. Scientific Frontline: Smilodon's saber teeth

Friday, December 9, 2022

Smilodon's saber teeth

Life-size reconstruction of three different species studied with their stress thermal maps at the three different angles for a right lower canine bite. The colder colors on the thermal maps of saber-toothed species indicate lower stress and higher force, especially when biting at larger angles.
Illustration Credit: Massimo Molinero

A team of researchers led by Narimane Chatar, doctoral student at EDDyLab at the University of Liège, tested the bite effectiveness of the Smilodon, an extinct species of carnivore close to current felines. Thanks to high precision 3D scans and simulation methods, the team has just revealed how these animals managed to bite despite the impressive length of their teeth. This study is the subject of a publication in the journal Proceedings of the Royal Society B

ancient carnivorous mammals have developed a wide range of skulls and teeth throughout their evolution. However, few of these developments have yet equaled those of the felidated saber-toothed emblematic Smilodon. Other groups of mammals, such as the now extinct nimravids, have also evolved into a similar morphology, with species with saber teeth but also much shorter canines, similar to those of lions, tigers, caracals, domestic cats, etc. that we know today. This phenomenon of the appearance of similar morphologies in different groups of organisms is known as convergent evolution; felines and nimravids being an astonishing example of convergence. As there are no modern animal equivalents with such saber-shaped teeth, the hunting method. Smilodon and other similar species remained obscure and the subject of heated debate. It was initially suggested that all saber-toothed species hunted in the same way, regardless of the length of their canines, a hypothesis which is today controversial. From then on, the question remained suspended ... How did this variety of "saber-toothed cats" hunt?

Barbourofelis fricki USNM PAL 531533 and the 3D model resulting from the scan.  Barbourofelis fricki is an extremely derived species and has the most impressive fangs of all the data.
Photo Credit: Narimane Chatar.

"The huge canines of the extinct saber-toothed cat Smilodon imply that this animal had to open its jaw in an extremely wide way, 110 ° according to some authors, in order to use them effectively, explains Pr Valentin Fischer, director of EDDyLab (Geology / Faculty of Sciences) of the ULiège. However, the mechanical feasibility and effectiveness of Smilodon and his loved ones biting at such a large angle are unknown, leaving a gap in our understanding of this very fundamental question about saber-toothed predators. Using high-precision 3D scanners and analytical methods from engineering, an international team of Belgian and North American scientists has just revealed how these animals probably used their impressive weapons.

Narimane Chatar, doctoral student at EDDyLab of the University of Liège and principal author of the study, gathered a large amount of three-dimensional data. She first scanned and modeled the skull, mandible and muscles of many extinct and existing species of felines and nimravids. “Each species has been analyzed according to several scenarios: a bite simulation was carried out on each tooth at three different bite angles: 30 °, as is commonly seen in today's felines, but also more important angles (60 ° and 90 °). In total, we performed 1074 bite simulations to cover all possibilities, explains Narimane Chatar. To do this, the young researcher used the finite element analysis technique. "This is an exciting application of the finite element approach, which allows paleontologists to modify and simulate by calculation different bite angles and to subject the skull models to virtual stresses without damaging the precious fossil specimens, takes Professor Jack Tseng, professor and curator of paleontology at the University of California at Berkeley and co-author of the study. Our complete analyzes provide the most detailed vision to date of the diversity and nuances of the bite mechanics of saber teeth."

One of the results obtained by the team is the understanding of the distribution of stress (the pressure) on the mandible during the bite. This stress shows a continuum through the animals analyzed, the highest values being measured in the species with the shortest upper canines and the lowest stress values being measured in the most extreme saber-toothed species. Researchers also noted that stress decreases when the bite angle increases, but only in saber-toothed species. However, the way in which these animals transmitted the force at the bite point and the deformation of the mandible resulting from the bite are remarkably similar throughout the dataset, which indicates a comparable efficacy, regardless of the length of the canines.

“The results obtained show both the possibilities and the limits of evolution; animals facing similar problems in their respective ecosystems often end up looking like converging evolution. However, the results obtained by Narimane Chatar also show that there can be several ways of being an effective killer, whether one is saber-toothed or not, concluded Valentin Fischer. This phenomenon, called a multiple functional system, means that distinct morphologies can lead to a similar function, such as the fact that bears and cats are both effective fishermen. This multiplicity of morphologies indicates that there is not a single optimal form of saber-toothed predator.

Life-size reconstruction of three different species studied with their stress thermal maps at the three different angles for a right lower canine bite. The colder colors on the thermal maps of saber-toothed species indicate lower stress and higher force, especially when biting at larger angles.

Source/Credit: University of Liege

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