Creationists can't understand morphology
I've referenced this topic in previous posts, where different writers for AiG display their ignorance of the subject.
Between calling Protocetus a Pinniped or birds only have a pisiform, you can see how bad it is.
However, it also leads to hilarious contradicting opinions on transitional forms like Acanthostega or Homo habilis.
The concept of uniquely created kinds is challenged by morphology, which is why this happens, for there is no way to separate birds from dinosaurs, humans from apes, or whales from ungulates. transitions in the fossil record demonstrate gradual morphologic change, instead of distinct groups unrelated to anything else.