Ancient Seafly Predator rewrites arthropod evolution

A finger-sized marine predator with three eyes and an abnormal respiratory system is challenging what scientists think they know about the early evolution of arthropods, including modern insects, crustaceans and spiders.

Canadian researchers found Mosura FentoniThis is a 5006 million creature from the famous Burgess shale fossil bed, with unprecedented physical arrangements among its evolutionary relatives. New species provide new insights into how today’s diversification plans for arthropods emerge first.

Named after the fictional Japanese monster Mothra, the ancient resident predator has a dedicated breathing fragment arrangement at its back end, very similar to the features seen in modern arthropods such as horseshoe crabs, woody and insects.

“Mosura has 16 tightly packed segments lined with gills at the rear end of its body. This is a neighbor example of evolutionary convergence with modern groups, like horseshoe crabs, woodlice, and insects, which share a batch of segments bearing respiratory organizations at the rear of the body,” said Joe Moysiuk, Curator of Palaeontology and Geology at the Manitoba Museum, who led the study published today in the journal Royal Society Open Science.

The significant fossil preservation reveals not only the external characteristics of the organism, but also its internal anatomy, including the nerves, circulatory and digestive systems. This provides researchers with an unprecedented glimpse into how these ancient animals operate.

“There are few fossil sites in the world that have such in-depth understanding of soft internal anatomy. We can see that in image processing represents a pack of nerve bondage, as in living arthropods, the details are astonishing as in research.

Not your average radiation

Mosura belongs to an extinct group called Radiodonts, one of the earliest arthropods. The most famous member, Anomalocaris canadensisis a meter-long apex predator who shares the ancient ocean with Mosora. While other radiators usually have a rather uniform body segment arrangement, Mosura destroys the mold.

The bodies of newly discovered species are clearly divided into different functional areas: three prominent eyes on the head, a neck, a belly with large swimming flaps, and a dedicated breathing section on the back. This level of body fragments was previously believed to be specialized in tagmosis, which later evolved in the history of arthropods.

“radiodonts were the first group of arthropods to branch in evolutionary trees, so they provide the entire population with key insights into ancestral traits. The new species emphasize that these early arthropods have been surprisingly diverse and adapted to distant modern relatives in comparable ways.”

Preserve ancient circulation systems

Another important aspect of the discovery is how it helps to shed light on the controversial features seen in other Hamburg shale fossils. Mosura’s very preserved internal structure includes the researchers identifying it as a void – the large blood that forms part of its open circulatory system.

“Mosura’s well-preserved circulatory systems help us explain similar but less clear features. Their identities have been controversial,” said Moysiuk, who is also a research assistant at ROM. “The preservation of these structures proves to be extensive, confirming the ancient origins of such circulatory systems.”

Despite its violent predatory equipment – including a prickly claw and a round mouth lined with teeth, Mosora is relatively small and can only reach the length of the index finger. Its body design suggests that it is an agile swimmer who may have hunted smaller prey in the ancient ocean.

The power of museum collections

The discovery emphasizes the ongoing scientific value of carefully planned fossil collections. Of the 61 specimens examined, all except one specimen were collected by ROM between 1975 and 2022, mainly from the site of Yoho and Kootenay National Park in British Columbia, Canada.

“The old and new museum collections are about the bottomless treasures of the past. If you think you’ve seen everything, you just need to open a museum drawer,” Moisik said.

The Burgess shale fossil site, now managed by Parks Canada and designated as a UNESCO World Heritage Site, continues to produce important discoveries about the explosive diversity of animal life during the Cambrian period.

Visitors can view many Radiodont fossils in the ROM Willner Madge gallery in Toronto and will be exhibiting specimens of Mosura for the first time at the Manitoba Museum in Winnipeg later this year, giving the public a glimpse into this key chapter of the story of life evolution.

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