Strontium isotopes and australopithecine habits

Viewers of Channel 4’s Time Team will be used to seeing eating habits and places of habitation being derived from strontium isotopic analyses of the teeth of modern humans found by archaeologists. The methods enabled scientists to work out where ‘Ötzi the Iceman’, whose mummified remains were found on the alpine border of Austria and Italy, hailed from: it was most likely to have been the South Tyrol province of Italy. Other isotopes (nitrogen and carbon) shows that he was predominantly vegetarian; i.e. he was neither a hunter, nor an especially privileged member of Tyrolean Chalcolithic society.

The same methods offer insights into the life styles of far earlier hominins and has recently been used on teeth of australopithecines (Australopithecus africanus and Paranthropus robustus) found in the famous Sterkfontein and Swartkrans caves South Africa (Copeland, S.R. et al. 2011. Strontium isotope evidence for landscape use by early hominins. Nature, v. 474, p. 76-78). The caves formed in Precambrian dolomites and it was expected that all the teeth would show signs that the individuals from whose jaws they were collected lived their entire lives in a small tract of dolomites (~30 km²) surrounding the caves. For large individuals that was indeed the case, but teeth from smaller fossils show ⁸⁷Sr/⁸⁶Sr ratios that are significantly different from those characteristic of local rocks and soils. That suggests the smaller individuals came from further afield than the restricted tract of carbonate strata. Although pelvic remains are normally the best guide to the sex of primate fossils, they are less frequently found than those of crania and dentition. Size variations of adults in a primate species, however, may indicate sexual dimorphism – larger males than females – and this is well-accepted for australopithecines. The implication is that for both species males had small home ranges on the dolomites, or that they preferred that tract. Yet females had dispersed from their parental groups and moved into the area.

Most living primates do not show this kind of sexual dispersion pattern, termed male philopatry,  it being common among modern humans, chimpanzees and bonobos. In the case of the australopithecines that were being studied, both were diminutive creatures living in open savannah with risks of predation from a range of large carnivores. Perhaps the bands living in the dolomite area had better refuges in caves than those elsewhere, and therefore able to attract females.

Arctic Neanderthals

The last Neanderthals known to have been alive were close to the southernmost limit of Europe, in caves on the Rock of Gibraltar at about 24 ka, shortly before the last glacial maximum. Their remains have been found in a >6000 km west-east zone at temperate latitudes, south of 50°N, which extended from western Europe to the Denisova cave in the Altai republic of Russia (50°N, 87°E). This suggests that they subsisted in deciduous woodland and temperate steppe, diffusing southwards as conditions cooled during 2 or 3 past glacial periods. Consequently, sites at higher northern latitudes that preserve only cultural remains – Palaeolithic tools – have hitherto been regarded as signs of fully modern human occupation; it takes considerable skill to distinguish Neanderthal from early modern human artefacts, which are very similar during the time of overlapping occupation (~40-30 ka). A site in northern Siberia at Byzovaya  in the Polar Urals, close to the Arctic circle, is a case in point. A French, Norwegian and Russian team of archaeologists re-examined the site (Slimak, L. et al. 2011. Late Mousterian persistence near the Arctic Circle. Science, v. 332, p. 841-845) and dated it to between 31-34 ka. They also analysed a suite of stone tools, finding that they are directly comparable with Mousterian (Middle Palaeolithic) implements from western Europe rather than products of modern human’s industry of similar antiquity. At that time high-latitude climate was well on its way to frigid, dry conditions (there were no substantial continental ice sheets in northern Russia). The animal remains found at the site were dominated by those of mammoth, with minor proportions of other cold-steppe large mammals, such as woolly rhino, musk ox, horse and bear.

A notable feature of the results is that they suggest that Neanderthals, or others people with a Mousterian culture, were occupying this bleak terrain at roughly the same time as modern humans, who left considerably richer suites of artefacts, including tools, ornaments and figurines carved from bone and ivory, but were after more or less the same prey species. Both groups clearly were able to cope with and thrive on the harsh conditions, until recently only within the scope of highly specialised cultures such as the Innuit and original Siberian peoples. The dating shows that whoever produced and used the Mousterian tools not only shared the terrane with modern humans, but lingered until well after the previously accepted time (~37 ka) of the Neanderthals’ demise except for a few refuges in the Iberian Peninsula and Balkans. Despite the occupation of northern Siberia by different cultural groups, until their bones are found who they were is not certain. Denisova Cave showed that Neanderthals and the genetically different Denisovans co-occupied temperate central Siberia (see Other rich hominin pickings in the May 2010 issue of EPN) so there are currently two options.

Related articles

• Ancient Female Ancestors Roamed Far and Wide for Mates (news.sciencemag.org)
• Schoeninger, M.J. 2011. In search of the Australopithecines. Nature, v. 474, p. 43-44.
• An Arctic refuge for Neanderthals? (blogs.nature.com)