Paleontologists from the University of Liège and elsewhere have investigated the evolutionary patterns behind the development of saber teeth in two groups of carnivores: felids (family of domestic cats, lions, tigers, etc.) and nimravids (often labeled as false cats).
Felidae, a highly diverse carnivoran family, emerged during the Oligocene in Eurasia and quickly spread worldwide during the Miocene. Although Felidae represents the sole extant cat-like clade, the sabertoothed morphotype is a textbook example of iterative evolution, having evolved many times among placentals, marsupials, and gorgonopsians. Nimravidae is a well-diversified yet fully extinct carnivoran clade that extensively explored a range of cat-like morphologies, and although they have been commonly called ‘false cats’ or ‘false sabertooth cats’ in opposition to the ‘true cats,’ they evolved cat-like morphologies, including both saber-toothed and non-saber-toothed forms, tens of millions of years prior to the appearance of felids. Image credit: Narimane Chatar / Université de Liège.
Saber teeth, those iconic elongated upper canine teeth, have long fascinated both scientists and the general public, notably because they have appeared several times in the fossil record, including two particularly well-known lineages of saber-toothed tigers: felids and nimravids.
However, the process by which these lineages acquired their elongated upper canines remains rather unclear.
Using state-of-the-art 3D scanners and analytical methods, University of Liège paleontologist Narimane Chatar and colleagues collected and analyzed data from a diverse set of living 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,” Dr. Chatar said.
“Unlocking the secrets of saber tooth evolution not only enriches our understanding of the Earth’s past, but also documents the mechanisms leading to evolutionary convergence,” said University of Liège’s Professor Valentin Fischer.
“The study revealed some surprising results,” the paleontologists said.
“The first is that rather than contrasting two distinct cranial morphologies in species with elongated upper canines and those with short teeth, there is instead a continuum of form linking the smallest present-day cats and their extinct saber-toothed counterparts.”
“From a morphological point of view, the skull of a present-day small cat is just as strange and modified as that of a large saber-toothed felid,” said Dr. Margot Michaud, a paleontologist at the University of French Guyana.
“These are therefore the two extremes of a continuum of forms that feline predators have seen evolve over geological time.”
“Our study suggests that what we often think of as examples of evolutionary patterns in textbooks are actually simplified for educational purposes,” said Dr. Davide Tamagnini, a paleontologist at the University of Rome La Sapienza.
“However, when we immerse ourselves in statistical analyses, we discover much more complex scenarios in these cases, as suggested by the results of our convergence tests.”
“The second surprise concerns the path taken by evolution to produce saber-toothed species.”
“In fact, the work revealed that saber-toothed species show faster rates of morphological evolution at the start of their evolutionary history than species with shorter canines.
“Among other fascinating discoveries, we have shown that craniomandibular integration in saber-toothed species is reduced, facilitating greater adaptability and diversification in the jaw and cranial morphology,” Dr. Michaud said.
“Thus, rapid morphological diversification and a fairly plastic skull have been identified as two key components that facilitated 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 feline-like predators,” Dr. Chatar said.
The research also highlights the decline of saber-toothed forms as well as the broader trends of feline-like 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 epoch (between 23 and 5 million years ago).
“Some of these feline predators, particularly the saber-toothed species, rapidly occupied fairly specialized niches, which made them more susceptible to extinction,” Dr. Tamagnini said.
“This phenomenon, known as ‘ratchet’ or macroevolutionary ratchet, has been proposed as a potential driver for 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 later in the history of the lineage.”
“Predators have their own evolutionary pathways and risks of extinction,” Professor Fischer concluded.
“Studying how ancient predators prospered and declined provides us with information about the possible futures of our ecosystems.”
The study was published in the journal Current Biology.
_____
Narimane Chatar et al. Evolutionary patterns of cat-like carnivorans unveil drivers of the sabertooth morphology. Current Biology, published online May 16, 2024; doi: 10.1016/j.cub.2024.04.055
