New Ape-Fossil Types Found : Discovery May Fill Gap in Earliest Human Link

Fossils from two previously unknown types of apes that may be ancestors of humans have been found along the western shore of Lake Turkana in Kenya, anthropologist Richard E. Leakey announced. He said the fossils probably date from the early Miocene era, about 16 to 18 million years ago.

The new primates may fill a crucial gap in the fossil records that would link the earliest known primates to humans, Leakey said in an interview in Los Angeles this week. Anthropologists have long believed that an ancestor of man lived in Africa during the early Miocene, but they have not been able to find fossils of such a primate until now.

Scientists have been particularly eager to obtain primate fossils from the Miocene era in Africa because only one genus, called Proconsul , had been previously found. And for many years, scientists believed that this baboon-like hominoid was an ancestor of man simply because no better candidate existed.

But by 1984, most scientists had concluded, according to anthropologist David Pilbeam of Harvard University, “that its form was too specialized for it to be an ancestor of any living hominid.” In short, Proconsul was an evolutionary dead end that eventually disappeared completely.

The discrediting of Proconsul as a human ancestor left a large gap in the fossil record, according to anthropologist Jeffrey H. Schwartz of the University of Pittsburgh. The only available candidate to fill the gap was an orangutan-like primate called Sivapithecus , which also dated from the Miocene era.

Sivapithecus has been found only in Asia, however, and most paleontological evidence indicates that the ancestor of humans must have lived in Africa.

Then in 1983, Leakey found a skull fragment at Buluk, on the eastern shore of Lake Turkana, that he and anatomist Alan Walker of Johns Hopkins University identified as Sivapithecus. The discovery of Sivapithecus in Africa would have made it a better candidate for a human ancestor. But that identification has been very controversial and many scientists have refused to accept it.

Leakey said he now believes the Buluk primate to be identical to one of the new specimens he found at Kalodirr. Either of the new genera could be an ancestor of man, he speculated.

Suggests Possibility

Alternatively, the fact that at least three genera now are known to have existed in the early Miocene era could suggest that an even larger number of genera existed simultaneously, he added. That leaves open the possibility that an as-yet-undiscovered genus could be man’s ancestor, Leakey said.

Schwartz added in a telephone interview Wednesday that the new fossils further suggest that the primate lineage including man and the chimpanzee split off from the lineages of other large apes at a point much earlier in history than had been thought.

The two new primate fossils were among the first specimens taken from a newly discovered deposit of Miocene fossils that dwarfs previously known Miocene sites in Africa, Leakey said. The new site at Kalodirr contains about 500 square miles of fossil-bearing sedimentary deposits, he said. All previous Miocene fossils obtained in eastern Africa were taken from locations whose areas totaled no more than 30 square miles, he added.

Report Published

Leakey, director of the National Museums of Kenya, and his anthropologist wife, Meave, report the new fossil discoveries in today’s issue of the British journal Nature.

The two new specimens are quite different. The larger of the two, Leakey said, “is a mixture of the long, distinct muzzle of Sivapithecus and a number of things never seen before.” It is identical to the Buluk specimen, and Leakey has named it Afropithecus.

The second specimen is a short-faced small ape, about the size of Proconsul , distinguished from all others by the shape of its teeth. Leakey calls it Turkanapithecus .

Not everyone agrees with Leakey and Schwartz’s interpretation of the new discoveries, however. A small group of scientists believe that the separations of the lineages occurred in the last 10 to 13 million years, long after the early Miocene era. Such researchers include biochemist Vincent M. Sarich of the University of California, Berkeley, who has used the techniques of molecular biology to date the divergence of the different species of apes based on differences in the DNA of living primates.

‘Rest Are Extinct’

“The probability that any Miocene species has a living relative is damned near zero,” Sarich said in a telephone interview. “The molecular data indicate that only one lineage made it and that all the rest are extinct.”

Leakey, however, argued that the molecular biologists “are going to have to readjust their thinking” as a result of his new discoveries.

In any case, Sarich agreed that the new site at Kalodirr has great scientific importance.

“What I would really like to see from the new site,” he said, “are parts of the body other than the cranium.”

It is these parts that enable scientists to precisely define lineages, he said.

Most scientists believe that the scarcity of body parts reflects the fact that most carcasses of primates were devoured by scavengers who ate everything but the exceptionally hard jaw and teeth.

Used Airplane

Leakey discovered the new site, which he said is “a long way from nowhere,” when he flew over it last year in his airplane and later visited it on foot for a day. He began excavations in January and discovered the fossils in February.

Leakey in 1984 also used radar imagery from the U.S. space shuttle to try to locate Miocene deposits. Results from that attempt were unsatisfactory. A second such experiment was aboard the ill-fated Challenger when it exploded in January.

He said that he has “an enormous program of future work” planned for the site and that the work will involve many other scientists.

Leaky was in Los Angeles on a fund-raising trip. Philanthropist Gordon Getty has pledged $5 million to the L.S.B. Leakey Foundation, named after Richard Leakey’s anthropologist father, on the condition that an equal amount can be raised from other sources. The grant, foundation officials said, would be the largest ever given to support anthropology.