Megalonyx fossil map
Where fossils of Megalonyx have been found, shown on the Earth as it looked about 0 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 0 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 | Ice Age & later mammals |
|---|---|
| Lived | 9.4 million years ago to the present (Tortonian to Holocene) |
| Periods | Neogene, Quaternary |
| Family | Megalonychidae |
| Named by | Jefferson 1799 |
| Fossil records | 168 occurrences at 130 locations (PBDB) |
| Found in | United States, Mexico, Canada, El Salvador, Guatemala, Honduras |
| Rock formations | txn:43596, Palm Spring, Snake Creek, San Timoteo, Tamiami, Blanco |
About Megalonyx
Megalonyx (Greek, "great-claw") is an extinct genus of ground sloths of the family Megalonychidae, native to North America. It evolved during the Pliocene Epoch and became extinct at the end of the Late Pleistocene, living from ~5 million to ~13,000 years ago. The type species, M. jeffersonii (also called Jefferson's ground sloth), the youngest and largest known species, measured about 3 m (9.8 ft) in length and weighed up to nearly 1,300 kg (2,900 lb).
Megalonyx is suggested to have descended from Pliometanastes, a genus of ground sloth that had arrived in North America during the Late Miocene around 9 million years ago, prior to the main phase of the Great American Interchange. Megalonyx had the widest distribution of any North American ground sloth, having a range encompassing most of the contiguous United States, extending as far north as Alaska during warm interglacial periods.
Megalonyx is notable for having been originally described by future U.S. President Thomas Jefferson in 1799 based on remains found in West Virginia; the species M. jeffersonii was described later, named in honor of him.
Text in “About” is quoted from the Wikipedia article Megalonyx (revision 1374150583), licensed under CC BY-SA 4.0; introduction excerpted verbatim, formatting removed. Ages, family, authority and fossil records: Paleobiology Database, accessed 22 October 2026. Ages are those of the rock layers the fossils were found in. Wikidata: Q134380.
