| Named By: | Richard Harlan in 1825 |
| Time Period: | late Miocene to Pleistocene, 10.3-0.011 Ma |
| Location: | Across North and Central America |
| Size: | Up to 3 meters long |
| Diet: | Herbivore, possibly omnivorous |
| Fossil(s): | Many specimens |
| Classification: | | Chordata | Mammalia | Xenarthra | Pilosa | Megalonychidae | |
Megalonyx (Greek, "large claw") is an extinct genus of ground sloths of the family Megalonychidae endemic to North America from the Hemphillian of the Late Miocene through to the Rancholabrean of the Pleistocene, living from ~10.3 Mya--11,000 years ago, existing for approximately 10.289 million years. Type species, M. jeffersonii, measured about 3 m (9.8 ft) and weighed up to 1,000 kilograms.