WASHINGTON – Imagine a vicious velociraptor(食肉鸟) like those in "Jurassic Park(侏罗纪公园)," but only as big as a modern chicken. That's what Canadian researchers say they have found, the smallest meat-eating dinosaur yet discovered in North America. This pint-sized(小型的) cousin of velociraptor, weighing in at 4-to-5 pounds, "probably hunted and ate whatever it could for its size — insects, mammals(哺乳动物), amphibians(两栖动物) and maybe even baby dinosaurs," according to Nicholas Longrich of the University of Calgary(卡尔加里，加拿大西南部城市).
The creature lived 75 million years ago in the swamps(沼泽) and forests of southern Alberta, Longrich and colleague Philip J. Currie report in Tuesday's edition of Proceedings of the National Academy of Sciences.
There has been plenty of evidence for large and medium-size dinosaurs in North America, but not small ones, Longrich said in a telephone interview. Now researchers see there was a dinosaur filling that niche also.
The bones of the small raptor were discovered among fossils(化石) that had been collected a quarter-century(25年) ago and remained in a museum drawer, Longrich explained.
Similar small dinos have been uncovered in China in the last few years, and studying those helped the researchers identify this North American version.
"It was hard to tell because it was still encased in rock," Longrich said. "It is only because I had been studying the Chinese dinosaurs I could tell what it was."
"Once we got it out of the rock it was a pretty nice specimen(标本)," he added.
Like the velociraptor, the tiny raptor had claws(爪). At first the small claws were thought to come from juveniles, Longrich said. "But when we studied the pelvis(骨盆), we found the hip bones were fused, which would only have happened once the animal was fully grown."
Previously the smallest carnivorous(食肉的) dinosaurs found in North America have been about the size of a wolf.
The creature has been named Hesperonychus elizabethae, after the late Canadian paleontologist Elizabeth "Betsy" Nicholls, who recovered the specimen. Hesperonychus means "western claw," a reference to the enlarged sickle-shaped(镰刀状的) claw on its second toe.
The find "emphasizes how little we actually know, and it raises the possibility that there are even smaller ones out there waiting to be found," said Longrich.
Matthew Carrano, a paleontologist(古生物学家) at the Smithsonian's National Museum of Natural History, agreed.
"I think there's increasing awareness among vertebrate(脊椎动物) paleontologists that we have overlooked a lot of small species of dinosaurs. They are harder to find, but also the early history of our science had a lot to do with finding the big and impressive specimens," said Carrano, who was not part of Longrich's team.
"I would predict that the diversity of small dinosaurs will continue to go up in the coming years, all over the world," Carrano said.