Mesonyx was a wolf-like mammal of the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Mesonychidae

Mesonychidae

Mesonychidae is an extinct family of medium to large-sized omnivorous-carnivorous mammals closely related to artiodactyls which were endemic to North America and Eurasia during the Early Paleocene to Late Eocene living from 65—33.9 mya, existing for approximately .- Description :The mesonychids...

, the type family of the order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Mesonychia (sometimes referred to by its older name, "Acreodi"), existing 51.8—51.7 Ma (AEO

Appearance Event Ordination

Appearance Event Ordination or AEO is a scientific method for biochronology through the ordering of the appearance of fossil mammal genera by multivariate analysis, using conjunctional and disconjunctional range distributions in large sets of data.-Process:AEO is based on faunal overlap and...

). It may have been ancestral to cetaceans.

It was a fast predator from the Middle 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...

 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...

, and it probably hunted hoofed plant eaters, moving lightly on its toes. However, instead of claws, Mesonyxs toes ended in small hooves. Its long skull had a relatively large sagittal crest

Sagittal crest

A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull of many mammalian and reptilian skulls, among others....

 above the braincase to anchor large jaw muscles and give it a powerful bite.

Mesonyx specimens have been unearthed in Colorado

Colorado

Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...

, 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...

, and Utah

Utah

Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...

. Mesonyx uintensis from the Upper Eocene of Wyoming is described as having a total cranium length of 429 mm. (17 inches) and a facial length of 206 mm (8 inches). Another specimen of Mesonyx uintensis is known from the Upper Eocene of northern Utah.