Name ID 1240
Prominent Hominid Fossils
Discovered in 1978 by Paul Abell at Laetoli in Tanzania. Estimated age is 3.7 million years. The trail consists of the fossilized footprints of two or three bipedal hominids. Their size and stride length indicate that they were about 140 cm (4'8") and 120 cm (4'0") tall. Many scientists claim that the footprints are effectively identical to those of modern humans (Tattersall 1993; Feder and Park 1989), while others claim the big toes diverged slightly (like apes) and that the toe lengths are longer than humans but shorter than in apes (Burenhult 1993). The prints are tentatively assigned to A. afarensis, because no other hominid species is known from that time, although some scientists disagree with that classification.
Dente, Jenny Mary Douglas Nicol Leakey 1913-1996
Page Number: 13
Extract Date: 1974-1978
Mary first visited Laetoli, an area 30 miles south of Olduvai, in 1935 but didn't establish a permanent site there until 1974. In July of 1975, the first serious excavations began. Early digs revealed an abundance of hominid materials which were dated (by finding the age of overlying lava flows) at more than 2.4-million-years-old, placing them much earlier in time than any found at Olduvai. An even more exciting find occurred in 1976 when visitors to the site accidentally stumbled upon what seemed like fossilized animal prints. "Site A," as it came to be called, ended up containing almost 18,400 individual prints.
Then, in 1978, two short parallel trails of hominid prints were found by a man named Paul Abell, again by accident. Eventually, these trails were found to extend more than 80 ft in rock that was dated at 3.6-million-years-old. The prints were made by two individuals walking side-by-side, with a third deliberately stepping in the footprints of the largest individual; Mary liked to believe that they were of the genus Homo, but other scientists, including Donald Johanson (of "Lucy" fame) think they might be of the Australopithecus line. (In fact, this was a big point of contention in a vicious feud between Leakey and Johanson.)
Despite all of the questions that the footprints raised, and that remain unanswered even today, Mary deemed their discovery as one of the most important made in her lifetime. For instance, the absence of stone tools at the site leads scientists to believe that bipedalism preceded the use of tools. Mary later explained, "The discovery of the trails was immensely exciting-something so extraordinary that I could hardly take it in or comprehend its implications for some while." After their excavation, Mary finished her stay at Laetoli, ending also the most memorable stage of her archaeological career.
For several decades Laetoli had just missed as a hominid fossil site. Louis Leakey had a try there in 1935, but came up emptyhanded. He did not know that a tooth he had sent to the British Museum labeled as a baboon's was a hominid canine. Not only was it the first adult australopithecine tooth ever found, but it was the first of any kind since the discovery of the Taung Baby. Nevertheless, it lay unnoticed in the Museum collection until 1979, when it was spotted and properly identified by White.
Leakey, meanwhile, not realizing that he had had in his hand the oldest hominid fossil then known, packed up and moved to Olduvai. He was followed at Laetoli in 1938-1939 by a German named Kohl-Larsen, who recovered a bit of an upper jawbone with a couple of premolars in it, and a well-preserved alveolus - or socket - for a canine tooth.
The trouble with those early Laetoli finds was that they were far too old and far too primitive for anyone then to dream that they were not apes or monkeys; the imagination of the 1930s was simply not elastic enough to accommodate them, even though that same imagination was saying to itself, 'Look deeper into time for older ancestors.' This is an odd, schizophrenic view that still persists today.
By 1974, when Mary Leakey decided to have a go at Laetoli, her mind at least was ready to recognize and accept very old specimens of Homo. When one of the Leakey-trained Kenyan field experts, Karnoya Kimeu, took it upon himself to cut a road in to the deposits through the thicket and came out with a hominid, Mary Leakey moved in with a team of her own. In the next couple of years she or her workers found forty-two teeth, some of them associated with bits of jawbone. One in particular, LH-4 (Laetoli Hominid 4), was a fine specimen, a mandible with nine teeth in place.
But what sets Laetoli apart from every other site in the world is some footprints that have been found there, certainly one of the most extraordinary cases of preservation and discovery in all of paleoanthropology.
