''Hyaenodon'' ("

hyena Hyenas, or hyaenas (from Ancient Greek , ), are feliform carnivoran mammals of the family Hyaenidae . With only four extant species (each in its own genus), it is the fifth-smallest family in the Carnivora and one of the smallest in the cl ...

-tooth") is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus of

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

hyaenodont mammals from tribe Hyaenodontini, within subfamily

Hyaenodontinae Hyaenodontinae (" hyena teeth") is a subfamily of extinct predatory hyaenodontid mammals from extinct family Hyaenodontidae. Fossil remains of these mammals are known from early Eocene to early Miocene deposits in Europe, Asia and North Am ...

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Hyaenodontidae Hyaenodontidae ("hyena teeth") is a family of extinct predatory mammals from extinct superfamily Hyaenodontoidea within extinct order Hyaenodonta. Hyaenodontids arose during the early Eocene and persisted well into the early Miocene. Fossils of ...

,Malcolm C. McKenna, Susan K. Bell (1997.
"Classification of Mammals: Above the Species Level"
Columbia University Press, New York, 631 pages. that lived in

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelag ...

and

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 th ...

during the middle

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

to early

Miocene The Miocene ( ) is the first 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 means "less recen ...

, existing for about 25.1 million years.

Description

Typical of early carnivorous mammals, individuals of ''Hyaenodon'' had a very massive

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, th ...

, but only a small

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

. The skull is long with a narrow snout - much larger in relation to the length of the skull than in

canine Canine may refer to: Zoology and anatomy * a dog-like Canid animal in the subfamily Caninae ** ''Canis'', a genus including dogs, wolves, coyotes, and jackals ** Dog, the domestic dog * Canine tooth, in mammalian oral anatomy People with the surn ...

carnivores, for instance. The neck was shorter than the skull, while the body was long and robust and terminated in a long tail. Compared to the generally larger (but not closely related) ''

Hyainailouros ''Hyainailouros'' (" hyena-cat") is an extinct polyphyletic genus of hyainailourid hyaenodont mammal of the polyphyletic tribe Hyainailourini within paraphyletic subfamily Hyainailourinae, that lived during the early to middle Miocene, o ...

'', the dentition of ''Hyaenodon'' was geared more towards shearing meat and less towards bone crushing. Some

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

of this genus were among the largest terrestrial carnivorous

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

s of their time; others were only of the size of a

marten A marten is a weasel-like mammal in the genus ''Martes'' within the subfamily Guloninae, in the family Mustelidae. They have bushy tails and large paws with partially retractile claws. The fur varies from yellowish to dark brown, depending on ...

. Remains of many species are known from North America, Europe, and Asia.X. Wang, Z. Qiu and B. Wang (2005.
"Hyaenodonts and carnivorans from the early Oligocene to early Miocene of the Xianshuihe Formation, Lanzhou Basin, Gansu Province, China."
Palaeontologia Electronica 8(1):1-14 The average weight of adult or subadult ''H. horridus'', the largest North American species, is estimated to about and may not have exceeded . ''H. gigas'', the largest ''Hyaenodon'' species, was much larger, being and around . ''H. crucians'' from the early Oligocene of North America is estimated to only . ''H. microdon'' and ''H. mustelinus'' from the late Eocene of North America were even smaller and weighed probably about .

Tooth eruption

Studies on juvenile ''Hyaenodon'' specimens show that the animal had a very unusual system of tooth replacement. Juveniles took about 3–4 years to complete the final stage of eruption, implying a long adolescent phase. In North American forms, the first upper premolar erupts before the first upper molar, while European forms show an earlier eruption of the first upper molar.

Paleoecology

The various species of ''Hyaenodon'' competed with each other and with other hyaenodont genera (including ''

Sinopa ''Sinopa'' ("swift fox") is a genus of hyaenodontid mammal from family Sinopidae, that lived in North America and Asia during the early to middle Eocene. Description ''Sinopa'' was a small genus of hyaenodontid mammals. Its carnassial teeth ...

'', ''

Dissopsalis ''Dissopsalis'' ("double scissors") is a genus of teratodontine hyaenodonts of the tribe Dissopsalini. The older species, ''D. pyroclasticus'', lived in Kenya during the middle Miocene, while the type species, ''D. carnifex'', lived in Pakis ...

