Fossil Record

The Bryozoa have an incomplete fossil record because of the poor fossilization-potential of non-calcified forms such as the Ctenostomata. Bryozoans appeared in the early Ordovician and underwent a rapid burst of evolution. Particular groups were dominant at different periods in Earth history.

• Palaeozoic: Trepostomata or "stony bryozoans" were the most abundant and diverse, though the Cryptostomata were also important during the Early Palaeozoic. The fenestrate bryozoans were important in the Late Palaeozoic.

• Mesozoic: The Cyclostomata, which survived both the end-Permian and end-Cretaceous mass extinctions became enormously abundant in the Jurassic and Cretaceous Periods, though they declined in numbers in the Cenozoic.

• Cenozoic: The Cheilostomata became hugely important in the Cenozoic. Bryozoans of this order express a high degree of colonial integration and every zooid is connected. This may have involved some modification to the structure of their colony to make effective use of water currents while feeding.

Redrawn from Clarkson (1998)

• Characters/ anatomy
• Major subgroups in the phylum
• Fossil record
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Author: Luke Mander
Last updated: 20.11.05
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