North America’s smallest dino predator

Sickle-clawed creature was likely no larger than a chicken

Paleontologists rummaging through museum drawers in Canada have discovered the remains of North America’s smallest carnivorous dinosaur — a theropod about the size of a chicken.

RUNT OF THE LITTER Tiny Hesperonychus elizabethae (far left), North America’s smallest meat-eating dinosaur, probably weighed no more than a chicken and was dwarfed by many of its contemporary relatives (human shown for scale). Longrich and Currie
KILLER KICK Hesperonychus, North America’s smallest carnivorous dinosaur (artist’s reconstruction at right), brandished sickle-shaped claws that easily fit on a 24-millimeter-wide Canadian quarter (left). Longrich and Currie

The first fossils of the 1.9-kilogram Hesperonychus elizabethae, which lived about 75 million years ago, were actually unearthed in southern Alberta in 1982, says Nicholas Longrich, a vertebrate paleontologist at the University of Calgary in Canada. But they lay forgotten and unstudied until Longrich and colleague Phil Currie of the University of Alberta in Edmonton rediscovered them, along with the fragmentary remains of several other specimens, the team reports online March 16 in Proceedings of the National Academy of Sciences.

Hesperonychus, which loosely translates as “west claw,” is substantially smaller than the previous record-holder from North America, a 10-kilogram relative from the dromaeosaur genus Saurornitholestes. Hesperonychus lived “in a bizarre ecosystem,” says Longrich: Most meat-eating dinosaurs known from that era were either really large, weighing more than 1,000 kilograms, or really small, with no medium-sized predators. Like most of these petite meat eaters, Hesperonychus probably dined on insects, lizards, birds or small mammals, Longrich says.

Features of Hesperonychus’spelvic bones also suggest that the sickle-clawed predator was more closely related to microraptors found in China (SN: 1/25/03, p. 51) than to previously known relatives in North America.

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