I was thinking of extinct animals. (Maybe I should have said "paleontologists".) Whenever there's a structure or physical feature in a fossil whose purpose we c

I was thinking of extinct animals. (Maybe I should have said "paleontologists".) Whenever there's a structure or physical feature in a fossil whose purpose we can't identify, the default assumption is "it was probably used for mating displays." Sometimes further study (or comparison to extant species) comes up with a more practical use later. It's all hypothetical, of course, but so is "religious purposes." :)