Mesonyx fossil map
Where fossils of Mesonyx have been found, shown on the Earth as it looked about 45 million years ago and on today’s map.
Dots are fossil collections recorded in the Paleobiology Database. The “then” view moves today’s fossil sites back to their positions 45 million years ago (the time slice nearest the median age of the fossils) using the Merdith et al. (2021) plate model; positions are approximate. Open on the timeline map →
| Group | Early mammals |
|---|---|
| Lived | 56–37.71 million years ago (Ypresian to Bartonian) |
| Periods | Paleogene |
| Family | Mesonychidae |
| Named by | Cope 1872 |
| Fossil records | 32 occurrences at 9 locations (PBDB) |
| Found in | United States, China |
| Rock formations | Bridger, Uinta, Huerfano, Uqbulak, Green River, Aycross |
About Mesonyx
Mesonyx ("middle claw") is an extinct genus of mesonychid, one of two families that is part of the extinct order Mesonychia. Mesonychians were a clade of hoofed mammals closely related to ungulates, that first appeared in the fossil record during the Early Paleocene, roughly 63 million years ago. However, the order is thought to have arisen in the Late Cretaceous at least 66.7 Ma.
Fossils of the various species in both North America and East Asia. The North American species, M. obtusidens were found from Bridgerian to middle Uintan localities of the Early to Middle Eocene in North America. On the other hand, M. uqbulakensis and M. nuhetingensis, were exclusive to the Arshantan of the Early Eocene in East Asia.
Mesonychids within the Bridger Formation were thought to have been one of the top predators of the time along with crocodyliforms and the oxyaenid Patriofelis.
Text in “About” is quoted from the Wikipedia article Mesonyx (revision 1379841594), licensed under CC BY-SA 4.0; introduction excerpted verbatim, formatting removed. Ages, family, authority and fossil records: Paleobiology Database, accessed 23 October 2026. Ages are those of the rock layers the fossils were found in. Wikidata: Q289716.
