Mammals, birds and crocodilians show complete separation of the heart into two pumps, for a total of four heart chambers; it is thought that the four-chambered heart of birds and crocodilians evolved independently from that of mammals. Double circulatory systems permit blood to be repressurized after returning from the lungs, speeding up delivery of oxygen to tissues.
mammals birds and crocodilians show complete separation of the heart into two pumps for a total of four heart chambers; it is thought that the four-chambered heart of birds and crocodilians evolved independently from that of mammals double circulatory systems permit blood to be repressurized after returning from the lungs speeding up delivery of oxygen to tissues