Troodon is often considered the smartest dinosaur yet discovered. It's been suggested that they were as smart as most modern birds, perhaps smarter. Troodon was a small dinosaur, attaining an adult size of about 6-10 feet long and just over 100 pounds. Their large toe claws and sharp teeth would have been efficient weapons. Multiple studies questioning the validity of Troodon have been proposed, with a number of them determining it was not a valid species. Troodon lived in North America about 75 million years ago.