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An international team led by scientists from the University of Liège has been investigating the evolutionary patterns behind the development of sabertooths, with some unexpected results along the way. Their study is published in the journal Current Biology.

Saber teeth, those iconic elongated upper canines, have long fascinated scientists and the general public alike, especially because they appear several times in the fossil record, including two particularly well-known lines of saber-toothed tigers: the felines (sem. of our domestic cats, lions, tigers etc.) and the Nimravids (a completely extinct family). However, the process by which these lineages acquired their elongated upper canines remains quite unclear.

Narimane Chatar, lead author of the study, who completed her PhD at the EDDy Lab at the University of Liège and is now a postdoctoral fellow at UC Berkeley in the United States, is leading an ambitious study to unlock the secrets of sabertooth evolution. Using state-of-the-art 3D scanners and analytical methods, the team meticulously collected and analyzed data from a diverse array of current and extinct species.

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

“Unlocking the secrets of sabertooth 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.

The study revealed some surprising results. The first is that, rather than contrasting two distinct cranial morphologies in species with elongated upper canines and those with short canines, there is instead a continuum of shape connecting today’s smallest cats and their extinct sabre-toothed counterparts.

“From a morphological point of view, the skull of today’s small cat is as strange and modified as that of a large saber-toothed cat,” said 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 feline carnivores have seen evolve over geologic time.

“Our study suggests that what we often think of as examples of evolutionary models in textbooks are actually simplified for educational purposes. However, when we dive into statistical analyses, we find much more complex scenarios in these cases, as suggested by the results of our convergence tests,” explains Davide Tamanini, a postdoctoral researcher at Rome’s La Sapienza University.

The second surprise concerns the path evolution took to create saber-toothed species. Indeed, the team’s work revealed that sabre-toothed species showed faster rates of morphological evolution early in their evolutionary history than species with shorter canines.

“Among other fascinating findings, we have shown that craniomandibular integration is reduced in sabertooth species, facilitating greater adaptability and diversification in jaw and skull morphology,” Margot Michaud points out.

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

Finally, the team’s research highlighted the decline of saber-toothed forms as well as broader trends in 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 actually been in decline since the Miocene epoch (between 23 and 5 million years ago).

“Some of these feline predators, especially the saber-toothed species, quickly occupied quite specialized niches, which made them more vulnerable to extinction,” explains Dr Tammagnini.

This phenomenon, known as “ratcheting” or macroevolutionary ratcheting, has been proposed as a potential driver of the decline of certain groups, where evolution favors the loss of early generalized forms, leading to the emergence of more specialized but also more vulnerable forms – late in the history of the genus.

“Predators have their own evolutionary paths and risks of extinction. Studying how ancient predators prospered and declined provides us with information about the possible futures of our ecosystems,” concludes Professor Fischer.