Hypacrosaurus (meaning "almost the largest lizard") was a large, plant-eating, hollow-crested duck-billed dinosaur similar to "Corythosaurus". It was about 30 feet (9 m) long, had almost 40 rows of cheek teeth, and a short toothless beak. A row of long spines from its vertebrae formed a high fin along its back. The fossils are dated as 75 to 67 million years ago. 