New research analyses the behavior of primates based on teeth remains

The international research team discovered that the vegetable remains recovered from the dental calculus record of chimpanzees from the Taï Forest (Ivory Coast) coincide, in general terms, with the dietary data collected over the last 20 years by the project Chimpanzee Taï, carried out by the Max Planck Institute for Evolutionary Anthropology (Leipzig, Germany). Extrapolating from this correlation, the key point is that these remains give very precise information on behaviours that cannot be observed directly in these primates -genetically closest to human beings-, what they are like, at what age they wean and when they start to master the ability to crack nuts.

Thus, dental calculus, or plaque, has become a source of much data on the life of these individuals, dead or alive, and it is gaining ground to become considered invaluable for the objective reconstruction of history of life.

Researchers increasingly use the particles of plants trapped in dental calculus in order to reconstruct the alimentary choices of past populations. For example, vegetable microremains from dental calculus have been used to identify the use of plants by hominid species, like Neanderthals and 'Australopithecus sediba'.

However, deducing the use of plants from dental calculus is still a challenge that needs to be refined and improved, for until now very few studies have tried to correlate the data provided by dietary records. In this sense, chimpanzees, as well as other live relatives closer to human beings, constitute one of the best analogies for testing this method and discovering older human behaviours.

"In our study we compare the information from the composition of dental calculus of the animals with the long-term observed data on the behaviour of chimpanzees from Taï National Park in Ivory Coast," explains PhD student Robert Poder, from the Max Planck Institute for Evolutionary Anthropology, whose thesis is directed by researcher Domingo C. Salazar Garcia from the Universitat de València. With this goal, researchers carried out a high resolution analysis of the microremains of dental calculus from 24 dead chimpanzees ('Pan troglodytes verus') from Taï and, on the basis of the mixture of microremains (phytoliths and starch) from the vegetable remains, reconstructed the diet of the animals. Meanwhile, researchers identified proof of important events occurring in the life of individuals, like weaning and the acquisition of the ability to use tools, like cracking nuts.

The understanding of diet ecology is fundamental to recognising which evolutionary pressures gave rise to great apes and humans. It has long been known known that factors like diet specialisation, the acquisition of feeding tools and weaning age are of great importance in great apes and human beings, and also that they differ significantly between species. Nonetheless, until now many of the approaches used to reconstruct diet have left unanswered key questions about its composition and the events that occurred in the lifetime of individuals, especially for fossilized specimen. In this context then it becomes necessary to use new methods to recover data about the diet of different populations that bypass some of the shortcomings of other techniques, such as direct observation or the analysis of stable isotopes. Of course, direct observation is simply not possible in some cases, like that of great apes and extinct human populations.

This study is one of the first to confirm that the dental calculus record can provide an essential snapshot of diet and stresses the importance of this method for the study of populations whose eating habits it is not possible to observe directly, like in isolated primate groups and human ancestor groups. "These results clarify how we can use dental calculus to reconstruct diet ecology in archaeology, primatology and human evolution," affirms researcher Domingo C. Salazar-García, from the department of Prehistory and Archaeology at the Universitat de València. These findings show that dental calculus is probably a very useful source of information on diet, though at the same time more complicated than it initially appear.