Not really fixed, the whole mixed match fossils are based off of real life Chimera fossils. When bones a found and just put together to recreate the skeleton, but the bones all come from different animals. The horrid abominations that exist in defiance of the natural order are fully intended to look that way.

That's the idea. They should evoke the feeling of being an abomination. It's like wanting to watch a horror film but remove the scary parts.