Okay, point taken, but we have complete skeletons, and scientist and artists (conceptualizing). today.
These stones are said to be at least 400 years and more old!
How could they draw these so anatomically correct hundreds of years before paleontology?
read the articles about the illustrations, There are details they could have known only if they saw them.
ancient stylization is understood, but these etchings are impressive.
whether you accept them or not, they would be a serious blow to current evolutionary thought.
Fossils have been discovered exposed naturally by erosion. I don't see any reason to assume that if someone had seen that 400 years ago they couldn't "conceptualize" what the creature that skeleton came from might look like just as well as someone today might.
You seem terribly impressed with the detail of their knowlege of the subject, which I find puzzling since we've never seen one. That means we really don't know how accurate that depiction really is.