Oxyaenidae ("sharp hyenas") is a family of extinct carnivorous placental mammals. Traditionally classified in order Creodonta, this group is now classified in its own order Oxyaenodonta ("sharp tooth hyenas") within clade Pan-Carnivora in mirorder Ferae. Phylogenetic analysis recovered them as a sister group to Carnivoraformes, a clade that consisted of Carnivora and close relatives. The group contains four subfamilies comprising fourteen genera. Oxyaenids first appeared during the late Paleocene in North America, with smaller radiations of oxyaenids in Eurasia occurring during the Eocene.F. Solé, E. Gheerbrant and M. Godinot (2011.) New Data on the Oxyaenidae from the Early Eocene of Europe; biostratigraphic, paleobiogeographic and paleoecologic implications Palaeontologia Electronica, Vol. 14, Issue 2; 13A: Pages 1-41 They would go extinct in the Middle Eocene being replaced by nimravids, which took over the cat-like niche once occupied by oxyaenids.
Etymology The name of order Oxyaenodonta comes , name of hyena genus Hyaena and .
The name of family Oxyaenidae comes , name of hyena genus Hyaena and taxonomic suffix "-idae".
Characteristics
They were superficially otter- or badger-like placental mammals that walked on flat feet, in contrast to most modern Carnivora, which walk and run on their toes. Though most genera were medium-sized by modern standards, they may have been the earliest group of large carnivorous mammals. The largest known oxyaenid was Sarkastodon mongoliensis, which could have weighed . However, this may have been an overestimate. All had two molars on each side of both the upper and lower jaw. While many oxyaenids, such as Patriofelis, were hypercarnivores, some such as Oxyaena were more omnivorous, with meat-based but varied diets similar to modern brown bears and racoons. Of the four families:
The Tytthaeninae were the earliest representatives of the group, generally smaller and with more unspecialized bodies and primitive features. The Paleonictinae included intermediate-sized hypercarnivores and mixed feeders. The Oxyaeninae included the largest genera, such as Sarkaskadon, Patriofelis, and Oxyaena. Some genera showed Hunter-Schrager bands on their molars, typical of bone-cracking. They were adapted for terrestrial locomotion and probably hunted or scavanged on forest floors. The Macheroidinae were a small group of specialized hypercarnivores adapted for arboreal locomotion, with long slender bodies and strong grappling forelimbs This group was the first saber-toothed mammals in the fossil record. A flange on the lower jaw partially protected their long, slender saber canine teeth. They ranged from civet- to leopard-sized, probably lived in the trees of closed-canopy forests, and ambushed prey larger than their bodies. Since most large herbivores at the time were terrestrial, it is likely they dropped from trees onto their prey.
Overall, oxyaenids had long, flat heads, long bodies with short legs, large claws, and reinforced, inflexible lower spines. The forelimbs were strong and flexible, and could twist to embrace and grapple, like the forelimbs of cats and unlike those of dogs. These adaptations suggest that hunting oxyaenids were solitary ambush predators that would capture larger prey.
Evolution Oxyaenodonts were believed to have evolved in the middle Paleocene in North America with the oldest known oxyaenodont, Tytthaena, being found there.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: 254–261P. D. Gingerich. (1980.) "Tytthaena parrisi, Oldest Known Oxyaenid (Mammalia, Creodonta) from the Late Paleocene of Western North America." Journal of Paleontology 54(3):570-576 Oxyaenodonts would disperse into Northwestern Europe near the Paleocene-Eocene boundary via the De Geer route, however the timing of arrival in Asia is unknown. In North America, oxyaenids increase in diversity, peaking at around 7 species during the Wasatchian stage. Including supplementary materials The dispersal of oxyaenids into Northwestern Europe is suggested to have been one dispersal event and saw a low number of species.
Extinction European oxyaenids would go extinct during the Intra-Ypresian Mammal Turnover. The last paleonictines would go extinct at the end of the 5th biochronology of the Wasatchian stage. Oxyaenines would go went extinct in North America at the end of the Bridgerian, with only macheroidines persisting into Uintan. Macheroidines would go extinct around 41.5 Ma, which may be linked to the significant faunal overturn during the transition period between the middle and late Eocene.
The cause of oxyaenids extinction has been debated by experts. Chester et al. (2010) suggested the extinction of paleonictines, as well as other oxyaenids, went extinct because of competition with canivorans. Zack et al. (2022) argued the extinction of North American macheroidines was possibly due to competition with nimravids. However, other experts find it unlikely competition with carnivorans to be the cause of their extinction.
The excellent North American fossil record indicates oxyaenids were declining well before the appearance of the replacement taxa such as nimravids. In addition, the youngest records of machaeroidines predate the oldest records of nimravids in North America. Fischer et al. (2026) found a there was a notable temporal gap between similar sized European oxyaenids and carnivoramorphans suggesting competitive replacement likely wasn't responsible for the extinction of oxyaenids in Europe.
Kort (2019) hypothesized that oxyaenids likely went extinct due to the inability to adapt to the open forested habitats that replaced closed forests due to their inflexible spines, which reduced maneuverability and running speed in more open environments.
Classification and phylogeny Taxonomy The family Oxyaenidae is divided into four subfamilies, containing a total of fifteen genera between them. Family: Oxyaenidae Subfamily: Machaeroidinae Genus: Apataelurus Genus: Diegoaelurus Genus: Isphanatherium Genus: Machaeroides Subfamily: Oxyaeninae Genus: Argillotherium Genus: Dipsalidictis Genus: Malfelis Genus: Oxyaena Genus: Patriofelis Genus: Protopsalis Genus: Sarkastodon Subfamily: Palaeonictinae Genus: Ambloctonus Genus: Dipsalodon Genus: Palaeonictis Subfamily: Tytthaeninae Genus: Tytthaena
Phylogeny Cladogram according to Gunnel in 1991:
Temporal distribution Within clade Pan-Carnivora
Within family Oxyaenidae
See also Mammal classification Ferae Creodonta
References
Further reading David Lambert and the Diagram Group. The Field Guide to Prehistoric Life. New York: Facts on File Publications, 1985.