You'll probably get a lot of T-Rexes with trunks.
I think, the reason for misinterpretation of skeletons is the missing information about other material than bones.
However, taking the hippo as an example, some convex bone shapes seem to be a hint for neighboring body fat and muscle. I'd check first, if current artists would do better after training themselves on living animals. Also, I'd check whether reptiles can get as fat as mammals, etc.