Weird Lifeform From 500 Million Years Ago Wasn’t an Animal at All : ScienceAlert

We have a curious case of mistaken identity to report. Fossils previously believed to have been left by prehistoric tentacle-bearing aquatic invertebrates called Bryozoans may actually have been created from a different source: seaweed.

That’s the conclusion of a new study of 500-million-year-old fossils, which took a new look at Protomelission gateshousei fossils thought to represent the oldest Bryozoan remains on record.

As well as seemingly setting the record straight, the findings again change what we know about the evolution of Bryozoans. To this day, they are the only fossilized animals that weren’t around during the Cambrian explosion, when life on Earth really started to accelerate.

The team identified several new fossils. (Yang et al., Nature, 2023)

“We tend to think of the Cambrian explosion as a unique period in evolutionary history in which all the plans for animal life were drawn up,” says paleontologist Martin Smith, of Durham University in the UK. “Most subsequent evolution comes down to smaller-scale complications in these original body plans.”

“But if Bryozoans really did evolve after the Cambrian period, it shows that evolution kept its creative touch after this critical period of innovation—perhaps the trajectory of life wasn’t set in stone half a billion years ago.”

The study authors examined small fossils of P. gateshousei found in the hills of southern China, separated from the group known as Bryozoans, and discovered previously unseen evidence of soft parts in their samples.

These new findings make these fossils more suitable for green algae, in a group known as the Dasycladales, the new study suggests – particularly in the signs of an outer membrane that were not present in the other fossil samples.

This in turn may teach us more about the Cambrian explosion: that these algae may have played a more significant role than previously thought in the rapid increase in biodiversity that occurred around that time.

“Where previous fossils preserved only the skeletal framework of these early organisms, our new material revealed what lived inside these chambers,” says paleontologist Zhang Xiguang, of Yunnan University in China.

“Instead of the tentacles we’d expect to see in Bryozoans, we discovered simple leaf-like flanges—and realized we weren’t looking at fossil animals, but seaweed.”

This means that the earliest bryozoan fossils that experts are most confident about do not appear until the post-Cambrian, Ordovician geologic period—that’s about 40 million years after the point at which these fossils are dated.

The mysterious case of extinct Bryozoan fossils has apparently been cracked open once again. Why is this class of creatures the only one not to appear in one of the most unexpected bursts of life in the history of organisms?

One answer might be that we just haven’t found the right data yet. It is possible that the earliest forms of Bryozoans had softer parts, which means that they would not have left behind fossils in the early stages of their evolution.

“A growing number of Cambrian fossils… display features that are compatible with a bryozoan affinity—but on the basis of currently available material, no taxon can be interpreted with sufficient certainty to document a pre-Ordovician origin of Bryozoa,” the researchers write. in their published paper.

The research is published in Nature.