Australopithecus anamensis

This hominin is the earliest known australopithecine and lived over 4 million years ago.

Background to discovery

Age

3.8 to 4.2 million years ago.

Important fossil discoveries

In 1965, a four-million-year old fossil arm bone was found in a remote area of Kenya but scientists needed more information before they could confidently name it. Thirty years later, a fossil hunting expedition led by Meave Leakey returned to the site. Additional fossil discoveries showed that this was a new species and, in 1995, Australopithecus anamensis was proclaimed.

In 2006, a new A.anamensis find in Ethiopia was announced. The find included a large canine tooth and the earliest known Australopithecus femur.

Key specimens:

  • KNM-KP 29283 – a partial upper jaw with teeth discovered in 1994 in Kanapoi, Kenya. This specimen deomstrated the typical shallow palate and robust canine teeth with well developed roots and a pointed crown.
  • KNM-KP 29281 – a partial lower jaw with teeth discovered in 1994 by Peter Nzube and Maeve Leakey in Kanapoi, Kenya. This is the ‘type specimen’ or official representative of this species. The teeth are arranged in parallel rows, which is an ape-like feature typical of this early ancestor.
  • KNM-KP 29285 – upper and lower ends of a tibia discovered in 1994 in Kanapoi, Kenya

What the name means

Australopithecus is the genus or group name. It is derived from the Latin word ‘australo’ meaning ‘southern’ and the Greek word ‘pithecus’ meaning ‘ape’. This ‘southern ape’ name was created for another species discovered in South Africa but the name ‘Australopithecus’ is now shared by several different species whose similarities place them into the same group.

The word anamensis is based on the word ‘anam’ from the Turkana language used in the area where fossils for this species were discovered. ‘Anam’ means ‘lake’ and is a reference to the ancient lake-side environment once inhabited by this species.

Distribution

Fossils of this species have been found in the Middle Awash in northeast Ethiopia and at three sites (Allia Bay, Kanapoi and Sibolot) scattered around Lake Turkana in Kenya, Africa.

Relationships with other species

Many scientists think this species may be an ancestor of the well-known species, Australopithecus afarensis. Some even think these individuals are members of A.afarensis rather than a separate species but if this is the case, A.afarensis contains a highly variable population.

Key physical features

Body size

  • size was probably similar to that of modern chimpanzees
  • there was an enormous difference between the body sizes of males and females. This difference between the sexes (sexual dimorphism) in body size was similar in degree to that shown by modern gorillas and orang-utans.

Brain

  • probably had a relatively small brain but more fossil material of the cranium is needed before brain size can be estimated

Jaws and teeth

  • jaws were ape-like in having: a jaw shape in which the side rows of teeth were arranged in parallel lines; a lower jaw in which the bone below the front teeth was sloping backward rather than projecting forward into a chin; and an upper jaw with a shallow palate (roof of the mouth)
  • teeth were intermediate between those of apes and humans and included: tooth enamel that was thicker than that found in earlier ape-like ancestors; canine teeth that were still relatively large and pointed but were shorter than those found in earlier ape-like ancestors.

Limbs

  • the knee-end of the tibia (shin bone) was human-like as the upper surfaces of the two knobs (condyles) at the top of the tibia were similar in size and concave in shape. This feature indicates this species could walk bipedally (on two legs).
  • marks on the wrist bones indicate these individuals had strong hand tendons useful for tree climbing
  • the elbow joint was more human-like in being relatively flexible, rather than the more rigid, locking elbows that quadrupedal (four-legged) apes have to support their bodies as they move about
  • forearms were relatively long and ape-like and useful for climbing

Lifesyle

Culture

Australopithecus anamensis 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

Plant and animal fossils and the analysis of ancient sediments and rocks provide clues about this species’ environment. They lived near an ancient inland lake that existed in the basin where Lake Turkana is now found.

The region was subject to volcanic activity and various volcanic eruptions produced layers of volcanic ash that covered the ground. The fossilised remains of this species were found trapped between different layers of ash and this has enabled this species’ fossils to be reliably dated to between 3.8 and 4.2 million years in age.

These early ancestors lived in forests and woodlands that grew near the lake. Their skeletons show that they walked on two legs when on the ground and they probably spent a lot of time climbing trees, perhaps searching for food or avoiding predators. Their teeth indicate they were plant-eaters, eating both fruits and hard-to-chew foods such as nuts.


Fran Dorey , Exhibition Project Coordinator
Beth Blaxland , Education Project Officer
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