B Buoyancy Control Device or BCD is a piece of diving equipment containing a bladder which is worn by divers to establish neutral buoyancy underwater and positive buoyancy on the surface, when needed. (ambassadordivers.com)
In the water, you'll review all the basic scuba skills with a focus on good buoyancy control. (latchidivecentre.com)
Unlike terrestrial theropods, the pelvic girdle is downsized, the hind limbs are short, and all of the limb bones are solid without an open medullary cavity, for buoyancy control in water. (science.sciencemag.org)