Small but deadly: Prior to this, the smallest carnivorous dinosaurs known from the U.S. were about the size of a wolf.
Credit: University of Calgary/University of Alberta
WASHINGTON DC: A meat-eating dinosaur the size of a small chickens roamed areas of North America 75 million years ago, according to Canadian experts.
The mini-dinosaur, similar in appearance to the Velociraptor, is named Hesperonychus elizabethae and is the smallest carnivorous dinosaur known to have lived in North America.
"Hesperonychus is currently the smallest dinosaur known from North America," said University of Calgary palaeontologist Nick Longrich. "Its discovery just emphasises how little we actually know, and it raises the possibility that there are even smaller ones out there."
Another similarly sized carnivore, Compsognathus, is known from the Jurassic Period of Europe, but not North America.
Large sickle-shaped claw
Longrich, together with University of Alberta co-worker Philip Currie, are authors of a study on the small creature that is described this week in the journal Proceedings of the National Academy of Sciences.
Hesperonychus weighed about two kilograms and stood about 50 cm tall. It ran on two legs and, like Velociraptor – the deadly, agile dinosaurs made famous in the Jurassic Park movies – had razor-sharp teeth and a large sickle-shaped claw.
"Judging by the amount of material that was collected, we believe animals the size of Hesperonychus must have been quite common on the landscape," said Longrich.
Hesperonychus probably hunted and ate insects, mammals, amphibians and maybe even baby dinosaurs that lived in the marshes and forests common in the area during the late Cretaceous period, the scientists said.
The Hesperonychus fossils were collected in 1982 from several sites, including the Dinosaur Provincial Park in the western province of Alberta, famous for its rich dinosaur fossil beds.
Curiously absent
However the fossils remained unstudied until 2007. "The claws were thought to come from juveniles – they were just so small," Longrich said. "But when we studied the pelvis, we found the hip bones were fused, which would only have happened once the animal was fully grown."
Small carnivorous dinosaurs "seemed to be completely absent from the environment, which seemed bizarre because today, the small carnivores outnumber the big ones," Longrich said.
"It turns out that they were here and they played a more important role in the ecosystem than we realised. So for the past 100 years, we've completely overlooked a major part of North America's dinosaur community."
In 2008 Currie and Longrich discovered another, slightly larger North American dinosaur, an insectivore named Albertonykus borealis.
Until now, "the smallest carnivorous dinosaurs we have seen in North America have been about the size of a wolf," Longrich said.
