Machaeroides is a genus of sabre-toothed creodont that lived during the Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

. Its fossils were found in the U.S. state of Wyoming

Wyoming

Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

. It is the earliest known sabre-toothed mammal.

Description

Either species bore a passing, or superficial resemblance to a very small, dog-sized saber-toothed cat

Saber-toothed cat

Saber-toothed cat or Sabre-toothed cat refers to the extinct subfamilies of Machairodontinae , Barbourofelidae , and Nimravidae as well as two families related to marsupials that were found worldwide from the Eocene Epoch to the end of the Pleistocene Epoch ,...

. Machaeroides could be distinguished from actual saber-toothed cats by their more-elongated skulls, and their plantigrade

Plantigrade

right|151px|thumb|Human skeleton, showing plantigrade habitIn terrestrial animals, plantigrade locomotion means walking with the podials and metatarsals flat on the ground. It is one of three forms of locomotion adopted by mammals...

 stance. Machaeroides species are distinguished from the closely related Apataelurus by the fact that the former genus had smaller saber-teeth.

M. eothen weighed an estimated 10-14 kg, thus matching in size a smallish Staffordshire Terrier

American Staffordshire Terrier

The American Staffordshire terrier is a medium-sized, short-coated American dog breed. In the early part of the twentieth century the breed gained social stature and was accepted by the American Kennel Club as the American Staffordshire Terrier in 1936...

. M. simpsoni was smaller.(Egi 2001)

Taxonomic Placement

Although it is undeniably a creodont, its placement within the order is in dispute. Experts seem equally divided over whether Machaeroides and its sister-genus, Apataelurus, belong in Oxyaenidae

Oxyaenidae

Oxyaenidae is a family of the extinct order Creodonta; it contains three subfamilies comprising ten genera. The placement of a fourth subfamily, Machaeroidinae, is unsure; it may belong here or in Hyaenodontidae....

 or Hyaenodontidae

Hyaenodontidae

Hyaenodontidae is a family of the extinct order Creodonta, which contains several dozen genera.The Hyaenodontids were important mammalian predators that arose during the late Paleocene and persisted well into the Miocene...

.