Fossil Sponge from Flamborough

This fossil sponge was collected from the beach at Selwicks Bay, Flamborough Head, on a Rockwatch weekend in the early 1990s.

It was embedded in a fragment of chalk that had fallen from the cliff, so it dates from the Upper Cretaceous Period, 95 to 65 million years ago. I drew it for my 1996 book Yorkshire Rock, A Journey Through Time but since then the chalk that surrounded it has split into shards. The collar of the smaller sponge has disintegrated too.

How I imagine it might have looked, growing in the chalky ooze of the Cretaceous sea bed.

Sponges were common as the age of the dinosaurs drew to a close. They had a sac-like body with a central cavity known as the cloaca.

The nearest species that I can find is Laosciada, a mushroom-shaped lithistid, a kind of demosponge, informally referred to as a calcisponge. It lived in deep water, between 100 and 400 metres.

The skeleton of the collar of this sponge is made up of interlocking spicules, which look like little pyramids in close-up. They’re made of silica which, remineralised, forms the layers of flint found in the chalk.

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