March 21, 2001 – After the partial skeleton of a 3.2-million-year-old human relative known as Lucy was found in Ethiopia in 1974, many researchers believed her species – Australopithecus afarensis – was the ancestor of modern humans. Now, in a stunning discovery, scientists working in Kenya have found the skull and partial jaw of a completely different genus and species, with a flattened face and small molar teeth much different than those of afarensis. The discovery of the 3.2- to 3.5-million-year-old fossils raises the question of whether modern humans descended from Lucy’s species or from the newly discovered species.
“We’ve always assumed Lucy was our ancestor and now we need to re-evaluate that idea,” said geologist Frank Brown, dean of the College of Mines and Earth Sciences at the University of Utah.
Discovery of the fossils of Kenyanthropus platyops – meaning flat-faced human from Kenya – will be reported in the March 22 issue of the journal Nature by a team led by paleoanthropologist Meave Leakey of the National Museums of Kenya. Brown and University of Utah geology undergraduate Patrick Nduru Gathogo co-authored the study, along with Fred Spoor of University College London, Ian McDougall of The Australian National University in Canberra and Christopher Kiarie and Louise Leakey of the National Museums of Kenya. Louise Leakey is Meave Leakey’s daughter.
The field work was funded by the National Geographic Society, except the geology work by Utah researchers was financed by the L.S.B. Leakey Foundation.
By studying the geology of volcanic ash and other sediments in Kenya’s Lake Turkana basin, Brown, Gathogo and McDougall helped determine the age of the new fossils, including the 3.5-million-year-old skull.
“In the absence of any other fossils in the time between about 3.8 million and 3 million years ago, the only possible human ancestor that could be claimed was Australopithecus afarensis,” Brown said. “Now that we have a new form of early hominid from the same time period that is quite distinct from afarensis, the anthropologists will have to decide which of these forms of early human actually lies in our ancestral tree. It cannot be both.”
The study in Nature scrupulously avoids taking a position on which species may be the direct ancestor of modern people.
“Kenyanthropus shows persuasively that at least two lineages [of early human relatives] existed as far back as 3.5 million years,” Meave Leakey said in a statement issued by the National Museums of Kenya. “The early stages of human evolution are more complex than we previously thought.”The smaller molars in Kenyanthropus suggest it probably had a different diet than Australopithecus, so both could have lived in the same area at the same time without directly competing for food, Leakey and Spoor said.
The Kenyanthropus platyops fossils were discovered in 1998 and 1999, with the skull found in August 1999 by Justus Erus, a Kenyan research assistant working with Meave Leakey near the Lomekwi River in the western Turkana basin in northern Kenya. Erus noticed a tooth protruding from the mudstone sediment. Gathogo was there at the time.
“I knew what they found without them telling me,” said Gathogo, a native of Kenya who will graduate from the University of Utah this spring. “Having seen hominid fossils for a long time, it was obvious it was a hominid. … Everyone was so excited we started rejoicing.”
Brown and Gathogo had suggested Leakey look for fossils in the area where Kenyanthropus platyops ultimately was found because they noticed lots of undisturbed antelope and hippopotamus fossils there, indicating it had not yet been picked over by field crews. The fossil was found soon after Brown flew home to Salt Lake City.
The skull apparently is the oldest known, nearly complete cranium of any form of early human.Brown said the Kenyanthropus discovery illustrates that “at almost every time in the past back to 4 million years, there were two or more species of hominid existing on Earth. So where we used to see a very simple ladder of evolution from one form to the next, the current thinking is that the evolutionary history of man and manlike creatures is more like a bush with many dead ends and only one stem that leads all the way to us.”
Kenyanthropus platyops resembles skull 1470 found in the eastern Turkana basin in the 1970s. Called Homo rudolfensis by some researchers and a member of genus Australopithecus by others, the Nature article suggests researchers now must consider if it instead descended from Kenyanthropus.
Brown, Gathogo and McDougall estimated the Kenyanthropus skull’s age by indirectly dating surrounding layers of tuff, which is rock deposited when ash from volcanic eruptions in Ethiopia was carried to the Turkana region by rivers and wind. Brown has worked with Richard and Meave Leakey since 1980, helping determine ages for fossils they found.“It’s immensely satisfying,” Brown said.
The new study lists three dozen teeth, jaw fragments and other fossils found in the same rock formation as the Kenyanthropus skull and that appear to be different than Lucy’s species. Spoor said only the skull and a partial upper jaw are confirmed as belonging to the new species. The others ultimately will be studied to determine if they also are fossils from Kenyanthropus. One of them is a temporal bone – from the skull’s ear region – that Gathogo found in 1998.
Before enrolling at Utah in 1999, Gathogo attended Kenya Polytechnic and did field work with Meave Leakey, who encouraged him to work with various geologists. Brown invited Gathogo to attend the university in Salt Lake City.
“As an undergraduate, Patrick was the best person I’d seen in the field for years – very quick at learning things, very observant,” Brown said.
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