Study Clarifies Mystery of Crocodilian Hemoglobin

A Nile crocodile swallows an impala, its reward for lying in wait beneath the water’s surface. By resurrecting the hemoglobin of ancient crocodilian ancestors, a research team has helped explain why other vertebrates failed to evolve the adaptations that allow crocs to go hours without air. (Credit: Cell Press / Current Biology / Shutterstock / Scott Schrage, University of Nebraska–Lincoln).

It can pogo-stick along at 50-plus miles per hour, leaping 30-odd feet in a single bound. But that gold-medal athleticism falls by the wayside at a sub-Saharan riverside, the source of life and death for the skittish impala stilling itself for a drink in 100-degree heat. A Nile crocodile has silently baptized itself in that same muddy river for the past hour. When the unseen apex predator lashes from the water to seize the impala, its infamous teeth latch onto a hindquarter, jaws clenching with 5,000 pounds of force. Yet it’s the water itself that does the killing, with the deep-breathed reptile dragging its prey to the deep end to drown. The success of the crocodile’s ambush lies in the nanoscopic scuba tanks—hemoglobins—that course through its bloodstream, unloading oxygen from lungs to tissues at a slow but steady clip that allows the crocodile to go hours without air. The hyper-efficiency of that specialized hemoglobin has led some biologists to wonder why, of all the jawed vertebrates in all the world, crocodilians were the lone group to hit on such an optimal solution to making the most of a breath.