I read an article about alligators on sciencenewsforkids.org. Scientists have recently discovered that alligators are able to move their lungs up and down to adjust their buoyancy in the water. They have muscles attached to their liver (sounds painful, doesn't it?) and hip bones. When they pull down on the muscles, the lungs get pulled down too. They use these muscles to shift lungs up (to surface), down towards their tail (to dive) and sideways (to help them roll). This reminds me of a cartesian diver, which many of you may have made or played with in earlier science classes.
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The scientists who studied the alligators think that this other use for lungs (other than breathing) evolved to help the animals move quietly and sneakily through the water. This makes sense, because it would create much more of a disturbance in the water when they use their tail to swim. One thing that I think is kind of strange is that scientists are just figuring this out! It just shows that there is still a lot that we have to learn.