Dolphins are mammals that live under water. You can tell there age by there teeth like you can tell the age of a tree by the rings of the tree and for the dolphin the age is by the rings on the teeth. yes there is go on google.com
Tree rings are circles on the wood of a tree that are laid down each year. You only see them when the tree is cut down. You can tell the age of the tree and what kind of summer it was any given year by counting them.