One of the defining characteristics of mammals is their highly developed dental system. While we can marvel at the dental “batteries” of hadrosaurs and Triceratops or discuss the differentiation of teeth in theropods and mosasaurs, it is among our mammalian relatives that we find the most remarkable variety in the form, size, and function of teeth.

Sharp, self-sharpening incisors of rodents or the impressive tusks of elephants are so familiar that they hardly elicit surprise. However, there are mammals whose enormous canines consistently raise questions—these are the sabertooth cats.

Discovered by paleontologists in the mid-19th century, sabertooth cats quickly became the epitome of a “killing machine.” The image of a beast armed with saber-like fangs, capable of taking down a mammoth, has endured in popular culture and remains prevalent in artistic depictions. On the other hand, a recent trend of “debunking” everything has also targeted these animals. Critics argue that the canines were too fragile and likely broke during bites, suggesting that sabertooth cats couldn’t hunt large prey and instead scavenged on soft tissues, using their long canines mainly for display during mating.

The answer to the question of the functionality of “saber” teeth lies not only in the anatomy of these cats but also in the broader history of synapsids.

The first “saber” teeth appeared long before sabertooth cats—or mammals for that matter. To meet their original owners, we must travel back to the Permian period, at the dawn of synapsid evolution. It’s widely known that all tetrapods (four-limbed vertebrates) except for amphibians are divided into two major groups: synapsids and diapsids. Diapsids include dinosaurs, birds, and other reptiles, while synapsids include mammals and their ancestors. In essence, the history from the late Carboniferous period to the present can be viewed as a competition between these two groups of animals.

The earliest synapsids were pelycosaurs, known for the distinctive “sail” formed by a skin membrane stretched over elongated vertebral spines. Their descendants, the therapsids, inherited a scaleless skin, a tendency toward thermoregulation, and differentiated teeth set in sockets, or alveoli. Therapsid teeth were divided into incisors for biting, molars for chewing, and canines for inflicting deep wounds and holding onto prey. Canines, thus, were initially distinguished from other teeth as the primary weapon, so it’s unsurprising that they grew larger over time.

Gorgonopsians, the dominant predators of the Permian period, were the first in history to develop massive canines. Their incisors differed from their canines only in size and position—five on the upper jaw and four on the lower. Gorgonopsian canines were long, sharp, and slightly curved backward. In Inostrancevia, a three-meter-long gorgonopsian with a skull measuring 43-60 cm, these canines could reach 15 cm or more, comparable in size to the teeth of Tyrannosaurus rex, excluding the root. Meanwhile, post-canine teeth were small, few in number, or absent altogether. Gorgonopsians didn’t chew meat or crack bones to access marrow as modern predators do.

Little is known about the hunting tactics of gorgonopsians. Their bite mechanics resembled those of crocodiles. Their jaw joint allowed them to open their mouths more than 90 degrees, after which powerful muscles would snap their jaws shut with force. A bite from their formidable array of incisors and canines could inflict serious injury. Most likely, they attacked from ambush, delivering one or two powerful bites and then pursuing their bloodied prey until it weakened, at which point they would finish it off. Damaged and broken canines suggest that they weren’t picky about where they bit, but this wasn’t a problem for gorgonopsians. Their teeth were replaced continuously, with a new tooth always growing behind the functional canine.

The Paleozoic era ended with the Great Permian Extinction, after which the rivals of synapsids, the archosaurs, flourished. The ancestors of mammals were relegated to small sizes, and the concept of the sabertooth predator was forgotten until the Cenozoic era.

Another mass extinction, the Cretaceous-Paleogene event, gave synapsids—now in the form of mammals—a new lease on life. Over the next several million years, mammals grew from mouse-sized creatures (with some reaching the size of badgers) to boar-sized animals weighing several hundred kilograms. Their dietary habits also changed. The species that survived the extinction were mostly omnivores, and by the Paleocene, specialized herbivores and carnivores had appeared. Initially, primitive ungulates, the mesonychians, rose to the top of the food chain. These large-headed, powerful-toothed predators held a significant place in the ecosystems of the Northern Hemisphere. Their evolutionary strategy focused on increasing overall size and jaw strength, leading to the emergence of true monsters. Andrewsarchus, the largest land predator among mammals, with a skull up to 83 cm long, terrorized the Eocene plains of Mongolia.

However, mesonychians eventually lost their dominant position. In the Eocene, they were displaced by creodonts, which quickly pushed mesonychians into the role of scavengers, and by the early Oligocene, they had taken over that ecological niche as well. By the Miocene, even creodonts had disappeared, outcompeted by the true carnivores, the Carnivora. A significant advantage for both creodonts and carnivores was the presence of carnassial teeth. These specialized molars and premolars, shaped like sharp, serrated blades, sliced through muscles, tendons, and small bones with ease.

