Understanding Evolution

The tetrapod limb

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.

Homologous Tetrapod Limbs

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 (the humerus) attached to two other long bones (the radius and ulna), with a branching series of smaller bones (carpals, metacarpals and phalanges) on the end.
Here you can see the same bones labeled in these different limbs:

Tetrapod limbs with bones highlighted

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


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Understanding Evolution © 2018 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California