Dinosaur hip bones unearthed by a University of Alberta paleontology student are shaking up the family tree of a group of small meat-eaters that lived 75 million years ago.

Aaron van der Reest was doing field work in Dinosaur Provincial Park, about a two-hour drive southeast of Calgary, as part of his undergraduate studies in June 2014.

It was starting to rain and the group was about to pack it in for the day, but there was a spot up the hill van der Reest and his partner wanted to check out.

Close to a collection of small bone fragments, van der Reest spotted a bone sticking out that turned out to be the pelvis of what was believed to be a Troodon formosus — a dinosaur similar to the raptors seen in the Jurassic Park movies.

It was uncommon for the remains of that species to be so well-preserved in North America, van der Reest said.

'Exceptionally rare'

"At that point I kind of started freaking out because I knew what it was right away and it was one of these exceptionally rare animals," he said.

There was something strange about the bones, though — the pubis bone was rotated backwards.

"It's the only of the more advanced troodontids that do this. Every other one, it's directly pointing straight down," said van der Reest.

"We knew right away that it was something different. It represented something we had never seen before."

The hip bone discovery caused van der Reest to take a closer look at cranial bones that were previously collected in southern Alberta.

As a result, Troodon formosus is no longer considered a valid species.

Aaron Van Der Reest

"We knew right away that it was something different," said Aaron Van Der Reest. "It represented something we had never seen before." (Supplied)

Research published Tuesday in the Canadian Journal of Earth Sciences describes two new classifications that have taken its place. It's possible even more species will be identified in the future.

For one of the new species, van der Reest resurrected the name Stenonychosaurus inequalis.

He called the other Latenivenatrix mcmasterae — a tribute to his late mother Lynne van der Reest, whose maiden name was McMaster.

She died of cancer a year before the discovery.

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