Silicified Sponge – Cystospongia monostoma

Cretaceous

Garraf, Catalonia, Can Casanyas Castellet, Spain.

45mm silicified sponge. It is literally made of glass!

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 developed remains a mystery.