Traces at Laetoli
The Laetoli site is located in northern Tanzania, about 30 miles south of the Olduvai Gorge. Laetoli means “red lily” in Maasai. In 1979, members of an expedition led by Mary Leakey noticed some signs on the ground. They turned out to be fossilized animal tracks. Among them were what looked like hominid footprints. The footprints were imprinted in layers of volcanic ash with a potassium-argon age of 3.6 to 3.8 million years.
“The National Geographic posted an article by Mary Leakey titled “Footprints on the Ashes of Time.” During her analysis of the prints, Leakey quoted Louis Robbins, a print specialist at the University of South Carolina, who said: “They, found in such ancient tuff, looked so human, so modern.”
Readers who have accompanied us on our intellectual journey so far will find it somewhat difficult to recognize the Laetolian prints as potential evidence of the presence of anatomically modern humans in Africa more than 3.6 million years ago. We were, however, stunned by the appearance of such a startling anomaly as the unexpected use of more modern annals of standard paleoanthropological research. What amazed us most was that scientists of international repute, the best in their profession, could look at these prints, describe their humanoid features, and remain completely myopic about the possibility that these creatures who made them could be as human-like as you and I.
Their mental currents flowed in the usual established channels. Mary Leakey wrote: “At least 3,600,000 million years ago, during the Pleistocene, the one I believe to be the direct ancestor of man walked completely straightened out on two limbs in a free gait…the shape of his foot was quite like ours.”
Who was this ancestor? If we accept Leakey’s point, the Laetolian prints were made by an ancestor of intelligent man who was not Australopithecus. If Johansson White is to be believed, the Laetolian prints were made by Australopithecus afarensis. In both cases, the creature who left the footprints had an ape-like head and other primitive features.
But why not a creature with modern feet and a modern body? There is nothing in the footprints to rule it out. Moreover, in this book we have included only a small amount of fossil material, and little from Africa, consistent with the presence of anatomically modern humans in the Early Pleistocene and Late Pliocene.
Could it be that we are exaggerating the human characteristics of the Laetolian footprints? Let’s see what different researchers have said. Louis M. Robbins, who made the first assessment of the Laetoli footprints for Mary Leakey in 1979, later published a more detailed report. Several chains of footprints were found at Laetoli, which were labeled with letters. In examining Chain 6, representing the three individuals Mary Leakey described as a possible family group, Robbins found that the footprints “shared many features characteristic of the structure of the human foot.” She specifically noted that the big toe pointed straight ahead, as in humans, rather than to the side, as in monkeys. In monkeys, the big toe can be turned almost the same way as the thumb of the human hand. Robbins concluded that “the four functional areas – heel, arch, forefoot, and toes – of the hominid feet were imprinted on the ashes as typical human footprints,” and that “hominids walked on the ash-covered surface on two feet in a manner characteristic of humans.”
M. H. Day studied the footprints using photogrammetric methods. Photogrammetry is the science of achieving measurement accuracy through photography. His study showed that the footprints had “a close resemblance to the anatomy of the foot of an anatomically modern man used to walking unclothed, which is quite a normal human condition. Day concluded typically, “Now there cannot be any serious argument against the fact that Australopithecus stood upright and walked on two legs.”
But where is his evidence that Australopithecus left Laetolian footprints? There is no reason to rule out the possibility that some unknown creature, maybe very similar to modern intelligent man, caused them.
Р. H. Tuttle, a physical anthropologist, asserted, “The shape of the footprints is indistinguishable from that of the footprints of a man walking in large strides, accustomed to being barefoot.”
Tuttle concluded: “Taking the structure of footprints 6 as a rigid basis, their wearers can be classified as human … because their footprints are so similar to those of a reasonable man, but their early date may have kept many paleoanthropologists from making that decision. I suspect that if the prints hadn’t been dated, or if they had a younger age, probably most experts would have decided they were made by humans.” Tuttle also said: “They look like the footprints of a small, barefooted intelligent man.”
Further, Tuttle held that Australopithecus afarensis could not have made the prints. As we have seen, Australopithecus afarensis has long curled toes, and Tuttle said that it is difficult to imagine as if they “clearly matched the Laetolian prints.” The same would be true of the feet of other Australopithecines.
