Older than the dinosaurs, incredibly slow, and with a third eye to boot, there is no other species on Earth quite like the tuatara.

Now, after decades of work by a dedicated team at Chester Zoo in England, the first tuatara hatchling has been born outside of its native New Zealand.

“Breeding tuatara is an incredible achievement,” says Isolde McGeorge, the zoo’s tuatara keeper since 1977. “They are notoriously difficult to breed and it’s probably fair to say that I know that better than most as it has taken me 38 years to get here."

Weighing in at a tiny 4.21 grams following a 238-day incubation period, the newcomer hatched on 5 December 2015, but its arrival was only announced to the world this week. After a second egg failed, the zoo wanted to make sure the hatchling was going to survive.

“It was a very, very anxious time,” says McGeorge.

When it comes to breeding, tuatara do not make it easy for themselves.

Females only produce eggs every three to four years. Worse, to successfully hatch a tuatara, the incubation conditions have to be just right: eggs can fail if the environment is too wet or too dry or temperatures go beyond a very strict range of 18-22C.

“When you’ve worked with tuatara for as long as I have you come to realise that they don’t do anything in a hurry,” says McGeorge.

Every thing about these ancient reptiles is slow. Their hearts beat just six to eight times per minute, they breathe five times a minute, and their eggs take a year to hatch.

Tuatara once lived throughout the mainland of their native New Zealand, but thanks to introduced mammalian predators they only survive on 32 offshore islands.

“Tuatara lived before the dinosaurs, they lived with the dinosaurs and they survived after dinosaurs had died out. They really are a living fossil and an evolutionary wonder,” said McGeorge.

The name tuatara means “spiny back” in Māori. But their most extraordinary feature is in the middle of their heads.

The tuatara’s “third eye” is equipped with a lens, retina, cornea and connective tissue leading to the brain, but it is not used to see. Instead it is thought to be used for setting the tuatara's circadian rhythms.

McGeorge’s fellow keepers have unofficially named the new arrival Baby Isolde.

Baby Isolde will live on her own until she is seven to 10 years old, because baby tuatara are often eaten by other tuatara – mainly by accident.

“It has taken lots of hard work, lots of stressful moments and lots of tweaking of the conditions in which we keep the animals along the way but it has all been very much worth it,” says McGeorge.