“Breathing through the butt” sounds more like an internet joke than vertebrate physiology. Yet for a small group of freshwater turtles, there is real science behind the bizarre claim. These turtles still have lungs and breathe air, but while submerged they can also extract oxygen directly from water using specialized structures connected to the cloaca, the multipurpose opening reptiles use for excretion and reproduction. In some species, this form of aquatic respiration is so effective that it helps the animals remain underwater for hours, and, under the right conditions, far longer.
The mechanism has nothing to do with turtles inhaling air through their rear ends. Instead, it is an extraordinary example of bimodal respiration, in which an animal obtains oxygen through more than one respiratory route.
