Discovery of Alberta’s Oldest Plesiosaur Fossil Unearthed at Mildred Lake Oilsands Site

Most of Fort McMurray Wood Buffalo’s history was underwater. For millions of years, it was the Western Interior Seaway

The fossilized tail of a plesiosaur, a marine reptile that lived 115 million years ago, at Syncrude's Mildred Lake oilsands site after it was found on March 12, 2023.
The fossilized tail of a plesiosaur, a marine reptile that lived 115 million years ago, at Syncrude’s Mildred Lake oilsands site after it was found on March 12, 2023. Photo by Supplied Photo /Suncor Energy

An eagle-eyed shovel operator at Syncrude’s Mildred Lake mine has found the remains of Alberta’s oldest plesiosaur. The marine reptile lived 115 million years ago in an ancient seaway covering North America.Jenna Plamondon said she was using a hydraulic shovel during a March 12 shift when an unusual shape caught her eye.

“I kept staring at this little chunk of dirt. As a shovel operator, we’re trained to see things that are out of the ordinary. We take a lot of pride in our pit and keeping the area clean,” said Plamondon in a statement. “I called my leader and asked to have geology look and confirm. We made the decision to move the shovel just in case it was an actual fossil.”

Geologists studied Plamondon’s find and called the Royal Tyrrell Museum of Paleontology in Drumheller. After more study, they determined Plamondon found the fossilized tail of a plesiosaur.

Plesiosaurs are noted for their long necks and four flippers on their barrelled bodies. They swam like penguins or turtles, and spent most of their lives in the oceans. They had no gills and came to the surface to breathe. Despite their long necks, they had a limited range of motion that was not snake-like.

Prehistoric Fort McMurray was underwater

Most of Fort McMurray and Wood Buffalo’s history was underwater. For millions of years, it was the Western Interior Seaway. The ancient seaway stretched from the Yukon and Hudson’s Bay to the Gulf of Mexico.

A section of a fossilized tail from a plesiosaur, a marine reptile that lived 115 million years ago, is removed from Syncrude Mildred Lake site after it was discovered on March 12, 2023. A section of a fossilized tail from a plesiosaur, a marine reptile that lived 115 million years ago, is removed from Syncrude Mildred Lake site after it was discovered on March 12, 2023. Photo by Supplied Photo /Suncor Energy

The closest shoreline from what would become Fort McMurray was somewhere around the Alberta-Saskatchewan border. On land, temperatures were like the coast of Vancouver Island. The environment was forested, warmer and covered in ferns. There were no flowering plants and grass did not exist.

The continents shifted and collided as time went on. The sea bisecting the continent drained into the Gulf of Mexico as the crashing plates formed the Rocky Mountains.While plesiosaurs shared the Earth with dinosaurs, they are considered marine reptiles. Paleontologists believe the plesiosaur died in the inland sea and washed into shallow waters. The carcass was likely scavenged by predators, including dinosaurs.

Donald Henderson, curator of dinosaurs at the museum, speculates a storm may have buried the plesiosaur in sand.

“This presents very unusual preservation conditions,” Henderson said in a statement. “It’s so rare for things to become fossils, especially big things such as marine reptiles and dinosaurs. It’s only the fact that we’re shifting so much rock here that we’re fortunate to see this small piece of fossil.”

The plesiosaur’s final resting place will be in Drumheller at the Royal Tyrell Museum. It arrived at the museum using a similar method to transport a human bone cast. This allows a close fit of plaster to protect the fossil without touching the bone.

“I’m really excited because if the fossil ends up being displayed at the museum, I’ll get to show my one-year-old son what mom found,” said Plamondon. “Not every shovel operator gets to find one, so it’s pretty cool that I’m one of the few.”

Jenna Plamondon.
Jenna Plamondon. Photo by Supplied Photo /Suncor Energy

The first major marine reptile fossil was found at Syncrude in 1994. Dozens of other plesiosaurs have been found in the oilsands. A different long-necked marine reptile called an elasmosaur was found in 2012 during construction of the Parsons Creek Interchange.

The most significant find was at Syncrude’s Millennium Mine in 2011 when the preserved remains of a nodosaur, an armoured land-based dinosaur, was found.

Paleontologists believe the nodosaur drowned in a flood 110 million years ago and was swept out to sea. Gases in the rotting corpse kept the belly-up carcass floating and the armour acted like a ship’s hull. The bloated carcass burst, sank and landed in what would later become the Millennium Mine. It is currently the best preserved fossil of an armoured dinosaur.