They first appeared in the Early Paleocene, undergoing numerous speciation events during the Paleocene, and Eocene.
Mesonychids fared very poorly at the close of the Eocene epoch, with only one genus, Mongolestes, surviving into the Early Oligocene epoch.
  
Mesonychids probably originated in Asia, where the most primitive mesonychid, Yangtanglestes, is known from the early Paleocene.
They were also most diverse in Asia where they occur in all major Paleocene faunas.
Since other carnivores such as the creodonts and Carnivora were either rare or absent in these animal communities, mesonychids most likely dominated the large predator niche in the Paleocene of Asia.
 Throughout the Paleocene and Eocene, several genera, including Dissacus, Pachyaena and Mesonyx would radiate out from their ancestral home in Asia and into Europe and North America, where they would give rise to new mesonychid genera.
These animals would have migrated to North America via the Bering land bridge.

The term "mesonychid" is often used to refer to any of the various members of the order Mesonychia, though most experts prefer to use it to refer to the members of the family Mesonychidae, with many experts using the term "mesonychian" to refer to the order as a whole.
They first appeared in the Early Paleocene, undergoing numerous speciation events during the Paleocene, and Eocene. Mesonychids fared very poorly at the close of the Eocene epoch, with only one genus, Mongolestes, surviving into the Early Oligocene epoch.   
Mesonychids probably originated in Asia, where the most primitive mesonychid, Yangtanglestes, is known from the early Paleocene. They were also most diverse in Asia where they occur in all major Paleocene faunas. Since other carnivores such as the creodonts and Carnivora were either rare or absent in these animal communities, mesonychids most likely dominated the large predator niche in the Paleocene of Asia.  Throughout the Paleocene and Eocene, several genera, including Dissacus, Pachyaena and Mesonyx would radiate out from their ancestral home in Asia and into Europe and North America, where they would give rise to new mesonychid genera. These animals would have migrated to North America via the Bering land bridge.
The term "mesonychid" is often used to refer to any of the various members of the order Mesonychia, though most experts prefer to use it to refer to the members of the family Mesonychidae, with many experts using the term "mesonychian" to refer to the order as a whole.
Mesonychidae