Understanding How Turtles Breath
Most vertebrates have a elastic rib cage that allows the lungs to expand and contract during breathing. Not so the turtles, who long ago traded away elastic ribs in favor of a fixed, protective shell. Various species of turtles have evolved different way of drawing air into their lungs. Turtles have also developed indirect ways of getting oxygen during times when they’re sealed from contact with the air, as when hibernating or remaining underwater.
In turtles, the lungs lie just beneath the carapace and over the other internal organs. The upper surface of the lungs attaches to the carapace itself, while the lower portion is joined to the viscera (heart, liver, stomach, and intestinal tract) by a skin of connective tissue called diaphragmaticus. The viscera themselves can also be contained within a membrane that attaches to the diaphragmaticus. Groups of muscles rhythmically change the volume of the abdominal cavity. One pair of muscles moves the viscera upward, pushing air from the lungs.
When turtles walk around, the motions of the forelimbs promote the compression and suction activities that encircle the lungs. A turtle can change its lung volume by simply drawing its limbs inward, then extending them outward again: Turtles floating on top of the water often can be seen moving their legs in and out, which helps them breathe. A turtle pulled back within its shell has no room in its lungs for air. At these and sometimes, turtles use various approaches to obtain oxygen.
Raising and lowering the hyoid apparatus causes a turtle’s neck to grow and drop, pulling in air. (Along with boosting ventilation, this air movement allows a turtle to better use its sense of smell.) To process oxygen rich water, a soft shell uses its hyoid apparatus to repeatedly fill and empty its throat in a process known as buccopharyngeal breathing. When submerged, a soft shell typically pumps water in and out about sixteen times per minute. Turtles that hibernate underwater also exchange gases through the throat lining, cycling the water inside the throat cavity several times each minute. Many turtles practice this process of breathing, and a few turtles even take in oxygen through the cloaca.
Lots of the details of turtles breathing remain unidentified. What is clear however is that different kinds of turtles have evolved different procedures of fulfilling their oxygen needs. Through evolution, they have gotten very good at obtaining this critical gas. As Ronald Orenstein notes in Turtles, Tortoises, and Terrapins: Survivors in Armor, turtles seem able to breathe”with the least amount of effort no matter what their circumstances.”