Ardipithecus kadabba

Background of discovery

Age

5.8 to 5.2 million years ago

Important fossil discoveries

Eleven specimens, from five localities in Ethiopia, were discovered between 1997 and 2000. They represent at least five individuals and include teeth, jaws, hand, toe, arm and collar bones. The type specimen is a right lower jaw fragment, ALA-VP-2/10. Most of the fossils date to 5.6-5.8 million years old, however one of the toe bones is dated at 5.2 million years old. There is some concern over the classification of the toe bone to this species, as it was found 15 kilometres away from the other fossils and is younger in age. They were classified as a subspecies Ardipthecus ramidus kadabba.

In 2002, six teeth were found at Asa Koma in the Middle Awash. They date to between 5.6 and 5.8 million years old. Distinct features of these teeth led the finders to place all the fossils into a new species Ardipithecus kadabba rather than a subspecies of Ardipithecus ramidus.

What the name means

The name is derived from the local Afar language. ‘Ardi’ means ‘ground’ or ‘floor’, and is combined with the Latinised Greek word ‘pithecus’, meaning ‘ape’. The species name kadabba means ‘oldest ancestor’ in the Afar language.

Distribution

Eastern Africa in the Middle Awash, Ethiopia

Relationships with other species

The scientists that discovered the remains claim this species is a direct human ancestor and the earliest species yet discovered on the human branch of the family tree. Those that discovered Orrorin tugenensis dispute this claim as they believe their find is a better candidate for direct human ancestry. Some scientists assign these remains to the subspecies Ardipithecus ramidus kadabba, because it shares many similarities to Ardipithecus ramidus, but has more primitive, or ape-like, teeth features.

Key physical features

Brain

• similar in size to modern chimpanzees

Body size and shape

• similar to modern chimpanzees

Limbs

• the structure of the toe bones suggests that this species may have been bipedal. However, some scientists debate whether this fossil should be included with this species as it was found about 15 kilometres away from the other fossils and is dated several hundred thousand years younger.

Jaws and teeth

• some primitive dental features such as thick tooth enamel and relatively large canines compared to humans.
• some features of the teeth show a movement away from the primitive ape-like condition, such as molars that are larger than those of chimpanzees, a tendency towards incisiform lower canines and hominin-like upper pre-molars.

Lifestyle

Culture

There is no evidence for any specific cultural attributes, but they may have used simple tools similar to those used by modern chimpanzees, including:

• twigs, sticks and other plant materials that were easily shaped or modified. These may have been used for a variety of simple tasks including obtaining food.
• unmodified stones, that is stones that were not shaped or altered before being used. These tools may have been used to process hard foods such as nuts.

Environment and diet

Fossil evidence from the site indicates the area was a mosaic of woodland and grasslands with lakes, swamps and springs. The discovery that this species lived in a forest environment challenged the theory about what kind of environment fostered the evolution of bipedalism. Did bipedalism evolve to take advantage of new open grassland environments, as was once believed, or did it first evolve in the trees?

The large back molars and narrower incisors (compared to chimpanzees) suggest that the diet included more fibrous foods than just fruit and leaves.