A fossil of a brachiopod shell, center, with an associated primary eruption above, which was part of the new study.
Zhang Xiguang
It is believed that a 515-million-year-old fossil is the oldest known animal from a group called bryozoans that may actually be seaweed.
Bryozoans, commonly known as algae animals, are small, coral-like organisms that live in colonies in oceans and fresh water.
Almost all major animal groups first appeared in the fossil record between 541 and 520 million years ago during an evolutionary event known as the Cambrian Explosion. Until two years ago, algae were the only animal group missing from this event: the earliest fossil traces of bryozoans date to 40 million years later.
But in 2021, Paul Taylor at the Natural History Museum in London and his colleagues identified the Cambrian fossil Primary fission gate They were discovered in Australia and China, as bryozoans – suggesting that these animals didn’t arrive on the scene much later than other groups after all.
Now, Martin Smith of the University of Durham, UK, and colleagues have examined 12 new studies primary fissionSuch as fossils from Kunming in China, which have undergone a form of preservation that preserved their soft tissues.
The team found lumpy formations of individual tube-like structures in a honeycomb pattern – which can occur in both plants and animals. But they didn’t see any tentacles or regularly formed holes for tentacles to pass through—the tell-tale signs of later stone excavations, Smith says. Instead, the researchers observed long projections sticking out of the honeycombs that look like flanges, structures typical of certain types of green algae.
“Do you see those little conical lips?” He says. “That’s not a good way to be an animal, really. But it’s a very good way to capture sunlight and be a photosynthetic agent. We shifted this from thinking ‘This is a bryozoan’ to ‘This is definitely not a bryozoan.'” This is seaweed.”
Specifically, the organisms appear to be part of the order Dasycladales of green algae, he says.
It’s an “interesting and important finding” that adds to the “jigsaw puzzle” about Cambrian sea life, says Taylor, who was not involved in the new study, but doesn’t necessarily prove it. Primary fission gate He wasn’t an animal.
In particular, he wonders if the fossils are really new primary fissionespecially since there are large differences in the sizes of the samples’ structures.
Sarah Bruce of Smith College in Northampton, Massachusetts, has doubts about this, too. “It seems like their whole argument really hinges on this new fossil being the same as the one that was found before,” she says. “It gave me a moment’s pause.”
Even if they are the same, Taylor says, the long projections could be bryozoan tubular structures, and the smooth, shiny tissue probably wasn’t fossilized. “Their absence is not at all surprising,” he says.
As Bruce says he doesn’t particularly tell us. “Not having evidence is never good evidence, for a paleontologist,” she says.
If the fossils were indeed algae, that might actually help better explain the environment that supported the Cambrian Explosion, Smith says. “Seagrasses are wonderful habitats that can support this wealth of body plans that evolution has suddenly been able to produce,” he says.
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