Hmm...I guess my question stumped a lot of people. Ah well, here's the answer:
According to "The Mystery of the Jurassic", at the beginning of the Jurassic, when Pangaea was still around, there were not a whole lot of variety of dinosaurs, nor where they very big. But in the late Jurassic, we see dinosaurs like Apatosaurus, Allosaurus, and Stegosaurus. There is a whole diversity of dinos. Something happened in the mid Jurassic, but fossils from that era were rare, so it remained a mystery, until they found a graveyard in Argentina.
Based on what they discovered there, they came up with a theory of what could have transformed the dinosaurs. First, there was a weather change. Something was causing the supercontinent's weather to change, like one area became a mega monsoon. But weather change wasn't enough to transform the dinosaurs. If they could move, then they could just go where the climate suited them best.
So in addition to weather change, at the same time the supercontinent split up into smaller continents, trapping dinosaurs on different pieces where the weather was changing. Now trapped and isolated, the dinosaurs had to adapt or die. The new weather and environments promoted different species of dinosaur, and by the late Jurassic, we see the diversity of dinosaurs, all the theropods, sauropods, stegosaurs, etc.
Anyway, here's a new question:
Dinosaurs such as deinonychus and velociraptor belong to a group, the raptor family. They are characterized by sickle-shaped claws on their feet. What is the common misconcepction about these sickleclaws?
