Hyaenodonta Temporal range:63.8–8.8 Ma PreꞒ Ꞓ O S D C P T J K Pg N earlyPaleocene to lateMiocene (SuspectedLate Cretaceous origin, but unconfirmed by fossils yet)[1][2]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Mirorder:	Ferae
Clade:	Pan-Carnivora
Order:	†Hyaenodonta Van Valen, 1967[3]
Subgroups
[seeclassification]
Synonyms
Hyaenodontida(Solé, 2010)[4] Hyaenodontidae(Leidy, 1869) Proviverroidea(Morlo, 2009)[5]

Hyaenodonta ("hyena teeth") is anextinct order ofhypercarnivorousplacental mammals of cladePan-Carnivora from mirorderFerae.^[6][7] Hyaenodonts were important mammalian predators that arose during the earlyPaleocene inEurope^[8] and persisted well into the lateMiocene.^[9]

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.^[10] WhileSimbakubwa kutokaafrika may have been up to 1,500 kg (3,300 lb) (surpassing the modernpolar bear in size^[11]), 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 ofSimbakubwa,Hyainailouros andMegistotherium (the latter likely being the largest in the group), and the much earlier-living Hyaenodon gigas (the largest species from genusHyaenodon), 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-sizeddog.^[12] 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.^[10]

Hyaenodonts were ancestrallyplantigrade, but the later, larger forms were generallydigitigrade or semidigitigrade. Because of their size range, it is probable that different species hunted in different ways, which allowed them to fill many different predatoryniches, 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. Thecarnassials in a hyaenodonts are generally the second upper and third lowermolars. However, some hyaenodonts possessed as many as three sequential pairs of carnassials or carnassial-like molar teeth in their jaws.^[13] Hyaenodonts, like all creodonts, lacked post-carnassial crushing molar teeth, such as those found in many carnivoran families, especially theCanidae andUrsidae, and thus lacked dental versatility for processing any foods other than meat.^[13]

Hyaenodonts differed fromCarnivora in that they replaced their deciduous dentition slower in development than carnivorans.^[14] Studies onHyaenodon 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.^[15]

At least one hyaenodont lineage, subfamilyApterodontinae, was specialised for aquatic,otter-like habits.^[16]

Having evolved inEurope during thePaleocene,^[8] hyaenodonts soon after spread into Africa andIndia, implying close biogeographical connections between these areas.^[16][17] Afterwards, they dispersed intoAsia from either Europe or India, and finally,North America from either Europe or Asia.^[18][19]

They were important hypercarnivores in Eurasia, Africa, and North America during the Oligocene, but declined towards the end of the epoch, with almost the entire order becoming extinct by the close of theOligocene. Several representatives of this order, including hyainailouridsMegistotherium,Simbakubwa,Hyainailouros,Sectisodon,Exiguodon,Sivapterodon,Metapterodon, andIsohyaenodon, the prionogalidPrionogale, the teratodontidDissopsalis and the youngest species of genusHyaenodon,H. weilini, survived into or evolved during the Miocene, of which, onlyDissopsalis survived long enough to go extinct at the close of the Miocene.^[9] Traditionally, this has been attributed to competition with carnivorans, but no formal examination of the correlation between the decline of hyaenodonts and the expansion of carnivorans has been recorded, and the latter may simply have moved into vacant niches after the extinction of hyaenodont species.^[20]

Hyaenodonts were considerably more widespread and successful than theoxyaenids, the other clade of mammals originally classified along with the hyaenodonts as part ofCreodonta.^[10] In 2015 phylogenetic analysis of Paleogene mammals, by Halliday et al.,monophyly of Creodonta was supported and was placed in the cladeFerae, closer toPholidota than toCarnivora.^[21] However, order Creodonta is now considered to be apolyphyleticwastebasket taxon containing two unrelated clades assumed to be closely related (or ancestral) to Carnivora.^{[8][14][15][16][17][22][23][24][25][26][27]}

• Mammal classification
• Ferae
• Creodonta

• Hyaenodonts

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• Short description is different from Wikidata
• Articles with 'species' microformats