New footprints of a 3.66-million-year-old human relative discovered at Laetoli, Tanzania, indicate significant differences in body size among the species and provide new insight into its social organisation.
Writing in the journal eLife, a team of researchers from institutions in Italy and Tanzania suggest the impressive differences in body size indicated by the footprints point to a considerable difference in male and female characteristics in Australopithecus afarensis (Au. afarensis), the same species as the famous fossil Lucy.
The fact that the footprints suggest those of a male walking with a number of females supports the idea that social organisation and reproductive strategies of Au. afarensis are closer to the polygynous gorillas – where males have multiple female mates – than to other species, such as the promiscuous chimpanzees and most human beings, including those alive today and possibly those that are now extinct.
The footprints were uncovered in the same area where Mary Leakey and her team found 3.66-million-year-old footprints belonging to the same human ancestor in the 1970s. Surrounded by dozens of other mammals’ and birds’ footprints, along with raindrop impressions, the new tracks were left by two individuals walking on the same surface at the same time, and going in the same direction and at a similar speed to those found by Leakey.
“This novel evidence, taken as a whole with the previous findings, portrays several early hominins moving as a group through the landscape following a volcanic eruption and subsequent rainfall. But there is more,” says senior author Professor Giorgio Manzi, Director of the archaeological project in Tanzania which was supported by the Italian Ministry of Foreign Affairs.
“The footprints of one of the new individuals are astonishingly larger than anyone else’s in the group, suggesting that he was a large male member of the species. In fact, the 165-centimetre stature indicated by his footprints makes him the largest Australopithecus specimen identified to date.”
These findings provide independent evidence for large body-sized individuals among our early ancestors as ancient as 3.66 million years ago. They also support the idea that the size of the australopithecines and early Homo representatives was similar, but that the size of certain australopithecine individuals (or at least that of Au. afarensis) was comparable with later Homo species.
“Overall, our results point to a non-linear evolutionary trend in hominin body size and contrast with the idea that the emergence of the genus Homo and/or the first dispersal out of Africa was related to an abrupt increase in stature,” says first author Professor Fidelis Masao from the University of Dar es Salaam in Tanzania.
Marco Cherin, PhD, Director of the School of Paleoanthropology at the University of Perugia, adds that ascribing the larger tracks to a possible male means reconsidering the sex and age of the other Laetoli individuals, who have been the object of many interpretations since Leakey’s discovery.
“Perhaps the simplest explanation is that the sex and age of the hominins found in the 1970s cannot be determined, as young adults can possibly be present among them,” Cherin says. “However, the overall body-size estimates provide some clues, as a couple of the previously discovered footprints suggest Au. afarensis juveniles or small females, while another older pair of tracks and the smaller of the newer tracks hint at statures across the female range.
“All these individuals are definitely smaller than the large male. A tentative conclusion is that the group consisted of one male, two or three females, and one or two juveniles, which leads us to believe that the male – and therefore other males in the species – had more than one female mate.”
##
Media contacts
Emily Packer
eLife
e.packer@elifesciences.org
+441223855373
About
eLife is a unique collaboration between the funders and practitioners of research to improve the way important research is selected, presented and shared. eLife publishes outstanding works across the life sciences and biomedicine — from basic biological research to applied, translational, and clinical studies. All papers are selected by active scientists in the research community. Decisions and responses are agreed by the reviewers and consolidated by the Reviewing Editor into a single, clear set of instructions for authors, removing the need for laborious cycles of revision and allowing authors to publish their findings quickly. eLife is supported by the Howard Hughes Medical Institute, the Max Planck Society and the Wellcome Trust. Learn more at elifesciences.org.
