Mesonychidae

Mesonychidae Temporal range: Early Paleocene — Late Eocene, 63–34 Ma PreꞒ Ꞓ O S D C P T J K Pg N Suspected Late Cretaceous origin
Harpagolestes immanis skull
Model reconstruction of Mesonyx
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	†Mesonychia
Family:	†Mesonychidae Cope 1875
Type genus
†Mesonyx Cope, 1872
Genera
List †Ankalagon? Van Valen, 1980 †Dissacus Cope, 1891 †Guilestes Zheng & Chi, 1978 †Harpagolestes Wortman, 1901 †Hessolestes Peterson, 1931 †Honanodon Chow, 1965 †Hukoutherium Chow et al. 1973 †Hyaenodictis Lemoine, 1880 †Jiangxia Zhang et al., 1979 †Lohoodon Chow et al. 1978 †Mesonyx Cope, 1872 †Metahapalodectes Dashzeveg, 1976 †Mongolestes Szalay & Gould, 1966 †Mongolonyx Szalay & Gould, 1966 †Pachyaena Cope, 1874 †Shimenotherium Xiangxu, 2026 †Sinonyx Zhou et al. 1995 †Synoplotherium Cope, 1872 †Yantanglestes Ideker and Yan, 1980

Mesonychidae (meaning "middle claws") is an extinct family of small to large omnivorous-carnivorous mammals, one of the two families in the order Mesonychia. They were found in North America and Eurasia during the Early Paleocene to the Late Eocene. Once considered a sister-taxon to artiodactyls, recent evidence now suggests no close relation to any living mammal. Mesonychid taxonomy has long been disputed and they have captured popular imagination as "wolves on hooves", animals that combine features of both ungulates and carnivorans.

Taxonomy

Description

The mesonychids were an unusual group of mammals with a specialized dentition featuring tri-cuspid upper molars and high-crowned lower molars with shearing surfaces. These shearing surfaces were capable of cutting, but not as efficiently as the carnassals of hyaenodonts or carnivorans. Like the Paleocene family Arctocyonidae, mesonychids were once viewed as primitive carnivorans. Various genera and species coexisted in some localities, such as the Lushi Formation. In contrast to arctocyonids, the mesonychids had only four digits furnished with hooves supported by narrow fissured end phalanges. Mesonychids varied in diet from carnivorous or omnivorous to bone-crushing carrion specialists.

Evolutionary history

Mesonychids probably originated in Asia, where the oldest mesonychids, Yantanglestes, Dissacus rotundus, Hukoutherium, and Dissaccussium , are known from the Early Paleocene. Throughout the Paleocene and Eocene, several genera, including Dissacus, Pachyaena, and Mesonyx would radiate out from their ancestral home in Asia and disperse into North America via the Bering land bridge. From North America, mesonychids would disperse into Europe. Mesonychids fared very poorly at the close of the Eocene epoch. Originally, it was thought that only one genus, Mongolestes, survived into the Early Oligocene epoch, going extinct 33 million years ago. However, recent analysis found the supposed Early Oligocene biochronogical units have been revised to the Late Eocene age, suggesting the family went extinct just before the end of the Eocene.

References