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 from the Universities of Bonn and Opole (Poland) 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. The results are now published in the Journal of Anatomy.
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Source: Phys.org