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Bryozoan fossils alter evolutionary history of animals

Updated: Jun 26, 2022

Around 541 million years ago, the Cambrian radiation occurred, when multicellular animals (known as metazoans) rapidly diversified, setting the stage for the formation of the main animal groups (called phyla) we see today. Below, we see beautiful examples of bryozoans illustrated by historically renowned natural scientist and artist Ernst Haeckel.

Bryozoa fossils by Ernst Haeckel
Bryozoa fossils by Ernst Haeckel

Nearly all animal phyla can be traced back to the Cambrian radiation, when they first appeared. An exception has been with Bryozoa (also called moss animals), where links to the event have been missing. With an extensive fossil record, they have survived through the ages and we can still see them today, with around species currently existing on Earth. You may have spotted bryozoans as a lacy mesh-like growth on seaweed – a sea mat. They are simple, aquatic invertebrate animals using a ‘crown’ of tentacles to feed.

Research previously marked the first appearance of bryozoans in the fossil record around 480 million years ago during the Ordovician period. The oldest found in the fossil record were colonies of zooids, 50 million years later than when most other animal groups appeared to emerge during the Cambrian.

An earlier origin of the group was long suspected by scientists, but there’s been a lack of convincing evidence. But a new study published in Nature identifies bryozoan fossils from the Cambrian, pushing back the origins of bryozoans another 35 million years ago, filling in an important gap that was missing about our understanding of the evolution of animal life as we know it.

The team analyzed the fossil Protomelission gatehousei from the early Cambrian of Australia and South China, finding that the structures, organic composition, and phylogenetics indicated that this specimen is a stem-group bryozoan.


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