Laetoli has a nearby volcano, Sadiman, that is extinct today. Not quite four million years ago it was active. One day it spat out a cloud of carbonitite ash. This stuff has a consistency not unlike that of very fine beach sand, and it powdered down over the surrounding landscape in a layer that reached a thickness of about half an inch before the eruption stopped. This fall of superfine cinders must have been extremely unpleasant for the local animals and birds while it was coming down, but there is no evidence that it did more than make them uncomfortable, because they stayed in the area. That first puff of ash - probably not lasting more than a day - was followed by a rain. The ash became wet and, almost like a newly laid cement sidewalk, began taking clear impressions of everything that walked across it: elephants, giraffes, antelopes, hares, rhinos, pigs. There were also terrestrial birds like guinea fowl and ostriches, and even the small tracks of millipedes.
In the hot sun of Laetoli the wet ash layer quickly dried and hardened, preserving the footprints that crisscrossed it. Then, before it could rain again, Sadiman spoke a second time. Another cloud of ash drifted down, covering the first and sealing in the footprints. This happened a number of times over a period estimated to have been no longer than a month, producing a single volcanic tuff about eight inches thick. .But because of the periodic puffing of Sadiman and the periodic hardening of the ash that fell, the tuff is actually composed of between a dozen and two dozen distinct thin layers. Some of these layers have been exposed recently by erosion, and are visible here and there at Laetoli in the form of a gray substrate wherever the mat of coarse turf above them has been carried off.
One afternoon in 1976, some of the more boisterous members of Mary Leakey's field team were amusing themselves by throwing hunks of dried elephant dung at each other. This may seem a peculiar pastime, but recreational resources are limited on paleontological digs, and there are times when young spirits need to blow off steam. One who felt this urge was Andrew Hill, a paleontologist from the National Museum of Kenya, who, while ducking flying dung and looking for ammunition to fire back, found himself standing in a dry stream bed on some exposed ash layers. One of these had some unusual dents in it. When Hill paused to examine them, he concluded they probably were animal footprints. That diagnosis was confirmed when a larger area was surveyed and other prints found. But no serious effort was made to follow up this extraordinary discovery until the following year, 1977, when a number of large elephant tracks were found by Mary Leakey's son Philip and a co-worker, Peter Jones, and alongside them some tracks that looked suspiciously like human footprints.
The world heard about the footprints later that year when Mary Leakey came to the United States to report on them in a series of press conferences and interviews. To many it seemed almost inconceivable that anything so ephemeral as a footprint should have been preserved for so long. But Mary was positive about the hominid ones. She went on to describe the latter as having been made by a creature that was an imperfect walker; the prints indicated that it had shuffled. She also reported the probable presence at Laetoli of knuckle-walking apes and the existence of a water hole around which the animals and birds appeared to have clustered. She even saw some evidence of panic in the tracks, suggesting that the animals had been fleeing the eruption.
Those revelations by Mary Leakey electrified everybody who heard them. She resolved to devote much of the next season's effort at Laetoli to footprints, and asked the American footprint expert Louise Robbins to join her team. White went to the Laetoli site for the first time that year, and found three other young scientists there: Peter Jones, Paul Abell and Richard Hay. These men had some doubts about Mary's interpretation of the footprints. White questioned the presence of knuckle-walking apes; he had examined those prints and said that they had been made by large extinct baboons that walked flat-footed. Jones said there had been no panicky exodus from the area, because birds, which could have flown away easily and quickly, continued to walk about in the ash it was crisscrossed with their tracks. Hay could find no evidence of a water hole.
These disagreements made for a good many nights of heated argument in camp, during which the supposedly human footprints had their ups and downs. No one could agree on them. Then Paul Abell, prospecting alone one day, found a broken impression - but a much clearer one - that he said he was quite confident was a hominid print. White and Jones made some Polaroid shots of it and came back with a strong impression that Abell was right. They recommended that excavation in the area be started immediately. But Louise Robbins, the footprint expert, examined it and declared that it was the print of a bovid (a hoofed animal). She told Mary Leakey that further investigation would be a waste of time. The men objected.