Stern and Susman opposed it. Convinced that the foot of the ape-like Australopithecus afarensis left Laetolian footprints, they suggested that ancient hominids walked on volcanic ash with their toes tucked under the foot, as chimpanzees sometimes do. The tucked toes would explain why the footprints of Australopithecus afarensis are so similar to those left by a human foot with relatively short toes.
Could an Australopithecus walking with its toes twisted leave human-like footprints? Tuttle found this extremely improbable. If the Laetolian hominid had long toes on its feet, then, Tuttle said, we should expect two kinds of footprints – those with long extended toes and those with short twisted toes, with very deep joint impressions. But this was not the case, and that meant that the afarensis foot with long toes could not have left these footprints.
Even Tim White, who was confident that Australopithecus afarensis left these footprints, said: “Stern and Susman’s (1983) ‘chimpanzee-like’ toe curl model predicts a substantial variation in the thumb length of the Laetolian footprints. But the fossils do not support this prediction.”
Challenging Johanson, White, Latimer and Lovejoy, who claimed that Australopithecus afarensis made the Laetolian footprints, Tuttle said: “As shown by digital curvature and elongation and other skeletal features indicative of an arboreal lifestyle … it is implausible that Australopithecus afarensis from Hadar in Ethiopia could have left Laetolian-like footprints.” This statement provoked detailed counterattacks by Johansson and his followers, who continued to advance the idea that Australopithecus afarensis could have made these prints.
Tim White, for example, published a 1987 report on the Laetolian footprints study, in which he disputed Tuttle’s claim that their possessor was a hominid more massive than Australopithecus afarensis.
White argued, “There is not a shred of evidence among the 26 hominids in the collection of 5,000 vertebrate remains at Laetoli that would suggest the presence of a more Pliocene evolved hominid at this site.” But as we saw in our review of African hominid fossils, there is actually several “grams” of evidence for the presence of human-like intelligent creatures during the Pliocene, some of them near Laetoli. It is also common knowledge that human skeletal remains are extremely rare, even at sites where there are other unmistakable signs of human presence.
White predicted that “it will gradually be shown that the Laetolian prints are slightly different from those of anatomically modern humans left under similar conditions.” But, as anyone can see, they are indistinguishable from the footprints of modern humans. Even White himself once said: “If they were left on a California beach, and a four-year-old were asked what they were, he would immediately say that someone had walked here. He wouldn’t be able to tell them apart from a hundred other footprints on the beach, and neither would you. The exterior structure is the same. A well-built modern heel with a strong arch and good cushion in the forefoot. The big toe is pointing straight ahead. It doesn’t stick out to the side like a monkey’s.”
And Tuttle remarked, “In all the distinguishing features of the structure, the feet of those who left the footprints are indistinguishable from those of modern humans.”
So where did the ash at Laetoli come from?
We wrote about Russian scientists taking part in a study of the famous Laetoli site in Tanzania. Today, firsthand details.
A group of researchers, the authors of the article under discussion, against the backdrop of the Aldoinho Lengai volcano. A.N. Zaitsev – in the center (photo by E.O. Zaitseva)
Panorama of Sadiman volcano (Lemagrut volcano in the background, photo by S.V. Petrov) – February 2009. Photo courtesy of A.N. Zaitsev.
One of the famous trails in Laetoli. Source: http://www.discovering-tanzania.com/tag/laetoli/
Sadiman erupts and Australopithecines stroll by. Photo from http://www.gereth.net/
An article about the study was published in the electronic version of the Journal of Human Evolution on April 4.
Recall that we are talking about the site where those famous “human-like footprints on the ashes” were found. The chains of footprints of 3 individuals (39 footprints of a small individual and 31 footprints of two larger ones) were discovered by Paul Abell in 1978. “Laetoli Footprints” are considered one of the strongest confirmations that 3 and a half million years ago (which is the age obtained for the layer with footprints) upright creatures lived here. Since the remains of Afar australopithecines were found in Laetoli (belonging to the same era as the footprints), it is most likely that these very hominids were the “authors” of the footprints.
