How far did animal and human beings once get around in their habitat? Researchers report that high-resolution studies of strontium isotope signatures in the layers of tooth finds can now provide insights into this question. They were able to show how Neanderthals, a modern human and certain animals once used the region around a cave system in Portugal. It is becoming apparent that the Neanderthals roamed there rather extensively, while modern humans later only hunted in an area that was half as large.
Strontium isotope signatures have been used in archeology and anthropology for some time as a spatial clue. This takes advantage of the fact that the contents and ratios of different isotopes of the element in rocks differ from place to place. Through the weathering of the material, this signature is also found in the plants of an area and then enters the body tissues of animals and humans via the food chain. Among other things, the site-specific fingerprint is therefore also found in the tooth material.
So far, however, strontium isotope analyzes have mostly only been used to identify the places where people lived in their childhood. For example, their immigration to a certain area and their actual origin could be shown. So far, however, the technology has lacked the resolution to detect whereabouts in small areas and over short periods of time. The researchers led by Bethan Linscott from the University of Southampton have now explored the extent to which this is possible. To do this, they used the technique of so-called laser ablation, in which pulsed laser beams can mobilize sample material with pinpoint accuracy. The researchers have now used this method to obtain sample material from the fine layers of growth in the enamel of fossil teeth.
On the trail of small-scale mobility
The method was used on finds from the Almonda cave system near Torres Novas in Portugal. They were two Neanderthal teeth that are about 95,000 years old and a tooth from a modern human who lived there about 13,000 years ago, in the so-called Magdalenian period. The scientists also examined teeth from animals found in the cave system. As they explain, the surrounding region shows extremely high-resolution patterning in the strontium isotope signatures. This means that the geological “fingerprints” can even differ in places that are only a few kilometers apart.
As the researchers report, the approach actually yielded usable data. Linscott explains: “Enamel forms in stages and thus represents a time series that records the geological origin of the food consumed by an individual. Using laser ablation, we have now been able to measure the change in strontium isotopes over the two or three years it took for tooth enamel to form. By comparing the strontium isotopes in the teeth with the sediments collected from different locations in the region, we were able to map the movements of the creatures studied. The geology in the area surrounding the Almonda Caves is so variable that we were able to detect changes of just a few kilometers,” says the scientist.
Differences in habitat use
As for the four possible prey species studied by human beings, the results of the analysis revealed that ibex, red deer, horse and one species of rhino were either resident or seasonally present at a short distance from the karst sites in Almonda. The sequential layers in the human beings also revealed clues as to where they had temporarily stayed in the region, the researchers report. “Based on the mapping of the study area, we conclude that Neanderthals roamed an area of approximately 600 square kilometers,” the team writes.
In contrast, the Magdalenian individual subsisted primarily on resources derived primarily from two geological areas along a roughly 20-kilometer stretch of the right bank of the Almonda River. Compared to the Neanderthals, this shows a significantly smaller catchment area of 300 square kilometers. The results show that the method has the potential to provide insights into the use of the habitat of prehistoric creatures, say the scientists.
However, one can only speculate about the cause of the difference in the use of space that has now been identified. Senior author João Zilhão from the University of Lisbon says: “The difference in territory size between Neanderthals and Magdalenians may have been related to population densities: with relatively low population densities, Neanderthals were able to move further to hunt large prey such as horses, without encountering rival groups. In the Magdalenian period, increasing population density reduced available territory, and human groups moved down the food chain, occupying smaller areas where they mainly hunted rabbits and caught fish seasonally,” the researcher suggests.
Source: University of Southampton, Article: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2204501120
http://dx.doi.org/10.1073/pnas.2204501120
Caption: One of the examined Neanderthal teeth from different angles. © João Zilhão