A claw of the Hesperonychus dinosaur

Researchers have discovered North America's smallest known dinosaur - a meat-eating creature about the size of a modern chicken.  

Known as Hesperonychus, the dinosaur lived 75 million years ago in what is today Alberta, Canada.  Experts say the fully grown creature lived in swamps and forests, ran on two legs and was covered in feathers, like a modern chicken.  

Paleontologists say the meat-eating Hersperonychus probably had a diet that included insects, small mammals and whatever else it could find, including baby dinosaurs.

Paleontologists say Hesperonychus, which weighed about 2.2 kilograms and was knee-high, was a small version of Velociraptor, a vicious carnivore that also stood on two legs and had a sharp front claw for slashing prey.
 
Nicholas Longrich of the University of Calgary helped discover Hesperonychus, whose name means "Western Claw."  

The bones were found years ago and placed in a museum drawer because it was thought they were from juveniles, but Longrich says scientists recently made a discovery.

"... because the hip bones were actually completely fused together," said Nicholas Longrich. "They were completely knitted together; the individual bones.  And that is the type of thing that only happens when the animal stops growing.  And when we found those, we said 'Okay.  This is not a juvenile of something bigger."

Longrich says scientists had found evidence of large and medium size dinosaurs in North America, but nothing this small.  Small dinosaurs about the size of Hesperonychus have been found in China, so Longrich felt it was odd that nothing had been found here.

Longrich thinks there are many smaller, meat-eating dinosaurs like Hesperonychus waiting to be found because larger dinosaurs could not devour all of them.

"Something this size, if it ran into a small tyrannosaur, would have been a nice snack," he said. "So, that definitely would have been an issue for an animal of this size.  And presumably they just grew fast enough that they were able to keep producing more animals.  And that was probably one of their major strategies - sheer numbers.  The tyrannosaurus could not eat them all."

News of the discovery of Hesperonychus was published this week in the journal Proceedings of the National Academy of Sciences.