The ground trembled and the sky darkened with clouds of dust as the volcanic eruptions began. Startled, the animals gathered at the water hole—hyenas, saber-toothed tigers, giant elephants —took off in a great stampede. Joining in the flight were small creatures that though they looked like apes, walked upright. Before long, the rain of volcanic ash had completely buried the site and all signs of the life around it.
That dramatic scenario occurred nearly 4 million years ago in East Africa's Great Rift Valley. But last week it was vividly recalled by Anthropologist Mary Leakey, who announced that she and her co-workers had found new and revealing traces of our early roots at the site of that ancient African spa: the actual footprints of one of those man-apes. Radioactive dating showed that the prints had been made some 3.59 million to 3.75 million years ago, a hint the creature may be the oldest-known direct ancestor of man.
Leakey, a small, spunky woman of 64, is the widow of the famed anthropologist Louis Leakey, who died in 1972. Some four decades ago, when she and Louis were beginning their quest for the origins of man, they worked for a time in a remote area of northern Tanzania called Laetolil—the site of her latest find. But after unearthing nothing more than a few distinctly non-manlike animal remains, they moved on to Olduvai Gorge, 25 miles to the north, where their fossil discoveries were to push back man's lineage by at least a million years. In 1975, on a hunch that "we didn't look hard enough," Mary returned to Laetolil. She soon began finding jawbones, teeth and other fossils that were clearly of hominid (manlike) origin. She and her coworkers, including her son Philip, also discovered thousands of fossilized tracks under a layer of ancient volcanic ash that had been eroded by seasonal water. Most were made by animals, but Philip, the younger brother of Anthropologist Richard Leakey (TIME Cover, Nov. 7), spotted several prints that apparently were left by a creature much higher on the evolutionary ladder.
Leakey and her team compared the footprints with some left 80,000 years ago by Neanderthal man, generally accepted as the earliest human prints. Only about 15 cm (6 in.) long, but 11½ cm (4½ in.) across—much wider than either those of Neanderthal or modern man—the Laetolil markings indicate a manlike primate about 1.2 meters (4 ft.) tall that probably walked with what Leakey calls "a slow, rolling gait," like a chimpanzee's. Though there were many animal tracks nearby —including some of knuckle-walking apes—Leakey is "75% certain" that the prints were those of an early ancestor of man's. "The creature," as she calls it (because she cannot tell the sex), was not a hunter. Its plodding ways would seem to have precluded that. Says Leakey: "It probably ate anything and everything it could find: berries, fruits, scavenged meats. In those days, I would have too."