How many different dinosaurs were there?
There were thousands of species, with between 500 and 1000 non-avian species catalogued from their fossils. There were many hundreds of co-existing prehistoric birds and marine dinosaurs.
There are lists at the related links.
Dinosaurs are different from lizards in many ways. First off, dinosaurs walk with their legs underneath them, like an elephant or horse. Dinosaurs are also considerably larger than most lizards, but lizards and crocodiles have much larger relatives that lived during the time of the dinosaurs, even finding some dinosaurs as a food source! Lizards are cold blooded, while dinosaurs are considered to be warm blooded.