Blackwell Publishing

Fossils and the history of life - How are fossils formed?

In this sponge we can see a large circular area, and we can see the skeleton perforated by tiny holes. In life the sea water was sucked in through these small holes, the food in the sea water was extracted, and then the sea water (minus the food) was expelled through this central cavity. The type of feeding in sponges has not changed for more than half a billion years.

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