Ardipithecus ramidus is a species of australopithecine from the Afar region of Early Pliocene Ethiopia 4.4 million years ago (mya).

Its discovery, along with Miocene apes, has reworked academic understanding of the chimpanzee–human last common ancestor from appearing much like modern-day chimpanzees, orangutans and gorillas to being a creature without a modern anatomical cognate.

The facial anatomy suggests that A. ramidus males were less aggressive than those of modern chimps, which is correlated to increased parental care and monogamy in primates.

The first remains were described in 1994 by American anthropologist Tim D. White, Japanese paleoanthropologist Gen Suwa, and Ethiopian paleontologist Berhane Asfaw.

These were unearthed in the 4.4-million-year-old (Ma) deposits of the Afar region in Aramis, Ethiopia from 1992 to 1993, making them the oldest hominin remains at the time, surpassing Australopithecus afarensis.

Before the discovery of Ardipithecus and other pre-Australopithecus hominins, it was assumed that the chimpanzee–human last common ancestor and preceding apes appeared much like modern-day chimpanzees, orangutans and gorillas, which would have meant these three changed very little over millions of years.

However, the legs were not completely aligned with the torso (were anterolaterally displaced), and Ardipithecus may have relied more on its quadriceps than hamstrings which is more effective for climbing than walking.

[3] It may have predominantly used palm walking on the ground,[20] Nonetheless, A. ramidus still had specialized adaptations for bipedality, such as a robust fibularis longus muscle used in pushing the foot off the ground while walking (plantarflexion),[17] the big toe (though still capable of grasping) was used for pushing off, and the legs were aligned directly over the ankles instead of bowing out like in non-human great apes.

[7][9] Because of this, it is assumed that A. ramidus lived in a society similar to bonobos and ateline monkeys[16] due to a process of self domestication (becoming more and more docile which allows for a more gracile build).

[12] Australian anthropologists Gary Clark and Maciej Henneberg argued that such shortening of the skull—which may have caused a descension of the larynx—as well as lordosis—allowing better movement of the larynx—increased vocal ability, significantly pushing back the origin of language to well before the evolution of Homo.

[22][23] American primatologist Craig Stanford postulated that A. ramidus behaved similarly to chimps, which frequent both the trees and the ground, have a polygynous society, hunt cooperatively, and are the most technologically advanced non-human.

[25] The teeth of A. ramidus indicate that it was likely a generalized omnivore and fruit eater which predominantly consumed C3 plants in woodlands or gallery forests.

[9][10][16] Lacking the speed and agility of chimps and baboons, meat intake by Ardipithecus, if done, would have been sourced from only what could have been captured by limited pursuit, or from scavenging carcasses.

These animals indicate that Aramis ranged from wooded grasslands to forests, but A. ramidus likely preferred the closed habitats,[28] specifically riverine areas as such water sources may have supported more canopy coverage.

Predators of the area were the hyenas Ikelohyaena abronia and Crocuta dietrichi, the bear Agriotherium, the cats Dinofelis and Megantereon, the dog Eucyon, and crocodiles.

[30] Bayberry, hackberry and palm trees appear to have been common at the time from Aramis to the Gulf of Aden; and botanical evidence suggests a cool, humid climate.