The muscle that allows mammals to breathe deeply — the diaphragm — may have been present in some reptiles 300 million years ago, about 50 million years before it was thought to have appeared.
Markus Lambertz at the University of Bonn in Germany and his colleagues studied the fossilized skeletons of caseids: extinct mammal-like reptiles that lived 300 million years ago (artist's impression pictured). These creatures weighed around 500 kilograms, with short necks that would have made foraging difficult and barrel-shaped bodies that would have restricted their ability to move air into their lungs. Their bones were lightweight and filled with air bubbles, similar to modern whales. The researchers conclude that caseids were probably aquatic, similar to present-day manatees (sometimes known as sea cows), and must have had muscular diaphragms to inhale all the air they needed during brief trips to the surface.
Ann. N.Y. Acad. Sci. http://doi.org/btkw (2016)