Stepping back in time

Marco Cherin and Chris Smith step back millions of years into mankind's past...

Marco - We discovered new human-like footprints dated at about 3.66 million years in the known site of Laetoli, northern Tanzania. Laetoli is one of the most important paleoanthropological site in the world for two reasons – one is because of the discovery in the 70s of some very well-preserved fossils of human ancestors – Australopithecus afarensis – the same species as the famous Lucy. The second reason is the discovery of the earliest human-like footprints in the world dated at 3.66 million years.

Chris - You’ve now found more of the same?

Marco - Yes. The first set of footprints was discovered in 1978 by Mary Leakey. Mary Leakey’s discovery composed three different individuals walking in the same direction. We discovered just one year and a half ago, two more individuals walking on the same surface.

Chris - First of all, just set the scene for us and tell us what the Laetoli site where you’ve been working looks like to an observer.

Marco - The Laetoli site today looks like African savannah. It is included within one of the most amazing protected areas in the world, the Ngorongoro Conservation Area. But today, this is really a rough place rich in dust and acacia trees, and bushes, and shrubs. But sometimes in this savannah environment, a very, very peculiar rock can outcrop. This rock is a hard volcanic ash in which the footprints were preserved.

Chris - So these individuals, whoever they were, when walking across some freshly fallen dust from the volcano, left these impressions behind. How did they then get preserved so that you could come along 3.66 million years later and dig them up?

Marco - The preservation of fossil footprints is very rare. In that case, a near volcano was erupting several times in a few days. The ground was completely covered by this fine ash. But the other and fundamental thing is that we were in the beginning of the rain season. Some rain fell down on the ground. The ground was soft. Hominids and other animals were walking on this soft surface, leaving their tracks. Immediately after the passage of these creatures, another volcanic eruption covered the surface with new ash.

Chris - How did you come to stumble upon these tracks that these extremely famous people managed to not find 30 or 40 years ago?

Marco - The tracks were discovered by our Tanzanian colleagues who were working in the Laetoli area for a landscape impact assessment because the Tanzanian government wanted to build a new field museum to bring tourists to have a look. So Professor Masao was digging 50 or 60 test pits to evaluate the possible impact of this new building. During these digging activities, he discovered the new, printed surface.

Chris - When you look at these footprints, what can they tell you about the individuals that made them because one thing we know, if we look at humans who walk on the beach, we can tell quite a bit about the size, stature, speed, and so on of movement of the person who leaves footprints. So what can we learn about these ancestors of ours who left the footprints?

Marco - Footprints are very interesting tools in palaeontology because they can tell you much more things than simple bones. In our case, the human-like footprints from Laetoli, we can say that they were part of the same social group because the footprints were printed exactly on the same geological layer. The second thing is about the pattern of locomotion was not so different from Homo sapiens – our own species. So, this is a very interesting evidence of functional bipedalism in very, very ancient hominids.

Chris - What about the potential size, the proportions of the individuals that made them? What can you learn about that?

Marco - We were really, really shocked when we cleaned the new trackway because it is composed by very, very long footprints. So, we can expect that the owner of these feet was a tall individual. We found that one of our new individuals could reach the stature of something like 1.65, 1.7 meters. Comparable to modern humans, normally, we thought that these ancient human ancestors were tiny creatures. For the first time, we have sure independent evidence of the occurrence of individuals with very high stature. And, in the same site, we have individuals with different sizes. This is one of the most important novelty of this work. We have tall individuals and we have also tiny individuals for the first time in the same place at the same age.