Congratulations! You seem to already be an expert in homologies — you’ve selected all the homologous limbs. The four limbs you picked out all belong to tetrapods — animals with four legs.

Notice how these tetrapod limbs are similar to one another:

• They are all built from many individual bones.
• They are all spin-offs of the same basic bone layout: one long bone attached to two other long bones with a branching series of smaller bones on the end.

Here you can see the same bones labeled in these different limbs:

Even though these limbs are similar to one another, the animals they belong to are quite different from one another. To what animals do these homologous limbs belong?