I believe that the dinosaurs were all warm blooded. Yes they all evolved from archosaurs, but crocodiles had already evolved when by the time dinosaurs existed. Crocodilians are virtually no different today than they were back then... Why? Because they had no need to evolved further, it's the same with sharks. Meanwhile, active land predators begin to evolve into warm-blooded animals. Crocodiles are adapted to moving through water, it takes less effort for them to swim than to walk, they don't NEED to expend extra energy, so they don't NEED to evolve into a warm blooded creature. Dinosaurs on the other hand exert much more energy, so they evolved the capacity to to do so. What you have to realize is that dinosaurs evolved separately from crocodiles, They may have both been archosaurs, but there are MANY differences between crocs and dinos. Futhermore, we know that dinosaurs migrated... look at all other land animals that migrate (Except for insects). They're all warm blooded, You don't see cold-blooded animals travel such great distances, mostly because they're incapable of exerting the force neccessary to do so.

Since when did dinosaurs become a mammal?

Both!

Dinosaurs were first believed to be cold-blooded because they were thought to be related closely to reptiles which are cold-blooded creatures. Cold-blooded animals don’t actually have “cold” blood, instead they rely on the temperature from their environment to regulate their own body temperature. They do this by taking advantage of external heat by basking in the sun, and by lying in the shade to cool down. A more correct term is “ectothermic” which means “heat from outside.” On the other hand, a warm-blooded animal creates heat internally by chemical reactions inside their body. They are able to regulate their body temperature internally instead of relying on their environment.

http://www.priweb.org/ed/ICTHOL/ICTHOL04papers/13.htm

crocs are reptile!!!!!!!!! Where do you get your messed up info DC!?!?!?

I believe dinosaurs were warm-blooded, but, not in the way that mammals are. I think that they could maintain a constant core temperature, unlike reptiles who have to use the sun to get their body temperatures up.