Mosura fentoni, the ancient predator, was roughly the size of a human index finger and possessed three eyes, spiny jointed claws, a ring-shaped mouth lined with teeth, and a body featuring swimming flaps along its sides. It belongs to the extinct radiodont group, which also included the well-known Anomalocaris canadensis, a meter-long predator that coexisted in the same Cambrian seas.
However, Mosura stands out for a unique feature not seen in other radiodonts - an abdomen-like region at its rear composed of 16 closely packed segments lined with gills. "Mosura has 16 tightly packed segments lined with gills at the rear end of its body. This is a neat example of evolutionary convergence with modern groups, like horseshoe crabs, woodlice, and insects, which share a batch of segments bearing respiratory organs at the rear of the body," says Joe Moysiuk, Curator of Palaeontology and Geology at the Manitoba Museum, who led the study.
The function of this unusual body region remains uncertain, but researchers suggest it may relate to habitat preferences or specific behavioral traits that demanded more efficient respiration. Nicknamed the "sea-moth" due to its broad swimming flaps and narrow, segmented abdomen, the species draws its scientific name from the fictional kaiju Mothra, though it is only distantly related to moths, spiders, crabs, and millipedes.
Radiodonts were among the first arthropods to branch off the evolutionary tree, providing critical insights into the origins of this diverse animal group. "The new species emphasizes that these early arthropods were already surprisingly diverse and were adapting in a comparable way to their distant modern relatives," notes study co-author Jean-Bernard Caron, Richard M. Ivey Curator of Invertebrate Palaeontology at ROM.
Several Mosura fossils also revealed internal anatomical structures, including parts of the nervous, circulatory, and digestive systems. "Very few fossil sites in the world offer this level of insight into soft internal anatomy. We can see traces representing bundles of nerves in the eyes that would have been involved in image processing, just like in living arthropods. The details are astounding," Caron adds.
Instead of the closed circulatory systems seen in modern animals, Mosura had an open circulatory system, with its heart pumping blood into large internal cavities called lacunae, which have been preserved as reflective patches in the fossils. "The well-preserved lacunae of the circulatory system in Mosura help us to interpret similar, but less clear features that we've seen before in other fossils. Their identity has been controversial," adds Moysiuk, who is also a Research Associate at ROM.
The fossils, primarily collected by ROM from 1975 to 2022 at the Raymond Quarry in Yoho National Park, also included a specimen originally found by Charles Walcott, the discoverer of the Burgess Shale.
The Burgess Shale, part of the Canadian Rocky Mountain Parks UNESCO World Heritage Site, remains one of the world's most significant fossil sites, offering unparalleled insights into the early evolution of life. Parks Canada, which manages these sites, supports ongoing scientific research and public education through guided hikes and exhibits, including a new Mosura display set to open at the Manitoba Museum in Winnipeg later this year.
Research Report:Early evolvability in arthropod tagmosis exemplified by a new radiodont from the Burgess Shale
Related Links
Royal Ontario Museum
Explore The Early Earth at TerraDaily.com
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