The crocodile's ability to direct oxygen-depleted blood to its stomach may be instrumental in digesting large, bony meals and recovering from hunting-induced accumulation of lactic acid, some researchers propose. But other scientists argue that the croc's unique circulatory system is instead an adaptation for lengthy dives, during which the animal must hold its breath as it stalks and then drowns its prey.
The hearts of crocodilians, including crocodiles and alligators, have four compartments. Two chambers send oxygen-rich blood to most of the body, and two move deoxygenated blood toward the lungs to be replenished. Mammals and birds use that same basic hardware.