La Sapienza - Università di Roma

logo de La Sapienza per la stampa



New footprints of the first biped hominids found at Laetoli in Tanzania suggest significant variations in the dimensions of the bodies of our ancestors 3.65 million years ago and provide us with a new point of view on their social behaviour. The discovery was published by eLife, a prestigious Open Access Journal.

Fossilized bones and teeth reveal plenty about various aspects of human evolution, but footprints are something altogether different. They are rare. They may be preserved in the soil, over the course of ages, and rediscovered millions of years later almost by chance.

These fossil tracks provide us with data on the biomechanics of locomotion and on the dimensions of the body of these extinct hominids. Like a spotlight on a prehistoric scene, they reveal the differences between individuals and even shed light on their reproductive strategies.

A new lead has been unearthed in Laetoli, in the Ngorongoro conservation area in North Tanzania, by a research group from the University of Dar Er Salaam in collaboration with Sapienza University of Rome and the universities of Perugia, Pisa and Florence. This is the same area in which, at the end of the 1970s, Mary Leakey found evidence from 3.6 million years ago commonly attributed to Australopitecus Afarensis (Lucy’s famous species).

The new discovery reveals the footprints of two bipeds walking on the same paleo-surface at the same time and in the same direction at a moderate speed, found amongst dozens of footprints of other mammals and birds left by the rain. It’s the story of two biped hominids moving in a group after a volcanic eruption and abundant rainfall. The footprints of one of the individuals is much bigger than any other in the group, suggesting that he was a large male specimen of the species. In fact, the extraordinary dimensions of his body make him the biggest Australopithecus afarensis ever identified. The conclusions are that there was a man, two or three women and one or two younger individuals.

Both the new composition of the group and the striking difference in body dimensions suggests a remarkable sexual dimorphism in Australopithecus afarensis. Moreover, this projection highlights a social organization and reproductive strategy closer to that of polygamous gorillas than other moderately dimorph species, such as chimpanzees and the promiscuous bonobos, or most of existing human beings and probably of the extinct ones, too.