The Elements of Evolution (57) Ardipithecus


<em>Ardipithecus (the Afar word for “basal family ancestor”) (5.8–4.3 MYA) is a genus with 2 known species: Ar. kadabba and Ar. ramidus.

Little is known of the earlier Ar. kadabba, as only teeth and pieces of skeletal bones have been recovered, dated 5.6 MYA. Ar. kadabba lived in a habitat mix of woodland and grassland, with small lakes, swamps, and springs.

By contrast, a variety of Ar. ramidus fossils have been found, altogether comprising almost every part of the skeleton. The single most complete fossilized skeletal remains were of a female that lived 4.4 MYA, named Ardi.

Ar. ramidus had a modest stature: around 1.2 meters, and modest brain size (300–350 cm2). There was little sexual dimorphism: males and females were similarly sized, unlike chimpanzees. This suggests that that competition between males was minimal. Sexual dimorphism commonly occurs when males compete for sex.

Males and females may have both taken part in food gathering and taking care of offspring. Sociality may not have been as ritualized or segregated as it is with some other primates, notably baboons.

Many physical features suggest Ar. ramidus both walked upright and swung from limb to limb. Chimp feet are good for grasping trees. Ar. ramidus feet were better for bipedal locomotion but the arms and hands are consistent with clambering in trees.

Ar. ramidus lived in the woods, preferring the trees to the open plains of the savanna. They lived mostly during a time when drought was rare.

The Ar. ramidus teeth found are not sufficiently differentiated to indicate limited dietary preferences. This suggests an omnivore or broad vegetarian diet, as the molar enamel is thicker than that of chimps, but thinner than later hominins.

It is unlikely that Ar. ramidus ate hard foods, such as tubers and nuts, which require thick enamel for heavy chewing. Ar. ramidus probably enjoyed fruits, leaves, and softer vegetables, and perhaps insects, eggs, and small animals.