An Ancient Marine Predator from the Burgess Shale

Palaeontologists from ROM and the Manitoba Museum have discovered a remarkable new 506-million-year-old predator from the Burgess Shale fossil deposit in British Columbia.

A new paper published in the journal Royal Society Open Science names the discovery as Mosura fentoni, an ancient marine predator that lived during a time of rapid evolutionary change known as the Cambrian Period.

Dubbed the “sea-moth” for its resemblance to a moth in motion, Mosura was named after the fictional Japanese kaiju (or “strange beast”) Mothra, reflecting both its appearance and its predatory nature.

Mosura belonged to the radiodonts, an extinct group of stem arthropods distantly related to modern insects and crustaceans. Though only about the length of a human finger, it was a highly effective predator, featuring three eyes, spiny jointed claws, and a circular mouth lined with teeth—similar to a pencil sharpener.

Mosura’s standout feature was its abdomen-like back end made up of multiple segments, which included gill-like structures. Equipped with flaps on both sides of its body for swimming, and intimidating claws extending from its head, it roamed the sea looking for prey.

These well-preserved fossils offer an extraordinary snapshot of early life—revealing not only external anatomical features but also elements of the nervous system, circulatory system, and digestive tract.

“Very few fossil sites in the world offer this level of insight into soft internal anatomy,” says Jean-Bernard Caron, Richard M. Ivey Curator of Invertebrate Palaeontology at ROM. “The details are astounding.”

The discovery broadens our view of radiodont diversity and sheds new light on the complexity of early marine ecosystems and how arthropods began to evolve.

Led by Caron, ROM has been at the forefront of Burgess Shale research for 50 years, uncovering dozens of new fossil sites and species at this UNESCO World Heritage Site.

Visitors can view exceptionally preserved fossils from the Burgess Shale—which provide one of the best records of marine life during the Cambrian Period—in the Willner Madge Gallery, Dawn of Life, on Level 2.

Monika Tragarz is a Communications Coordinator at ROM