If you need to lurk at the bottom of a water body waiting for prey, it is wise to stay motionless without resisting against the buoyant forces of water. To do so you need a kind of diving belt that helps to sink. One large amphibian species Metoposaurus krasiejowensis, that lived more than 200 million years ago, compensated for buoyancy with a heavy shoulder girdle. Researchers examined the bones of the girdle under a microscope. The compactness in the interclavicle shows a striking resemblance to the pectoral bones of modern manatees.
