''Hyaenodon'' ("

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

-tooth") 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 ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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 nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...

placental Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished ...

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s from extinct tribe Hyaenodontini within extinct

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...

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

(in extinct

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 ...

Hyaenodontidae Hyaenodontidae ("hyena teeth") is a family of placental mammals in the extinct superfamily Hyaenodonta, Hyaenodontoidea. Hyaenodontids arose during the early Eocene and persisted well into the early Miocene. Fossils of this group have been found ...

),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 a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...

and

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 ...

from the early

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 ...

to 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 ...

Classification and phylogeny

Taxonomy

Description

The skull of ''Hyaenodon'' was 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 * Animals of the family Canidae, more specifically the subfamily Caninae, which includes dogs, wolves, foxes, jackals and coyotes ** ''Canis'', a genus that includes dogs, wolves, coyotes, and jackals ** Do ...

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 larger (but not closely related) ''

Hyainailouros ''Hyainailouros'' ("hyena-cat") is an extinct polyphyletic genus of hyaenodont belonging to the family Hyainailouridae that lived during the Early to Late Miocene, of which there were at least three species spread across Eurasia and Africa ...

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

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), ...

of this genus were among the largest terrestrial carnivorous

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. ''H. horridus'' was the largest North American species. While m1 regressions suggested it could’ve weighed , regressions based on limb morphology suggests the species instead could’ve been smaller, with adults weighing on average 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 .

Paleobiology

Predatory behavior

A 2003 study found that based on elbow morphology ''H. horridus'' was a

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 ...

predator and was the most cursorially Oligocene carnivore within the study. Furthermore a 2025 study found that based on elbow morphology found that ''H. crucians'' and ''H. horridus'' were a pounce-pursuit predators. On the other hand, analysis on the bony labyrinth of ''H. exiguus'' suggests this species was semi-

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...

and occupied a

-like niche. Much like ''H. horridus'', ''H. eminus'', ''H. gigas'', and ''H. pervagus'' were recovered as a cursorial predators. Zigzag Hunter–Schreger bands in the enamel indicate that European and North America ''Hyaenodon'' had slightly different niches. Microwear patterns suggests that North American ''Hyaenodon'' diet was more similar to

lions The lion (''Panthera leo'') is a large cat of the genus ''Panthera'', native to Sub-Saharan Africa and India. It has a muscular, broad-chested body; a short, rounded head; round ears; and a dark, hairy tuft at the tip of its tail. It is se ...

, on the other hand European ''Hyaenodon'' microwear was more similar to spotted hyenas and bone crushing was likely a part of their diet.

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.

Brain anatomy

While typically assumed that ''Hyaenodon'' had a very massive

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

, but a small

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

. This has been called into question as a recent study found that

Hyaenodonta Hyaenodonta (" hyena teeth") 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 w ...

, including ''Hyaenodon'', had

encephalization quotient Encephalization quotient (EQ), encephalization level (EL), or just encephalization is a relative brain size measure that is defined as the ratio between observed and predicted brain mass for an animal of a given size, based on nonlinear regre ...

similar to basal and some modern

carnivorans Carnivora ( ) is an Order (biology), order of Placentalia, 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 ...

. The endocast of ''Hyaenodon'' stands out from other Hyaenodontoids as they had relatively high EQ, in addition to relatively gyrencephalic and neocorticalized brains, although the increase in EQ for the genus is still unknown.

Paleoecology

The various species of ''Hyaenodon'' competed with each other and with other hyaenodont genera (including '' Sinopa'', '' Dissopsalis'' and '' Hyainailurus''), 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 early horses like ''

Mesohippus ''Mesohippus'' (Greek language, 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. ...

'',

Brontothere Brontotheriidae is a family of extinct mammals belonging to the order Perissodactyla, the order that includes horses, rhinoceroses, and tapirs. Superficially, they looked rather like rhinos with some developing bony nose horns, and were some of ...

s, early

camels A camel (from and () from Ancient Semitic: ''gāmāl'') is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. Camels have long been domesticated and, as livestock, they provide ...

oreodonts This category contains all articles concerning the extinct North American artiodactyl Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number ...

and even early rhinos. Species of ''Hyaenodon'' have been shown to have successfully preyed on other large carnivores of their time, including a nimravid ("false sabertooth cat"), according to analysis of tooth puncture marks on a fossil '' Dinictis'' 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 (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 ...

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

References

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