Fossil Primates Emit Elusive Species Clues

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Fossil primates emit elusive species clues

Paleoanthropologists who attempt to decipher the evolutionary history of humans and other primates, express increasing skepticism concerning their ability to identify long-extinct species from fossil evidence alone. New glimpses of the pitfalls of trying to squeeze primate species out of bone emerged last week at the American Association of Physical Anthropologists' annual meeting in Milwaukee.

Even the concept of "species" provokes dispute among investigators. Many assume a species consists of organisms that look alike and can mate to produce fertile offspring. But skeletal anatomy often changes rapidly in response to environmental influences, making a simple list of skeletal traits unreliable as a guidepost to species recognition, asserts William H. Kimbel of the Institute of Human Origins in Berkeley, Calif.

Moreover, the primate fossil record -- largely made up of partial skulls and teeth -- often yields underestimates of the number of related species represented in a collection of bones, says Ian Tattersall of the American Museum of Natural History in New York City.

Tattersall and Jeffrey Schwartz of the University of Pittsburgh examines 77 skulls from the seven modern lemur species making up the genus Lemur. Each species has distinctive external features, Tattersall notes. But identifying the species on the basis of skulls and teeth alone proved extremely difficult, he reports. In fact, Tattersall contends that most investigators would classify no more than three species in this skeletal sample. The major problem: Different lemur species share numerous anatomical features of the head and teeth that apparently evolved independently, thus shrouding the boundaries between species.

"The genus is the [meaningful] category with regards to teeth and crania, Tattersall says.

He argues that cranial and dental analyses may have led to an inappropriate lumping together of separate species of hominids, the evolutionary family that includes modern humans. For instance, he holds that fossils classed as Homo erectus -- a hominid species that lived in Africa and Asia from about 1.6 million to 300,000 years ago -- actually encompass several species, only one of which represents a direct human ancestor (SN: 4/25/87, p.264).

Terry Harrison of New York University concurs with Tattersall's cautions about deriving species from bones, but he sees no reason to split up H. …