Skull Find Is a 'Head Scratcher'

Member Part of 'Kenyan Man' Team

A 3.5-million-year-old skull found in eastern Africa is changing the way science views the origins of mankind.

At the same time, the discovery is also opening the door to a fresh look into the geology of a region that may have been the true cradle of humanity.

AAPG member Frank H. Brown, dean of the College of Mines & Earth Sciences at the University of Utah in Salt Lake City, began studying the geology of northern Kenya more than two decades ago.

Because of that work, he now shares center stage with one of the world's most famous fossil-hunters.

In March, noted paleontologist Maeve Leakey announced that she and a team of researchers had discovered and analyzed a 3.5-million-year-old cranium and partial jawbone from an arid region in northern Kenya.

Based on its differences from other hominid skulls, Leakey said, the fossils almost certainly represent a new genus and species in man's ancestral line. Those differences include a flat face, small teeth, a narrow nasal aperture and a small, chimpanzee-like ear canal.

Writing in the March 22 issue of the journal Nature, she named this being Kenyanthropus platyops, or flat-faced Kenyan Man.

Researchers from the National Museums of Kenya recovered the cranium in 1999 on the west side of Lake Turkana, formerly called Lake Rudolf.

Brown said the Lake Turkana area is associated with the African Rift, with the southern part of the lake "classic Rift."

"The northern two-thirds of the lake is very different," he said. "What we have is a series of faults, most of which are down on the east, so it's more of a basin-and-range structure."

Brown contrasted the arid Kenyan landscape of today with the fertile, animal-filled expanse that existed millions of years ago.

"Today it's incredibly dry," Brown said, "but when you look at the fossil record you find lots of big animals. There were elephants there, and lots of monkeys."

How About a Date?

Kenyan Man would have seen a lake, however.

"There was a lake in the area much like there is today," Brown noted. "Shortly after that the lake disappeared and there was a river. The Omo River in fact transports a lot of ashes into the area."

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A 3.5-million-year-old skull found in eastern Africa is changing the way science views the origins of mankind.

At the same time, the discovery is also opening the door to a fresh look into the geology of a region that may have been the true cradle of humanity.

AAPG member Frank H. Brown, dean of the College of Mines & Earth Sciences at the University of Utah in Salt Lake City, began studying the geology of northern Kenya more than two decades ago.

Because of that work, he now shares center stage with one of the world's most famous fossil-hunters.

In March, noted paleontologist Maeve Leakey announced that she and a team of researchers had discovered and analyzed a 3.5-million-year-old cranium and partial jawbone from an arid region in northern Kenya.

Based on its differences from other hominid skulls, Leakey said, the fossils almost certainly represent a new genus and species in man's ancestral line. Those differences include a flat face, small teeth, a narrow nasal aperture and a small, chimpanzee-like ear canal.

Writing in the March 22 issue of the journal Nature, she named this being Kenyanthropus platyops, or flat-faced Kenyan Man.

Researchers from the National Museums of Kenya recovered the cranium in 1999 on the west side of Lake Turkana, formerly called Lake Rudolf.

Brown said the Lake Turkana area is associated with the African Rift, with the southern part of the lake "classic Rift."

"The northern two-thirds of the lake is very different," he said. "What we have is a series of faults, most of which are down on the east, so it's more of a basin-and-range structure."

Brown contrasted the arid Kenyan landscape of today with the fertile, animal-filled expanse that existed millions of years ago.

"Today it's incredibly dry," Brown said, "but when you look at the fossil record you find lots of big animals. There were elephants there, and lots of monkeys."

How About a Date?

Kenyan Man would have seen a lake, however.

"There was a lake in the area much like there is today," Brown noted. "Shortly after that the lake disappeared and there was a river. The Omo River in fact transports a lot of ashes into the area."

About four million years ago, Brown said, there was a "huge outpouring of basalts" in the region. With eruption of the 4ma basalts, the basin that was filled by Pliocene and Pleistocene sediments is established.

"Later, with the building of Mt. Kulal southeast of the present lake, the whole topography and palaeography was being changed by the building of this volcanic structure, which was blocking the drainage out to the Indian Ocean," he said.

Dynamic changes continued to alter the landscape, producing a lake in the area from 4.33-4 million years ago, with no lake at 4-3.55 million years and a lake again from 3.55-3.4 million years, Brown said.

Evidence of an ancient river emptying into the Indian Ocean can be seen in a submarine canyon cut into the African shelf just south of the equator in southern Somalia, he noted.

Changes that affected the area's geology play a large role in determining the age of the K. Platyops skull. According to Brown's description, the cranium fossil was found near the contact of the Nachukui formation with Miocene volcanic rocks, above the Lokochot Tuff and below the Tulu Bor Tuff.

Interpolation between the 3.57 million-year-old Lokochot and the 3.4 million-year-old Tulu Bor tuffs gives an age of 3.5 million years for the skull's location, he said.

The K. platyops skull derived from a dark mudstone, originally deposited along the northern margin of a shallow lake. Volcanic-pebble conglomorates within the mudstone show streams flowing from hills to the west.

Other specimens found in floodplain deposits of the ancient Omo River indicate that hominids occupied the floodplains of major rivers, alluvial fans and lake-margin environments from 3.5-3 million years ago, he noted.

