XIME W6 of the week

Fossil Skull Diversifies Farnilv Tree Anthropologists have long held that

the earliest members of the human evolu- tionary family consisted of a group of closely related species known as australo- pithecines. A 3.5million-year-old skull un- earthed in Kenya now suggests that the australopithecines had a set of evolution- ary companions.

west of Kenya’s Lake Turkana. Dating of volcanic rock from below and above the finds-based on measures of potassium and argon isotopes in the rock-places them at about 3.5 million years old.

K. platyops and A. afarensis may have evolved in substantially different habi- tats, the investigators theorize. Other

theresearchers have assigned two Newly discovered skull of Kenyanthropus to K. platyops. platyops (left) flanks a skull of Homo

If anthropologists accept Kenyan- rudolfensis, which may be reassigned to the thropus into the evolutionary fold, it genus Kenyanthropus. will. change their thinking about early hominids. Consider the new skull’s unusual anatomy. Like Australopithecus afarensis-a species that existed from 4 million to 3 million years ago and in- cludes the partial skeleton named Lucy-K. platyops has a small brain and thickly enameled cheek teeth. Moreover, its small ear holes resemble those of both chimpanzees and an earlier ho- minid, Australopithecus anamensis.

In other respects, though, K. platyops looks like a 2-million-year-old skull previ- ously found in Kenya. Many researchers attribute that specimen to Homo rudolfen- sis, an extinct species in our own genus. Leakey’s group reassigns the skull to Kenyanthropus based on such shared traits as a flat, sloping lower face, raised cheeks, and flattened brow ridges.

If K. platyops had deeper evolutionary roots than A. afarensis, as well as a unique relationship to H. rudolfensis, a species that emerged much later, it rais- es doubts about Lucy’s legacy, Leakey’s team contends. Contrary to the most in- fluential current view, her kind might not have given rise to all ensuing hominids, the team says.

Whether or not the new skull repre- sents a unique genus, it indicates that a distinct line of hominids existed along- side A. afarensis, remarks William H. Kim- be1 of the Institute of Human Origins in Tempe, Ariz. Further study of Leakey’s finds may resolve whether A. afarensis truly served as an ancestor to all later hominids, says Kimbel, who directs A. afarensis excavations in Ethiopia.

Leakey and her colleagues unearthed the new skull and associated fossil frag- ments in August 1999 at a site located just

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ancient animals whose remains have been found at the Kenyan site appear to have been suited to a wetter, more vegetated habitat than that frequented

J by Lucy’s kind, the researchers say.

The new find’s surprising mix of anatomical features indicates that some parts of the skull can change in striking ways without affecting the shape of near- by areas, Leakey’s group adds. For exam- ple, K. platyops combined a forwardly positioned cheekbone with small cheek teeth. However, Paranthropus-a ho- minid genus that lived from around 2 million to 1 million years ago-blended a comparable cheek bone with large, peg- like molars.

“Many of the skeletal features of early hominids may have been acquired piece- meal, not as large anatomical complex- es,” Kimbel proposes.

Another approach holds that the evo- lution of crucial parts of the skeleton in various hominids triggered many other bony alterations (SN: 11/25/00, p. 346).

The position of K. platyops in the hu- man evolutionary tree will remain uncer- tain for some time, according to Daniel E. Lieberman of George Washington Univer- sity in Washington, D.C. “There’s no sim- ple way to figure out who’s related to whom,” he says. -B. Bower

New nanosize detector picks through DNA Researchers have developed a new between two volumes of a salt solution

technology for rapidly distinguishing be- and added DNA molecules with a sin- tween almost identical DNA molecules. gle, known base sequence to one side.

The highly sensitive device, called a Applying a voltage across the mem- nanopore detector, might eventually brane drew hairpin DNA molecules into be able to sort through DNA and iden- the pore one at a time. Initially, each tify a small variation that predisposes molecule got stuck in the pore, which a person to some disease. The tech- narrows from 2.5 nanometers in diame- nique might even permit DNA sequenc- ter to 1.5 nm. But then the hairpin ing at unprecedented speeds, report spontaneously untwisted into a single Wenonah Vercoutere and her col- strand, thin enough to zip farther into leagues at the University of California, the channel.

cules of so-called hairpin DNA, in Nanopore detector (left) pulls in a hairpin DNA which a single strand doubles molecule, which gets stuck (center). Once it back onto itself to create a tiny uncoils, the molecule can go farther into the loop at one end. narmwing passage (right). A characteristic current

In each molecule, the four change indicates which molecule is in the detector Y

types of nucleotide bases-the chemical units that code for genetic in- formation in DNA-followed a sequence chosen by the researchers. Along the in- tertwined stem of each hairpin, the bases paired up, while the loop at the top con- tained four unpaired bases.

The researchers placed a membrane

SCIENCE NEWS, VOL. 159

Each DNA molecule created a charac- teristic electrical signal as it blocked the pore and then moved on, says team member David Deamer. The researchers created a computer program that learned these signatures.

“We’re pulling [the molecules] into the

MARCH 24,2001