Thursday, June 7, 2001

Flatfaced skeleton find alters human evolution

The discovery of an ancient skull with human-like features has thrown new light on human evolution. Dick Ahlstrom reports

Scientists will have to rewrite the story of human ancestry follow ing the discovery of a 3.5 million year old "missing link". Recovered in Kenya, the fossil skull has modern features including a flat face and much smaller teeth than other apelike ancestors.

Research assistant Mr Justus Erus made the find while working with members of the Leakey family, near the Lomekwi River in northern Kenya. Christened Kenyanthropus platyops, the flat-faced man of Kenya, the skull featured in a science journal, Nature.

The near complete skull is battered and weathered but clearly is a new breed of early human. It is the oldest near complete human skull. The skull is 3.2 million years to 3.5 million years old. It was recovered in 1999 during field work sponsored by the National Geographic Society.

Its discovery has profound implications for our understanding of human ancestry according to Dr Maeve Leakey. Scientists believed for the past 20 years that there was a single common ancestor which led to successive hominid species.

The common link was Australopithecus afarensis, a species made famous by the partial Ethiopian skeleton discovered in 1974, christened "Lucy". Lucy was able to walk upright, but was ape-like with projecting mouth and heavy brow. The new skull, Kenyan thropus, has a much flatter face and raised cheek bones. The brow is smaller and has quite small molars compared to Lucy and her later relatives.

"Kenyanthropus shows persuasively that at least two lineages existed as far back as 3.5 million years. The early stages of human evolution are more complex than we previously thought," Dr Maeve Leakey said.

Palaeontologists can infer much from the ancient African fossils. Lucy's hip joints showed that she walked upright although powerful upper limbs suggested an expert tree climber.

Tooth size and face shape relate to the way a species chews its food, Dr Leakey pointed out. The stark differences between the two fossil skulls suggests entirely different diets and could have co-existed without competition for food resources.

Kenyanthropus looked different than hominids about at the time, with remarkably human features. It still had a long way to go in terms of brain power however, with a brain case no bigger than a modern chimp.

This find may also bring the reclassification of other fossil finds. Kenyanthropus is very similar to the skull KNM-ER 1470, discovered in the 1970s by Richard Leakey and colleagues on the eastern shore of Lake Turkana and named Homo rudolfensis.