The crocodilian edition of hemoglobins -- the scuba tanks of the blood -- work so well that crocs can go hours without air. The hyper-efficiency of that adaptation has led some biologists to wonder why, of all the jawed vertebrates, crocodilians were the lone group to hit on such an optimal solution to making the most of a breath. After resurrecting the hemoglobin of ancient crocodilian ancestors, a team may have an answer.
