When Chinese soft-shelled turtles (Pelodiscus sinensis) need to urinate, they open their mouths, according to a new study. As odd as it might seem, this actually makes sense for this amphibious organism.
The researchers published their findings in The Journal of Experimental Biology. These reptiles don’t have any gills, but they have structures inside their mouths that work like gills. This means that P. sinensis has the option of breathing underwater, though most of the time they just reach up and breathe air. But what researchers found perplexing was that when the turtles were on dry land, they would stick their heads in puddles and swish water around in their mouths. This was one of the clues that led researchers to consider that there was something more happening than respiration.
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The scientists bought P. sinensis specimens at a market in Singapore and found ways to collect their urine. They attached a flexible latex tube to each underside. They discovered that the animals were getting rid of a vast majority of their urea, which is a major component of urine, through their mouths instead of their undersides.
The team speculates that this might be because the animals have to drink a lot of water to make urine, which can be unhealthy in salt water environments where these turtles spend most of their time. If they are just rinsing out the water around their mouths, they avoid having to get rid of the salt.