Question

why crocodile have 4 chambered heart

Answer 1

Unlike mammals, crocodile's right ventricle pumps blood throughout the body.
Such a heart perfectly separates blood going to the lungs from that going to the body, which is a requirement for the high blood flow rates and high metabolic rates characteristic of warm-bloodedness. However, living crocodiles are cold-blooded, so it didn't make sense for them to have a warmblooded heart - a mystery!

Answer 2

The crocodile has the most complicated blood circulation of all vertebrates. They do have four chambers in their heart yes as well as two ventricles which is very unusual in reptiles. Crocodiles adapted to have a heart like this, because they evolved from smaller reptiles which don't have a four chambered heart