By then Mary Leakey had become thoroughly exasperated by all the arguing that had been going on. She announced that there would be no excavation. Jones, now convinced that it was a hominid, continued to plead with her for permission to make an excavation. A very small one, he said, was all he asked. Mary was adamant. Louise Robbins, the authority, had spoken; there was too much incomplete excavation at the site already. If there was going to be any digging, let it be done by somebody who had nothing better to do. She pointed to Ndibo, the maintenance man, the man in camp with the least archeological training.
Ndibo, however, proved equal to the task. He returned to camp the next day and reported not one, but two footprints. One was very large. He held his hands up, about a foot apart.
'Those Africans are always exaggerating,' said Mary. But she did go out to have a look, and there they were. White was permitted to start an excavation.
The direction of the prints indicated that their maker had been walking north under some sections of turf that had not yet been eroded. Because of the dense tangle of roots at the bottom of the turf, the task of exposing a clear ash surface without destroying it - not to mention the exact ash out of a dozen or more thin layers of it turned out to be extraordinarily difficult. But Tim is an extraordinarily patient and determined man. He found another print, and then another. He proceeded to protect the prints by hardening them with a preservative, which he poured into them in very small amounts, letting the material dry and then strengthening it by adding more. Working with agonising slowness, he inched his way farther and farther into the turf and discovered that the trail consisted of the tracks of two hominids.
Now he had the riveted attention of the entire camp. Others joined the work and ultimately were able to reveal more than fifty prints covering a distance of seventy-seven feet. Louise Robbins, her interest in the footprints suddenly rekindled, issued another opinion: indeed there were two hominids; they were probably walking together; one (with slightly larger prints) was a male; the other, possibly pregnant she said, was a female; on the evidence of the prints, this type of hominid had been an erect walker for at least a million years.
These are entertaining speculations. There is no way of telling what sex the makers of the footprints were, if one was pregnant, or how long their ancestors had walked erect. The hard truth is that 3.7 million years ago erect hominids of indeterminate sex did walk through fresh-fallen ash at Laetoli and leave an imperishable record of their passing. After seventy-seven feet their trails disappeared under the overlying ash; the particular layer that marked it has been washed away. Tim's work on the footprints stopped at that point, which also marked the end of the season. But he felt strongly that the trail could be picked up again a little farther along and that it would yield more prints if proper excavation were carried out. Work in that direction was done in 1979 by Ron Clarke, and the trail picked up again.
Tim was not a party to this further work. His arguments with Louise Robbins over interpretation of the footprints have made him as unwelcome now at Laetoli as he is at Lake Turkana - a pity, because in each instance he was only trying to help the proprietors.
Tim's concern today is that as more prints are found, they be handled with the utmost care. They are supremely fragile, and the slightest mistake in excavating them can destroy them completely. Some have already been damaged. They are not like fossils, those rocklike models of durability. They are only spaces, mere shapes in a relatively soft and frangible matrix. If that matrix is nudged incorrectly, it will crumble - and the footprints will be gone.
But, by a wildly improbable linkage of random events, they are there. Sadiman had to blow out a particular kind of ash. Rain had to fall on it almost immediately. Hominids had to follow on the heels of the rain. The sun had to come out promptly and harden their footprints. Then another blast from Sadiman had to cover and preserve them before another obliterating shower came along.
All this had to happen over a period of only a few days. And the volcano had to synchronise its activity with that of the seasons. If its bursts had not come just when they did - at the beginning of the rains - the footprints would not have been preserved. A month or two earlier, during the dry season, the ash would not have had the consistency to take a sharp imprint. It would have been a hopelessly blurry one, a mere dent, like the one a passerby today makes in the dry sand on the upper margin of a beach. If it had come later, at the height of the rainy season, it is overwhelmingly likely that there would have' been too much rain; the footprints would have been washed away before they could have been baked hard by the sun. Indeed, there had to be just what the beginning of a rainy season produces: sporadic showers interspersed with intervals of hot sun.
