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With the help of more than five dozen fossils, paleontologists have discovered a small third predator called “Seemos,” who swam in the Earth’s oceans 556 million years ago.
Mosura Fentoni, as the species is known, belongs to a group called Radiodonts, an early derivation of the arthropod evolutionary tree, according to a new study published Tuesday in the Journal Royal Society Open Science.
Radiodont is now extinct, but studying fossilized bodies can help light on how modern arthropods, such as insects, spiders, and crabs, have evolved. One of the most diverse animal groups, arthropods are thought to make up more than 80% of living animal species, said Dr. Joe Moischku, curator of paleontology and geology at the Manitoba Museum in Winnipeg.
The previously unknown well-preserved specimens of Mothra fentoni also reveal things not seen in other radiodonts. It is an abdominal-like body region with 16 segments containing gills at the posterior. This part of the creature’s anatomy resembles a batch of segments with respiratory organs on the back of the body, found in distant modern radiodon relatives such as horseshoe-shaped crabs, wood squirrels, and insects, Moischku said.
This feature, which is likely to be used to help Mothra capture more oxygen from the environment, may represent an example of evolutionary convergence. There, similarly-looking structures evolve independently in different groups of living things, he said.
“The new species highlights that these young arthropods were already incredibly diverse and adapted in ways comparable to their distant modern relatives,” said Dr. Jean Bernard Carron, Richard M. Ivy curator of invertebrate paleontology at the Royal Ontario Museum in Toronto, in a statement.
Mosiuk said there are no animals living like today’s Mothra Fentoni, but they were joined by claws similar to those of modern insects and crustaceans. However, unlike creatures that can have two or four additional eyes, which are used to maintain orientation, Mothra had a larger, more prominent third eye in the center of its head.
“Although not closely related, Mothra swims in a way that is probably similar to the rays of light, rippling its multiple swimmer flaps up and down, like underwater flight,” Moischk said in an email. “It also had a pencil sharpener-like mouth shape, unlike living animals, with rows of serrated plates.”
The size of an adult human index finger, Mothra and its swimming flaps are vaguely similar, and researchers called it “Seemos.”
Some Mothra specimens provided appetizing traces of the previous nails that helped Radiodont feed.
Caron used a miniature jacka hammer to remove the rock above the specimen’s head and found the perfect spiny claws that stretched downwards, Moisiuk said.
“Unlike many relatives, whose claws are lined with spine edges to catch prey, Mothra has long, smooth, lateral finger-like spines that branch out at their tips,” Moisiuk said. “It’s a bit of a puzzle that used these to catch prey, but I think (we) might have grabbed a small animal with the tip of a spine and handed it towards the mouth.”
There is no direct evidence of what Mothra ate, but we know that they lived with arthropods, like acorn worms, furry bugs and small crustaceans that radio-Yelods could prey on. Similarly, Mothra could have been the prey of other large radiozonts, such as the shrimp anomalocaris of canadensis shrimp and the giant jellyfish burgessomedususa phasmiformis.
“This includes many more examples of these animals, particularly active marine predators, filling in more photos of how this ancient marine ecosystem works,” says Dr. Russell DC Bicknell, a postdoctoral researcher at the Museum of Paleontology at the American Museum of Natural History. Bicknell was not involved in any new research, but previously wrote research on Anomalocaris canadensis.
Mothra’s unexpected stem region challenges how researchers understand the evolution of Radiodont’s body and how members of the group have moved from having a worm-like body, said Rudy Lerosey-Aubril, an invertebrate paleontologist at Harvard Comparative Zoology, who is not involved in new research.
“We may get a glimpse into the developmental process, especially in early members of the group, but before evolutionary changes lead to more consistent body tissues seen in most known species,” Lerosey-Aubril said in an email.
The first Mothra Fentoni specimens were discovered in the early 20th century by paleontologist Charles Walcott. Charles Walcott was the first person to collect fossils from Burgess Cher in British Columbia, a 580 million-year-old fossil bed. Walcott was the director of the US Geological Survey and was the administrator of the Smithsonian Association. However, no studies on the Mothra specimens he discovered have been published so far, and little was known about the radiozont at the time.
The other 60 fossils were collected by researchers at the Royal Ontario Museum between 1975 and 2022.
“The only time and study of related species that gradually became clear about the importance of these fossils,” Moisiuk said. “Recently, our team has begun to find additional specimens at the new Burgess Shale site in Kootenay National Park that will help spur this publication.”
Fossils in Burgesschère, within the Rocky Mountains of Canada, represent a wide range of animals since the end of the Cambrian era, when life was largely diverse. Burgess Shale Fossils are also known for being extremely well preserved.
“This study was able to identify traces of nerves, digestive and circulatory systems that are rarely preserved as fossils,” Moisiuk said in an email.
“This provides unique and important insight into life at this critical time in the history of the planet.”
The team was able to spy on traces representing bundles of nerves of the eye, like modern arthropods, Mothra used in image processing, Caron said.
Mothra was not an artery or vein, but also an open circulatory system. This means that the heart pumps blood into the una family or a large internal body cavity. The cavity was preserved as a reflective patch within the body.
The discovery of numerous complete small radio-elody specimens is surprising, said Lerosey-Aubril. The fine details preserved within the fossils highlight the importance of Burgesschelle, he adds, and a broader picture of the complete diversity of Cambrian animals requires examining other locations that hold evidence of fossils and soft-body organisms.
The Radiodont fossils are permanently on display at the Royal Ontario Museum’s “Life of Life” exhibition, with Masura specimens on display at the Manitoba Museum later this year.