Around 40-50 million years ago, during the Eocene, the first sabertooth predators since the Permian period appeared. These were machaeroids, known from well-preserved fossils found in Wyoming. Machaeroids were small, robust animals weighing around 10-14 kg. Their large canines were relatively shorter than those of sabertooth cats, and their jaws were stronger. Machaeroids lived in the tropical forests of North America and were likely ambush predators. A bit later, around 37 million years ago, the nimravids appeared in the order Carnivora. Nimravids resembled a cross between a fossa and a leopard and were related to the common ancestors of dogs and cats. They also had saber-like canines, earning them the nickname “false sabertooths.”

Nimravids inhabited tropical forests and shrubland savannas during the Oligocene. Over their 30-million-year existence, these predators occupied a wide range of ecological niches. The largest nimravid, Quercylurus major, was bear-sized and arboreal, while the smallest, Nanosmilus, was about the size of a small lynx. Nimravids used their canines not only for hunting but also in conflicts with one another and to eliminate food competitors. A skull of Nimravus bears a healed wound from the canines of a related species, Eusmilus. It’s unclear where nimravid evolution would have led if not for global landscape changes. In the Miocene, steppes and savannas began to replace tropical forests, leading to a decline in nimravid diversity. The last nimravids lived about 9 million years ago in relict wet forests of Europe.

While placental carnivores were competing with each other in the forests from France to Wyoming, marsupial carnivores in South America were slowly developing their own formidable teeth. The continent’s isolation turned it into a true testing ground for evolutionary experiments. Local mammals included xenarthrans, marsupials, and South American ungulates, which bore little relation to true ungulates beyond superficial similarities. In the Oligocene, rodents and primates joined this mix, having discovered the New World 40 million years before Columbus.

The ecological niches of herbivores had to be filled with what was available. Over a hundred genera of notoungulates (Notoungulata) are known, with species ranging in size from rabbits to rhinoceroses. Sloths grew to the size of elephants, while pyrotheres took on the roles of elephants and hippos. Giant armadillos grazed alongside graceful, long-legged litopterns. The top predators in this strange world were caimans, giant snakes, and flightless birds. Phorusrhacids, fast and fierce beasts standing up to 3 meters tall and weighing between 100 and 300 kg, were the terror of open spaces. Meanwhile, in forests and shrublands, marsupial sparassodonts (Sparassodonta), which resembled oversized opossums, prowled. By the Miocene, the shrinking of forests forced some sparassodonts to adapt to new environments. This evolution led to the emergence of Thylacosmilus, known as the sabertooth marsupial tiger.

Thylacosmilus resembled a stocky, low-slung jaguar and could weigh between 60 and 110 kg. It was the largest quadrupedal predator in Miocene Patagonia and the only mammal hunting large prey. Isotopic analysis of its teeth shows that its primary diet consisted of notoungulate herbivores. But how did it hunt? And did it even kill its prey? The temptation to label this sabertooth predator as a scavenger is strong, as its long canines seem too fragile for active hunting. However, anatomical features suggest otherwise.

Thylacosmilus‘s dental system was poorly suited for scavenging. The upper canines, positioned close together, could reach 12-15 cm in length, not including the alveoli that extended to the frontal part of the skull. The molars and lower canines were small, the upper incisors were absent, and the two lower incisors were highly reduced. Meanwhile, the bite force was much lower than that of a leopard or jaguar. This means Thylacosmilus couldn’t gnaw on bones, let alone crack them. Computer modeling shows that the structure of the skull was adapted to withstand the stresses from powerful vertical strikes with the canines. The jaw joint allowed the mouth to open 100 degrees. The strike itself was delivered by the neck muscles, which were even more powerful than those of Smilodon. To avoid horizontal stresses that could damage the teeth, Thylacosmilus had to hold its prey for some time, and its short, very strong forelimbs fit perfectly into this picture.

We don’t have a precise understanding of Thylacosmilus‘s hunting tactics yet. It was likely an ambush predator, capable of long, slow pursuits of wounded animals. The dismemberment of the carcass was done using the cheek teeth, as indicated by their wear patterns. Thylacosmilus probably also used its clawed forelimbs to assist in this process. The structure of its teeth made it a selective eater: it likely consumed only the internal organs and the softest muscle tissues, meaning it had to hunt more frequently than other predators. Thylacosmilus survived until the end of the Pliocene (2.5 million years ago) but went extinct during the Great American Biotic Interchange following the formation of the Isthmus of Panama. Another 1.5 million years later, the plains of South America became home to the largest sabertooth mammal—Smilodon.

