Mesonychia

Mesonychia Temporal range: Early Paleocene–Early Oligocene PreꞒ Ꞓ O S D C P T J K Pg N
Harpagolestes immanis skull
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Clade:	Pan-Euungulata
Mirorder:	Euungulata
Clade:	Paraxonia
Order:	†Mesonychia Van Valen, 1966
Families
†Hapalodectidae †Mesonychidae †Triisodontidae[1]

Mesonychia ("middle claws") is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. Mesonychians first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely when the last genus, Mongolestes, became extinct in the early Oligocene. In Asia, the record of their history suggests they grew gradually larger and more predatory over time, then shifted to scavenging and bone-crushing lifestyles before the group became extinct.^[2]

Mesonychians probably originated in China, where the most primitive mesonychian, Yantanglestes, is known from the early Paleocene. They were also most diverse in Asia, where they occur in all major Paleocene faunas. Since other predators, such as creodonts and Carnivora, were either rare or absent in these animal communities, mesonychians most likely dominated the large predator niche in the Paleocene of eastern Asia.

One genus, Dissacus, had successfully spread to Europe and North America by the early Paleocene. Dissacus was a jackal-sized predator that has been found all over the Northern Hemisphere,^[3] but species of a closely related or identical genus, Ankalagon, from the early to middle Paleocene of New Mexico, were far larger, growing to the size of a bear.^[4] A later genus, Pachyaena, entered North America by the earliest Eocene, where it evolved into species that were at least as large. Mesonychians in North America were by far the largest predatory mammals during the early Paleocene to middle Eocene.