Trent River Elasmosaur Excavation

A mighty marine reptile was excavated on the Trent River near Courtenay on the east coast of Vancouver Island, British Columbia, Canada in August 2020. The excavation is the culmination of a three-year palaeontological puzzle. The fossil remains are those of a plesiosaur — a group of long-necked marine reptiles found in the Late Triassic to the Late Cretaceous some 215 to 80 million years ago.

In the case of the Trent River, it is closer to 85 million years old. The rocks that make up this riverbed today were laid down south of the equator as small, tropical islands. They rode slow-moving tectonic plates across the Pacific — heading north and slightly east over the past 85 million years to where we find them today.

The plesiosaur fossil was excavated high up a cliff alongside the river. It took a month of work with planning, scaffolding, climbing gear and a team of dedicated souls to unearth what is likely a juvenile plesiosaur from his 15-meter high perch.

Bits and pieces of him have been eroding out for years — providing clues to the past and a jigsaw puzzle that has finally had the last pieces put together. The first piece of this marine reptile puzzle was found three years ago.

The Courtenay Museum hosts regular fossil tours here, led by Pat Trask. On one of those field trips back in 2017, Pat was leading a trip with a family and one of the field trip participants picked up a marine reptile finger bone. It was laying in the river having eroded out from a nearby cliff. She showed it to Pat and he immediately recognized it as being diagnostic — it definitely belonged to a marine reptile — possibly an elasmosaur — but what species and just where on the river it had eroded from were still a mystery. She kindly donated it to the museum and that was that.

While it was an exciting find, it was a find without origin. Just where the material was coming from was unknown. It could have eroded from anywhere upstream and while many had searched the river, no other bone bits were found.

Then in 2018, another piece of this paleontological puzzle was revealed. Pat was leading yet another Courtenay Museum Fossil Tour on the Trent River when one of the participants showed him a specimen that looked like a really tiny hockey puck. This second find was a wrist bone — again possibly from an elasmosaur but hard to be sure. Contemplating out loud where this material could be coming from, Pat looked down and found a vertebra in the water below his feet.

Pat put the bones in the lab at the museum. Intrigued by their origin, he began heading down to the river on his off hours to see where they might be coming from and thinking about where the erosion occurs on the Trent.

In 2019, "I came down here and I started thinking about where the water flow would go." He could see a ledge along the river where eroded material might gather. Once he checked, he found a crack and cleaned out all the rock gathered there, finding more than a dozen bone. Pat teamed up with members of the Vancouver Island Palaeontological Society (VIPS) to scale the cliff faces above that section of the river. Jason Hawley, VIPS, did some rappelling but missed the site by a matter of feet.

Initially, they thought there would be a small amount of fossil material, perhaps a few finger bones but over the past few weeks, they have found bones of at least half a marine reptile.

And the beauty of this find is that most of the bones do not have to be prepared. They are literally eroding out of the matrix. No prep means no tools. Tools can impact the shape of a bone as you prepare it. They've found the pelvis bones, humerus, radius — all diagnostic to identify the genus. And this may be a new species. If it is, there is a good chance it will be named after the Trask family.