Hyaenodonta (" hyena teeth") 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 ...

order of hypercarnivorous placental mammals of clade Pan-Carnivora from mirorder Ferae. Hyaenodonts were important mammalian predators that arose during the early

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

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 ...

and persisted well into the late

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 ...

Characteristics

Comparison of Carnivoran and Creodont Carnassials

Hyaenodonts are characterized by long, often disproportionately large skulls, slender jaws, and slim bodies. They generally ranged in size from 30 to 140 cm at the shoulder. While '' Simbakubwa kutokaafrika'' may have been up to (surpassing the modern

polar bear The polar bear (''Ursus maritimus'') is a large bear native to the Arctic and nearby areas. It is closely related to the brown bear, and the two species can Hybrid (biology), interbreed. The polar bear is the largest extant species of bear ...

in size), this estimate is suspect due to being based on skull-body size ratios derived from felids, which have much smaller skulls for their body size. Other large hyaenodonts include two close and later-surviving relatives of ''Simbakubwa'', '' Hyainailouros'' and '' Megistotherium'' (the latter likely being the largest in the group), and the much earlier-living '' Hyaenodon gigas'' (the largest species from genus '' Hyaenodon''), which may have been as large as 1.4 m high at the shoulder, 3.0 m long and weighed about 330 kg. Most hyaenodonts, however, were in the 5–15 kg range, equivalent to a mid-sized dog. The anatomy of their skulls show that they had a particularly acute sense of smell, while their teeth were adapted for shearing, rather than crushing. Hyaenodonts were ancestrally plantigrade, but the later, larger forms were generally digitigrade or semidigitigrade. Because of their size range, it is probable that different species hunted in different ways, which allowed them to fill many different predatory niches, with small or medium-sized forms filling roles similar to mustelids or smaller felids of today while the larger forms functioned as apex predators focusing on larger prey, wielding their mighty jaws as their principal weapon as they lacked grasping forelimbs. The

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 ...

s in hyaenodonts are generally the second upper and third lower

molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...

. However, some hyaenodonts possessed as many as three sequential pairs of carnassials or carnassial-like molar teeth in their jaws. Hyaenodonts, like all “creodonts”, lacked post-carnassial crushing molar teeth, such as those found in many carnivoran families, especially the

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 ...

and Ursidae, and thus lacked dental versatility for processing any foods other than meat.Wang, Xiaoming; and Tedford, Richard H. (2008). "Dogs: Their Fossil Relatives and Evolutionary History." New York: Columbia University Press Hyaenodonts differed from

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 ...

in that they replaced their deciduous dentition slower in development than carnivorans. Studies on '' Hyaenodon'' show that juveniles took 3 to 4 years in the last stage of tooth eruption, implying a very 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. At least one hyaenodont lineage, subfamily Apterodontinae, was specialised for aquatic,

otter Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic, or marine. Lutrinae is a branch of the Mustelidae family, which includes weasels, badgers, mink, and wolverines, among ...

-like habits.

Range

Having evolved in

during the

, hyaenodonts soon after spread into Africa and

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

, implying close biogeographical connections between these areas.Solé, Floréal & Smith, Thierry (2013)
"Dispersals of placental carnivorous mammals (Carnivoramorpha, Oxyaenodonta & Hyaenodontida) near the Paleocene-Eocene boundary: a climatic and almost worldwide story"
Geologica Belgica 16/4: 254–261 Afterwards, they dispersed into

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 ...

from either Europe or India, and finally,

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 either Europe or Asia. They were important hypercarnivores in Eurasia, Africa, and North America during the Oligocene, but declined towards the end of the epoch, with nearly the entire order becoming extinct by the close of 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 ...

. Several representatives of this order, including hyainailourids '' Megistotherium'', '' Simbakubwa'', '' Hyainailouros'', '' Sectisodon'', '' Exiguodon'', '' Sivapterodon'', '' Metapterodon'', and '' Isohyaenodon'', the prionogalid '' Prionogale'', the teratodontid '' Dissopsalis'' and the youngest species of genus ''Hyaenodon'', '' H. weilini'', survived into or evolved during the Miocene, of which, only ''Dissopsalis'' persisted into the Late Miocene.

Extinction

The extinction of hyaenodonts has been debated by experts. Many experts have argued that their extinction was due to competition with the carnivorans. Several experts have hypothesized that competitive displacement from the invading carnivorans forced African hyaenodonts to vary in size and become more hypercarnivorous. Lang et al. (2021) found that the evolutionary success of Carnivora compared to Hyaenodonta may have been largely influenced by the retention of a basal morphotype throughout their evolutionary history. The authors also suggested that carnivorans likely contributed in some way to the extinction of hyaenodonts, with the difference in functional morphology and adaptive potential of their carnassials possibly being a factor. However, this hypothesis has been contested by many experts. One analysis on hyaenodonts and carnivorans within the Cypress Hills Formation, found that only the smaller hyaenodonts and carnivorans had significant niche overlap, while larger hyaenodonts and carnivorans had very distinct niches, suggesting competition-driven extinctions were not likely in this formation and instead climate change was the contributor to their extinction during the Late Eocene. The global climatic cooling of the earliest Oligocene resulted in drier, more open landscapes and resulted in the extinction of large browsing herbivores, including brontotheres. With their relatively shorter legs, they were likely at a disadvantage in the increasingly open environments. However, this does not exclude the possibility of competitive-driven extinctions among early and middle Eocene hyaenodonts, or of competitive interactions with carnivorans that drove hyaenodonts toward more extreme niches, indirectly leading to their extinction. Morales et al. (2008) argued the extinction of African hyaenodonts was due to the aridification of Africa, as they were more adapted for forested environments than savannah, steppe, or deserts.

Classification and phylogeny

Relations

Hyaenodonts were considerably more widespread and successful than the oxyaenids, the other clade of mammals originally classified along with the hyaenodonts as part of Creodonta. (1985): ''The Field Guide to Prehistoric Life.'' Facts on File Publications, New York. In 2015 phylogenetic analysis of Paleogene mammals, by Halliday et al.,

monophyly In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent comm ...

of Creodonta was supported and was placed in the clade Ferae, closer to

Pholidota Pangolins, sometimes known as scaly anteaters, are mammals of the order Pholidota (). The one Neontology, extant family, the Manidae, has three genera: ''Manis'', ''Phataginus'', and ''Smutsia''. ''Manis'' comprises four species found in Asia, ...

than to

. However, order Creodonta is now considered to be a

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

wastebasket taxon containing two unrelated clades assumed to be closely related (or ancestral) to Carnivora.

Taxonomy

References

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