古生物学：あるカンブリア紀の化石の真の正体

Reinterpretation of fossils from the Cambrian period, over 500 million years ago, suggest that they were algae, not animals, a Nature paper reports. The findings challenge ideas about animal evolution and the role of algae in Cambrian ecosystems.

The fossil record reveals the evolution of animals during the Cambrian period, but one animal, an aquatic moss-like invertebrate called Bryozoa, has been absent from the strata of this time. In a Nature paper published in 2021, a Cambrian fossil called Protomelission was interpreted to be a bryozoan, but now Martin Smith and colleagues challenge this idea. They describe well-preserved Protomelission-like fossils from the Xiaoshiba Lagerstätte in southern China and conclude that they are a type of benthic, photosynthetic alga, from the order Dasycladales. The findings mean that there are, as yet, no unequivocal bryozoan fossils from the Cambrian period.

The authors also compared the Protomelission-like fossils to those of a geographically widespread group of small, spine-shaped fossils, known as cambroclaves, and concluded that some cambroclaves may also be dasyclad algae. Taken together, the findings indicate that benthic, biomineralizing seaweeds had a more significant contribution in early Cambrian ecosystems than was previously thought.