Happy New Year!
It’s been a while since you’ve heard from me between my honeymoon and the holidays. But I’m back!
Let’s start 2025 by looking at a unique animal: the tuatara.
Tuatara (Sphenodon punctatus) are reptiles found only in New Zealand. Growing up to 1.6 feet (0.5 meters) long and weighing up to 3.3 pounds (1.5 kilograms), tuataras are New Zealand’s largest reptile. While tuatara once lived throughout New Zealand, predators have decreased their range to offshore islands. There is also a population of tuatara living in Zealandia, an ecosanctuary in Wellington (this is where I saw a tuatara!).
“Tuatara” is a Māori word meaning “peaks on back” or “spiny back.” It refers to, you guessed it, the spiny crest on the back of both male and female tuatara. Male tuatara have bigger spines than the females, and they use them to attract mates.
Unique reptile
Tuatara may look like medium-sized lizards, but they’re not! Instead, they are the only living members of Rhynchocephalia, a group of reptiles that existed during the Mesozoic era. While tuatara are related to lizards and snakes (part of the order Squamata), fossil and genetic data show that the two groups diverged about 250 million years ago. What does this mean practically? According to the authors of a Current Biology review, “humans are more closely related to kangaroos, for example, than the tuatara is to a lizard.”
Being evolutionary separate from lizards has resulted in tuatara having many unique characteristics. For example, tuatara have no external ears, and they have more ribs than lizards do. Tuatara also have a weird way of chewing for a reptile. Their bottom jaw has a row of pyramid-shaped teeth that slot between two parallel rows of teeth on the upper jaw.
While tuatara will bask outside their burrows during the day, they are, unlike many reptiles, primarily nocturnal. This is because most of their food is predominantly active at night. Tuatara eat primarily insects like wētā and beetles but will also eat birds and bird eggs if the chance arises. Adult tuatara will even eat younger tuatara! To avoid becoming a snack for older tuatara, the young ones tend to eat during the day when the older ones are resting.
Third eye (kinda)
Tuataras are often described as having a “third eye” on the top of their heads, which is partly true. They have what is known as a “parietal eye,” serving as an additional sensory organ. This parietal eye is a small organ, and while you can see it on the top of a juvenile’s head, it is covered by scales in adult tuatara.
The parietal eye has lens-like and retina-like components but probably can’t detect movement or images. What it probably does is detect light. This light-detecting function likely helps regulate basking behavior and circadian rhythms in tuatara. It also helps tuatara tell what season or time of day it is.
Long incubation
Male tuatara begin waiting outside female burrows in March, hoping to impress them with their spiny crests. If the female is interested, they mate! But unlike other reptiles, male tuatara lack a hemipene (penis-like paired organ). Instead, they mate like birds: the male presses his cloaca to the female’s cloaca in a cloacal kiss. Perhaps because of this non-typical reptile mating, tuatara have some of the fastest-swimming sperm among reptiles!
After mating, the female lays her eggs in a nesting burrow before leaving them to their long incubation period. Tuataras have one of, if not the, longest incubation period of any reptile: 12 to 15 months. Unfortunately, this also gives predators like rats plenty of time to find and eat the precious eggs.
But if the tuatara survive and hatch, they have a chance at an incredibly long life. They have one of the slowest growth rates of any reptile and continue growing until they are 35. While the average tuatara life span is about 60 years, they can live to be 100 years old!
Cold survivors
New Zealand can get cold, so reptiles living there have to adapt to cold weather. Tuatara can be active in weather as low as 6 degrees Celsius (43 degrees Fahrenheit), although their preferred range is between 21 and 23 degrees Celsius (71 to 73 degrees Fahrenheit). They also have the lowest known optimal body temperature of any reptile. Side note: this cold tolerance helps explain how tuatara can be nocturnal since many reptiles rely on the sun to warm their bodies up to a minimum temperature.
How do they do it? We can get hints by looking at their genome. The tuatara’s genome is huge for a reptile. At about 5 gigabases, the tuatara’s genome is 2/3 bigger than the human genome and much larger than the typical snake or lizard genome of around 2 gigabases. The tuatara’s cold tolerance could be related to the large number of TRP genes in their genome, as TRP genes are related to temperature sensitivity and body temperature regulation.
More research will help us better understand these unique reptiles.
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