due to their retractable claws. Climate change, which led to the replacement of North American forests with grasslands, may also have been a factor; borophagines were less suited to running down prey than canines. Although these specific species developed powerful limbs that are capable of cracking bones in vicious pounce attacks, other carnivorous species that rely on quick ambush for catching prey were likely more successful than the slower Borophaginae.

Species

Classification

Extinction

References

Further reading