Strange life form from 500 million years ago wasn’t an animal at all: ScienceAlert

We have a curious case of mistaken identity to report. Fossils previously thought to have been left by prehistoric tentacled aquatic invertebrates called Bryozoans may actually have been created by a different source: algae.

That’s the conclusion of a new study of 500-million-year-old remains, which has taken a fresh look at Protomelission gateshousei fossils which have been thought to represent the earliest recorded Bryozoan remains.

In addition to seemingly setting the record straight, the findings again change what we know about bryozoan evolution. To date, they are the only fossilized animals not to be present during the Cambrian explosionwhen life on Earth really started to pick up speed.

Fossil records
The team identified several new fossils. (Yang et al., Nature2023)

“We tend to think of the Cambrian Explosion as a unique period in evolutionary history, during which all the blueprints of animal life were mapped out,” said paleontologist Martin Smith, from Durham University in the UK. “Most of the later evolutions come down to smaller-scale tinkering on those original body plans.”

“But if bryozoans really evolved after the Cambrian period, it shows that evolution retained its creative flair after that critical period of innovation – perhaps the trajectory of life wasn’t set in stone there. half a billion years ago.”

The study authors looked at tiny P. gateshousei fossils found in the hills of southern China, separated from the batch that had been recognized as bryozoans, and discovered new evidence of soft parts in their samples.

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

This in turn may tell us more about the Cambrian Explosion: that these algae most likely played a larger role than previously thought in the rapid increase in biodiversity that occurred at that time.

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

“Instead of the tentacles we would expect to see in bryozoans, we discovered simple leaf-like flanges – and realized we weren’t looking at fossil animals, but algae.”

This means that the first bryozoan fossils that experts are more sure of do not appear until the geological period after the Cambrian, the Ordovician – that is, some 40 million years after the time when these fossils were found. been dated.

The mysterious case of the missing bryozoan fossils has apparently been opened up again. Why is this class of creatures the only one not to feature in one of the most sudden bursts of life in the history of organisms?

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

“A growing number of Cambrian fossils…show features that could be reconciled with a Bryozoan affinity – but based on currently available material, no taxa can be interpreted with sufficient certainty to document a pre-Ordovician Bryozoan origin,” to write the researchers in their published article.

The research has been published in Nature.

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