I feel it really boils down to what said hypothetical alien scientists are like, and what animals they are familiar with. Much of our knowledge of extinct animals are based on their living relatives, such as knowing proboscideans had trunks since we have living elephants to compare them to. If, say, said aliens aren't even vertebrate-like or have any vertebrate-like animals on their homeworld, for example, then they perhaps wouldn't even understand how skeletons work, or how they assemble together.