In the land before time, a small carnivorous dinosaur named Hesperonychus elizabethae lived in Alberta and was known as a terror despite its small size. Seventy-five million years later, University of Calgary researcher Nicholas Longrich discovered the remains of North America's smallest known prehistoric carnivore thanks to some luck.

In 1982, Elizabeth Nicholls found a Hesperonychus elizabethae's fossilized claws and a well-preserved pelvis at the Dinosaur Park Formation, near Red Deer river. At the time, paleontologists thought the small bones belonged to a lizard and shelved it until Longrich decided to take a second look.

After stumbling across the bones in the University of Alberta archives, he compared the claw and pelvis to other fossils of the dromaeosauridae species discovered in China. The similarities between Hesperonychus and the other species he studied in China helped Longrich identify the new species.

"Microraptors and Sinornithosaurus are small dromaeosaurids covered with feathers and with dagger-like teeth," said Longrich. "The few bones we have from Hesperonychus are very similar, so we think they were similar to the Chinese things."

Longrich also identified the species by noticing how the pelvic bones fused together, a sign of maturity. The two Chinese species were less than a metre long, just like the Hesperonychus.

"There are opportunities for small animals that big animals don't have, like more agility, less need for food and being able to catch small prey," explained Longrich.

Longrich said the tiny, cat-like predators ran on two legs, fit in the palm of a human hand and weighed less than two kilograms.

"The foot claw is bladelike, so it's a predator," said Longrich. "But the foot claw is small compared to velociraptors. It's not possible [that] it could hunt big prey, so it could eat small vertebrates, like a cat."

Philip Currie, a University of Alberta paleontologist who worked with Longrich on the project, is excited about the discovery because it shows that tiny velociraptor-like dinosaurs didn't only live in China, but in North America too.

"The majority of our known dinosaurs are still large animals that weighed several tonnes when they were adults," said Currie. "We have always known that there would have been small dinosaur species too, but didn't expect to find one this small."

Longrich and Currie wrote an article describing the discovery, which was published in the Proceedings of the National Academy of Science two weeks ago.

Hesperonychus means "western claw" and "elizabethae" is a tribute to the late Nicholls, a Royal Tyrell Museum curator who originally unearthed the bones.