What is so surprising about this? Why would anyone suppose that Neanderthals would not eat shellfish? Hunting and gathering people will eat just about anything they can find, and mussels are very tasty, and full of good nutrients. They are also easy to prepare.
Directions for preparing mussels (from an old Neanderthal recipe):
1. Find mussels, Bring them back to cave or hut.
2. Have wife built fire.
3. Throw mussels around edges of fire.
4. When mussel shells open up, mussels are cooked — enough. Retrieve them, and when they are cool enough, eat them.
What is ‘fire’?.................
You left out the garlic and white wine reduction sauce. :-))