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From <em>Anatome Testudinis Europaeae</em> (1821) by Ludwig Heinrich Bojanus
From Anatome Testudinis Europaeae (1821) by Ludwig Heinrich Bojanus

Natural Selections: Turtle anatomy

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Turtles breathe backwards; that is, when they relax their diaphragms, they inhale rather than exhale. Martha Foley and Curt Stager discuss the oddities of anatomy that arise from living in armor.

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Turtles breathe differently depending on whether they are in the air or the water. This is due to the unique anatomical features of this fascinating animal.

“The reason turtles have this kind of different breathing system from us when they’re on land, but kind of the same as us when they’re in the water, has a lot to do with their anatomy,” said Curt Stager of Paul Smith’s College. He explained that turtles’ ribcages are embedded in their shells and therefore can’t flex in the same way that a human’s can. Turtles are also almost always “belly down,” and their lungs are found in the upper half of their shell while their guts are in the lower half.

“If you just think about that, there’s a diaphragm sort of separating the two, and the diaphragm controls breathing as in us,” said Stager. For a turtle on land, the weight of their innards is drawn downwards by gravity. This in turn pulls the floor of the lung cavity and makes it larger, which causes the turtle to inhale.

However, turtles breathe differently in the water. Stager said, “The water presses in on the side and there’s all that soft skin and tissues around their legs and neck and their sides where the water can push in. Well, that pushes that pile of innards upwards.” When this happens, the diaphragm also goes up, and the space for air in the lungs will shrink. Therefore, it requires more effort for the turtles to breath in than out.

“Maybe the easiest way to remember it, if you want to remember it, is that if the turtle’s in the water, they breathe like we do. So if you relax, all the air goes out, and if you’re on land and in the air, you don’t have the support of the water and they do the opposite of us,” said Stager.

Turtle breathing is easily observed when turtles are approached by a potential predator, such as a person. The turtle will hiss as it pulls into its shell and expels the air from its lungs.

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