Egyptian fossils illuminate primate roots.

Egyptian fossils illuminate primate roots

New fossil finds in Egypt provide an unusually clear glimpse of a creature that now ranks as the earliest firmly established simian species, an evolutionary forerunner of monkeys, apes, and humans. The tiny primate, which weighed only a few ounces, lived approximately 36 million years ago.

"Egypt was once an important center of primate evolution," asserts excavation director Elwyn L. Simons, an anthropologist at Duke University in Durham, N.C. "The best evidence is that the earliest primates came from Africa around 40 million years ago."

The new discoveries, described by Simons in the June 30 Science, follow on the controversial claim by another paleontological team that 45-million-year-old Chinese fossils belonged to a simian species (SN: 4/16/94, p.245). Scientists have extensive skull and tooth remains of the Egyptian primate, Catopithecus browni, but only two jaw pieces and four teeth of the Chinese Eosimias sinensis.

Simons conducted excavations at a site in Egypt's Fayum Desert, about 60 miles southwest of Cairo. He reported his first Catopithecus find, a single, badly crushed skull, in 1990. The latest discoveries, from 1992 and 1993, include four partial skulls. One specimen retains its lower jaw, a rare occurrence for such old and delicate fossils. Examples of all teeth from the front half of the mouth also turned up.

Catopithecus bears several anatomical traits that place it squarely in the simian realm, Simons maintains. Its front teeth extend vertically and have a spoonlike shape, rather than jutting forward and displaying the conical shape typical of prosimians. Also, in typical simian fashion, the two top front incisors are larger than the pair just behind them, the reverse of the pattern in bottom incisors.

Moreover, Catopithecus has enclosed eye sockets and a fused forehead bone. In prosimians, such as the modern lemur, the eye sockets consist of open rings of bone, and the forehead has two distinct halves.

The new fossils also shed light on whether lemurlike adapids or tarsierlike omomyids living between 55 million and 36 million years ago qualify as simian ancestors. The relative size, shape, and orientation of teeth in Catopithecus bear a closer resemblance to the dental features of adapids, Simons argues.

Greg Gunnell, an anthropologist at the University of Michigan in Ann Arbor, agrees that Simons' finds establish Catopithecus as the earliest known simian. Eosimias, the Chinese animal, remains an evolutionary enigma, based on the fragmentary remains uncovered so far, Gunnell adds.

Mary R. Dawson of the Carnegie Museum of Natural History in Pittsburgh, who helped excavate the Chinese finds, says more Eosimias fossils were recovered in fieldwork last May. She and her colleagues will describe the new specimens at a scientific meeting in November.