MARY LEAKEY, EMINENT FOSSIL-FINDER.

Byline: John Noble Wilford The New York Times

Mary Leakey, matriarch of the famous fossil-hunting family in Africa whose own reputation in paleoanthropology soared with discoveries of bones, stone tools and the footprints of early human ancestors, died Monday in Nairobi, Kenya. She was 83.

Her family announced her death but did not give the cause, saying only that she died peacefully.

Over half a century, Mary Leakey labored under the hot African sun, scratching in the dirt for clues to early human physical and cultural evolution. Scientists in her field said she set the standards for documentation and excavation in paleolithic archeology. They spoke of hers as a life of enviable achievement.

``She was one of the world's great originals,'' said Alan Walker, an anatomist at Pennsylvania State University who has long excavated fossils with the Leakey family. ``Untrained except in art, she developed techniques of excavation and descriptive archeology and did it all on her own in the middle of Africa. It was an extraordinary life.''

In a biography of the Leakey family, ``Ancestral Passions,'' published last year by Simon & Schuster, Virginia Morell characterized Mary Leakey as ``the grand dame of archeology.''

Beginning in the 1930s, Mary Leakey and her late husband, Louis, awakened the world to Africa's primary place in human origins with their spectacular discoveries and increasingly pushed back the time of those origins much earlier than had been thought. Until then, many scientists still believed the human birthplace would be found in Asia.

She discovered the skull of Proconsul africanus, an apelike ancestor of both apes and early humans that lived about 25 million years ago. In 1959, her discovery of a well-preserved skull of a hominid, a member of the extended human ancestral family, brought fame and substantial financial backing to the Leakeys. A few years later, the two Leakeys uncovered the fossils of the first known member of the genus Homo habilis, or ``able man,'' in recognition of the many stone tools found among the bones.

From then on, the name Leakey was synonymous with the study of human origins. The flamboyant Louis seemed to know just where to look to find revealing fossils; the envious spoke of ``Leakey's luck.'' Meanwhile, Mary Leakey worked in her husband's shadow, seeing to the plodding excavations and meticulous documentation of their finds.

``Louis was always a better publicist than scientist,'' said E. Barton Worthington, a fellow of the Royal Geographical Society in London and former African explorer. ``Mary was the real fossil hunter.''

After Louis Leakey's death in 1972, Mary Leakey overcame some of her natural shyness to assume direction of the family fossil enterprise, which by then one of their sons, Richard, joined as an expedition leader. Her operations centered on Olduvai Gorge and Laetoli, both in Tanzania. On the arid plain of Laetoli, she made her most sensational discovery in 1978: the earliest footprints of a human ancestor.

As often happens, the discovery of the prints was made by chance - more Leakey luck. While tossing dried elephant dung in a playful camp fight, one scientist on Mrs. Leakey's expedition fell down and saw in the gray surface some curious indentations. They were imprints of raindrops and animals, now hardened to stone and recently exposed by erosion and weathering.

After further exploration, scientists determined that the tracks were made about 3.7 million years ago. The animals had walked over volcanic ash when it was damp from rain, leaving impressions of their feet. The wet ash set like concrete and was later covered over by more ash and silt. There the tracks remained to be found by dung-throwing scientists.

It was two years before a scientist uncovered a heel print that hinted of an even more significant find. It seemed to belong to a hominid. On Aug. 2, 1978, Leakey spent three hours examining one of the clearest of these prints. She cleaned the crevices of the print with a small brush and dental pick. All the important elements were preserved: heel, toes and arch. She appraised the print from every possible angle.

Finally, Leakey stood up from her work, lit a cigar and announced, ``Now this really is something to put on the mantelpiece.''

She was at last sure that a hominid had left this print and a trail of prints extending more than 75 feet across the plain. Two and possibly three individuals had walked this way 3.7 million years ago: the larger one, presumably a male; the smaller one, presumably female, and an even smaller individual, perhaps their child, whose prints are sometimes superimposed on the others.

Somewhere along the way, as Leakey noted, the female appeared to pause and turn to her left. She might have sensed danger, possibly from a predator or the rumble of a volcanic eruption nearby. Then she resumed her walk to the north.

``This motion, so intensely human, transcends time,'' Leakey wrote in the National Geographic Magazine. ``A remote ancestor - just as you or I - experienced a moment of doubt.''

These evocative footprints are the earliest known traces of human behavior. At the time, the discovery established that human ancestors had begun walking upright much earlier than previously thought, long before the evolution of larger brains. Whether upright walking preceded the larger brain, or vice versa, was still a much-debated issue among scholars.

With the discovery of a species called Australopithecus afarensis, based on the famous Lucy skeleton, the most likely identity of these prehistoric strollers was established. The species lived between 3.9 million and 3 million years ago, and from the fossils paleontologists have determined that they were as capable of walking upright as modern humans.

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Photo

Photo: Mary Leakey, right, and her husband, Louis Leakey, excavate prehistoric artifacts at a dig in Tanganyika, Tanzania, in 1961.

The New York Times