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Fossils seaweed

A leading scientist from our Department of Earth Sciences has collaborated with researchers in China to reveal that a group of prehistoric sea creatures is not as ancient as we thought - their earliest fossils are actually seaweeds.

Fossils that were previously thought to be the oldest Bryozoans, are in fact green algae.


Bryozoans are tentacle-bearing animals that lived in skyscraper-like underwater colonies.

The researchers found that Bryozoans were the only group of fossil animals not to appear in the Cambrian “explosion”, a rapid burst of evolution 520 million years ago.

Ancient fossil material discovered in the hills of China revealed the previously unseen “soft parts” of Protomelission gateshousei, formerly believed to be the earliest Bryozoan.

This fragile tissue allowed the researchers to interpret Protomelission as a member of the green algal group Dasycladales.

Seaweeds living inside skeletal chambers

Where previous fossils only preserved the skeletal framework of these early organisms, the researchers’ new material revealed what was living inside these chambers.

Instead of the tentacles they would expect to see in Bryozoans, they discovered simple leaf-like flanges – and realised they were not looking at fossil animals, but seaweeds. 

This means that the oldest convincing Bryozoan fossils did not evolve until the next geological period, the Ordovician (480 million years ago).

The delayed appearance of bryozoans shows what the Cambrian did was not a unique period of innovation as conventionally thought; instead, new body plans continued to be carved out by evolution over a much longer time period.

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