Patrick Keating, his family and their dog Kitty were on an outing on the province's fossil-rich Northumberland shore when they found the fossil reptile scientists described as mammal-like because the species is thought to be the ancient ancestors of modern mammal species.
The Keatings and their dog found a fossilized rib cage, backbone and partial sail, and when they returned to the same area a week later they found the fossilized skull.
"We really had no idea how significant this was," Keating told the Canadian Broadcasting Corp. "My brother Peter and his kids took the pieces to the Nova Scotia Museum and when we learned what they were, we were truly amazed and so glad we brought them in."
Paleontologists say they believe the creature was a juvenile, about 3 feet long and weighing about 30 pounds.
"A new window into our ancient world has just opened," Deborah Skilliter, curator of geology for the Nova Scotia Museum, said. "This is just the beginning of the story as we undertake the task of determining exactly what type of sail-back reptile [the creature] is, where, and how, it lived and died."
Researchers put the age of the fossil at between 290 million and 305 million years.