page_title: Ardipithecus ramidus
section_title: Description
hierarchical_section_title: Ardipithecus ramidus / Description
caption_attribution_description: Ardipithecus
context_page_description: Ardipithecus ramidus is a species of australopithecine from the Afar region of Early Pliocene Ethiopia 4.4 million years ago. A. ramidus, unlike modern hominids, has adaptations for both walking on two legs and life in the trees. However, it would not have been as efficient at bipedality as humans, nor at arboreality as non-human great apes. Its discovery, along with Miocene apes, has reworked academic understanding of the chimpanzee-human last common ancestor from appearing much like modern day chimps, 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. It has also been suggested that it was among the earliest of human ancestors to use some proto-language, possibly capable of vocalizing at the same level as a human infant. A. ramidus appears to have inhabited woodland and bushland corridors between savannas, and was a generalized omnivore.
context_section_description: Assuming subsistence was primarily sourced from climbing in trees, A. ramidus may not have exceeded 35–60 kg (77–132 lb). "Ardi," a larger female specimen, was estimated to have stood 117–124 cm (3 ft 10 in–4 ft 1 in) and weighed 51 kg (112 lb) based on comparisons with large-bodied female apes. Unlike the later Australopithecus but much like chimps and humans, males and females were about the same size.
  A. ramidus had a small brain, measuring 300–350 cc (18–21 cu in). This is slightly smaller than a modern bonobo or chimp brain, but much smaller than the brain of Australopithecus–about 400–550 cc (24–34 cu in)–and roughly 20% the size of the modern human brain. Like chimps, the A. ramidus face was much more pronounced (prognathic) than modern humans. The size of the upper canine tooth in A. ramidus males was not distinctly different from that of females (only 12% larger), in contrast to the sexual dimorphism observed in chimps where males have significantly larger and sharper upper canines than females.
  A. ramidus feet are better suited for walking than chimps. However, like non-human great apes, but unlike all previously recognized human ancestors, it had a grasping big toe adapted for locomotion in the trees (an arboreal lifestyle), though it was likely not as specialized for grasping as it is in modern great apes. Its tibial and tarsal lengths indicate a leaping ability similar to bonobos. It lacks any characters suggestive of specialized suspension, vertical climbing, or knuckle walking; and it seems to have used a method of locomotion unlike any modern great ape, which combined arboreal palm walking clambering and a form of bipedality more primitive than Australopithecus. The discovery of such unspecialized locomotion led American anthropologist Owen Lovejoy and colleagues to postulate that the chimpanzee–human last common ancestor used a similar method of locomotion.
  The upper pelvis (distance from the sacrum to the hip joint) is shorter than in any known ape. It is inferred to have had a long lumbar vertebral series, and lordosis (human curvature of the spine), which are adaptations for bipedality. 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. However, it lacked foot arches and had to adopt a flat-footed stance. These would have made it less efficient at walking and running than Australopithecus and Homo. It may not have employed a bipedal gait for very long time intervals. It may have predominantly used palm walking on the ground, 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), 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.
caption: Reconstruction of Ardipithecus skeleton
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