"It was half the size of a domestic cat and probably hunted and ate whatever it could for its size – insects, mammals, amphibians and maybe even baby dinosaurs," Longrich said. "It probably spent most of its time close to the ground searching through the marshes and forests that characterized the area at the end of the Cretaceous."
Fossilized remains of Hesperonychus, which means “western claw,” were collected in 1982 from several locations including Dinosaur Provincial Park. The most important specimen, a well-preserved pelvis, was recovered by legendary Alberta paleontologist Elizabeth (Betsy) Nicholls, after which the species is named. Nicholls was the curator of marine reptiles at the Royal Tyrrell Museum in Drumheller and earned her MSc and PhD degrees at U of C. She passed away in 2004. The fossils remained unstudied for 25 years until Longrich came across them in the University of Alberta’s collection in 2007. Longrich and Currie focused on fossilized claws and a well-preserved pelvis for their description.
"The claws were thought to come from juveniles- they were just so small. But when we studied the pelvis, we found the hip bones were fused, which would only have happened once the animal was fully grown", Longrich said. "Until now, the smallest carnivorous dinosaurs we have seen in North America have been about the size of a wolf. Judging by the amount of material that was collected, we believe animals the size of Hesperonychus must have been quite common on the landscape."
Currie and Longrich last year described the previous record-setting small North American dinosaur, a chicken-sized insectivore named Albertonykus borealis.
The discovery of Hesperonychus is the first sign of small carnivorous dinosaurs in North America and also extends the timeframe of small, birdlike dromaeosaurs known as the Microraptorinae in the fossil record by approximately 45 million years. Specimens from China have been found dating to 120 million years ago, while Hesperonychus appeared to have thrived until the end of dinosaur age in the late Cretaceous.
Source: University of Calgary
University of Calgary paleontologist Nick Longrich explains the discovery of North America's smallest dinosaur species to date, Hesperonychus elizabethae.
(Photo Credit: University of Calgary)