How sabre-tooth tigers got their long upper canines

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Example of the morphological variation observed in the skull of felids and nirmavids, with species showing both short and long upper canines. Credit: Narimane Chatar / University of Liège

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Example of the morphological variation observed in the skull of felids and nirmavids, with species showing both short and long upper canines. Credit: Narimane Chatar / University of Liège

An international team led by scientists from the University of Liège has investigated the evolutionary patterns behind sabre-tooth development, with some unexpected results. Their research has been published in the journal Current biology.

Saber teeth, those iconic elongated upper canines, have long fascinated scientists and the general public alike, especially as they have appeared several times in the fossil record, including two particularly well-known genera of sabre-tooth tigers: the felines (the family of our domestic cats, lions, tigers, etc.) and the nimravids (a completely extinct family). However, the process by which these genera acquired their elongated upper canines remains rather unclear.

Narimane Chatar, lead author of the study, who completed her PhD at the EDdy Lab of the University of Liège and is now a postdoctoral researcher at UC Berkeley in the United States, has led an ambitious study to unravel the secrets of sabre-tooth evolution. Using state-of-the-art 3D scanners and analytical methods, the team painstakingly collected and analyzed data from a diverse range of current and extinct species.

“We quantified the shape of 99 mandibles and 91 skulls, from different eras and continents, giving us a better understanding of the evolution of these animals,” explains Dr. Chatar out.

“Unlocking the secrets of sabre-tooth evolution not only enriches our understanding of Earth’s past, but also documents the mechanisms leading to evolutionary convergence,” says Professor Valentin Fischer, director of the EDDyLab at ULiège.


Skull and mandible of Eusmilus sicarius, a sabre-tooth nimravid scanned at the Yale University Museum (Yale Paebody Museum, New Haven, USA). Credit: N.Chatar/Université de Liège

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Skull and mandible of Eusmilus sicarius, a sabre-tooth nimravid scanned at the Yale University Museum (Yale Paebody Museum, New Haven, USA). Credit: N.Chatar/Université de Liège

The research revealed some surprising results. The first is that rather than contrasting two different skull morphologies in species with elongated upper canines and those with short teeth, there is instead a continuum of shape linking the smallest modern-day cats and their extinct saber-toothed counterparts.

“From a morphological point of view, the skull of a modern-day small cat is as strange and modified as that of a large saber-toothed cat,” says Dr. Margot Michaud, a researcher at the University of French Guiana in Cayenne. . These are therefore the two extremes of a continuum of forms that have seen feline predators evolve over geological time.

“Our study suggests that what we often think of as examples of evolutionary patterns in textbooks have actually been simplified for educational purposes. However, when we delve into statistical analyzes we discover much more complex scenarios in these cases, as suggested by the results of our convergence tests,” explains Davide Tamagnini, postdoctoral researcher at the University of Rome La Sapienza.

The second surprise concerns the path evolution took to produce saber-toothed species. The team’s work has shown that saber-toothed species exhibit faster morphological evolution early in their evolutionary history than species with shorter canines.

“Among other fascinating discoveries, we have shown that craniomandibular integration is reduced in saber-toothed species, allowing greater adaptability and diversification in jaw and skull morphology,” explains Margot Michaud.

Thus, rapid morphological diversification and a fairly plastic skull have been identified as two key components that enabled the emergence of elongated upper canines in both felids and nimravids. “As a result, there appears to be a common recipe for evolving into saber-toothed cat-like predators,” says Dr. Chatar.

Finally, the team’s research highlighted the decline of sabre-tooth shapes, as well as the broader trends of feline predators over the course of their evolutionary history. Despite the relatively recent extinction of saber-toothed forms ‘only’ a few thousand years ago, feline predators have in fact been in decline since the Miocene (between 23 and 5 million years ago).

“Some of these feline predators, especially the sabre-toothed species, quickly occupied fairly specialized niches, making them more susceptible to extinction,” explains Dr Tamagnini.

This phenomenon, known as ‘ratchet’ or macroevolutionary ratchet, has been proposed as a potential driver for the decline of certain groups, with evolution favoring the loss of early generalized forms, leading to the emergence of more specialized, but also more vulnerable forms. later in the line’s history.

“Predators have their own evolutionary trajectories and risks of extinction. Studying how ancient predators thrived and declined gives us information about the possible future of our ecosystems,” concludes Professor Fischer.

More information:
Evolutionary patterns of feline carnivores reveal the driving forces behind sabre-tooth morphology Current biology (2024). DOI: 10.1016/j.cub.2024.04.05

Magazine information:
Current biology

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