Description: The Osteostracii are a primitive group of jawless fish. This one is known as Witaaspis and comes from the Silurian of Estonia. It had a rounded shield that covered most of the body and was presumed to have aided the fish in plowing through the substrate in search of food. The shield was one solid piece, and as such most likely did not grow as the animal aged. Presumably the larvae had no such protection, growing a shield only once they had reached the mature stage.

Also see: Paleozoic Fish Fossils