Protomelission Gatehouse may not be Bryozoan

15 mars 2023

According to a new study, Protomelission Gatehousei, a primitive organism that lived in the oceans 520 million years ago, may not be a bryozoan as previously thought, but rather a species of algae.

Although it may seem impossible to confuse an animal species with a plant species, differentiation can be difficult in certain specific cases, especially when dealing with a fossil that is 520 million years old!

Protomelission Gatehousei was first described in 1993. However, it was not until 2021 that scientists categorized it as an animal species, belonging to the bryozoan family, proving that its identification was not obvious from the beginning.

Colonies that closely resemble algae or corals Bryozoans are an important group of marine animals that form colonies attached to rocks and whose structure is more or less calcified. These animals feed by filtering seawater. The fleshy body of the animal has tentacles and is housed within an exoskeleton composed of carbonates. Bryozoans contribute to the construction of coral reefs. Some can even be confused with corals, which are not part of this group of animals. And the confusion does not stop there, as this type of animal colony closely resembles certain algae colonies that have the same architecture.

It seems that Protomelission Gatehousei has suffered from this confusion. The discovery of new fossils in southern China, which are better preserved than previous ones, has allowed for a more precise description of these primitive organisms dating back to the early Cambrian period. It turns out that what had previously been described as bryozoan tentacles were actually just typical outgrowths of certain algae. This analysis was published in the journal Nature.

Implications for the appearance of Bryozoans Protomelission Gatehousei would therefore not be an animal, but a plant species. This revision has strong implications, as it pushes back the age of the oldest known bryozoan fossil to 480 million years ago. Their appearance would therefore only date back to the beginning of the Ordovician period. As a result, Bryozoans would be the only important animal group not to have appeared during the Cambrian explosion, but rather after.

However, this interpretation is not unanimously accepted within the scientific community. Some still believe that Protomelission Gatehousei is a bryozoan. As for dating their appearance on Earth precisely, this naturally depends on paleontological discoveries. Things are not yet set in stone!