For one tuataras lack external ears. They have hooklike extensions on some of their ribs (which can also be found in birds) and males lack a penis (another birdy trait).Tuataras also have a pineal or "third eye" on the top of their heads. Although this "eye" is also found on lizards and is comprised of a lens, retina and nerve connection to the brain. In lizards this pineal eye is used for temperature regulation, giving the animals a fairly good idea of the surrounding temperature and allowing them to know when they are too hot or too cold. Since tuataras are nocturnal forest dwellers it is harder to say what their pineal eye is used for.
Males and females are sexually dimorphic with males being much larger and heavier. Males also have prominent nuchal and dorsal crests along with narrower abdomens than females.Tuataras are also capable of caudal autotomy, just like many lizards.