Oldest fossils of mysterious animal group are actually seaweeds

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

Bryozoans

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.

Find out more

• Learn more about the work of Dr Martin Smith.
• Check out Dr Smith’s personal website.
• Read the full paper published in Nature.
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