Here is how the famous paleoanthropologist Donald Johanson described this prehistoric event in his book “Lucy: The Origins of the Human Race”:
“An improbable coincidence of fortuitous circumstances led to the fact that traces did survive. Sadiman threw out ash of a certain type, followed by rain. Then hominids walked across the layer of wet ash, and the sun quickly dried their footprints. Soon another Sadiman eruption occurred, and the footprints were covered with a new layer of ash, which protected them from another downpour. […]
When all this is taken into account, it becomes clear that the preservation and discovery of the footprints at Laetoli was akin to a miracle. The footprints confirmed with absolute certainty what Lucy’s discovery had already told the world: three million years ago, if not earlier, hominids were already moving freely on two legs.
Donald Johanson, Maitland Eady. Lucy: the origins of the human species. M., 1984.
The quote mentions Sadiman. That is the name of the extinct volcano which, you see, was considered the most likely source of the Laetolian ash.
The purpose of the study was to find out: is this really the case?
Our Editor’s questions were kindly answered by the study participant, Anatoly Nikolaevich Zaitsev, associate professor of mineralogy at the Department of Geology, St. Petersburg State University.
Why exactly St. Petersburg specialists took up the study of tuff in Laetoli? What is the background to this study?
This story began in the summer of 2000, when I was invited to participate in a geological expedition in the northern part of Tanzania. The offer came from the famous German volcanologist Jörg Keller. Of course, I agreed… As a result, for the last 11 years my scientific work was connected with mineralogy and geochemistry of volcanic rocks in the area of “Lake Natron – Lake Manyara – Crater Plateau”. Four trips were organized (each lasted about 3-4 weeks) and the most interesting geological material was collected. A large and friendly team was formed – these are, of course, Russian researchers, as well as scientists from Germany, Great Britain, Canada, Hungary and Switzerland.
This area of the Gregory Rift is well known to geologists, because there is the only active volcano here, from which lavas of alkaline carbonatites (this is a rock consisting of calcium and sodium carbonates, with small amounts of fluorite and sylvin) pour out. One of the tasks of our research was to find other volcanoes, where such rocks could erupt in the geological past, and Sadiman was considered as one of the manifestations of alkaline carbonatite volcanism. That is why we investigated this volcano, and interest in tuff deposits in the Laetoli area came later.
As far as I understand, you eventually came to the conclusion that the Sadiman volcano apparently has nothing to do with the famous ash at Laetoli?
The Laetoli imprinted tuffs were originally described as the result of deposition of carbonatite and melilitite tuffs. It should be noted that the American geologist Richard Hay, who studied the volcanic rocks of Olduvai Gorge and the Laetoli area for many years, believed that it was the deposition of alkaline carbonatite ashes that led to such good preservation of the remains of our ancestors, animals and their footprints.
Our approach was very simple – we compared the mineralogical and geochemical data obtained for the rocks of Sadiman volcano with the known data for the Laetoli tuff layer, in which Australopithecus afarensis prints are preserved. The result is that the Sadiman volcano contains none of the rocks described from the Laetoli sediments. Mainly it refers to the absence of melilite (silicate of calcium, sodium, aluminum and magnesium) in the rocks composing Sadiman, there are also differences in the chemical composition of nepheline and pyroxene. This was the basis for our conclusion.
Which volcano then is a candidate for this role? And if they are not found, could it be, for example, that the traces in Laetoli are younger or older than the age to which they are attributed?
If we consider other volcanoes in the Crater Highlands or the Gregory Rift, none of them today qualify as the source of Laetoli tuff. On the one hand there is a similarity in the mineralogy of the rocks, but the age of their formation is very different; on the other hand, the situation is the opposite – the age fits, but the mineralogy of the rocks is different. Where is the solution to this question? It seems that the available data on the age of the imprinted tuff are correct and the formation of the rock took place 3.66 million years ago (this is the last data on the age of the Laetoli tuff published this year). It is possible that the source of the ash was subsequently overlapped by later volcanic rocks, then, with a high probability, we will not be able to find it. On the other hand, the degree of mineralogical study of volcanoes in this area, in spite of recent publications, is low – we are convinced that additional geological, mineralogical and geochemical studies of volcanic rocks composing the Crater Plateau and Gregory Rift are needed.
Are you planning further studies in this direction?
Yes! Of course, first of all, it depends on financing – we would like very much to see these rocks with our own eyes, but it is an expensive pleasure…. But the first steps have already been made – for example, geologists from Austin University, USA will give us samples of Laetoli tuffs for detailed study of silicate minerals in them. Negotiations with other American researchers are also underway. There is a very great desire to work!