The toothed sea bird Hesperornis was flightless. Its strong hind limbs and large webbed feet served to propel it in the water when it hunted fish. The sharp teeth in its beak were used to grip prey.

Birds evolved from small carnivorous dinosaurs. These bird ancestors had teeth in their mouths, while modern birds have toothless beaks. Some early birds were transitional: they had teeth, while otherwise resembling the birds of today.