A major transformation in vertebrate evolution took place when breathing shifted from being driven by head and throat muscles — like in fish and frogs — to the torso — like in reptiles and mammals. But what caused the shift? A new study posits that the intermediate step was locomotion. When lizards walk, they bend side-to-side. The ribs and vertebrae are crucial to this movement, and the mechanics follow the same pattern as when they inhale and exhale.
Click here for original story, Ribs evolved for movement first, then co-opted for breathing
Source: ScienceDaily