Saturday, 12 September 2020

TRENT RIVER EXCAVATION

Pat Trask with a Fossil Rib Bone. Photo: Rebecca Miller
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 or elasmosaur 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.   

Pat Trask Wrapping the plaster casing
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.  

Pat had his neighbour fly a drone along the cliff face but it, too, turned up with nothing. Then at the beginning of August, Pat was back on the river in the morning with a family and said to one of the kids, "Hey, let's go look for baby elasmosaur." then they walked right over and saw a neckbone or tailbone in the river. Pat knew it hadn't been there the day before. He looked up and thought it must be coming from right up here. He came back later in the day with Deb Griffiths, his wife, set up his telescope on the river aimed at the likely portion of the cliff and bingo — he could see a bone sticking out.

He returned the next day with his brother Mike Trask. Mike found the elasmosaur on the Puntledge River back in 1988.  "We took a long pole and I said here's my target — and I hit one little piece, maybe three inches by three inches. When it fell down it had bones in it." Excited, they began planning a larger excavation that would include scaffolding, safety planning, climbing gear, permits... a lot of work in a short time. 

Plesiosaur Gastrolith
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. 

I caught up with Pat and the team from the VIPS out on the river on August 23, 2020 — the day of the excavation. Loose rib bones, gastroliths, wrist bones, finger bones and part of the back and pelvis were recovered — and possibly the head, too. 

The bulk of the specimen was wrapped in plaster and carefully lowered to the ground by Pat and members of the VIPS, under Mike Trask's careful eye. We know that there is a femur in that jacket and possibly all the bones associated with that. Also included are the fibula and tibia and their associated bones — and I'm truly hoping there is a skull in there, too! I've popped a link below of a wee video showing the final moments as the plaster cast is lowered down from the excavation site. Take a look! It was quite an exciting moment.

It is not quite a baby, but this diminutive fellow is about four-metres long, making it a juvenile of his species. We have prepped enough of the material now to safely call it an elasmosaur. James Wood of the VIPS has done an amazing job on the preparation of this specimen using a new smaller air abrasive purchased by the Courtenay Museum.

I hope to see it published with the Trask family name. Their paleontological history is forever tied to the Comox Valley and the honour would be fitting.   

Photo One: Rebecca Miller, Little Prints Photography — she is awesome!

Photo Two: James Wood prepped the material and Pat Trask labelled and oriented the bones.

Photo Three: Pat Trask perched atop scaffolding along the Trent River. And yes, he's attached to a safety line to secure him in case of fall. 

Photo Four: A Plesiosaur gastrolith recovered amongst the stomach contents of the Trent River excavation. A gastrolith is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. The grain size depends upon the size of the animal and the gastrolith's role in digestion. Other species, including marine reptiles, use gastroliths as ballast — which may have been the case here. 

See the Excavation Moment via Video Link: https://youtu.be/r82EcEF7Pfc