Hominoid lineages and keystone clues.

Hominoid lineages and keystone clues

When attempting to distinguish betweenearly members of the human line and their now-extinct relatives known as the robust australopithecines, does the nose know?

In 1985, Todd R. Olson of the CityUniversity of New York Medical School answered in the affirmative. Connecting the nasal bones, he reported, was a keystone-shaped pattern of sutures that characterizes only robust australopithecines, also known as Paranthropus, as well two other distinct suture patterns marking modern apes and humans. He used these patterns to label the more than 3-million-year-old skull of a child found at Hadar, Ethiopia, as a member of the Paranthropus line, and another infant skull from about 2 million years ago --the Taung child--as a member of the Homo line.

But Olson's analysis is now being challenged.According to Robert B. Eckhardt of Pennsylvania State University in University Park, the paranthropine keystone pattern occurs on about 8 percent of modern ape skulls. This configuration of sutures appears to be a normal variation in facial structure and part of the common heritage of hominoids, or apes and humans, and is not confined to robust australopithecines, concludes Eckhardt in the July 23 NATURE.

He examined the crania of 66 chimpanzees,99 gorillas and 108 orangutans obtained from the U.S. National Museum of Natural History in Washington, D.C., and the Field Museum of Natural History in Chicago. The three groups contained both sexes and ranged in age from infancy to adulthood. Most of the crania had been collected in the wild.

Nasal bone outlines sometimes displayconfusing similarities across different hominoid groups, adds Eckhardt. For example, one chimp had nasal bones resembling those of a recently discovered robust australopithecine even though the two specimens share no other cranial features. The lesson of the survey, he says, is that "the anatomical region including the nasal bones is so highly variable that to abstract a few patterns is seriously to misrepresent reality.'

Olson, however, says his 1985 analysishas not been disproved. "There is certainly variation in hominoid nasal bone anatomy,' responds Olson, "but there is a consistent pattern. More than 90 percent of Eckhardt's specimens fit my previous description [of nasal bone outlines] in hominoid groups.'

On the basis of Eckhardt's finding, saysOlson, the probability is that in 9 out of 10 cases a fossil skull with the keystone pattern will be of the paranthropine lineage.

Olson also holds that Eckhardt misinterpretednasal bone anatomy by concentrating on the skull surface and not the pattern of sutures on the inside of the skull. Olson estimates that only one specimen in the three groups of apes actually displayed a paranthropine pattern.

Photo: The nasal bone keystone pattern on theskull of a modern chimp.