Oxyaenidae

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. 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.

Etymology

The name of order Oxyaenodonta comes from Ancient Greek ὀξύς(oxús) 'sharp', name of hyena genus Hyaena and from Ancient Greek ὀδούς(odoús) 'tooth'.

The name of family Oxyaenidae comes from Ancient Greek ὀξύς(oxús) 'sharp', 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 800 kg (1,800 lb). 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 number 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. Their extinction in the Eocene may be connected to the reduction of closed-canopy tropical jungles, which dominated the world in the hothouse of the Paleocene-Eocene Thermal Maximum. No modern carnivoran has an inflexible spine, which would reduce maneuverability and running speed in more open environments.

Evolution

Oxyaenodonts were believed to have evolved in the middle Paleocene in North America with the oldest known oxyaenodont, Tytthaena, being found there. Oxyaenodonts would disperse into Europe near the Paleocene-Eocene boundary via the De Geer route, however the timing of arrival in Asia is unknown.

Classification and phylogeny

Taxonomy

The family Oxyaenidae is divided into four subfamilies, containing a total of fifteen genera between them.

• Family: Oxyaenidae Cope, 1877 Subfamily: Machaeroidinae Matthew, 1909 Genus: Apataelurus Scott, 1938 Genus: Diegoaelurus Zack, Poust & Wagner, 2022 Genus: Isphanatherium Lavrov & Averianov, 1998 Genus: Machaeroides Matthew, 1909 Subfamily: Oxyaeninae Cope, 1877 Genus: Argillotherium Davies, 1884 Genus: Dipsalidictis Matthew & Granger, 1915 Genus: Malfelis Stucky & Hardy, 2007 Genus: Oxyaena Cope, 1874 Genus: Patriofelis Leidy, 1870 Genus: Protopsalis Cope, 1880 Genus: Sarkastodon Granger, 1938 Subfamily: Palaeonictinae Denison, 1938 Genus: Ambloctonus Cope, 1875 Genus: Dipsalodon Jepsen, 193) Genus: Palaeonictis de Blainville, 1842 Subfamily: Tytthaeninae Gunnell & Gingerich, 1991 Genus: Tytthaena Gingerich, 1980

Phylogeny

Cladogram according to Gunnel in 1991:

Temporal distribution

Within clade Pan-Carnivora

Within family Oxyaenidae

See also

• Mammal classification
• Ferae
• Creodonta

Further reading

• David Lambert and the Diagram Group. The Field Guide to Prehistoric Life. New York: Facts on File Publications, 1985. ISBN 0-8160-1125-7