There are two mental glands, one on each side of the head. They are behind the jawbone.[1][3]
Function
Mental glands make chemicals that come out through the skin. These chemicals help the animal tell when another animal is the same or a different species from them. The chemicals also help them choose mates.[1][3][4]
Turtles bob their heads up and down when they see another turtle. Perhaps bobbing the head up and down helps the chemicals from the mental glands get in the air.[1] Salamanders move when they see another salamander. For example, they snap their jaws. Only salamanders that have mental glands do this, so this also spreads the chemicals through the air.[2]
Origins and evolution
Not all reptiles and amphibians have mental glands. Some species in the same family have mental glands and others do not.[1][2]
In 2021, one team of scientists found that most turtles that have mental glands live in the water. Mental glands occurred just once in turtles, in the family Testudinoidea. Then some kept their glands and some lost them. Probably all turtles that have mental glands develop them from the same tissue.[1]
