In chapter 319 page 3, "Kaka" (Atom in disguise) shows Terry, Kiss, and Quinn a piece of skin or fur of an animal that makes the three scared. What is this skin?
Unknown creature's skin: ATOM possesses a mysterious piece of skin that appears to have belonged to a creature of tremendous power and vicious bloodthirsty ferocity. Just showing this little piece of skin could invoke paralyzing fear in the hearts of Terry, Kiss, and Quinn.
Taken from Toriko Wikia.
So, it seems never to be resolved from what kind of creature this skin was.