fossils are non stackable items that can be found in mines. mines are heaps of stone with a door in it, on th door is a sign of a pickaxe.
when found lieng around they have a circle shape made out of stone, with a paw on the top.
when in your inventory it still has the oval shape, but it has the picture of a randomly choosen hybrid.
there is no use yet, but we do know that in the near future, there is gonna be an update so we can trade with the , a new npc in a mine close to the town Yandi. he will bu fossils off of you.