Reptile & Amphibian Forums

My friend and I had a debate about Crocodilians. He claims that if a croc dies, it sinks to the bottom of the water because its body is denser than the water around it (as with a shark.) He further claims that he's seen evidence to bear this out. He says that when a croc or gator has its eyes above water while stalking prey, that its tail is moving back and forth to keep it afloat.

I, myself, seem to remember seeing a croc or gator from an underwater video that was perfectly still, its arms, legs, and tail sprawled out and completely immobile. Then when it wants to descend, it seems to just slowly submerge, as if by sheer will. I would think that a moving tail (to provide lift and buoyancy) would be counterproductive to stalking prey at the water's edge - until the animal actually strikes out of the water to kill.

Which of us is right? Are crocodilians less dense than water and can float at will, or are they denser and heavier because of their bony skin? (bone floats, doesn't it?)

GregB
coralsnake@coralsnakes.com

I think the amount of air in the system is what keeps the animal above neutral buoyancy. I see crocodilians perfectly stationary and floating and then exhale and sink. A lot of animals sink when they die, particularly if the cause of death is drowning - the inhaled water dispaces the air in the lungs creating negative buoyancy. Then when the bacteria begin producing carbon dioxyide, the body regains positive buoyancy and floats back to the top.