Troödons are currently my favorite dinosaur. But for the extraterrestrial impact that wiped out the dinosaurs in the Gulf of Mexico about 65 million years ago, they would have been top candidates to become the dominant intelligent species on Earth.
A Troödon "is a large-brained nocturnal Troodontid theropod, which lived in the latter part of the Cretaceous period. It . . . may have had camouflage markings on its hide, to help it catch the nocturnal mammals which formed a small part of its diet. . . . it was also feathered. Troodon had abnormally large eyes, and these helped Troodon to see after the setting of the sun . . . . Troodon . . . is generally accepted as having been . . . warm - blooded. . . . It lived in what is now North America during the late Cretaceous Period (100-65 mya) and grew to be about 8 feet to 10 feet long and about 110 lbs. in weight. This slender little dinosaur might be the most intelligent dinosaur ever to exist. Troodon ate mammals, small dinosaurs, eggs and juvenile Hadrosaurs. It also specializes in pack hunting to hunt bigger prey.
From the Dinosaur Wiki.