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| Isotelus rex, the King of Trilobites |
In the remote limestone flats of northern Manitoba, a remarkable fossil lay undisturbed for nearly half a billion years. Sunken in gray stone, its broad armored body preserved in exquisite detail, it waited silently—until a team of Canadian paleontologists happened upon it during a summer field expedition in 1999.
What they uncovered would change the story of trilobites forever.
Meet Isotelus rex, the largest complete trilobite ever discovered—a 70-centimetre-long prehistoric titan from the Ordovician seas. It's more than just a big trilobite. It’s a window into an ancient world and a landmark find in Canadian paleontology.
A Fossil Giant in a Forgotten Sea
Trilobites, extinct marine arthropods, are among the most iconic fossils in the world. Their hard, segmented exoskeletons and alien-like eyes make them favorites among collectors and scientists alike. They first appeared more than 520 million years ago and thrived in Earth’s oceans for over 270 million years before vanishing in the Permian extinction.
Many trilobites are palm-sized or smaller. But Isotelus rex was something else entirely.
Discovered near William Lake in the Hudson Bay Lowlands of Manitoba, Isotelus rex was preserved in limestone laid down when central Canada was submerged beneath a warm, shallow sea. That sea teemed with life—brachiopods, nautiloids, sea lilies, and trilobites like Isotelus, which would have cruised the muddy bottom looking for food.
With its broad, paddle-shaped tail, deeply segmented body, and large compound eyes, Isotelus rex was a slow-moving but imposing presence on the seafloor.
The Paleontologists Behind the Discovery
The discovery was made by a team of seasoned Canadian researchers: Dr. David Rudkin of the Royal Ontario Museum, Dr. Graham Young and Edward Dobrzanske of the Manitoba Museum, and Dr. Robert Elias from the University of Manitoba.
All were participating in a joint field expedition to study the fossil-rich limestone of the Churchill River Group, near Churchill in northern Manitoba.
Dr. Rudkin is one of Canada’s leading experts on Paleozoic arthropods, with a particular passion for trilobites and other ancient sea creatures.
His work at the Royal Ontario Museum has helped bring the stories of long-extinct animals to life through detailed study and public exhibition.
Dr. Young, curator of geology and paleontology at the Manitoba Museum, specializes in ancient marine ecosystems—piecing together how life functioned and interacted in prehistoric oceans.
Dr. Elias, a geologist and paleontologist at the University of Manitoba, focuses on Paleozoic reefs and ancient sedimentary environments. Dobrzanske, a collections technician and field expert, brought deep practical knowledge to the fieldwork.
It was the perfect blend of expertise and passion.
One overcast morning, while surveying outcrops of Ordovician limestone, the team spotted a familiar ripple in the rock—a faint curve suggesting a trilobite’s cephalon, or head shield. As they slowly and carefully uncovered more of the fossil, its remarkable size and completeness became apparent.
The mostly complete holotype specimen of Isotelus rex, from the Churchill River Group, measures a staggering 720 millimetres (28 inches) in length, 400 millimetres (16 inches) in maximum width across the cephalon, and 70 millimetres (3 inches) in height at the posterior midpoint of the head. It remains the largest complete trilobite ever found.
“We thought it might be a fluke,” Rudkin later recalled. “A fragment from a large individual. But as we kept going—it just kept going. That was when we realized we were looking at something truly extraordinary.”
Perfect Conditions for Preservation
Unlike many trilobite fossils, which are found in fragments or disarticulated pieces, Isotelus rex was remarkably well-preserved—fully articulated, lying in life position.
Paleontologists believe it was buried rapidly by fine carbonate mud, likely during a sudden underwater event like a storm or sediment slump. The seafloor at the time was likely anoxic—lacking oxygen—which would have prevented decay and scavenging, allowing the trilobite’s body to remain intact as minerals slowly fossilized it over millions of years.
“It’s one of the most complete large trilobites ever found anywhere in the world,” said Young. “It offers a rare look at what these creatures really looked like, in full form.”
While its size is headline-grabbing, Isotelus rex offers deeper scientific insights. It shows that trilobites—already known for their diversity—could grow far larger than previously thought. Its presence in northern Manitoba also highlights how much of Canada’s paleontological richness remains underexplored.
The fossil was later transported to Winnipeg, where it became a highlight of the Manitoba Museum’s paleontology collection. A custom case was built to display it—regular trilobite mounts just wouldn’t do for a specimen of this scale.
The name Isotelus rex—Latin for “equal end king”—reflects both its classification and its grandeur.
Today, Isotelus rex is more than just a museum centerpiece. It’s a reminder of the power of curiosity, collaboration, and exploration. It represents a frozen moment from 450 million years ago, when trilobites were the dominant animals of Earth’s seas.
And thanks to the eyes, hands, and minds of Rudkin, Elias, Young, and Dobrzanske, we now know what the king of trilobites looked like and he is an impressive specimen, indeed!
Image credit: Isotelus rex TMP 2009.003.0003 (cast). 445 million years old, late Ordovician, Churchill River Group, Churchill, Manitoba. At the Royal Tyrrell Museum of Palaeontology. Bloopityboop
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