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In Alberta's dinosaur-rich Badlands, bigger has always been better.

But new research suggests a "collecting bias," which historically favoured the recovery of massive predators such as Tyrannosaurus rex, has caused paleontologists to overlook tiny dinosaurs, including one partially covered with feathers that dined on insects and small animals and was smaller than a cat.

The discovery of Hesperonychus elizabethae, a slender, pint-sized carnivore with dagger-like teeth, was published yesterday in the Proceedings of the National Academy of Sciences.

It is believed to be the smallest dinosaur species ever found in North America, and its discovery is being hailed as an important step in fully understanding what the continent's ecosystem looked like more than 75 million years ago.

"There's got to be other things out there like this. If we could have overlooked this for so long, there is a very good chance we are overlooking other things," said Nick Longrich, a University of Calgary paleontologist who co-authored the study with Philip Currie, a renowned University of Alberta paleontologist. "You see what you are looking for."

Their research concluded that the delay in identifying Hesperonychus, which means "western claw," was partly due to a "collecting bias that has favoured the recovery of large, relatively complete dinosaur skeletons."

Dr. Longrich said he had suspected that mini-dinosaurs roamed North America after small adult dinosaurs were discovered in China and Mongolia in recent years.

That hunch and lots of luck were on his side as he rummaged through drawers storing a 25-year-old fossil collection at the University of Alberta in 2007.

He soon found a well-preserved piece of hip bone that ultimately proved to belong to a previously unknown species, Hesperonychus. The bones had been recovered in 1982 in southeastern Alberta but never studied.

"People collect stuff faster than they can be studied. ... So there is a big backlog of work ready to be done," Dr. Longrich said.

He suspects Hesperonychus was quite common because lots of small claws and other fossils have been recovered over the years in Alberta but never fully investigated.

Until this discovery, the smallest carnivorous dinosaur ever recovered in North America was the size of a wolf.

Hesperonychus, which weighed about two kilograms and stood about 50 centimetres tall, had sharp claws, including an enlarged sickle-shaped claw on its second toe.

Dr. Currie said the discovery of Hesperonychus represents the start of new research opportunities for paleontologists in Alberta, a hotbed of dinosaur activity for the past 100 years.

"When we first started working with dinosaurs in Alberta, everybody came here to collect big specimens because they are good display specimens," he said.

However, those results gave researchers and the public "a very skewed understanding of the old ecosystem, where just about everything is big," Dr. Currie said.