Amphicyonidae is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

terrestrial Terrestrial refers to things related to land or the planet Earth, as opposed to extraterrestrial. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on o ...

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 belonging to the

suborder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

Caniformia Caniformia is a suborder within the order Carnivora consisting of "dog-like" carnivorans. They include Canidae, dogs (Wolf, wolves, foxes, etc.), bears, raccoons, and Mustelidae, mustelids. The Pinnipedia (pinniped, seals, walruses and sea lions) ...

. They first appeared in

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 ...

in the middle

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

(around 45 mya), spread to

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

by the late Eocene (35 mya), and further spread to

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

and

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

by the early

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

(23 mya). They had largely disappeared worldwide by the late Miocene (5 mya), with the latest recorded

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

at the end of the Miocene in Africa. They were among the first carnivorans to evolve large body size. Amphicyonids are colloquially referred to as "bear-dogs".

Taxonomy

The family was erected by Haeckel in 1866 (also attributed to Trouessart 1885). Their exact position has long been disputed. Early paleontologists usually defined them as members of

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 ...

(the dog family) or

Ursidae 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 ...

(the bear family), but the modern consensus is that they form their own family. Some researchers have defined it as the sister clade to ursids, based on morphological analysis of the ear region. However, cladistic analysis and reclassification of several species of early carnivore as amphicyonids has strongly suggested that they may be basal caniforms, a lineage older than the origin of both bears and dogs. Amphicyonids should not be confused with the similar looking (and similarly nicknamed) "dog-bears", a more derived group of caniforms that is sometimes classified as a family (

Hemicyonidae Hemicyoninae is an extinct subfamily of Ursidae, often called dog bears (literally "half dog" (Ancient Greek, Greek: )). They were bear-like carnivorans living in Europe, North America, Africa and Asia during the Oligocene through Miocene epoch ...

), but is more often considered a primitive subfamily of ursids (

Hemicyoninae Hemicyoninae is an extinct subfamily of Ursidae, often called dog bears (literally "half dog" (Ancient Greek, Greek: )). They were bear-like carnivorans living in Europe, North America, Africa and Asia during the Oligocene through Miocene epoch ...

). They should also not be confused with Amphicynodontidae (another family of extinct caniforms which were related to bears or

pinnipeds Pinnipeds (pronounced ), commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant families Odobenidae (whose only living member is the walr ...

) or

Arctocyonidae Arctocyonidae (from Greek ''arktos'' and ''kyôn'', "bear/dog-like") is an extinct, possibly polyphyletic family of placental mammals which lived from the late Cretaceous to the early Eocene. They were initially regarded as creodonts, though ha ...

(a family of "

condylarths Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates and is now largely considered to be a wast ...

" which literally translates to "bear-dogs").

Description

Amphicyonids ranged in size from as small as and as large as and evolved from wolf-like to bear-like body forms.

Skull

Amphicyonids tended to have relatively large skulls, with the snout shorter than the rear portion of the cranium. In some large members of the family, such as ''Amphicyon'', the back of the skull develops a sharp

sagittal crest A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are excepti ...

which defines attachment points for large jaw muscles. Amphicyonids had a relatively rudimentary form of

auditory bulla The tympanic part of the temporal bone is a curved plate of bone lying below the squamous part of the temporal bone, in front of the mastoid process, and surrounding the external part of the ear canal. It originates as a separate bone (tympanic b ...

, a bony sheath which encases the middle ear cavity. The bulla is small, mostly formed by the crescent-shaped

ectotympanic The ectotympanic, or tympanicum, is a bony structure found in all mammals, located on the tympanic part of the temporal bone, which holds the tympanic membrane (eardrum) in place. In catarrhine primates (including humans), it takes a tube-shape. ...

bone below the middle ear. The entotympanics only make a minor contribution whenever they are ossified, which only becomes commonplace in Miocene amphicyonids. In these regards, amphicyonids are similar to living bears,

otters Otters are carnivorous mammals in the Rank (zoology), subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic animal, aquatic, or Marine ecology, marine. Lutrinae is a branch of the Mustelidae Family (biology), family, whi ...

, walruses,

eared seals An eared seal, otariid, or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera (another species became extinct in the 1950s) and are commonly known either ...

, and the

red panda The red panda (''Ailurus fulgens''), also known as the lesser panda, is a small mammal native to the eastern Himalayas and southwestern China. It has dense reddish-brown fur with a black belly and legs, white-lined ears, a mostly white muzz ...

. The bulla also helps to distinguish the evolutionary trajectory of amphicyonids: early bears such as '' Cephalogale'' have large bullae which are reduced through the course of their evolution, while dogs start out with large bullae which persist through their entire existence. Amphicyonids differ from both dogs and bears in that they start with a small bulla which gradually becomes more strongly developed later in their evolution.

Teeth

Like most carnivorans, amphicyonid teeth were adapted for carnivory, with large canines near the front and shearing carnassials at the back of the jaw. Amphicyonids were typically mesocarnivorous (majority meat-eating, like dogs) or

hypercarnivorous A hypercarnivore is an animal that has a diet that is more than 70% meat, either via active predation or by scavenging. The remaining non-meat diet may consist of non-animal foods such as fungi, fruits or other plant material. Some extant example ...

