Fossil finds diversify ancient apes.

Fossil Finds Diversify Ancient Apes

The Miocene period of 25 million to 10 million years ago was marked by the appearance of ape-like ancestors of modern apes and humans, known as hominoids, in Africa, Asia and Europe. Although questions and debates persist about the evolutionary relationships of various fossil hominoids to one another, two new types of the early apes have now entered the scene.

The fragmented fossil skulls, jaws and limb bones found along Lake Turkana in northern Kenya suggest that there was a greater diversity of hominoid lines than previously believed, report Richard Leakey and Meave G. Leakey in the Nov. 13 NATURE. The new material also supports arguments for the spread of hominoids from Africa to Asia early in the Miocene period, say the investigators, both of the National Museums of Kenya in Nairobi.

The age of the sediments in which the fossils were found has not been determined yet, but various animal remains in the same sediments are similar to those uncovered at other east African sites dated at 16 million to 18 million years old.

"The most interesting thing about these finds," paleontologist Peter Andrews of the British Museum in London told SCIENCE NEWS, "is that they show the number of hominoid species during the Miocene to have been rather greater than was previously known." It is not clear how the new hominoids fit into the evolutionary scheme, adds Andrews; answering this "key question" requires a closer examination of the remains, particularly the structure of the jaws and tooth enamel.

Nevertheless, say the Leakeys, when compared with other fossil hominoids, the fossils represent two distinct genera. The larger, baboon-size ape was dubbed Afropithecus, and the slightly smaller ape was named Turkanapithecus.

Afropithecus, explain the researchers, displays the characteristics of a variety of hominoids combined in a single, distinctive category. Its palate is shallow, long and narrow and the nasal passage is "remarkably narrow and high." The forehead inclines steeply to a long muzzle. The size of the canine teeth of the best-preserved specimen suggests that it was a male.

Another 17-million-year-old east African hominoid recently discovered by Richard Leakey and Alan Walker of Johns Hopkins University in Baltimore (SN: 12/7/85, p.360) is also a representative of Afropithecus, according to the investigators. Leakey and Walker originally assigned the find to another genus, Sivapithecus. There are two controversial lines of thought about Sivapithecus: Some scientists argue that it was an early African ape and human ancestor that migrated to Asia, while others contend it developed along a separate family line that led to Asian orangutans.

The new finds do not resolve this conflict, but the Leakeys now believe that Sivapithecus was restricted to Asia. They hold, however, that ancestral forms of this group first appeared in Africa.

The second new hominoid, Turkanapithecus, is short-faced with a narrow palate and tooth rows converging toward the back. Little is known about the cranial features of small-bodied Miocene apes, but the teeth of Turkanapithecus clearly separate it from other hominoid categories, say the researchers.

One possibility, says paleontologist Terry Harrison of New York University, is that Turkanapithecus is related to a European hominoid known as Oreopithecus. Harrison discusses new 17-million-year-old Oreopithecus specimens in the December AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY.

He has seen the Leakeys' new finds, but says it is not yet clear if there is a link between the African and European apes. "The ancestry of Oreopithecus appears to be from east Africa," notes Harrison.

The first Oreopithecus fossil was discovered in 1872, and since then a number of well-preserved partial skeletons have been unearthed. Still, much about this group of hominoids is poorly understood. They apparently evolved on a group of islands near northern Italy over a period of 5 million to 10 million years. Oreopithecus remains reveal a number of curious specializations, says Harrison, including teeth used for browsing combined with human-like canines. It is a mystery how this line of hominoids settled on islands, he adds, since they had long arms and short legs ill-suited for swimming.

The Leakeys also express puzzlement that Afropithecus and Turkanapithecus have not been found at more abundant Miocene ape sites in western Kenya. It may be that different environments fostered different hominoids. "These new fossils come from a nonforested part of Kenya," says the British Museum's Andrews. "This is a new area and habitat for early hominoids."