An international scientific team led by researchers from the University of Liège and the University of California, Berkeley, has studied the shape and mechanical function of the lower molars of carnivorous mammals. By combining 3D modelling, 3D printing and materials testing, they have highlighted a functional trade-off: a single tooth can be effective at either slicing or grinding, but rarely at both. These findings are the subject of a paper published in the scientific journal Science, and even feature on its cover!
T
eeth constitute the primary interface between vertebrates and their food. Their close link to diet, biomechanics and ecology, combined with their good preservation in the fossil record, makes them a valuable source of information for studying mammalian evolution. As with humans, it is perhaps obvious to assume that each type of tooth corresponds to a specific function. When it comes to cutting, there are only a few effective tooth shapes. For grinding, there are more possibilities. However, fewer than 1 per cent of predatory mammals have teeth capable of performing both functions simultaneously, thanks to the emergence of the tribosphenic molar – a dental architecture that combines two functional regions: the trigonid, primarily dedicated to cutting, and the talonid, responsible for grinding. However, this key innovation also appear to have induce some mechanical constraints which drove the evolution of mammals.
A study, led by Narimane Chatar - a palaeontologist who graduated from ULiège (and still collaborator) and is now a postdoctoral researcher at the University of California, Berkeley, and the University of Málaga - focused on the first lower molar of 250 specimens of extant and fossil carnivores (felids, canids, hyenas, bears, mongooses, viverrids) as well as extinct lineages (hyaenodonts and oxyaenids). “Carnivores possess lower molars in a wide variety of shapes, but some species retain a tooth similar to the tribosphenic molar, the ancestral architecture of mammalian molars,” explains the researcher. “This makes it a system of study well suited to our project.”
Specialization spectrum from slicing (left) to crushing (right) on the lower molar of carnivorous mammals | © Université de Liège / University of California, Berkeley / N.Chatar / M.Vankelst
To quantify both the shape and the mechanical efficiency of the teeth, the team developed a new protocol in which each crown was first scanned in three dimensions to create a highly accurate virtual twin. “The shape of each tooth was then recorded using a geometric approach that enabled us to quantify the entire morphology with great precision,” explains Melvin Vankelst, a PhD student at the University of Liège EDDyLab and the Royal Belgian Institute of Natural Sciences, who was responsible for the digitisation and quantification of the shapes. “Combining precise shape measurement with mechanical tests on printed teeth enabled us to directly link morphology to function.”
The models were then 3D-printed and subjected to two series of tests. To measure cutting efficiency, the teeth were pressed into a stack of medical gelatin simulating different layers of soft tissue (skin, muscle, fat). To assess grinding ability, the same teeth were pressed against sections of bone printed in a material that replicates the mechanical properties of bone.
The analyses revealed a fairly clear trade-off: a tooth that is effective at cutting is rarely effective at grinding, and it is structurally difficult to perform well in both functions. “Slicing, moreover, appears to be more constrained, limited to a narrow range of shapes and concentrated in a small number of lineages,” continues Melvin Vankelst, “whereas efficient grinding can be achieved using a wider variety of shapes. Fewer than one per cent of the predatory mammals we studied had a tooth optimised for both slicing and grinding.”
Reproduction of tribosphenic molars from extant and fossil carnivores, as well as extinct lineages, and testing of their functions. | © Université de Liège / University of California, Berkeley / N.Chatar / M.Vankelst
According to the authors, this trade-off stems from the very architecture of the tribosphenic molar. As its two regions are specialised for opposing functions, the development of one tends to be at the expense of the other. “It is possible to achieve a tooth that is effective for grinding whilst retaining both regions, but to obtain a tooth that is effective for slicing, one of the regions tends to disappear,” summarises Narimane Chatar. “This simplification seems difficult to reverse especially in hypercarnivorous species, specialised in cutting, embark on an evolutionary path from which it appears difficult to turn back.”
This research demonstrates how an evolutionary innovation in mammals may have contributed to their success whilst subsequently limiting the diversity of available dental forms. By distinguishing between slicing and grinding—two functions that are largely incompatible within a single tooth—the study sheds light on the mechanical trade-offs that have shaped the dietary history of carnivores.
Chatar, N., Vankelst, M., Pérez Ramos, A., Pollock, T. I., Tamagnini, D., Michaud, M., Yoder Raskin, L. & Tseng, Z. J. (2026). Performance trade-offs define a fundamental dental dichotomy in mammals. Science. doi: 10.1126/science.aee3453
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