Troodon formosus was a relatively small, bird-like dinosaur from the delayed Cretaceous time (68–65 MYA). Discovered in 1855, it was in the middle of the first dinosaurs found in North America, and is supposed to have been one of the most intelligent.
This small dinosaur was approximately 2 m (6.5 ft) in length, 1 m (3 ft) tall and weighed 60 kg (130 lb). Its eyes were big (suggesting nocturnal activity) and slightly onward facing, giving Troodon some depth perception.
Troodon (pronounced "Tro-odon") is Greek for "wounding tooth", and refers to the dinosaur's sharp teeth with jagged edges. Its diet consisted of smaller animals, counting mammals and perhaps a significant amount of plant material as well.
Troodon' had long arms that folded back like a bird's, and its hands obsessed partially opposable thumbs. It had large, sickle-shaped claws on its second toes which were raised off the ground when running. This claw is common in the superfamily Maniraptora, to which Troodon belongs.
Troodon had one of the main known brains of any dinosaur family member to its body mass (comparable to modern birds). Eggs have also been discovered, in nests.
Troodon has very long, slender limbs suggestive of that the animal was quite fast. Although at first thought to be a predator, there is some proof that Troodon may either have been an omnivore or an herbivore. The jaws get together in a broad, U-shaped symphysis similar to that of an iguana, and the teeth bear large serrations like those of herbivorous dinosaurs. In adding, the teeth are short but broad, and bear wear facets on their sides; in these respects Troodon is again more like plant consumption dinosaurs than carnivores such as Dromaeosauridae. A specimen of Troodon is known from Montana sitting atop a clutch of eggs.