Crocodiles were much bigger then they are now a long time ago.
This is possible but i would have to read and see scientific evidence before i beleived this but evolution means that this can happen. Evolution is a crazy thing. It is said that we evolved from single cell organisms that lived in the ocean a few billion years ago so the evolutionary changes between single cell organisms and humans is much smaller then what pt447 said.
WL2FU, I am not sure about Sharks but Crocodiles are indeed dinosaurs. The Giant Crocodile(Sarcosuchus Imperator) was around 40 feet and lived approx 100 million years ago and they weighed around 10 tons. There is another ancient species of crocodile that has a head similar to a T-Rex's head.