Fossil Jawbone Is From New Ape Species, Scientists Say : Paleontology: 13-million-year-old specimen found in Namibia may shed light on human evolution. It is the earliest evidence of primates below the Equator in Africa.

A 13-million-year-old fossil jawbone discovered in Namibia appears to be that of a new species of ape and may open a new window on the origin and evolution of humans, an international team of researchers reports today.

The jawbone, from a primate that lived shortly before the evolutionary lines of humans and apes split, is the first such specimen found south of the Equator in Africa.

Most previous fossils from this era, called the Miocene Epoch, were found in eastern Africa, above the Equator, especially in Kenya and Uganda, and researchers had believed much of the early evolution of human predecessors must have occurred in that area.

The discovery, reported in the British journal Nature, suggests that evolution was occurring throughout the African continent. The fact that the Miocene primates lived over an even wider geographic range than had been supposed attests to their versatility and adaptability.

“Obviously, these pre-ape and pre-human animals ranged much farther than scientists had ever known before” and had a much greater diversity in appearance, said anthropologist Glenn C. Conroy of Washington University in St. Louis, the leader of the expedition.

“When we had only a few fossil bones, we developed a very simple evolutionary path (for humans),” he said. “Every time we find a new fossil like this, the situation becomes more complex.”

“It’s a new kind of fossil ape that is unlike anything that we’ve known previously from Kenya or from Europe and Asia,” said anthropologist Brenda Benefit of Southern Illinois University in Carbondale. “We don’t really understand its relationship to the great apes or to humans.”

The new species, named Otavipithecus namibiensis, may be a direct ancestor of apes and humans or an evolutionary dead end that shared a common ancestor with apes and humans, Benefit said. Making that distinction will require the discovery of more specimens and other bones.

The plains of Kenya, particularly around the Olduvai Gorge, have been a fertile site for excavating well-preserved Miocene fossils, but few other sites in Africa have the requisite geological properties for proper preservation, such as the abundance of limestone or other sedimentary rock. Even though scientists suspected that early primates lived in the southern regions, they have found few locations where remains might be preserved.

Conroy suspected that the limestone Otavi Mountains of northern Namibia might prove to be another source of Miocene remains, and brief surveys had shown many fossils in tailings from mines there. He organized an expedition to the area last summer with colleagues from the Museum of Natural History in Paris, the University of Lyon and the American Museum of Natural History in New York City.

The jawbone was found by paleontologist Martin Pickford of the Museum of Natural History only 30 minutes after the group arrived at the site. He discovered it on a large chunk of limestone that had been removed from the mine. Freeing it was a painstaking process that took months, during which vinegar was gently brushed onto the specimen to slowly dissolve the limestone. Ironically, despite the ease with which they located the jawbone, they found no other specimens of hominoids--a category that includes humans, apes and their ancestors--during their stay.

The fossil is the right side of the animal’s lower jaw and contains several teeth. The size of the teeth indicates that Otavipithecus was about the size of a small chimpanzee, weighing about 35 pounds. Because a wisdom tooth had emerged from the gums, the researchers estimated that, based on chimpanzee maturation rates, the creature was about 10 years old.

The thin layer of enamel on the teeth and the small amount of wear suggest that it subsisted on foods such as leaves, berries, seeds, buds and flowers.

Conroy speculates that the hominoid died in a cave because the jawbone was found with fossils of at least 37 other mammals, mostly night-feeding rodents, insect-eating mammals, bats and the like. Such an accumulation of bones would most likely be found in a cave, where they would be deposited by owls and other predators.

The smallish Otavipithecus could have been dragged into the cave by a larger predator, he speculated, or fallen into it and been unable to get out.