Machairodontinae

The Machairodontinae were a specialized subfamily of extinct carnivoran mammals. They belong to the Felidae family, which includes all modern cats. However, they represent the earliest major branch of this family. Their name comes from the Ancient Greek words for "sword" and "tooth."

While many people call them "saber-toothed tigers," this is actually a misleading term. They were not closely related to modern tigers. They also did not necessarily have tiger-like coat patterns. Instead, they were a unique group of predators that lived a very long time ago.

These predators used a very specific hunting mechanism to kill their prey. Modern big cats usually bite the muzzle or throat to cause asphyxiation. This means they squeeze the throat so the prey cannot breathe. In contrast, machairodontines used their specialized teeth for a different purpose. They would first immobilize their prey. Once the prey was held still, they used powerful neck muscles to drive their saber-like canines into the throat. The lower jaw acted as an anchor during this process. This method caused rapid death through significant blood loss.

Scientists categorize these extinct cats into different types based on their physical traits. The two most famous groups are the dirk-toothed and scimitar-toothed cats. Dirk-toothed cats, such as the genus Smilodon, had very long and narrow upper canines. They also tended to have stocky, heavy bodies. Scimitar-toothed cats, like the genus Homotherium, had broader and shorter upper canines. These cats generally had more lithe bodies with longer legs.

One unusual genus, Xenosmilus, combined these traits. It possessed the heavy limbs of a dirk-toothed cat but the stout teeth of a scimitar-toothed cat.

Our understanding of how these cats evolved has changed due to new fossil discoveries. For a long time, scientists thought the saber-tooth shape appeared very quickly. However, the discovery of the Batallones-1 fossil site in Spain changed this view. This site provided fossils of ancestors like Promegantereon ogygia and Machairodus aphanistus. These finds support the theory of mosaic evolution. This means the saber-tooth phenotype developed gradually over time. Different body parts, such as the skull or limbs, changed at different speeds.

Evolutionary pressure likely drove these physical changes. Scientists believe the need for rapid killing was a primary driver. The environment was likely very competitive for food. Many fossils show broken teeth, which suggests frequent contact with bone. This could happen if predators were fighting over carcasses or eating prey very quickly. If a predator cannot kill quickly, it might lose its food to a competitor. This could lead to starvation or exhaustion. Therefore, the ability to kill fast provided a major survival advantage.

To accommodate such massive teeth, machairodontines had to undergo significant skull modifications. A modern lion has a gape of about 95 degrees. If a lion had nine-inch teeth, it could not open its mouth wide enough to use them. To solve this, machairodonts changed their jaw anatomy. They reduced the coronoid process, which is a jutting strip of bone on the jaw. This reduction allowed the temporalis and masseter muscles to change shape. These muscles are usually thick and not very elastic, but modifying them allowed for a much larger mouth opening.

Machairodontines were once incredibly successful and widespread. They likely originated in Eurasia during the Middle Miocene. From there, they spread to almost every continent except Australia and Antarctica. During the late Miocene and Early Pliocene, they were the dominant large predators in North America and Afro-Eurasia. At that time, the ancestors of modern cats were mostly small. However, the group eventually began to decline. Environmental changes and competition with other large cats, like pantherins, played a role.

Environmental shifts and the arrival of humans contributed to their final disappearance. The last species of Smilodon and Homotherium became extinct around 12,000 to 10,000 years ago. This occurred during the end-Pleistocene extinction event. This was a time when many large mammals in the Americas also died out. This period followed the arrival of humans in the Americas at the end of the Late Pleistocene. Their disappearance marked the end of a major chapter in the history of the cat family.