Sometimes, even professional fossil-seekers can be surprised to find a fossil. That’s exactly what happened recently at the Enchanted Designs Ammonite Mine, south of Lethbridge, Canada, when workers (who mine for ammonite fossils) ran into a Plesiosaur fossil estimated to be around 75 million years old.

This particular specimen was likely an adolescent at the time of its death judging from its size, local news outlets report.

Suddenly, Plesiosaurus

“The guys started scraping and noticed there were some vertebrae that appeared below the concretion line, and right away we knew we had a new fossil,” said Michael Shideler, manager of the Enchanted Designs Ammonite Mine.

Plesiosaurs were highly specialized marine dinosaurs. They had a small head on a very long neck, long tear-shaped bodies, a stumpy tail, and four wide flippers. They were pretty similar in shape to what you’d imagine the Loch Ness monster to be.

And just like with the Loch Ness monster, none of the workers at the mine expected to run into this fossil. The Enchanted Designs Ammonite Mine has been shut down during winter, so activity at the site is still picking up as the mining season is still fresh. One of the crews digging for ammonites there ran into a large and compact mass of material (a ‘concretion’) that stood out from the mine’s rock walls.

Based on the fossilized fragments recovered so far, the specimen was likely 7 meters (~23 ft) long when it died; almost half of that length is just neck. This would mean that the animal was still pretty young, likely an adolescent, when it met its end. Other plesiosaur specimens that we’ve recovered reach up to 14 m (46 ft) in length, with a similar neck-to-not-neck ratio.

What made the discovery particularly surprising is that marine reptile fossils are very rare in the Bearpaw Formation, which stretches through Alberta, Saskatchewan, and Montana, and into which the mine delves. Around 75 million years ago, when this formation was still on the surface, the area was the bottom of a shallow tropical sea. A large number of ammonites, fish and marine reptiles lived here, which is why the formation is such a rich source of fossils. However, this is the first time a specimen of this kind has been recovered from the mine.

The plesiosaur and other undetermined fossils have been collected and taken to the Royal Tyrrell Museum, where they will be removed from their rocky prisons for research.