Amphicyonids Middle | |
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Skeleton of Amphicyon | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Carnivora |
Suborder: | Caniformia |
Superfamily: | † Amphicyonoidea |
Family: | † Amphicyonidae Haeckel, 1866 |
Subfamilies | |
†Amphicyoninae Contents |
Amphicyonidae is an extinct family of terrestrial carnivorans belonging to the suborder Caniformia. They first appeared in North America in the middle Eocene (around 45 mya), spread to Europe by the late Eocene (35 mya), and further spread to Asia and Africa by the early Miocene (23 mya). They had largely disappeared worldwide by the late Miocene (5 mya), with the latest recorded species 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". [1]
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 (the dog family) or Ursidae (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. [2] [1] 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. [3] [4] [5]
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), but is more often considered a primitive subfamily of ursids (Hemicyoninae). They should also not be confused with Amphicynodontidae (another family of extinct caniforms which were related to bears or pinnipeds) or Arctocyonidae (a family of "condylarths" which literally translates to "bear-dogs").
Amphicyonids ranged in size from as small as 5 kg (11 lb) and as large as 100 to 773 kg (220 to 1,704 lb) [6] and evolved from wolf-like to bear-like body forms. [7]
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 which defines attachment points for large jaw muscles. [8] [9]
Amphicyonids had a relatively rudimentary form of auditory bulla, a bony sheath which encases the middle ear cavity. The bulla is small, mostly formed by the crescent-shaped ectotympanic 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, walruses, eared seals, and the red panda. [10] [8] 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. [10] [9]
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 (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. [9] [11]
At the start of their evolution, amphicyonids retained the typical placental dental formula of 3.1.4.33.1.4.3, but each subfamily follows their own trend in modifying their teeth. [8] [9] Daphoenines, for example, have dog-like teeth, with substantial premolars and reduced second and third molars. Temnocyonines and haplocyonines take this approach even further, with massive crushing premolars akin to hyenas. 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. [8] [9] Thaumastocyonines were the most specialized for hypercarnivory, emphasizing massive blade-like carnassials at the expense of the rest of their postcanine teeth. [12] [11]
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 teeth, the only functional cheek teeth being several milk premolars. [13] This period is suggested to be short and would have left the animal somewhat vulnerable. [14]
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 or semiplantigrade, walking with most or all of the surface of the foot against the ground like bears. This was the norm for amphicyonines, [9] thaumastocyonines, [15] and most daphoenines. [8] 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). [9]
Many amphicyonid lineages instead adopted a digitigrade posture and locomotion (walking on their toes) and long legs specialized for running with a primarily front-to-back arc of movement. These cursorial wolf- or hyena-like forms included temnocyonines, [16] haplocyonines, [17] and some species of the large daphoenine Daphoenodon . [18] [8]
It has long been uncertain where amphicyonids originated. It was thought that they may have crossed from Europe to North America during the Miocene epoch, but recent research suggests a possible North American origin from the miacids Miacis cognitus and M. australis (now renamed as the genera 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. [3]
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, dating to 7.4-5.3 mya. [19] The species is classically named Arctamphicyon lydekkeri, which may actually be synonymous with a species of Amphicyon . [20]
Amphicyonids are suggested to have ranged in ecology from omnivores to hypercarnivores, with some amphicyonids suggested to have engaged in bone-crushing like some modern hyenas. [11] At least some amphicyonids are suggested to have been solitary hunters. [14]
Family Amphicyonidae
Not assigned to a subfamily | Subfamily Amphicyoninae | Subfamily Haplocyoninae (Eurasia) [21] [15] | Subfamily Daphoeninae (North America) | Subfamily Temnocyoninae (North America) [16] | Subfamily Thaumastocyoninae [12] |
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Carnivora is an order of placental mammals that have specialized in primarily 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 on every major landmass and in a variety of habitats, ranging from the cold polar regions of Earth to the hyper-arid region of the Sahara Desert and the open seas. Carnivorans exhibit a wide array of body plans, varying greatly in size and shape.
Caniformia is a suborder within the order Carnivora consisting of "dog-like" carnivorans. They include dogs, bears, raccoons, and mustelids. The Pinnipedia are also assigned to this group. The center of diversification for the Caniformia is North America and northern Eurasia. Caniformia stands in contrast to the other suborder of Carnivora, the Feliformia, the center of diversification of which was in Africa and southern Asia.
Creodonta is a former order of extinct carnivorous placental mammals that lived from the early Paleocene to the late Miocene epochs in North America, Europe, Asia and Africa. Originally thought to be a single group of animals ancestral to the modern Carnivora, this order is now usually considered a polyphyletic assemblage of two different groups, the oxyaenids and the hyaenodonts, not a natural group. Oxyaenids are first known from the Palaeocene of North America, while hyaenodonts hail from the Palaeocene of Africa.
Viverravidae is an extinct monophyletic family of mammals from extinct superfamily Viverravoidea within the clade Carnivoramorpha, that lived from the early Palaeocene to the late Eocene in North America, Europe and Asia. They were once thought to be the earliest carnivorans and ancestral to extant ones, but now are placed outside the order Carnivora based on cranial morphology as relatives to extant carnivorans.
Miacidae is a former paraphyletic family of extinct primitive placental mammals that lived in North America, Europe and Asia during the Paleocene and Eocene epochs, about 65–33.9 million years ago. These mammals were basal to order Carnivora, the crown-group within the Carnivoraformes.
Amphicyon is an extinct genus of large carnivorans belonging to the family Amphicyonidae, subfamily Amphicyoninae, from the Miocene epoch. Members of this family received their vernacular name for possessing bear-like and dog-like features. They ranged over North America, Europe, Asia, and Africa.
