Salt Glands in Birds and Reptiles
Marine reptiles for example, iguanas, estuarine sea turtles, crocodiles, sea snakes and marine birds like the marine teleosts do not produce urine which is hyperosmotic to their body fluids. Instead they have specialised organs for the secretion of salts known as salt glands, located in the cranium of the animals. In birds these are generally present on the bill below the eyes and in lizards they are near the nose or eyes. In the brackishwater crocodiles salt glands are found in the tongue. Although neither reptilian nor avian kidneys are capable of producing a very hypertonic urine, the salt glands of marine reptiles and birds secrete enough salt to enable them to drink salt water even though their kidneys are unable to produce urine more concentrated than seawater.
Figure: Salt Glands in Birds and Reptiles
Salt glands, along with the gills of marine teleosts, compensate in these groups for the inability of the sub-mammalian kidney to produce a urine that is strongly hypertonic to their body fluids.