Silicified Sponge – Moretiella elegans
Cretaceous
Garraf, Catalonia, Can Casanyas Castellet, Spain

72mm silicified sponge.

Moretiella is a genus of sea sponge best known from the Early Cretaceous of Europe but also present in the Late Cretaceous.

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 developed remains a mystery.