What a Tuatara feels like
They feel cold and soft to touch. Their spine is also quite soft and made of keratin the same as feathers and fingernails. It does not have bird talon like grip with its toes but the claws are reasonably sharp and are good for digging burrows.

Third Eye (pineal eye)
On top of a Tuatara skull, above the brain, is a third eye. This is a complex organ which actually has a lens and retina. It can sometimes be visible through the skin of newly hatched Tuatara for about six months, but as they grow, the eye becomes covered over with opaque scales. This eye initially may act more like a pineal gland which detects the seasonal changes by sensing the length of daylight and darkness.

Teeth
Tuatara do not have separate teeth but sharp serrations on the jawbone. The upper jaw has a double row of teeth. Their bite is very strong and can hold a vice-like grip for a long period of time.

Skin Shedding
A Tuatara sheds its skin just like a snake or lizard does. This can happen once or twice a year. The shin sloughs off in a pond almost completely but otherwise it can take several days coming off in pieces. The new exposed skin is much more colorful.

Dimorphism
Males are distinguished by their size, with an adult male being twice as large as a female. In most cases the males crest are larger. A male can reach a weight of 1000 grams and a female 500 grams

Growth
Studies in captivity on Tuatara growth would indicate that 50-60 years may be required to attain full size for a male and 20-30 years for a female. Like lizards, the Tuatara can shed its tail. The tail does not completely regenerate back to its normal size, but is shorter and stunted.
Sexual maturity has been at 13 years of age in captivity and in the wild, it is suggested to be 18-20 years

No Penis
Unlike lizards, but like Birds, Tuatara do not have a copulatory organ.
Fertilisation requires the male to position his cloaca (bottom) opposite the female’s cloaca as birds do.

Eggs
The eggs are soft tissue, lightly calcified and can expand as they develop, up to 400% of their original laid size (egg laid weight 4-7 grams and 14-16 grams at hatching). Hatchlings are around 90-100 mm long and weigh 5-7 grams.
Studies indicate with Tuatara eggs sex determination is temperature determined.