The New Zealand herpetofauna post you’ve all been waiting to see— the iconic tuatara. Despite its uncanny resemblance to a lizard, the tuatara belongs to a distinct order called Rhynchocephalia (meaning “beak-head”). This lineage diverged from squamata (lizards & snakes) ~250 mya, approximately the same time as turtles diverged from birds and crocodilians. Back in the Mesozoic, rhynchocephalians were once a morphologically diverse clade with currently over 40 species described from fossil records across the globe. But in the modern era, only a single extant species remains.
Endemic to New Zealand, the tuatara (Sphenodon punctatus) once inhabited both mainland and offshore islands. However, after the arrival of the Māori people over 700 years ago, and Europeans a few hundreds of years ago, tuatara have since been extirpated from the mainland. The introduction of the Polynesian rat (Rattus exulans), is thought to have been the primary factor in population declines, though nowadays other invasive species such as cats, possums, and mustelids pose further threats. The only localities where tuatara currently occupy their native range include islands of the Cook Strait and islets off North Island’s northeast coast. Recent efforts have been made to reintroduce tuatara on the mainland in predator-free exclosures. Through careful population monitoring, individuals such as this tuatara from the Orokonui sanctuary are provided with a substantially greater probability of survival. Unfortunately, due to the long incubation time (>12 months) and slow maturation (~10 years to attain sexual maturity), tuatara populations are unable to bounce back rapidly.
Apart from their evolutionary history, tuatara are remarkable due to a number of characteristics. They were thought to have serrated projections of the jaw bone in place of teeth, though new evidence indicates their teeth are instead entirely fused with the jaw bone. The premaxillary bones of the snout are also fused, giving it a beak-like appearance. Curiously, tuatara have two rows of upper teeth that encase the bottom row when the mouth is closed. When feeding, the upper and bottom jaws move along two perpendicular axes to shear prey.
Tuatara have exquisite adaptations to thrive in cold climates; they can remain active down to 6°C with an astonishing average of 11 heartbeats per minute. These animals are also capable of exceedingly slow metabolic rates among reptiles, and may live more than 60–100 years in the wild. Previous claims have suggested these traits make the tuatara unique among reptiles, but more research has revealed similar capabilities widespread among endemic New Zealand geckos and skinks. Owing to their longevity and adaptations to cold environments, I would have expected tuatara to be slow-moving and mostly sessile.. After observing the individual pictured above for 15 minutes, it suddenly darted into a hole under a rock, resurfacing and scuttling outward to resume its stony pose.