Tuatara
- The two temporal fossae and location of the parietal eye
Tuataras (Sphenodon punctatus) are a relict of an earlier era. They are therefore considered to be “living fossils” and are the only survivor of the extinct Rhynchocephalia, an order of reptiles regarded by zoologists as a separate order equal to those of the tortoises, crocodiles, lizards, and snakes.
The Rhynchocephalia were evident as the dinosaurs were evolving in the Mesozoic two hundred million years ago. There is fossil evidence of twenty one species in the Triassic and another one in the Cretaceous. For a long time the Rhynchocephalia were generally thought to be extinct. Then, in 1831, GRAY discovered the tuatara, which he placed among the agamids, and it wasn’t until 1867 that GÜNTHER recognised the tuatara’s special significance. As the only genus of Rhynchocephalia, once distributed throughout the world, including Europe, the tuataras survived on the islands of New Zealand.
The characteristic feature of tuataras is their two large openings, or so-called temporal fossae, in their skull. In addition, tuataras have abdominal ribs and their young a parietal eye with the remains of a cornea and lens. The teeth of the tuatara’s lower jaw are pushed between the double row of teeth in the upper jaw like a pair of scissors. Unlike the lizards and snakes the tuatara’s teeth form part of the jaw instead of having their own sockets. On the other hand, tuataras do not have an auditory canal, although they emit noises. Unique in the kingdom of reptiles the male tuatara does not have a reproductive organ. The tuatara’s body temperature is only 6.2 to 14 °C, and they are unable, at least for long periods, to cope with ambient temperatures over 23 °C.
- Transport crate with young tuataras
Tuataras are medium-sized, burrowing lizards that can live for over sixty years. They reach sexual maturity after nine to thirteen years. The females normally lay an average of eleven eggs only every four to five years, which take twelve to fifteen months to hatch. As early as 1894 BERG at Zoo Berlin reported on how he kept the tuataras that came to the zoo in 1893. In 1887 Amsterdam Zoo received two tuataras for a short time. The tuataras of Uppsala University reached fame when they arrived at the zoo in 1908 and lived there for over twenty six years.
Although New Zealand prohibited the unregulated capture of tuataras in 1895 and the collection of their eggs in 1898, the nature conservation authorities continued to agree to sending individual tuataras to the zoos of Europe after World War II, for example in 1957 a female to Basel that three months later laid four unfertilised eggs before it died. In 1958 Basel Zoo received another female. From 1956 to 1960 and from 1964 tuataras lived at the Frankfurt Senckberg Museum. From 1965 to 1975 Cologne Aquarium kept a tuatara in a cooled terrarium directly at the entrance to the house.
Although the Cologne tuatara terrarium was not exactly big at the time, the really simple solution to the temperature problems then convinced many colleagues. Yet in spite of many attempts from various quarters no other tuataras officially came to Germany following the arrival of the Cologne tuataras in August 1965 – until 1990 ZOO-AQUARIUM BERLIN was suddenly offered a group of Sphenodon punctatus juveniles in cooperation with the New Zealand Department of Conservation and the Victoria University of Wellington, and that as quickly.
When we consider that today only 137 tuataras are being kept at ten institutions, of which only forty three animals at six zoos outside of New Zealand and a tuatara that arrived at the Senckenberg Museum in 1965, such an offer as this was of course fascinating, yet it also meant special responsibility and a high level of commitment if these rare reptiles were to be given the optimal care.
Following intensive field research by DAUGHERTY et al. since 1985/86 we today know significantly more about the extant population of tuataras and their biology than in the early seventies. Contrary to the opinions prevalent at the time we today know not only of one, but two extant species, Sphenodon guntheri and Sphenodon punctatus. The latter in turn consists of two subspecies, Sphenodon p. punctatus und Sphenodon p.n.ssp. These two Sphenodon species still live on thirty small, even tiny islets off the coast of the New Zealand’s two principal islands, or an area smaller than 0.1% of their former distribution. Alone in the last century tuataras have become extinct on one hundred islands, and as early as 1980 on two. The species S. diversum is known only from bones found on the east coast of the northern island and no living animal of the species S.p. reischeki has been witnessed on Little Barrier Island since 1978 (DAUGHERTY, CREE, HAY & THOMPSON, 1990). Today there are a total of three hundred S. guntheri adults living on Brother’s Island, about ten thousand representatives of S. p. punctatus on twenty five small islands, and 45,000 animals of S.p.n.ssp., the so-called Cook Strait population, on four islets between New Zealand’s two principal islands (CREE, DAUGHERTY, TOWNS, & BLANCHARD, 1994).