If the Paleogene period could be called the age of tropical forests, then the Neogene was the age of steppes and savannas. About 25 million years ago, a new type of ecosystem emerged in the arid regions of continental Eurasia: vast grass-covered plains with large herds of ungulates. By the end of the Miocene, about 7-8 million years ago, isolated patches of these grassy plains merged into one enormous steppe belt that stretched from North Africa to Chukotka and beyond, extending westward to the Mexican plateau. These spaces were home to the Hipparion fauna complex, named after the three-toed ancestors of horses.

The emergence of sabertooths was a natural result of the “arms race” between predators and prey. In open spaces, the key to survival for herbivores became speed, a herd lifestyle, and increasing size. This strategy can be seen in the evolution of horses, antelopes, and cattle. Meanwhile, the sheer size of some animals became a defense in itself, especially for solitary creatures like rhinoceroses and elephants. In such a situation, predators had two effective solutions. The first, collective exhaustive pursuit of prey, was fully realized by the Canidae family. The second, solitary ambush attacks with rapid kills, became the foundation of the evolutionary success of the Felidae family.

The members of the subfamily Machairodontinae (sabertooth cats) achieved the highest specialization in this hunting tactic. Their homeland was the savannas of Africa, from where sabertooth cats spread to Eurasia and through Beringia to America. It seems that the “sabertooth” trait complex arose from intense competitive pressure among predators in the African savannas. Similar adaptations also developed in the archaic barbourofelids, which coexisted with true sabertooth cats until the end of the Miocene. By the Pliocene, sabertooth cats had produced a plethora of species ranging in size from an ocelot to a large lion. In the Pleistocene, some of them, like Smilodon, crossed the Isthmus of Panama into South America, where they grew to record sizes. A Smilodon populator skull from Uruguay measures 38 cm long, suggesting the animal weighed up to 430 kg and stood about 1.2 meters at the shoulder. Smilodon‘s canines could reach 28 cm in length, including the root.

Discussions about how sabertooth cats used their canines are among the longest-running in paleontology. On one end of the spectrum is the idea that they served a purely ornamental function, reinforced by sexual selection. On the other, they are seen as terrifying weapons capable of crushing mastodon vertebrae and piercing armored armadillos. As is often the case, the truth lies somewhere in between. The wear patterns on the canines and the nature of skull injuries suggest that these were functional tools, used both during hunting and in fights between predators.

There are several models for the bite mechanics of sabertooth cats. In the first stage, the prey is knocked down and held with the forelimbs, a behavior typical of modern large cats. Lions, tigers, and leopards try to break their prey’s neck or strangle it by biting its throat. Smilodon‘s bite force was a third weaker than that of a lion, but like Thylacosmilus, this was compensated by its powerful neck muscles. The enormous canines allowed it to kill its prey as quickly as possible, usually with a single bite to the throat that severed blood vessels. The risk of breaking a canine was relatively low since the bite was delivered to soft tissue. The target could also be the prey’s abdomen, but this was riskier as it exposed the predator to the possibility of a dangerous kick. This tactic was more feasible when hunting in packs, where some individuals held the prey while others slashed at its belly with their teeth. Whether Smilodon (or other sabertooth cats) was social remains an open question.

Sabertooth cats went extinct at the end of the Pleistocene, with the end of the last Ice Age. In northern regions, this was due to the disappearance of the mammoth-steppe fauna and the spread of taiga forests. In tropical savannas and prairies, other feline species, with more flexible feeding behaviors, played a significant role in their decline.

Saber-like canines appeared among synapsids with remarkable regularity through the convergent evolution of different groups of organisms. In the Oligocene forests of North America, in the Miocene savannas of Africa, and in the prairies of Patagonia, environments with intense competition among predators fostered the development of a strategy for killing prey as quickly as possible with a single bite. Similar conditions may have existed during the Permian period.

As a result, a stable complex of “sabertooth” traits emerged:

• Hypertrophied canines
• Flexible jaw joint
• Low bite force
• Powerful neck muscles
• Strong forelimbs

Effective use of this complex was only possible when actively hunting large prey. The inability to gnaw bones ruled out regular scavenging. At its peak, with the development of these traits and the increase in the size of their owners, the animals transitioned into the niche of a super-predator with a narrow specialization. The downside of this process was the loss of evolutionary flexibility, which inevitably led to extinction when environmental conditions changed.