Variety reigns in ancient hominid's skull.

Fossil discoveries of Australopithecus boisei, a member of the human evolutionary family that lived in Africa from around 2 million to 1 million years ago, show that this creature possessed huge teeth and a nutcrackerlike jaw the likes of which even Jay Leno, or Kirk Douglas would envy.

New A. boisei finds, described in the Oct. 2 Nature, indicate that this hominid's massive jaw rested beneath an unexpectedly diverse array of skull features.

The striking skeletal variations encompassed by this species challenge the increasingly common practice of using subtle anatomical differences to define new species in the hominid fossil record, concludes a research team headed by anthropologists Gen Suwa of the University of Tokyo and Berhane Asfaw of Rift Valley Research Service in Addis Ababa, Ethiopia.

"We're saying, `Wait a minute, let's not be so quick to split hominids into new species,'" remarks anthropologist Tim D. White of the University of California, Berkeley, who assisted in the analysis of the new A. boisei fossils. "We still don't understand the extent of biological variation in fossil hominid species."

Ongoing excavations in Ethiopia, at a site known as Konso, yielded nine skull and tooth specimens attributed to A. boisei, the researchers report. Dating of Volcanic ash layers surrounding the sediment in which the fossils rested places their age at between 1.4 million and 1.5 million years.

Earlier work at Konso turned up remains of Homo erectus and numerous stone hand axes that also date to around 1.4 million years old (SN: 1/2/93, p. 6). It now appears that A. boisei and H. erectus coexisted in a dry grassland environment, Suwa and his coworkers assert. The researchers do not yet know whether the two hominid species interacted or if A. boisei participated in making and using stone tools.

Jaw and tooth features in the new specimens resemble those of A. boisei fossils found at two other locations in eastern Africa, the scientists hold, but A. boisei at Konso displays a distinctive look above the jaw.

For instance, the Konso skull exhibits relatively flat cheeks, unlike the flaring, visorlike protrusions on the cheeks of prior A. boisei finds. Moreover, only at Konso does A. boisei's palate appear broad and short--similar in shape to that of Homo species. Also, a bony crest that runs down the middle of the Konso cranium rises sharply at the back of the head, unlike such crests on other A. boisei skulls.

Reasons for the anatomical disparities in A. boisei populations remain unclear, White notes. The variations may have stemmed from random genetic changes or from different survival challenges faced by A. boisei groups living in dissimilar habitats.

Scientists who have led the charge to identify a greater number of fossil hominid species welcome the Konso discoveries but see no reason to quell their efforts.

"This is an important new collection of fossils that should reassure us that A. boisei is a valid species," comments anthropologist Bernard Wood of George Washington University in Washington, D.C. "But I think we'll continue to find more, rather than [fewer], fossil hominid species."

Some skeletal features, such as A. boisei's distinctive jaw, persist over long stretches of time and serve as valuable species markers, Wood argues. Anatomical variations in other parts of the face and cranium have been evident in previous A. boisei finds and merit far more cautious use as markers by scientists who classify fossil species, he adds.

In contrast, White holds that the Konso evidence, combined with observations of considerable anatomical diversity among modern apes, indicates that there may have been fewer ancient hominid species than many investigators now assume.