Puma-like, the northclaw slinks through the grasses of the prairie, its tawny stripes blending it into the dry yellows and browns of the vegetation. Its reptilian eye is fixed on an unconcerned grazing group of crested sprintosaurs, its instinctive cunning guiding it towards the most effective attack. For long hours its sleek body moves, slowly but surely towards the unsuspecting herd. Suddenly a male sprintosaur, looking round, notes something in the grass that does not quite fit. He trumpets out a warning blast and the herd scatters in a cloud of dust. With an instant reflex the northclaw darts up from its place of hiding and arrows down on the slowest of its prey. Its powerful hind legs thrust the horizontal body forward, balanced by the stiff rod of a tail. Then, when almost upon the young sprintosaur, which is still deciding which way to run, the single long claw springs out, hooks into the skin and pulls the animal over, kicking and struggling in the dust and the grass. Another blow of the claw and the prey is disembowelled, and the northclaw settles down to feast.
The northclaw is a coelurosaur, one of the more lightly built theropod dinosaurs and, apart from its large head and furry coat, it differs little from its Jurassic and Cretaceous ancestors. The main difference is the massive single claw, the killing organ on its right forelimb.