Tag Archives: hominins

Ancient footprints

To see traces of where our forebears walked, such as the famous Australopithecus afarensis trackway at Laetoli in Tanzania, the footprints of Neanderthal children in 350 ka old Italian volcanic ash (The first volcanologists? Earth Pages March 2003) or even those of Mesolithic families in estuarine mud is about as heart stopping as it gets for a geologist. But imagine the astonishment of members of a multinational team working on Miocene shore-line sediments on Crete when they came upon a bedding surface covered with what are almost certainly the footprints of another bipedal animal from 5.7 Ma ago (Gierliński, G.D. et al. 2017. Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete? Proceedings of the Geologists’ Association, online; https://doi.org/10.1016/j.pgeola.2017.07.006). Trackways preserve a few moments in time, however old they are and the chances of their being preserved are very small, yet they can supply information that is lost from even the best preserved fossil, such as gait, weight, speed and so forth.

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Track bearing surface; (b) two footprints in 5.7 Ma old Miocene sediments at Trachilos, Crete (credit: Gierliński, G.D. et al. 2017; Figures 2 and 8)

The tracks clearly indicate that whatever left them was bipedal and lacked claws, and closely resemble those attributed to A. afarensis at Laetoli in a 3.7 Ma old volcanic ash. What they do not resemble closely are those of non-hominin modern primates, such as chimpanzees. They are diminutive compared with adult modern human prints, being about 12.5 cm long (equivalent to a UK child’ shoe size 4 – US size 4.5, EU 20) and about a third to half the size of those at Laetoli. Were they around the age of those at Laetoli or younger there seems little doubt that they would be widely interpreted as being of hominin origin. But being from an island in the Mediterranean as well as far from sites in Africa that have yielded Miocene hominins (Ardipithecus kadabba from Ethiopia, Orrorin from Kenya and Sahelanthropus from Chad),  such an interpretation is bound to create controversy. Somewhat less controversial might be to regard them as having been created by a late-Miocene primate that convergently evolved a hominin-like upright gait and foot. Being preserved in what seem to be coastal marine sediments, there is probably little chance of body fossils being preserved in the exposed horizon. Since foot bones are so fragile, even if a primate fossil is discovered in the late Miocene of Crete the chances of resolving the issue are pretty remote. Yet fossil primate specialists will undoubtedly beat a well-trodden path to the Trachilos site near Kissamos on Crete

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Tree-climbing australopithecines

We know that Lucy, the famous Australopithecus afarensis, could climb trees because her many bone fractures show that she fell out of a tree to her death. But that does not mean her species was an habitual tree-climber: plenty of modern humans fall to their deaths from trees, cliffs and the like. But the issue seems to have been resolved by using X-ray tomography of Lucy’s limb bones (Ruff, C.B. et al. 2016. Limb bone structural proportions and locomotor behaviour in A.L. 288-1 (“Lucy”).  PLOS ONE v. 11, e0166095. doi:10.1371/journal.pone.0166095) during the skeleton’s triumphal series of exhibits in the US.

The authors, including two of those who showed that Lucy died after a fall using similar data, compared the digital 3-D models of her surviving arm- and leg bones with those of other hominins and living primates, estimating their relative strengths at different positions. Lucy was probably stronger in the arm than in the leg, but not to the same degree as chimpanzees. This is a feature that would significantlyassist climbing , but her bipedal locomotion on the ground would have been only slightly different from that of later Homo species. If anything, her strength relative to size would have been greater than ours, perhaps reflecting less reliance on tools for getting food and defending herself. But almost certainly Australopithecus afarensis habitually spend more time in trees, perhaps foraging and as a defence against predation, especially at night.

The new data for Lucy allows palaeoanthropologists to better judge the capabilities of other hominins. Interestingly Homo habilis, the earliest of our genus, may have had similar habits. But later species, beginning with H. erectus/ergaster, were as Earth-bound as we are. This suggests a shift in hominin ecology from an early and probably long history of semi-arboreal behavior until humans became masters of their terrain about 1.9 Ma ago, probably through their invention of better tools and the controlled use of fire.

Read more about human evolution here and here