This is the hard part about making ESO in a time no one is familiar with. They have to include the creatures people have seen so they can tie it to what they know about Elder Scrolls.
Imagine if you went into the game without ever seeing a single Mudcrab. But instead saw a Sand Crab that is afraid of water. No one would understand.
Evolution does not work that fast. It would stand to reason that any critters around today would be around 1000 years ago. If it was like our world, a 1000 years ago we had some more interesting things, like Aurochs
How about that fossilized giant mudcrab that was in Skyrim?