This tree shows how the octopus is related to tetrapods, and the points in their evolutionary histories when their limbs evolved. Tetrapod and octopus limbs evolved independently after their point of common ancestry, so they were not inherited from a common ancestor. Therefore, they are not homologous. The same is true of the grasshopper leg and the sea star arm.
Image use policy: For non-commercial, educational purposes, this image may be used with a Creative Commons CC BY-NC-SA 4.0 license. Please credit as follows: © University of California Museum of Paleontology, Understanding Evolution, www.understandingevolution.org
This image is part of a series: