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 & 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

Lifespan 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.