All things considered, the preservation and recovery of the Laetoli footprints are nothing short of a miracle. They confirm without a shadow of a doubt what Lucy confirmed at Hadar: that hominids were fully erect walkers at three million B.C. and earlier. At Hadar the evidence is in the fossils, in the shape of leg and foot bones. But at Laetoli, where the fossil remains - some extremely scrappy and enigmatic postcranial bits, jaw parts, and some teeth - are of very poor quality, there is no way without the footprints of deducing how those hominids got around.
'Make no mistake about it.' says Tim. 'Thev are like modern footprints. If one were left in the sand of a California beach today, and a four-year-old were asked what it was, he would instantly say that somebody had walked there. He wouldn't be able to tell it from a hundred other prints on the beach, nor would you. The external morphology is the same. There is a well-shaped modern heel with a strong arch and a good ball of the foot in front of it. The big toe is straight in line. It doesn't stick out to the side like an ape toe, or like the big toe in so many drawings you see of australopithecines in books.
I don't mean to say that there may not have been some slight differences in the foot bones; that's to be expected. But to all intents and purposes, those Laetoli hominids walked like you and me, and not in a shuffling run, as so many people have claimed for so long. Owen Lovejoy deduced all that from studying the Hadar bones. Now the footprints prove him right. I think they rank with the most wonderful and illuminating discoveries in decades. Although it didn't end too happily for me, I'm still grateful that. I was lucky enough to have participated in the work on them.'
Mail and Guardian
Extract Author: ELISABETH LICKINDORF
Extract Date: December 20 1999
Dr Ronald Clarke used circus chimpanzees to prove his theory about the Laetoli footprints in Tanzania.
ELISABETH LICKINDORF reports
TWENTY years ago, Dr Ronald Clarke was invited by famed palaeoanthropologist Mary Leakey to continue an excavation begun at Laetoli in Tanzania.
An American chemistry professor from Rhode Island, Paul Abell, had discovered a hominid heel impression in 3,6-million-year-old volcanic tuff, or sediment formed out of volcanic ash. Subsequent excavation by Tim White of the University of California at Berkeley uncovered the first footprints of a trail made, apparently, by two individuals.
Clarke accepted Leakey's invitation -- and inadvertently entered an arena of fierce debate.
The prints were clearly made by individuals walking bipedally (upright on two legs) but Leakey and Clarke differed in their interpretations. Says Clarke, "I was struck by the fact that the prints did not seem fully human: there was separation of the big toe from the other toes, and, behind the end of the big toe, a smallish round impression that looked like a toe.
"Mary -- advised by other experts -- insisted it was Homo, and that the second of the two trails must have been made by one individual walking in another's footprints. I, on the other hand, thought the prints were [made by one creature:] ape-like with long toes -- not fully human."
Public outcry greeted Clarke when he stated his views in 1985 at the conference celebrating the 60th anniversary of the Taung discovery, and he didn't publish them. But he was not convinced he was wrong. Later that year he arranged an experiment with the Boswell Wilkie Circus in Johannesburg -- and a friendly trainer -- to coax a female and a male chimpanzee to walk next to each other bipedally over wet sand.
"The circus chimps produced prints that looked like the Laetoli footprints," Clarke recalls. "Not only did those of the male look similar -- big toe aligned with the others plus the 'apparent' toe within, caused by the imprint of a joint -- but also the female had a completely different footprint. She was more timid -- she dug her heels in and spread her big toe wide and kicked up a lot of sand -- whereas he was confident and tended to walk with his big toe most often close to the other toes.
"The circus prints showed that apes with toes capable of opening up to a wide degree can also bring that toe into alignment when they walk upright -- they are capable of doing both."
The conclusion -- in a scientific paper published this month -- is that "when the chimpanzee walked bipedally in a confident manner, it preferred to align its big toe with the others, presumably for more efficient locomotion".
The foot bones of the 3,33-million-year-old skeleton at Sterkfontein have inadvertently given Clarke a further -- perhaps clinching -- argument. Comparing the evidence of the foot bones, the footprints in Tanzania, and those made by the circus chimps, Clarke has announced: "The Laetoli footprints could [in fact] have been made by feet with slightly divergent big toes as represented by the Sterkfontein Australopithecus StW 573."
-- The Mail & Guardian, December 20 1999.