'', and ''

Hyainailurus ''Hyainailouros'' (" hyena-cat") is an extinct polyphyletic genus of hyainailourid hyaenodont mammal of the polyphyletic tribe Hyainailourini within paraphyletic subfamily Hyainailourinae, that lived during the early to middle Miocene, o ...

''), and played important roles as predators in ecological communities as late as the Miocene in Asia and preyed on a variety of prey species such as primitive horses like ''

Mesohippus ''Mesohippus'' (Greek: / meaning "middle" and / meaning "horse") is an extinct genus of early horse. It lived 37 to 32 million years ago in the Early Oligocene. Like many fossil horses, ''Mesohippus'' was common in North America. Its shoulder hei ...

'',

Brontothere Brontotheriidae is a family (biology), family of extinct mammals belonging to the order Perissodactyla, the order that includes horses, rhinoceroses, and tapirs. Superficially, they looked rather like Rhinoceros, rhinos, although they were actua ...

s, early camels, oreodonts and even primitive rhinos. Species of ''Hyaenodon'' have been shown to have successfully preyed on other large carnivores of their time, including a

nimravid Nimravidae is an extinct family of carnivorans, sometimes known as false saber-toothed cats, whose fossils are found in North America and Eurasia. Not considered to belong to the true cats (family Felidae), the nimravids are generally considered ...

("false sabertooth cat"), according to analysis of tooth puncture marks on a fossil ''

Dinictis ''Dinictis'' is a genus of the Nimravidae, an extinct family of feliform mammalian carnivores, also known as "false saber-toothed cats". Assigned to the subfamily Nimravinae, ''Dinictis'' was endemic to North America from the Late Eoce ...

'' skull found in North Dakota. In North America the last ''Hyaenodon'', in the form of ''H. brevirostrus'', disappeared in the late

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 t ...

. In Europe, they had already vanished earlier in the Oligocene.

Classification and phylogeny

Taxonomy

* Tribe: †Hyaenodontini ** Genus: †''Hyaenodon'' *** †''Hyaenodon brachyrhynchus'' *** †''Hyaenodon chunkhtensis'' *** †''Hyaenodon dubius'' *** †''Hyaenodon eminus'' *** †''Hyaenodon exiguus'' *** †''Hyaenodon filholi'' *** †''Hyaenodon gervaisi'' *** †''Hyaenodon heberti'' (Europe, 41-33.9 mya) *** †''Hyaenodon leptorhynchus'' *** †''Hyaenodon minor'' *** †''Hyaenodon pervagus'' *** †''Hyaenodon pumilus'' *** †''Hyaenodon requieni'' *** †''Hyaenodon rossignoli'' *** †''Hyaenodon weilini'' (China, 23-16,9 mya) *** †''Hyaenodon yuanchuensis'' *** Subgenus: †'' Neohyaenodon'' ^{(paraphyletic

In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
subgenus)} **** †''Hyaenodon gigas'' **** †''Hyaenodon horridus'' **** †''Hyaenodon incertus'' **** †''Hyaenodon macrocephalus'' **** †''Hyaenodon megaloides'' **** †''Hyaenodon milvinus'' **** †''Hyaenodon mongoliensis'' **** †''Hyaenodon montanus'' **** †''Hyaenodon vetus'' *** Subgenus: †'' Protohyaenodon'' ^{(paraphyletic

In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
subgenus)} **** †''Hyaenodon brevirostrus'' **** †''Hyaenodon crucians'' **** †''Hyaenodon microdon'' **** †''Hyaenodon mustelinus'' (North America, 38-30 mya) **** †''Hyaenodon raineyi'' E. P. Gustafson (1986.
"Carnivorous mammals of the Late Eocene and Early Oligocene of Trans-Pecos Texas."
Texas Memorial Museum Bulletin 33:1-66 **** †''Hyaenodon venturae''

Phylogeny

The phylogenetic relationships of genus ''Hyaenodon'' are shown in the following cladogram

References

{{Taxonbar, from=Q131465 Hyaenodonts Eocene mammals Oligocene mammals Miocene mammals Miocene genus extinctions Cenozoic mammals of Asia Cenozoic mammals of North America Cenozoic mammals of Europe White River Fauna Eocene genus first appearances Prehistoric placental genera Fossil taxa described in 1838