Silicified Sponge – Cystospongia monostoma

Cretaceous

Garraf, Catalonia, Can Casanyas Castellet Spain.

70mm 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.  The oldest undisputed sponge fossils are Cambrian age and bear the same biomineralized skeletal structure as modern forms.  How that skeleton transitioned from a more simple form remains a mystery.