The Machaeroides are a genus of dog-size carnivores that lived during the early Eocene, about 50 million years ago. They lived before the nimravidae family developed, and are likely the oldest mammals with saber teeth, Tseng said.
Some of the Machaeroides had serrated sabers, he added.
"If it was totally smooth, without serrations, the teeth might get stuck," he said, "With a serration, you can cut through [the prey]."
The genus Homotherium migrated from Eurasia to North America. But though its remains are also found in the La Brea Tar Pits,Homotherium is far less common than the saber-toothed cat, according to a 1993 study in the journal PaleoBios.
Homotherium is also known as the scimitar-toothed cat (after the sword), largely because its upper canines were long, but not long enough to pass its lower jaw, according to Prehistoric Wildlife. Its sabers were also serrated, but relatively fragile, and would have plunged into prey in a vertical, not horizontal, motion.