Assertion: manatee's bone | /r/CapableOf | act as ballast
Facets:
value: to help keep sirenians
type: PURPOSE
Source sentences:
text: These heavy bones, which are among the densest in the animal kingdom, may act as a ballast to help keep sirenians suspended slightly below the water's surface.
text: They have heavy bones that act as ballast to counteract the buoyancy of their blubber.