As a femur-shaped island paradise that snapped away from the Gondwana supercontinent some 80 million years ago, New Zealand is home to eccentric forms of wildlife that look like pets for a Hobbit.
There is the kiwi, of course, with its dense, furlike feathers, its catlike whiskers and its long, slender, curving bill tipped by a pair of ultrasensitive nostrils; and the kakapo, a heavy, flightless, nocturnal parrot with the flat-cheeked face of an owl; and the giant weta, a cricket the size of a human hand that displays by waving its formidably serrated rear legs high in the air as if brandishing a pair of saws.
Yet the animal that may well be New Zealand’s most bizarrely instructive species at first glance looks surprisingly humdrum: the tuatara. A reptile about 16 inches long with bumpy, khaki-coloured skin and a lizardly profile, the tuatara could easily be mistaken for an iguana. Appearances in this case are wildly deceptive. The tuatara, whose name comes from the Maori language and means “peaks on the back”, is not an iguana, is not a lizard, is not like any other reptile alive today.
As a series of recent studies suggest, it is not like any other vertebrate alive today. The tuatara, scientists have learned, is in some ways a so-called living fossil, its basic skeletal layout and skull shape almost identical to that of tuatara fossils dating back hundreds of millions of years, to before the rise of the dinosaurs. Certain tuatara organs and traits also display the hallmarks of being, if not quite primitive, at least closer to the evolutionary baseline than comparable structures in other animals.
For example, the tuatara has a third eye at the top of its skull, the legendary if poorly understood pineal eye, which is found in only a sprinkling of reptile species and which vision researchers suspect harks back to nature’s original eye – pretty much a few light-sensitive cells on a stalk. Its teeth likewise follow the no-nonsense design seen in dinosaur dentition, erupting directly from the jawbone and without the niceties of tooth sockets and periodontal ligaments that characterise the teeth of all mammals and many reptiles. Yet in a startling counterpoint to the notion of the tuatara as a holdover from Triassic Park, researchers lately have discovered that a few regions of tuatara DNA appear to be evolving at hyperspeed, possibly the fastest mutation rate yet clocked in a vertebrate genome. The quick-changing sequences are limited to so-called neutral regions of the tuatara’s DNA, affecting filler codes, rather than the molecular blueprints for how to build a tuatara. The researchers have yet to determine what the observed hypermutability is all about, but obviously, said David M Lambert of Griffith University, in Brisbane, Australia, an author of the study, “the processes that govern skeletal morphology are decoupled from the biological processes that govern changes in DNA.”
Resembles its distant ancestors
Moreover, while the modern tuatara resembles its distant ancestors anatomically, life aboard a long-isolated land mass clearly has wrought major changes in the reptile’s physiology and behaviour, pushing the tuatara to Guinness-worthy extremes. “Their biology is quite distinctive,” said Charles Daugherty of the Allan Wilson Centre for Molecular Ecology and Evolution at Victoria University of Wellington in New Zealand.
“They have a unique type of hemoglobin, and their enzymes are set to function at lower temperatures than in most reptiles.” Tuataras are living fossils in more than one. Through long-term capture, tag and recapture studies that were begun right after World War II, researchers have found that tuataras match and possibly exceed in attainable life span that other Methuselah of the animal kingdom, the giant tortoise.
“Tuataras routinely live to 100, and I couldn’t tell you they don’t live to 150, 200 years or even more,” said Daugherty. “We know there are females that are still reproducing in their 80s,” said Daugherty.
At the Southland Museum and Art Gallery in Invercargill, New Zealand, a captive male tuatara named Henry, a local celebrity that had been nasty and unruly for decades until a malignancy was removed from his genitals, mated with an 80-year-old female named Mildred and last year became a first-time father – at the age of 111.
In every way, tuataras are late bloomers and passionate procrastinators. They don’t reach sexual maturity until age 15 to 20. The tuatara’s stately pace is also its Achilles’ heel, he added. That’s why the reptile today is found only on diligently monitored islands away from the New Zealand mainland.
Sphenodon, survivor of an old order
The New Zealand tuatara, or Sphenodon, is the sole surviving member of a reptilian order that once was as widespread and species-rich as are today’s other three reptilian clans – the crocodilians, the snakes and lizards, the turtles and tortoises.
Among the tuatara’s unusual reptilian traits are the relatively simple structure of its heart and lungs, the somewhat froggy style of its gait and the absence of any sort of male intromission organ, or penis. The tuatara also has a unique approach to mastication. As Neil Curtis and colleagues at the University of Hull in England have shown through computer simulations, the tuatara slides its single row of lower teeth across a groove between a double row of upper teeth, shearing the food.
New Zealand’s breakaway land mass proved an ideal tuataran sanctuary, for it lacked any terrestrial mammals that would dig up the reptile’s eggs or pick off the adolescents before they had a chance to breed. Without mammalian predation pressure, the tuatara life cycle became ever more protracted. The edenic age ended some 900 years ago with the arrival of the first Polynesians and their happenstance co-travellers, the rats. Then came pigs, dogs, cats, goats, Europeans. By the 19th century almost no tuataras survived on the New Zealand mainland. Today maybe 50,000 survive and are considered a national treasure. A vast majority live on Stephens Island, a mecca for herpetologists, where tuatara densities reach more than 1,000 reptiles per acre.
New York Times News Service