Brown credited Ian McDougall, professor of earth sciences at Australian National University, with conducting the potassium argon and 40/39 argon dating that determined the age of volcanic layers in northern Kenya.

"We can tie these closely together, and each of these volcanic eruptions in fact has its own, distinct chemical composition," Brown explained.

He said McDougall has dated 20 levels in that part of Africa from 0.74 plus or minus 0.01 million years down to 3.96 plus or minus 0.03 million years.

"Ian's contribution to this was to date two underlying volcanic ash layers at 3.96 and 3.94 million years," he said. "Above it there's a palaeomagnetic reversal at 3.57-3.58 million years, the Gilbert-Gauss Boundary."

Marine sediments research by Peter deMenocal of the Lamont-Doherty Earth Observatory provided additional support for identifying the relevant time and geological sequences, according to Brown.

Confirmation of the fossil dating "has come from as many different directions as you can think of," he said.

Kenyan Man, Meet Lucy

Placing Kenyan Man in eastern Africa between three million and four million years ago is not only a key finding, but also one cause for the controversy over the proposed new Kenyanthropus genus designation.

That dating means Kenyan Man lived at approximately the same time and in the same part of the world as the previously identified hominid Australopithecus afarensis, exemplified by the famous fossil, Lucy.

Scientists studying human evolution originally assumed a fairly direct line of descent, with man's more apelike ancestors moving ever closer to modern human form. A. afarensis was thought to be one stop on that train-track of development.

Now it seems that numerous hominid sidetracks may have existed, with no clear line leading to Homo sapiens.

The advent of Kenyan Man as a contemporary of Lucy led one anthropologist to describe this new view of human evolution as a family tree with two trunks.

Brown said he first worked for Meave Leakey's husband, Richard Leakey, on the east side of Lake Turkana in 1980, then spent a week working with him on the west side of the lake the following year.

Richard Leakey is the son of Louis and Mary Leakey, who discovered hominid fossil evidence at the Olduvai Gorge in Tanzania in the 1930s.

In 1985, Amoco asked Brown to return to Kenya "to explain the later geology" of the area. Amoco had been investigating Kenya's prospectivity, but later sold its interests to Shell, he said.

"We did find a good little source rock, but it probably wasn't thick enough to produce econimic accumulations of petroleum," Brown recalled.

Kenya and Ethiopia are rich hunting grounds for hominid fossils partly because of past volcanism.

"Bone preserves exceptionally well in sediments that are high in calcium and fluoride. In part, the volcanics help with the preservation of the fossils," he said.

Also, in a tectonically active area, he observed, fossils are brought up and then exposed through erosion.

Geology Gets Its Due

Brown's studies of the Turkana Basin reveal an area of sedimentation in fluvial environments interspersed with lacustrine episodes.

At the Kenyan Man discovery site, the Lokochot Tuff contains clay and volcanic etritus, according to Brown. A volcanic pebble conglomerate overlies the tuff, followed by a quartz-rich sandstone that includes a burrowed, fine sandstone marker bed.

A dark mudstone above the sandstone contains volcanic pebbles at its base with thin pebble conglomerate lenses in its upper portion. Overlying brown mudstone is directly beneath the Tulu Bor Tuff.

In an earlier paper describing the Koobi Fora formation east of Lake Turkana, Brown described two phases of deposition that characterize the Lokochot member in an interval of about 170,000 years.

Coarse-grained detrital clastics deposited in a fluvial environment give way to finer-grained detrital and bioclastic material of a lacustrine episode.

The Tulu Bor shows well-developed, upward-fining cycles and pedogenesis of a fluvial environment, with minor lacustrine intervals of fine-grained detrital clastic and bioclastics. Deposition of the Tulu Bor member occurred over an interval of about 880,000 years.

Brown has correlated and traced the Tulu Bor Tuff to Hadan in Ethiopia, where the Lucy A. afarensis partial skeleton was discovered -- another link to the coeval existence of Lucy and Kenyan Man.

Cycles of changing physical environment may have had an effect on hominid development, but the extent of that effect remains uncertain. Some recent research contradicts theories that hominids began to walk upright as broad savanna replaced forest habitat.

Leakey's researchers determined, tentatively, that the Kenyan Man locale was wetter and more vegetated than other sites that produced hominid fossils of a similar age.

AustralopithEcus -- the name means "southern ape" -- once stood alone as an accepted ancestor to human beings. Scientists then recognized its later species as belonging to a different genus, Paranthropus.

A tentative designation, Ardipithicus, added an earlier genus to the hominid line, but not all anthropologists agree with this assessment. Now Kenyanthropus has blurred the picture even more.

It's possible that Kenyan Man someday will be seen as merely an example of AustralopithEcus, known to be a very diverse genus, just as Java Man (Pithecanthropus) and Peking Man eventually were categorized as Homo erectus.

Researchers into human evolution are much closer to the beginning of the story than to the end. For Brown, the gathering of pieces for this puzzle brings new opportunity to study the geology of eastern Africa.

"In a way, the hominids get in the way of the geology," he said, "but if it wasn't for the hominids, no one would give a damn about the geology."

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