Troodon was a small, bird-like dinosaur that lived during the Cretaceous Period, about 76 million years ago. An egg-layer, it had behaviors in common with both crocodiles and birds. Troodon had a very large brain for its size—even larger, relatively speaking than the brains of modern reptiles. That suggests it may have been smarter than the average dinosaur, and perhaps even as intelligent as modern birds.