In lieu of my usual making a guessing game out of things, I'm just going to blurt out my thoughts:

Snails = our future paleontologists assumed these looked quite similar to their Squid relatives, misinterpreting a poorly preserved head and tail as 2 tentacles
Crab = claws mistaken as actual heads; maybe not all that realistic, but it was too fun an idea to ignore
Fish = based more on cartoon depictions of a fish skeleton than the actual thing; again, not that realistic, but I love these vertically flat little beasts
Oysters = OK, not really different from real oysters, but a cow bone I found on the beach was encrusted with oysters and wanted to reflect the visual here. I suppose our future paleontologists can get it right at least once!

Giraffe = the tongue is actually pink, but using the background blue-green for the shadows makes it look... well, exactly like a real giraffe's.