| Named By: | Joseph Leidy in 1850 |
| Time Period: | Late Eocene to Early Oligocene,38-24.8 Ma |
| Location: | Canada & USA |
| Size: | 2 meters long, 1.2 meters tall at the shoulder |
| Diet: | Carnivore/Possibly omnivore |
| Fossil(s): | Multiple specimens |
| Classification: | | Chordata | Mammalia | Artiodactyla | Entelodontidae | |
| Also known as: | | Eotherium | Pelonax | Scaptohyus | |
Archaeotherium (Greek: arkhaiotherion, meaning "ancient beast") is an extinct genus of entelodont artiodactyl endemic to North America during the Eocene and Oligocene epochs (38--24.8 mya), existing for approximately 6 million years. Archaeotherium was about 1.2m tall at the shoulder and around 2m long and weighing around 270 kg.
Although superficially pig-like, Archaeotherium, along with all other entelodonts, was more closely related to anthracotheres, hippopotamuses, and whales. Evidence from the Wyoming Dinosaur Center suggests that the omnivorous Archaeotherium, like many modern predatory mammals, kept caches of food for times when their hunting was less successful.