Following the field research over recent years we know today that normally the maximum population density is 1,500 animals per hectare of natural habitat, or one animal for every seven square metres. For this reason terrariums like those earlier at Cologne Aquarium or Basel Zoo are today considered to be far too small for keeping tuataras. Moreover, keeping single animals is always ill advised, and even pairs in the case of tuataras. Field and terrarium observations have shown that successful tuatara pairing depends essentially on the rivalry between various males and females. Tuatara groups should therefore consist of at least 3.5 animals. And accordingly the terrarium must be dimensioned to match. No less than five square metres per animal are regarded as necessary. Even nine square metres per animal would be desirable. Terrarium sizes of twenty square metres per animal, although repeatedly discussed and desired by nature conservation, are certainly feasible only for field terrariums and a climate as in New Zealand. – Experience, though, has shown that juveniles can still be kept on a much smaller space, up to ten animals per square metre.
Although in Berlin we have converted our largest terrarium into a climatic chamber for tuataras, it still has only 22 m2 of floor space, and not 45 m2 as deemed necessary for a group of 3.6 adult sphenodons. Fortunately though, tuataras grow only relatively slowly. They first reach sexual maturity after nine to thirteen years, adulthood after thirty, after which they can certainly live to be a hundred. For this reason the New Zealand authorities considered our terrarium, at least in the beginning, to be big enough, particularly since all concerned of course were hoping, but didn’t know whether all juveniles would at all continue to live to sexual maturity. According to a letter written by DAUGHERTY, 1.5–2.0 m2 per adult tuatara may also be sufficient if the terrarium features the corresponding terracing and layout.
- Insight into the tuatara terrarium
According to more recent research findings by CREE, THOMPSON & DAUGHERTY (1995) the incubation temperature is decisive for the sexual differentiation of tuataras, just as it is for many reptiles. At 18 °C 100% of hatching S. punctatus are females, at 20 °C this was down to 91%, and at 22 °C only 23%. S. guntheri eggs were incubated at 18 °C, 22 °C, and varying temperatures (18–23–18 °C) and the sex ratio was 0.17 at 18 °C, 0.3 at 20 °C, but 7.0 for the varying temperatures. We can safely assume that the decisive factor promoting male sex development is a temperature exceeding 22 °C for two weeks in the middle of incubation. It is therefore important that the ten sphrenodon juveniles that we received in October 1990 and that originally came from Stephens Island had hatched at different incubation temperatures. We could therefore assume mixed sexes. In collaboration with the Leibniz Institute for Zoo and Wildlife Research in Berlin we could verify this year after ultrasonic examinations that we are in possession of 3.6 animals.
- The animals are examined, measured, and weighed at regular intervals.
After hatching between January and October 1987 our tuataras arrived at Victoria University in October 1988 and there were first measured and weighed in November of that year. Then they tipped the scales at 13.1–20.2 g and were 7.1–8.5 cm in length excluding the tail. Finally, on 27 October 1990 the ten juveniles from Wellington arrived in Berlin via Hawaii. They were all placed together in a wooden crate, but each in its own separate box. A wet foam sponge placed in each box kept the humidity at the necessary level. The base of each animal box consisted of wire gauze secured at a distance from the base of the crate. This gap contained cooling elements that were replaced during the stopover on Hawaii as a precautionary measure for maintaining the cool temperatures for the whole duration of transport: earlier, 36% of tuataras kept since 1952 in terrariums outside of New Zealand had died within a year of capture, probably as a consequence of overly high transport temperatures.
On arriving at ZOO-AQUARIUM BERLIN the tuataras were first placed in smaller glass terrariums, and over the next few days their general condition and faeces were examined for any parasites. At least animals captured in the wild are often infected by parasites, some of them peculiar to individual species, such as the trematode Dolichosaccus leiolopismae, the ascarid Hatterianerna hollandei, and two species of mite Neotrombicula sphenodonti and Aponomura sphenodonti (AINSWORTH, 1994). LAIRD (1950–51) reports of a haemogregarine peculiar to the tuatara species (Haemogregarina tuatarae). We discovered an infection with Salmonella baildon that we treated successfully with Baytril.