Man has grown older by at least 600,000 years with the discovery of what are believed to be the fossil footprints of an early man called a hominid who lived in Tanzania 3.6 million years ago.
Five hominid footprints and the jawbones and teeth of 20 individuals who appear to be huminids were found in soft volcanic ash exposed a year and a half ago by a river 30 miles south of Olduvai Gorge in northern Tanzania. This is a region in East Africa south of Kenya that has produced so many fossils of early man that it has come to be called "The Cradle of Mankind."
The footprints and fossil bones were found in soft ash buried under 15 feet of a coarser ash rich in a bioite, a form of milax, whose age was dated by radiometric techniques at 3.59 million years. The earliest known hominid fossils before this discovery are 3 million years old.
The announcement of the find was made yesterday at the offices of the National Geographic Society by Dr. Mary D. Leakey, the anthropologist who, with her late husband, Louis, and son, Richard, has had many of the major fossil finds of early humans.
"The general consensus is that these footprints are hominids," Leakey said at a news conference yesterday. "As for me, I'm 75 percetn cetain that they're hominids, but I myself prefer to be 100 percent certain."
Leakey said the footprints will be cast and removed to a laboratory from the site in Tanzania. There they will be examined microspically to make sure they are the prints of hominids and not apes.
If the prints are in fact hominids, Leakey said, they suggest a creature who was about four feet tall. She said that all five of the prints were made by feet that are the "broadest of any hominids we've seen, if they are indeed hominids."
The two most distinct footprints suggest that the feet crossed during walking, one in front of the other, The big toe, the heel and the arch of the foot are clear in these two footprints.
"These footprints tell us what the creature's gait was like," Dr. Leakey said. "He appears to have swayed back and forth when he walked, which means his progress was slow. He did not walk like a modern man."
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Most hominid fossils are between 2 million and 3 million years old. The fossils and footprints decribe four different creatures who range in size from 3 1/2 feet to 5 feet tall. All walked arect, like modern man.
The big difference between hominids and man is brain size. The tallest hominid had a brain about two-thirds the size of a human's. The shortest had a brain no longer than half a human's brain.
Dr. Leeakey said that if the teeth and jawbones found at the Tanzanian site are from hominids they are suggestive of skulls that carried brains "that are quite small, perhaps half the size of human brains.
Most prehistorians believe that only the biggest hominid became man. They think the three smallest hominids became extinct, falling victim to time, predators and climate changes along the way.
The footprints and bones were found by accident, when members of Leakey's party stumbled on a site that had been washed clean at the edge of a river. The prints and bones had been preserved by a series of ancient volcanic eruptions, which covered the entire site in a matter of days.
Together with the hominid prints there were countless footprints of elephants, hyenas, jackals, antelope and rhinoceros. Leakey said the uncovered region appeared to be near a water hole used by all the creatures of the neighborhood, hominids included.