Mini dinosaurs prowled North America

Massive predators like Albertosaurus and Tyrannosaurus rex may have been at the top of the food chain, but they were not the only meat-eating dinosaurs to roam North America, according to researchers who have discovered the smallest dinosaur species on the continent to date. Their work is also helping re-draw the picture of North America’s ecosystem at the height of the dinosaur age 75 million years ago.

“Hesperonychus is currently the smallest dinosaur known from North America. But its discovery just emphasizes how little we actually know, and it raises the possibility that there are even smaller ones out there, waiting to be found,” said Nick Longrich, a paleontology research associate in the University of Calgary’s Department of Biological Sciences. “Small carnivorous dinosaurs seemed to be completely absent from the environment, which seemed bizarre because today, the small carnivores outnumber the big ones,” he said. “It turns out that they were here and they played a more important role in the ecosystem than we realized. So for the past 100 years, we've completely overlooked a major part of North America's dinosaur community."

In a paper published in the scientific journal Proceedings of the National Academy of Sciences, Longrich and University of Alberta paleontologist Philip Currie describe a new genus of carnivorous dinosaur that was smaller than a modern housecat and likely hunted insects, small mammals and other prey through the swamps and forests of the late Cretaceous period in southeastern Alberta, Canada. Weighing approximately two kilograms and standing about 50 centimetres tall, Hesperonychus elizabethae resembled a miniature version of the famous bipedal predator Velociraptor, to which it was closely related. Hesperonychus ran about on two legs and had razor-like claws and an enlarged sickle-shaped claw on its second toe. It had a slender build and slender head with dagger-like teeth.

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