NAIROBI, Kenya (AP) _ Scientists working in Kenya have found skull fragments from what they say was an early, tool-making human that lived more than 900,000 years ago, perhaps filling an important gap in the fossil record.
Scientists from the United States, Britain and Kenya found part of a skull of a small adult with some characteristics of Homo erectus, in Olorgesalie, 100 miles southeast of the capital, Nairobi, said Richard Potts, the lead researcher.
The skull fragments were found between July and August 2003, and the scientists' analysis was published in Friday's edition of Science magazine.
Because scientists only found a brow ridge, the left ear region of the skull, and some skull fragments, it is difficult to know whether the find means a new species of pre-human, said Potts, who is director of the Human Origins Program at the Smithsonian Institution in Washington D.C.
``This partial skull comes from a gap in the African fossil record, a gap that extends from about 1 million years ago to about 600,000 years ago,'' Potts said.
In the human family tree of Africa, an early common ancestor known as Homo ergaster lived until about 1.3 million years ago. One species branching from that ancestor included Homo erectus, which is believed to have survived until about 50,000 years ago and spread from Africa to Asia.
Separate from Homo erectus, other species emerged more recently along different branches, including our own species, Homo sapien, as well as neandertals.
All of these early humans, or hominids, were hunter-gatherers living in cooler grasslands. They had larger brains, walked upright and made stone tools, but scientists disagree whether that means the branches on the human tree should remain separate, or whether all hominids should belong to the same category of early humans.
During this sketchy period of human evolution, there are few specimens to add physical details.
Potts said these fragments will put ``a bit of face, a bit of an individual'' on the time period, but may not provide definitive proof. He said the skull fragments contain traits associated with Homo erectus, but it also have unique traits, including its smaller-than-expected size.
Researchers said the fossils' most significant contribution might be to convince scientists that early humans came in a variety of shapes and sizes, even among local populations and family groups.
The Olorgesalie site where the skull fragments were discovered has long been important to paleontologists. Beginning in 1942, hundreds of ancient stone hand axes were found at the site by Louis and Mary Leakey. But Potts said it the handaxes probably were made by larger individuals, raising questions as to how many types of early humans were present there.
The National Museums of Kenya manages the 62-year old prehistoric site of Olorgesalie.