Archaeotherium

Extinct genus of mammals

Archaeotherium (αρχαιοθήριον, meaning "ancient beast") is an extinct genus of entelodont artiodactyl endemic to North America during the Eocene and Oligocene epochs (35—28 mya), existing for approximately Archaeotherium fossils are most common in the White River Formation of the Great Plains, but it has also been found in the John Day Basin of Oregon and the Trans Pecos area of Texas.

Archaeotherium was named by Joseph Leidy (1850). Its type is Archaeotherium mortoni. It was synonymized subjectively with Entelodon by Leidy (1853) and synonymized subjectively with Elotherium by Leidy (1857). It was assigned to Entelodontidae by Leidy (1850), Peterson (1909), Scott (1940), Galbreath (1953), Russell (1980), Carroll (1988) and Effinger (1998). Archaeotherium, along with all other Entelodontidae, is an artiodactyl whose exact taxonomic position has been disputed, but taxonomists agree the group lies between the Suina (pigs and peccaries), and the anthracotheres, hippopotamuses, and whales.

Archaeotherium was about tall at the shoulder and around long. Adults weighed 150–250 kg (330 530 lbs). The largest specimens, though much less common, which had been described under the name Megachoerus had skulls up to long, stood about tall at the shoulder and weighed up to
There is no sign of sexual dimorphism in the canine teeth; females and males may have been similar in size. Though Archaeotherium is one of the best preserved of all entelodonts, skulls of entelodonts are far more commonly preserved than full skeletons, and the large size of the head in proportion to the body makes it difficult to accurately estimate the animal's living size and weight. In life, Archaeotherium probably somewhat resembled a cow sized peccary with a longer face, humped shoulders, wide cheekbones, and bosses on the face similar to male warthogs, but without a pig like nasal disk.

It lived in forested and riverbank environments before the evolution of grasslands. Like all entelodonts, the genus had typical artiodactyl legs but lacked specializations for fast running; though it supported its weight on cloven hooves, the foot bones remained unfused, and the toes could spread as camelid feet do. This structure, unique to entelodonts, may have helped the living animal move on soft ground. The head was unusually large, and the high spines on the vertebrae above the shoulders supported strong neck muscles and tendons to handle the weight of the head. The brain was tiny, but had relatively large olfactory lobes, suggesting that the animal had a keen sense of smell.

Archaeotherium, like all entelodonts, possessed huge jugal projections. These projections are sexually dimorphic, with the males having much larger jugals than the females. Due to dimorphism, the function of the expanded jugals was likely used more for display than diet. This same sort of dimorphism can be seen in giant forest hogs, so it can be reasonably assumed that entelodont jugals supported large preorbital glands used for chemical communication signaling the intention to mate. Males would have fought for dominance through non lethal intraspecific biting as seen by bite marks. Fossil evidence suggests that in North America they may sometimes have hunted the early camel Poebrotherium, severing the body in half and crushing and swallowing the foot long rear section Bite marks on the cervical vertebrae of the camels suggests they attacked by running alongside their prey, snapping at their necks. The remains of these camels have been found together, implying Archaeotherium brought its kills to caches for later consumption.) Adult Archeotherium had huge temporalis muscles, but they were normal sized in juveniles and only developed as the animal matured. This suggests the expanded cheekbones and extreme jaw strength of the genus may have been involved in adult social behavior more than eating. It is also possible that younger animals had softer diets, or Archaeotherium had significant parental care. Like other entelodonts, the jaws had an unusually wide gape; one entelodont skull shows the animal survived a bite mark near the orbit by another of the same species. Adult entelodonts may have had aggressive jaw gaping displays and biting fights like living hippos, which have the same adaptation; in male camels, similar wounds result when one animal gets a rival's head between its jaws and bites down with the canines. The gape may also have been used to grab and position large, hard food objects like bones or nuts between the jaws to be cracked by the rear teeth, as in pigs and peccaries.