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Fossil find creates ancient ape puzzle.

Fossils find creates ancient ape puzzle

The first discovery of substantial limb remains from an ancient ape known as Sivapithecus, unearthed from 9- to 11-million-year-old sediments in Pakistan, raises perplexing questions about the creature's evolutionary standing.

Although previously excavated skull fragments indicated Sivapithecus was an early cousin of the orangutan, two new upper-arm bones more closely resemble those of chimpanzees, gorillas and many monkeys, assert anthropologists David Pilbeam of Harvard University and his colleagues. The shape of these nearly complete bones suggests Sivapithecus principally walked on all fours rather than spending much of its time climbing in trees and hanging from branches, the scientists report in the Nov. 15 NATURE.

Two possible evolutionary scenarios now exist for Sivapithecus, they point out. One argument supports an ancestral link between the ancient Asian ape and modern orangutans based on shared features of the face, nose and palate, while maintaining that limb similarities between Sivapithecus and African apes represent independent developments. The other proposes that Sivapithecus was not clearly related to any living ape and that its facial resemblance to orangutans fails to indicate a common ancestry.

Individual variation in the shape and size of bones among ancient and modern apes belonging to the same species creates serious problems for anthropologists attempting to reconstruct evolutionary relationships (SN: 8/18/90, p.106). Thus, Pilbeam and his co-workers maintain, further fossil discoveries of Sivapithecus probably will not reveal its definitive ancestral standing.

The two arm bones possess curved shafts similar to those of two groups of ancient African apes as well as most modern, knuckle-walking monkeys, the researchers note, whereas tree-dwelling apes such as the modern orangutan have straight upper-arm bones. The elbow joints resemble those of modern apes, suggestinig that specialized anatomical features for climbing and suspension also developed in animals that spent most of their time on the ground, the anthropologists contend.

They add that previous fossil finds indicate Sivapithecus also shared with living African apes some important hand and foot features that aid in four-legged walking.

Sivapithecus dates to between approximately 13 million and 7 million years ago. Its remain have turned up in Greece, Turkey, India and Pakistan. Once considered a precursor of humans, it was first aligned with orangutans about 10 years ago.
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Title Annotation:Sivapithecus
Author:Bower, Bruce
Publication:Science News
Date:Nov 17, 1990
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