The mouth and esophagus of the leatherback turtle are a perfect example of how an animal can become adapted to its diet and habitat. When the turtle consumes jellyfish (and it must eat many, as jellyfish have low nutritional value), the esophagus stores both the jellyfish and the seawater that have been swallowed. However, to prevent the stomach filling with water, the seawater must be expelled. So how does this happen?
The answer lies in the backwards-pointing spikes you see in the mouth of the turtle, which continue down the esophagus and grow progressively larger. As the muscles of the esophagus squeeze the seawater out, the spines keep the jellyfish in place. Once all the water has been expelled the jellyfish are then passed into the stomach. This strange adaptation is one of many that have kept this magnificent species in existence for 90 million years.