You are at the aquarium looking at a freshwater mammal tank and an adult manatee swims close to the glass. On his front flippers you see fingernails. What is a likely explanation for the presence of fingernails on a manatee?

Answer: They are vestigial structures

Explanation: Vestigial structures are those which have lost their original original function over a very long period of time for evolution, most of these functions if not all, and there are only remnants of those structures, as in this case fingernails in the manatee. Such vestigial structures are also found in humans, which means the remains of those structures that used to be larger and had a function that they do not have in the human body today. The characteristic of vestigial structures is that they are, for example, normal in some other species and therefore have specific function, while in some species they do not have that function that they had many millions of years ago, i. e before evolution. So these vestigial structures are in fact evidence of evolution.