The Sunday TimesPlus

1st June 1997

| TIMESPORTS

| HOME PAGE | FRONT PAGE | EDITORIAL/OPINION | NEWS / COMMENT | BUSINESS

Unearthing the missing link

Oldest known common ancestor of both men and apes found in Uganda, scientists say

Fossils unearthed from ancient rock in Uganda have revealed what scientists say is by far the oldest known common ancestor of both men and apes: a shockingly big, tree-dwelling lug that could hang around comfortably in an upright position, but that walked somewhat awkwardly on all fours when on the ground.

The finding, reported by a diverse international team in a recent issue of the journal Science, dates the remains to 20.6 million years ago. That is about 10 million years before the next oldest viable fossil candidate for a common ancestor. And it is roughly the period in which a great evolutionary split presumably occurred, producing one lineage that would go on to become various kinds of latterday monkeys and another group, called hominoids, that would become modern apes and humans.

If the new analysis is confirmed - and some experts are sceptical - the heretofore uncategorised creature, which the researchers have named Morotopithecus Bishopi, will shatter the widespread assumption that the common ancestors of modern apes and humans in that era were probably small as contemporary gibbons.The find also "really pushes the time scale a long way back," said Terry Harrison of New York University, a scholar of fossils from the Miocene epoch, as the period from 25 million to 5 million years ago is known. "What it means " said Harrison, who was not involved in the work, "is that hominoids had already diverged by 20 million years ago," a development that some had suspected but that remained frustratingly absent from the fossil record.

The Ugandan fossils, which include cranial material parts of the spine and shoulder socket, and remnants of a thigh bone, belonged to an animal about four feet tall weighing 90 to 110 pounds, that was a "cautious climber," according to the researchers. M. Bishopi (named for Moroto, the Ugandan town near which it was found, and W. Bishop, who discovered the first fossils) was "mostly a fruit-eater," said David Pilbeam of Harvard, part of the international team.

The creature’s capacity to hang by its arms while browsing through the heavy forests that covered central Africa at the time may have given it a competitive advantage in dining.

"The general consensus now," said Pilbeam, is that arm suspension allows an animal of substantial weight "to get into parts of trees that others can’t because it can distribute its weight better than animals that place all their weight on top of the branch." Contrary to what might be imagined, the creature probably walked on its palms when travelling on the ground knuckle-walking, experts said, was a later development.

Prior to M. Bishopi, the best fossil evidence of early Miocene ape-like creatures was much more monkey-like. "Very few of the remains," said Bill Kimbel, science director of an American Institute of Human Origins, "approached the anatomy that would have been expected."

Specifically, three critical features that are logically necessary to the eventual development of modern apes and humans were conspicuously missing. For example, any animal that is going to spend an appreciable amount of time in an upright posture needs a fairly stiff lower back. That entails broad, short lumbar vertebrae with bony outcroppings to anchor the spine in muscle, reducing flexibility. (Monkeys, by contrast, have supple, flexible spines adapted for more horizontal postures.) In addition, an arboreal creature that often has its backbone in a vertical position - an essential anatomical prerequisite to walking on two legs - would probably require two other elements: a thigh bone thick enough to absorb a lot of vertical stress, and a shoulder socket that permits ample swivelling movement, especially raising the arms directly over the head to pull up. (Monkeys can’t do this. They climb like cats.) None of the leading candidates for a common hominoid ancestor including the dozen species of ape-like creatures known to have existed 18 million or 20 million years ago, quite fit the bill. The ones that did dated from nearly 10 million years later. As a result, Kimbel said scientists "have been looking for and not finding the creature that would be at the root stock of all living hominoids."

With one possible exception: A group digging around Moroto in the 1960s had turned up the remains of a highly intriguing creature that seemed to satisfy many of the ancestral criteria. But scientists were baffled by its seemingly contradictory features.

The skull, jaw and teeth appeared appropriately primitive. Yet its stiff back seemed a bit too much like modern apes.

In 1994 and 1995, the collaborators whose work is published recently (including researchers from several American universities) set out to revisit the site. They dug up many new skeletal samples apparently belonging to the same enigmatic species, and then subjected their find to rigorous and precise modern geochemical dating methods not available in the ’60s. The result showed that the creature despite its misleadingly modern-looking anatomical features, was nearly 21 million years old.

Several experts remain unconvinced that M. Bishopi constitutes the real paleoanthropological McCoy. "The material, although important and interesting, is very scrappy," said David Begun of the University of Toronto. "It’s very difficult to interpret," and "I wouldn’t go so far as to say this is evidence of modern anatomy."

What is needed, Begun said, "are some parts of the body that will show unambiguous linkages to great apes." The collaboration is enthusiastic about providing just that. We’re going to keep looking in the Moroto localities," said team member Laura MacLatchy of SUNY at Stony Brook, perhaps as early as the end of this year.-LAT-WP


Continue to Plus page 9 - Musical duo shows their gratitude

Return to the Plus contents page

Read Letters to the Editor

Go to the Plus Archive

Sports

Home Page Front Page OP/ED News Business

Please send your comments and suggestions on this web site to
info@suntimes.is.lk or to
webmaster@infolabs.is.lk