Saber-toothed tiger

The saber-toothed tiger was an ancient, extinct species of large feline native to Earth.

Sylvia, an extragalactic alien who inhabited Pyris VII, took the form of an immense cat, as she attempted to destroy Captain Kirk and his landing party.

Kirk inquired to Spock why she took the form of a cat, to which Spock explained that "the cat is the most ruthless, most terrifying of animals, as far back as the saber-toothed tiger."