(entirely meat-eating, like cats), and some were adapted for tough abrasive food. Only two small Miocene amphicyonines, '' Pseudarctos'' and '' Ictiocyon'', show any evidence for a hypocarnivorous (majority plant-eating) diet. At the start of their evolution, amphicyonids retained the typical placental dental formula of , but each subfamily follows their own trend in modifying their teeth. Daphoenines, for example, have dog-like teeth, with substantial

premolars The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mout ...

and reduced second and third molars. Temnocyonines and haplocyonines take this approach even further, with massive crushing premolars akin to

hyenas Hyenas or hyaenas ( ; from Ancient Greek , ) are feliformia, feliform carnivoran mammals belonging to the Family (biology), family Hyaenidae (). With just four extant species (each in its own genus), it is the fifth-smallest family in the orde ...

. Amphicyonines follow the opposite path, reducing most premolars and greatly enlarging and strengthening the carnassials and second molar. Bears also have large molars, but their teeth are modified into wide rectangular forms for grinding plant material. Amphicyonids did not pursue the same adaptations; their upper molars always maintain a roughly triangular profile for shearing and crushing meat. Thaumastocyonines were the most specialized for hypercarnivory, emphasizing massive blade-like carnassials at the expense of the rest of their postcanine teeth. Fossils of juvenile '' Agnotherium'', '' Ischyrocyon'', and '' Magericyon'' all show an unusual type of tooth eruption in which there is a vulnerable stage at about two or three years of age where the subadult animal has no functional molar or

carnassial Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. This adaptation is found in carnivorans, where the carnassials are the modified f ...

teeth, the only functional cheek teeth being several milk premolars. This period is suggested to be short and would have left the animal somewhat vulnerable.

Postcrania

Many amphicyonids had cat-like bodies, with a long tail and relatively short, strong limbs suitable for stalking and pouncing on their prey. Later and larger species tended to be

plantigrade 151px, Portion of a human skeleton, showing plantigrade habit In terrestrial animals, plantigrade locomotion means walking with the toes and metatarsals flat on the ground. It is one of three forms of locomotion adopted by terrestrial mammals. ...

or semiplantigrade, walking with most or all of the surface of the foot against the ground like bears. This was the norm for amphicyonines, thaumastocyonines, and most daphoenines. It is entirely possible that the largest amphicyonids were capable of both bear-style hunting (chasing down and mauling their prey with teeth and claws) and cat-style hunting (a quick ambush where the prey is killed with a bite to the neck). Many amphicyonid lineages instead adopted a

digitigrade In terrestrial vertebrates, digitigrade ( ) locomotion is walking or running on the toes (from the Latin ''digitus'', 'finger', and ''gradior'', 'walk'). A digitigrade animal is one that stands or walks with its toes (phalanges) on the ground, and ...

posture and locomotion (walking on their toes) and long legs specialized for running with a primarily front-to-back arc of movement. These

cursorial A cursorial organism is one that is adapted specifically to run. An animal can be considered cursorial if it has the ability to run fast (e.g. cheetah) or if it can keep a constant speed for a long distance (high endurance). "Cursorial" is often ...

wolf- or hyena-like forms included temnocyonines, haplocyonines, and some species of the large daphoenine '' Daphoenodon''.

Evolution

It has long been uncertain where amphicyonids originated. It was thought that they may have crossed from Europe to North America during the

epoch, but recent research suggests a possible North American origin from the miacids ''Miacis cognitus'' and ''M. australis'' (now renamed as the

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

'' Gustafsonia'' and '' Angelarctocyon'', respectively). As these are of North American origin, but appear to be early amphicyonids, it may be that the Amphicyonidae actually originates in North America. Other New World amphicyonids include the oldest known amphicyonid, '' Daphoenus'' (37–16 Mya). Amphicyonids began to decline in the late Miocene, and disappeared by the end of the epoch. The exact reasons for this are unclear. The most recent known amphicyonid remains are teeth known from the Dhok Pathan horizon, northern

Pakistan Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...

, dating to 7.4-5.3 mya. The species is classically named ''Arctamphicyon lydekkeri'', which may actually be synonymous with a species of ''

Amphicyon ''Amphicyon'' is an extinct genus of large carnivorans belonging to the family Amphicyonidae (known colloquially as "bear-dogs"), subfamily Amphicyoninae, from the Miocene epoch. Members of this family received their vernacular name for possessin ...

''.

Ecology

Amphicyonids are suggested to have ranged in ecology from

omnivores An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize t ...

to hypercarnivores, with some amphicyonids suggested to have engaged in bone-crushing like some modern hyenas. At least some amphicyonids are suggested to have been solitary hunters.

Classification

Family Amphicyonidae

References

External links

Whence the beardogs? Reappraisal of the Middle to Late Eocene 'Miacis' from Texas, US, and the origin of Amphicyonidae
{{Authority control Pliocene extinctions Eocene first appearances Taxa named by Ernst Haeckel Prehistoric mammal families Taxa described in 1886