Mesonychidae

Mesonychidae Temporal range: Early Paleocene — Late Eocene, 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-sized omnivorous-carnivorous mammals and were one of the two families of 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

Classification

Mesonychidae was named by Cope (1875), with its type genus, Mesonyx, being assigned to Carnivora. However, in a later paper, mesonychids would be moved to Creodonta by Cope (1880). In their 1966 paper, Van Valen recovered mesonychids from as Condylarthra. In their following paper, Van Valen would rank up mesonychids to an order known as Mesonychia, a consensus supported by all recent studies.

Relationship with Cetacea

Because skulls and teeth of mesonychids have similar features to early whales, and the family was long thought to be the ancestors of cetaceans. However, fossil discoveries have overturned this idea; the consensus is that whales are highly derived artiodactyls. Some researchers now consider the family a sister group either to whales or to artiodactyls, close relatives rather than direct ancestors. Other studies define Mesonychia as basal to all ungulates, occupying a position between Perissodactyla and Ferae. In this case, the resemblances to early whales would be due to convergent evolution among ungulate-like herbivores that developed adaptations related to hunting or eating meat.

Description

The mesonychids were an unusual group of condylarths with a specialized dentition featuring tri-cuspid upper molars and high-crowned lower molars with shearing surfaces.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 the carnivorous to bone-crushing carrion specialists.

Evolutionary history

Restoration of Mesonyx

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

Cited sources

• Agusti, Jordi; Anton, Mauricio (2002). Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe. Columbia University Press. ISBN 0-231-11640-3.
• Cope, E. D. (1880). "On the genera of the Creodonta". Proceedings of the American Philosophical Society. 19: 76–82. OCLC 45016526. Retrieved 11 August 2013.
• Jin, Xun (2005). "Mesonychids from Lushi Basin, Henan Province, China" (PDF). Vertebrata PalAsiatica (in Chinese and English). 43 (2): 151–164. Retrieved 11 August 2013.