Silicified Sponge

Cretaceous

Garraf, Catalonia, Can Casanyas Castellet, Spain

53mm silicified sponge.

Paleontologists consider sponges to be among the oldest groups of modern animals.  It appears that they diverged from their ancestors in Precambrian time because Cambrian-age sponges already bear the same biomineralized skeletal structure as modern forms.  How that skeleton evolved from a more simple form and what that simple form was remain a mystery.