Hemicyon, also known as the "dog-bear", is an extinct genus of hemicyonine bear, which probably originated in Eurasia but was found in Europe, Asia and North America during the Miocene epoch, existing for approximately 16 to 13 mya. Hemicyon is the best-known genus in the Hemicyoninae, a subfamily intermediate between bears and their Caniform ancestors but most often classified as bears. Hemicyonid bears should not be confused with Amphicyonids (bear-dogs), which are their own separate family of carnivores.
Ursoidea is a superfamily of arctoid carnivoran mammals that includes the families Subparictidae, Amphicynodontidae, and Ursidae. The last family includes the extant lineages of bears, as well as the extinct Hemicyoninae and Ursavinae.
Agnotherium is a genus of large sized carnivoran mammals, belonging to the Amphicyonidae, which has been found in Western Europe, and possibly China and Northern Africa, and lived during the Late Miocene epoch. Despite only being known from fragmentary remains, the genus notable for hypercarnivorous adaptions, which have been said to represent the "apex" among its family.
Gobicyon is an extinct genus of large-sized carnivoran mammals, belonging to the Amphicyonidae, that was discovered in China, Mongolia, and Serbia, and lived during the Middle Miocene epoch. Despite only being known from rather fragmentary remains, recent discoveries showcase that it was an aberrant member of the subfamily Haplocyoninae, with adaptions towards bone-crushing similar to those of a hyaena.
Ysengrinia is an extinct genus of carnivoran in the family Amphicyonidae, that lived during the Late Oligocene to Early Miocene. Fossil remains have been discovered in Western Europe, the United States and possibly China. The European species are among the earliest known members of the Thaumastocyoninae, a group of aberrant amphicyonids showcasing hypercarnivorous adations, but are only known from fragmentary remains. The American species is much better preserved and shows a robust, black-bear sized predator. These fossils play an important role in our understanding of the biotic interchange between Eurasia and North America during the earliest Miocene. However, more recent research suggests that the genus might be polyphyletic, and that several of its species should be excluded from Ysengrinia.
Gustafsonia is an extinct genus of carnivoran belonging to the family Amphicyonidae. The type species, Gustafsonia cognita, was described in 1986 by Eric Paul Gustafson, who originally interpreted it as a miacid and named it Miacis cognitus. It was subsequently considered to be the only species of the diverse genus Miacis that belonged to the crown-group Carnivora, within the Caniformia, and it was ultimately assigned to the family Amphicyonidae. The type specimen or holotype was discovered in Reeve's bonebed, western Texas, in the Chambers Tuff Formation in 1986. The University of Texas holds this specimen. It is the only confirmed fossil of this species.
Hyaenodonta is an extinct order of hypercarnivorous placental mammals of clade Pan-Carnivora from mirorder Ferae. Hyaenodonts were important mammalian predators that arose during the early Paleocene in Europe and persisted well into the late Miocene.
Magericyon is an extinct genus of Amphicyonid ("bear-dog") that lived during the Miocene 10-9 Ma in what is now Spain.
Ammitocyon is a genus of large sized carnivoran mammals, belonging to the Amphicyonidae, that lived during the Late Miocene in what is now Spain. It is notable for its extreme adaptations towards hypercarnivory, its extremely robust skeleton, and was one of the last surviving members of its family.
Thaumastocyoninae is an extinct subfamily of amphicyonids, large terrestrial carnivores, which inhabited what is now Europe during the Miocene epoch. The subfamily was erected by Hürzeler (1940), and is defined by the complete suppression of m1 metaconid, reduction of the premolars, except the p4, which is reinforced, and the oblique abrasion of the teeth, and the possession of hypercarnivorous tendencies. Thaumastocyonines are poorly known, with only about 65 dental specimens, most of those isolated teeth, being known as of 2020, although more complete remains have recently been discovered.
Myacyon is an extinct genus of large sized carnivoran mammals, belonging to the family Amphicyonidae, that lived in Africa during the Miocene epoch. Due to the limited scope and fragmentary nature of the severely damaged holotype, as well as the illustrations in its descriptions, which have been called inadequate, usage of this genus poses serious issues. However, it is notable for being one of the last surviving members of its family and its adaptions to hypercarnivory. Its relationships to other amphicyonids are obscure, and it is not closely related to Bonisicyon, the other late surviving African genus, although it has been proposed that it descends from a species of Cynelos or Namibiocyon.
Bonisicyon is an extinct genus of carnivoran mammals, belonging to the family Amphicyonidae. It is the last-surviving member of its family, living in East Africa during the end of the Miocene epoch. Known only from a damaged mandible and isolated teeth from the Nawata Formation, and possibly also the Lukeino Formation, its closer taxonomic affinities are unclear. It is notable for both its small size, and its unique dentition.
Namibiocyon is an extinct genus of carnivoran mammals, belonging to the family Amphicyonidae, that lived in Namibia during the Early Miocene epoch. Before the erection of this taxon in 2022, the type and only species, N. ginsburgi, had been assigned to a variety of other genera. It is notable for its adaptions toward hypercarnivory.
Peignecyon is an extinct genus of large carnivorans belonging to the family Amphicyonidae. It belongs to the subfamily Thaumastocyoninae, which is characterized by their adaptions towards hypercarnivory. Whereas most other thaumastocyonines are often only known from fragmentary remains and isolated teeth, Peignecyon is known from a variety of well-preserved remains. It contains a single species, P. felinoides from the Early Miocene of the Czech Republic.
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