Each of the letters on the cladogram represents the appearance of a certain inherited feature.

Click on each of the letters to learn more.

Begin with the feature that evolved first (A), then proceed in alphabetical order.

The inheritance of these features provides evidence of ancestry and relatedness.

Two additional openings (besides the eyes and nostrils) on the side of the skull behind the eyes. Animals with such openings are called "diapsids."

Fine filaments growing from the skin, consisting of special epidermal cells, and providing insulation.

Egg that can be laid on land due to the presence of a fluid-filled amniotic sac that cushions and protects the developing embryo.

Possessing four limbs for terrestrial locomotion, unless secondarily lost or modified for other types of locomotion, as in the flippers of whales or wings of bats. Animals with four limbs are called tetrapods.

Although "bone" tissue evolved earlier, a true bony skeleton does not appear until the ancestors of bony fishes and consists of hardened bone, not cartilage.

The skeletal units of the spinal column, or backbone, that protect the spinal cord and support the body.