How far do humans and animals roam in their environment? The researchers report that high-resolution studies of strontium isotope signatures in dental discovery layers can now provide insights into this question. They were able to show how Neanderthals, modern humans and certain animals, used the area around Portugal’s cave system. It became clear that Neanderthals roamed there on a fairly large scale, while later modern humans only hunted in an area that was half its size.
Strontium isotope fingerprints have been used in archeology and anthropology for some time as a spatial guide. This takes advantage of the fact that the contents and ratios of different isotopes of the element in rocks vary 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 through the food chain. Among other things, the location-specific imprint is also found in the tooth material.
However, until now, analyzes of strontium isotopes have mostly only been used to determine where people spent their childhoods. For example, their migration to a particular area and their actual origin can be shown. To date, however, the technology lacks accuracy for detecting whereabouts in small areas and over short periods of time. Researchers led by Bethan Linscott of the University of Southampton have now discovered just how possible. To do this, they used a technique called laser ablation, in which pulsed laser beams can pack sample material with extreme precision. The researchers have now used this method to obtain a sample of the tiny growth layers in the enamel of fossil teeth.
On trail hopping on a small scale
This method has been used in finds from the Almonda cave system near Torres Novas in Portugal. They were two Neanderthal teeth about 95,000 years old and one from a modern human who lived there about 13,000 years ago, in the so-called Magdalenian period. Scientists also examined the teeth of animals found in the cave system. As they explain, the surrounding region shows very high-resolution etching in strontium isotope fingerprints. This means that geological ‘fingerprints’ can vary in places as little as a few kilometers apart.
As the researchers report, the approach has already yielded usable data. “Enamel forms in stages, and thus represents a time series that records the geological origin of the food an individual consumes,” explains Linscott. 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 strontium isotopes in “With the sediments collected from different locations in the area, we were able to map the movements of the studied organisms. The geology of the area around the Almonda Caves is so variable that we were able to detect changes only a few kilometers away,” the scientist says.
Differences in habitat use
As for the four potential prey species studied by humans, the results of the analysis showed that caribou, red deer, horse and one species of rhinoceros were either resident or present seasonally within a short distance from the karst sites in Almonda. The researchers report that sequential castings in humans also revealed clues to where they temporarily stayed in the region. “Based on the mapping of the study area, we conclude that Neanderthals roamed an area of about 600 square kilometres,” the team wrote.
In contrast, the Magdalenian individual subsisted primarily on resources drawn mainly from two geological regions along a stretch of about 20 kilometers from the right bank of the Almonda River. Compared to Neanderthals, this shows a much smaller catchment area of 300 square kilometres. The results show that this method has the potential to provide insights into the habitat use of prehistoric creatures, say the scientists.
However, one can only speculate as to the reason for the difference in space utilization that was determined now. “The difference in territory size between Neanderthals and Magdalenians may be related to population density: with relatively low population density, Neanderthals were able to move farther to hunt large prey such as horses, without encountering groups,” says senior author João Zilhão of the University of Lisbon. The researcher suggests that in the Magdalenian period, increasing population density decreased available land, and human groups moved down the food chain, occupying smaller areas where they hunted rabbits and fished seasonally.
Source: University of Southampton, Article: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2204501120
Caption: A Neanderthal tooth examined from different angles. © Joao Zilhao
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