Several groups of mammals, including echidnas, insectivorous hedgehogs, and some shrew-like Madagascan mammals, all share prickly protrusions of the skin. These animals live in sufficiently distant environments that their interbreeding is unlikely. Since their habitats share similar features, however, scientists conclude that these animals independently evolved prickly skin to serve similar functions.
Which of the following would it be most useful to establish in order to evaluate the scientists’ hypothesis?