Evolution has a fondness for saber-toothed creatures. Time and again, animals with elongated canine teeth have roamed the planet. The ferocious Smilodon of the Ice Age is among the most famous: a lion-sized cat with huge fangs that hunted ancient horses and bison across the Americas. But that’s only the tip of a saber-toothed history going back more than 250 million years.
Most of the time, paleontologists use the term “saber-toothed” for carnivorous mammals who use long, flattened canine teeth to puncture or shear away the flesh of other creatures. But the designation isn’t quite so simple. Other mammals and even proto-mammals have been called saber-toothed even though they’re herbivores, using very similar teeth to tussle with each other rather than bite into prey. On that score, there are technically still some saber-toothed animals around today. Male musk deer compete with each other every mating season by fighting with their fangs.
Even among saber-toothed carnivores, though, more than one tooth shape or dental arrangement has worked. Saber-toothed cats, for example, are often divided into the dirk-toothed and scimitar-toothed groups. Most of the dirk-toothed cats had longer, finely serrated fangs, while scimitar-toothed cats had shorter canines with shorter serrations, and paleontologists suspect that the different tooth shapes indicate different biting techniques. Such differences underscore that there were many ways to be saber-toothed, and the following creatures help highlight the variety of fanged creatures that have walked the earth.
One of the oldest saber-toothed creatures we know about was an herbivore. Named in 2011, Tiarajudens eccentricus was a squat, tubby proto-mammal that roamed prehistoric Brazil about 260 million years ago. Relatively little of the animal’s skeleton is known so far, but paleontologists nevertheless uncovered a beautifully preserved cranium that shows the creature had long, flattened canine teeth jutting from the upper jaw. Those teeth weren’t for piercing prey, though. Most of the proto-mammal’s teeth were suited to grinding and crushing—the teeth of an herbivore—and so paleontologists think that Tiarajudens used their fangs in combat with each other the way those modern musk deer do.
Of all the saber-toothed carnivores to stalk the planet, Inostrancevia was one of the largest. The biggest adults could be more than ten feet long and weighed more than 600 pounds, about the size of an adult black bear. And while the earliest examples of Inostrancevia were found in Russia, paleontologists recently discovered that the proto-mammal made it to prehistoric South Africa, too, indicating members of the genus migrated 7,000 miles across the ancient continent of Pangaea.
Named Inostrancevia africana, the new species was similar in size to those found in Russia and is likely descended from them. The carnivore is thought to have walked across Pangaea to reach the area now preserved in South Africa’s Karoo Desert. The move might have been one of desperation. Rapid climate change caused ecosystems to quickly shift and collapse, perhaps driving the saber-toothed animal to wander farther in search of adequate prey. Inostrancevia africana likely replaced earlier carnivores in South Africa that had gone extinct, itself disappearing during a drawn-out, million-year mass extinction driven by volcanic activity at the end of the Permian Period around 252 million years ago. Another saber-toothed carnivore of comparable size wouldn’t arise until more than 200 million years after the extinction of Inostrancevia.
Uintatherium anceps is surprisingly famous considering that we still know relatively little about it. The huge herbivore roamed what’s now the western United States between about 38 million and 56 million years ago. The mammal’s instantly recognizable skull had three sets of blunted horns and a set of long, flat canine teeth that rested against a bony sheath on the lower jaw.
Paleontologists have been puzzling over Uintatherium since the late 19th century. In fact, the infamous “Bone Wars” between cantankerous naturalists Edward Drinker Cope and Othniel Charles Marsh did not start over a dinosaur, but over specimens of Uintatherium that both researchers gave different names in their rush to publication. The paleontologists and field crews they hired collected multiple specimens of the mammal, as well as other prehistoric creatures, and tried to outdo each other in being first to name and describe as many fossil creatures as possible.
To this day, the mammal is placed within its own order—the Dinocerata—but paleontologists don’t know how the dinoceratans fit into the broader mammal family tree or much at all about the animal’s biology other than it was a large plant-eater. Experts suspect that the long teeth played some role in how the mammals selected mates, like Tiarajudens, but details will remain speculative until experts turn their attention back to this neglected fossil celebrity.
Around 42 million years ago, mammal evolution was really taking off. Beasts were getting bigger in a world where the only remaining dinosaurs were birds, and mammals evolved into all sorts of shapes and sizes. Among them was Diegoaelurus vanvalkenburghae, the oldest carnivorous saber-toothed mammal yet known.
Despite its superficially cat-like appearance, Diegoaelurus was no feline. The animal belonged to an as-yet-mysterious group of carnivores called machaeroidines that thrived before the origin of true cats. In life, the carnivore was about the size of a bobcat and probably behaved like a civet or fossa. Early in the Age of Mammals, it was predators like Diegoaelurus who chased our own early primate ancestors through the trees.
No group of animals spun off saber-toothed members quite like the feliforms. This major branch of the carnivoran family tree—roughly meaning “cat forms”—includes civets, hyenas, cats and totally extinct forms like the nimravids, cat-like predators that were saber-toothed millions of years before true cats were. The most iconic nimravid of all might be Hoplophoneus occidentalis.
Nimravids evolved into sizes ranging from bobcat to lion, with Hoplophoneus occidentalis reaching sizes comparable to modern leopards. The cat’s skull was quite a bit different from that of a leopard, however. Nimravid skulls did not have the enlarged, domed cranium space that true cats do, and nimravids often evolved elaborated flanges of bone on their lower jaws that acted as sheaths for their long canines. They were also fractious beasts. Multiple nimravids have been found with tooth marks around their eyes, and one specimen represents two nimravids that died together when one got stuck biting into the arm of another.
Some saber-toothed creatures looked downright gnarly—few more so than Barbourofelis fricki. The carnivore stalked what’s now western North America between about 7 million and 13 million years ago, filling a similar niche to the later Smilodon even though it was not quite a cat.
Barbourofelis also belonged to the nimravids. The resemblances between nimravids and saber-toothed cats is one of evolutionary convergence, or evolving similar forms due to a shared niche—in this case, hunting down the big prey of its time such as horses and rhinos.
Some saber-toothed animals broke the rules. In the fossil cat family tree, Xenosmilus hodsonae is closest to the “scimitar tooth” cats with shorter, more serrated canines. But the teeth of Xenosmilus are different, bigger and thicker, and the cat is more heavily built, more of an ambush predator than a runner.
The cat definitely wasn’t gentle with its food. Paleontologists hypothesize that Xenosmilus was capable of biting out massive chunks of flesh from prey, perhaps backing off to let the animal die from blood loss and trauma before returning. The fossil peccary Platygonus was likely favored prey for the cat, and damaged Platygonus bones indicate that Xenosmilus could use its closely packed incisor teeth to efficiently scrape meat off the skeleton. Of all the saber-toothed cats to ever live, Xenosmilus stands out as one of the most formidable.
Smilodon is the most famous saber-toothed animal of all time, the feline equivalent of Tyrannosaurus rex when it comes to fossil fame. And there wasn’t just one species in this iconic genus. Paleontologists have uncovered at least three, including the relatively small Smilodon gracilis and the Smilodon fatalis, notably preserved by the hundreds in the La Brea asphalt seeps. But largest of all was Smilodon populator, a species that evolved in South America after the cat’s ancestors crossed the land bridge in modern-day Panama.
Large Smilodon populator reached nearly half a ton in weight, and the proportions of the cat hint that it was an ambush hunter that used its powerful arms to wrestle prey to the ground before delivering a devastating shear bite to the throat that severed the windpipe and major blood vessels. Sometimes the cats even turned their fangs on each other. Fossils from South America, as well as Smilodon fatalis from La Brea, indicate that sometimes Smilodon bit each other on the head and were able to drive their fangs through the skulls of their opponents.
But the cat’s life was not all “nature red in tooth and claw.” Recent research has indicated that Smilodon cubs stayed with their mothers for an extended period of time, living and hunting as families before the cat’s extinction about 10,000 years ago.