Hesperonychus

Hesperonychus was a diminutive predatory dinosaur that lived in what is now Alberta, Canada, during the Late Cretaceous epoch. Known primarily from a fused pelvic girdle discovered in Dinosaur Provincial Park, it was recognised as a member of the Microraptorinae, extending the known geographic range of these tiny dromaeosaurs into North America. Weighing less than two kilograms, it was roughly comparable in size to a domestic chicken or small cat. Hesperonychus likely scurried through wetland underbrush and climbed fallen trees, hunting insects, frogs, small lizards, and early mammals. Before its formal recognition, scientists thought small ecological predatory niches in Late Cretaceous North America were dominated exclusively by juvenile large dinosaurs and mammals. Its presence proved that specialised miniature adult theropods successfully coexisted alongside giant apex tyrannosaurs.

It was the smallest known carnivorous non-avian dinosaur from North America at the time of its description.

Where and when

Hesperonychus lived in the Late Cretaceous, from 76.5 to 74.8 million years ago (Campanian age). Its remains come from Canada, in the Dinosaur Park Formation.

The numbers

Length 0.9 m (estimates run from 0.8 to 1 m). Mass about 1.7 kg. Hip height about 0.3 m. That is 0.5 human-lengths, or 0.08 of a double-decker bus. These are estimates from partial skeleton; fields marked estimated by the site are length, mass, hip height.

Compare Hesperonychus with a bus Place on the timeline