Tuatara

• The sex of the hatchlings depends on the nest's incubation temperature.
• It has the longest breeding cycle known in any reptile: it lays only once every 4 years on average.
• It may live up to 100 years by some estimates.
• anatomíaIt has a third eye (a parietal eye) on top of its head, sensitive to light though it forms no image.
• fisiologíaIt has one of the slowest metabolisms known in any reptile and stays active at body temperatures lower than most lizards and snakes can manage.

Skeleton type

Vertebrate - internal bony skeleton (reptile, the only surviving member of its order)

Habitat and environment

Cold rocky coastal islands of New Zealand, with low vegetation tolerant of wind and salt

Birth weight

The hatchling weighs 1.2-1.3 times the egg's original mass (it takes up moisture during incubation); no precise figure in grams found

Size at birth

The sources consulted give no precise size on hatching beyond the mass relative to the egg

Sexual maturity

10-20 years (some sources give 13-14 years for females)

Gestation / incubation

11-16 months (12-15 months in other sources); development halts over the winter

Litter / clutch size

5 to 18 eggs per clutch, on average once every 4 years — the longest breeding cycle known in any reptile

Life expectancy in captivity

Individuals documented at over 90 years; the best known, 'Henry', was more than 110 years old and still breeding

Sources consulted: AnAge (genomics.senescence.info); Animal Diversity Web; ScienceDirect Topics; A-Z Animals; Animalia.bio; iNature Species ID Guide; PMC (transcriptome study)

Best time: All year round, at dusk, on the New Zealand islets where it survives; it is most active on mild, damp nights.