The species, which lived about 520 million years ago and was thought to be the oldest known bryozoan, instead formed a type of colony-forming algae, a new study suggests.
Bryozoans are filter-feeding, tentacle-bearing animals that live in complex habitats, such as colonies attached to rocks, reefs, or other surfaces on seashores or at the bottom of lakes. The trouble is some other animals and algae inhabit the same modular construction. while Protomelission of the gatehouse first described in 1993, scientists did not classify it as a bryozoan until 2021.
Now, analyzes of better-preserved fossils than previously described show that it wasn’t a bryozoan species after all, says Martin Smith, a paleobiologist at the University of Durham in England.
Where previous fossils preserved only the skeletal framework of colonies, the new fossils unearthed in southern China also include soft parts of the organism, says Smith. And instead of arms found in immaculately preserved bryozoans, the fossils have the simple leaflet flanges typical of certain types of algae, he and his colleagues report on March 8. nature.
If highlighted, the new find represents the oldest unequivocal bryozoan fossil known to be only about 480 million years old. According to Smith, bryozoans were the only major group of animals that did not appear until the Cambrian period, a burst of biological diversification that some scientists have referred to as the “big bang of life” and which ended approximately 488 million years ago (SN: 4/24/19).
As a result, the Cambrian was not, as previously thought, a unique interval of innovation in evolutionary history in which all blue animal life was deformed, the researchers conclude.
“The question is, has evolution lost its ability to create new body designs?” Cicero said. The team is not suggesting new discoveries, he said.
Not everyone agrees that bryozoan fossils are not new. The leaflet flanges described by Smith and colleagues could easily be interpreted as the body parts of individual animals in a bryozoan colony, says Paul Taylor, an invertebrate paleontologist at the Natural History Museum in London, who was not involved in the study.
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Because the plates that bryozoans use to grab prey from the water are soft tissues and typically don’t preserve well, their absence from the new fossils isn’t surprising, Taylor notes.
For Taylor, the new discoveries are not enough to let him go P. gatehousei such as the Cambrian bryozoan, but highlight the inherent uncertainty in identifying fossils with simple body plans. Preserving more fossils with additional characteristics, such as those preserved in the early growth of organisms, is needed to solve the problem, he says.
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