Tenontosaurus (TEN-onn-toe-SORE-us) Plant eater, 20 feet long, Early Cretaceous Period. 115 million years ago located in western North America. Tenontosaurus was the most common dinosaur in its world. Like a cow, it was built to graze on low-growing plants. Tenontosaurs were the favorite lunch food for Deinonychus. Tenontosaur bones are found near four out of every five Deinonychus discoveries.