When one looks at the history of life, one often discovers that the similar forms develop again and again independently. This convergent evolution occurs because a good solution is a good solution, no matter how it arises. Thus for example, we find that sharks, Ichthyosaurs and dolphins are all have similar shapes - even though they evolved independently - because they are hydrodynamic shapes that allow them to easily move through water. Likewise, we can find several cat-like animals with saber-teeth, as these seems to be a good solution for hunting prey.

The best known saber-toothed cat is Smilodon, the so-called "saber-toothed tiger". It evolved in North America about 2.5 million years ago, and eventually spread to South America when the isthmus of Panama joined these two continents. Smilodon was a large and powerful animal that hunted large prey, but it died out about 10,000 years ago when its prey when into decline.

Thylacosmilus was a cat-like marsupial, again with long canine saber-teeth. It lived between 20 million and 5 million years ago, and was thinner in build than Smilodon. You can recognize Thylacosmilus by the bony flanges on its lower jaw which acted as scabbards protecting its canine saber-teeth. It is important to realize that Thylacosmilus, was not closely related to any of the cats, or even any of the Carnivora - it developed its cat-like form, as well as its saber-teeth, entirely independently.

Machairodus was another a saber-toothed animal. It lived in much of the northern hemisphere, between about 13 million and 2 million years ago. It was not particularly closely related to Smilodon, although it was in the same Family. Machairodus' saber-teeth had a unique serrated edge.