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Tuatara: Volume 2, Issue 2, July 1949

The Tuatara

page 91

The Tuatara

As the name of this journal is that of one of New Zealand's most unique animals, it is time that a few remarks on the tuatara itself were included. Although the tuatara now appears to be absent from the mainland, it is stated that it formerly occurred in a number of localities in the South Island especially the banks of the Waimakariri River. Some have been collected in the Wellington district and in an account by Newman in 1878 it is stated that four had been taken from Mt. Victoria thirty years previously, two from Hutt Valley, and several from Makara in 1864. One of the effects of Maori and then European settlement in New Zealand has been the disappearance of the colonies on the mainland, and the tuatara is now confined to a number of outlying islands north of Auckland, in the Bay of Plenty and in Cook Strait. Those known in 1935 have been listed by Dr. Falla, and more have been found since. One of the most famous localities is Stephens Island about two miles north of D'Urville Island. Here the tuataras are fortunately still present in abundance.

During a walk at Stephens Island in daylight there may be few signs of tuataras unless it is sunny enough for them to bask in the warmth at the entrance of their burrows. Even then, the first indication of their presence is usually the noise of a quick scuffle, and in turning to the source of sound one may be in time to see the disappearing tip of a tail. Anyone who catches a glimpse of the rapid movement will immediately lose any preconceived ideas about their sluggishness. It is a curious fact that almost every account of the tuatara mentions its “sluggishness,” a statement probably due to many observations of its long periods of immobility. A stealthy approach towards an occupied burrow may allow a closer inspection of the tuatara before it disappears.

Those seen at burrow mouths in daylight are usually fully grown, and their general appearance is fairly well known. Their size appears to be less well known. Adults are approximately two feet in length and two lbs. in weight, although some may grow larger. Nearly half of the total length is made up by the rather massive tail, which like that of lizards, is capable of regenerating after a break. Quite a number of tuataras at Stephens Island have obviously regenerated tails of varying lengths. Along the mid-back of adult animals there is a fold of skin fringed with large softish spines or scales, which gave the tuatara its early English name, Fringe-back lizard. There is a shorter fold from the back of the head to the anterior part of the neck and both these folds can be raised as turgid, erect crests. The only specimens seen with them fully raised at Stephens Island, were some found foraging at night. In daylight all the crests seen were lowered as in the animal figured. One writer (Thomas, 1890) has claimed that the page 92 crests are more strongly developed in males, but the external difference between the sexes must be very small, as no foolproof method for separating them has yet been devised—excepting by the tuatara.

There is a range of colour variation in tuataras but most of it is due to the difference in brilliance before and after moulting. A freshly moulted tuatara is quite a striking olive colour with very distinct lemon coloured spots over all the body except for the dorsal side of the head. The colours lose their brilliance until it becomes an almost uniform brown before next moult. Buller, in 1877, proposed separating the genus Sphenodon into three species on the basis of colour differences but this has not been upheld, and all the tuataras are regarded as the one species S. punctatus (Gray, 1842). Dark brown wart-like spots are present on many specimens, but these projections are ticks (Aponomma sphenodonti) about ¼ inch in diameter. They may be quite numerous, but their numbers are often exceeded by the much smaller red mites which may give the appearance of a red mould especially on the flanks. The latter were present even on the smallest tuatara examined.

A two foot long tuatara at the mouth of its burrow in open coastal forest on Stephens Island.

A two foot long tuatara at the mouth of its burrow in open coastal forest on Stephens Island.

page 93

Young tuataras are rarely seen in the open either by day or night, but during a search under boulders, they will quite frequently be found in an appropriate sized burrow under the protection of the rock. Very small specimens may be found in the spaces and crevices where they have sufficient room without the need to construct burrows. Smaller animals resemble the adults in shape except for their less clearly defined crests. One juvenile probably from this season's hatch was only a quarter of an ounce in weight in April and had no crest except for very slight projections at points along the back. The colour is different only in shade except for the presence of very distinct longitudinal stripes under the chin. Professor Dendy (1899) found the striped pattern especially marked during late development in the egg when the young are marked by longitudinal and transverse stripes of alternate grey and white, a pattern which is completely lost in the adult.

It is not until after dark that one can find tuataras away from their burrows and about in appreciable numbers. In most types of country from exposed bouldery ridges to the shelter of the rather open forest or tussocky slopes they may be seen, and one may occasionally hear their frog-like croak. Presumably they are in search of the beetles, wetas and snails that form the bulk of their food. The motionless pause near a large weta, followed by a dart which is too rapid to be clearly observed and then the audible crunching that follows, have been commented on by the lighthouse keepers. The common geckos and skinks have certainly been attacked and eaten by tuataras in captivity, so the smaller lizards are probably an occasional item of diet. There have been some records of tuataras eating dove petrel chicks in their burrows and Professor Thomas in 1890 stated that he had four times seen or captured tuataras with muttonbirds in their mouths at Karewa Island, Bay of Plenty. At Alderman Island Sladden and Falla found storm petrels with heads off possibly because the birds put their heads in the wrong burrow. However they point out that the number killed by tuataras is relatively small, and death by entanglement in branches is a more important cause of mortality.

The breeding season of tuataras appears to be late spring and early summer as egg laying has been observed at Stephens Island from September to November, and captive animals have laid during December and January. The eggs are a little more than an inch long and covered by a white parchment-like membrane instead of a firm shell. A clutch may contain up to fourteen eggs, all of which must mature at nearly the same time, as they are all laid within one or two days. The earlier searches for new-laid tuatara eggs were made in their burrows and proved fruitless until it was later found that the tuatara excavates a hollow in soft soil, deposits the eggs at the bottom, and after filling in the hole covers it with leaves. Professor Dendy's studies have shown that the eggs first develop comparatively rapidly during the summer, then development slows during April, after which “hibernation” occurs page 94 during the winter months. Although it has been claimed that adults hibernate during the winter, the tuataras of Stephens Island are said to be active all the winter, especially on misty nights. Egg development is resumed again in the following spring. This “hibernation,” of a developing embryo within the egg is a very rare phenomenon, the only other case known being that found in the European water tortoise (Emys orbicularis). Late in incubation, the egg swells noticeably until the parchment like shell becomes tense. The embryo develops a horny egg tooth on its snout (as compared with a calcified egg tooth in true lizards) and with this it cuts the membrane, commencing near one end and extending along the long axis round the other end to a point approximately opposite the first incision. This egg breaker disappears within a week of hatching. Hatching occurs in the summer approximately one year after the eggs are laid. The young which must burrow to the surface in natural conditions, are quite active shortly after hatching. Some which were hatched in England and studied by Prof. Howes (1901) were 3 inches long at hatching, had their first moult after 7 weeks, and had reached a length of 6 inches in four months. This appears to be the only available record of growth rate in tuataras and neither the time taken to reach maturity, nor their maximum longevity is yet known. Although fourteen years is the longest period of survival during captivity listed by Flower (1925) in his account of the longevity of reptiles, a tuatara has been kept by Europeans in New Zealand for 77 years and the specimen was believed to be very old when first obtained. Dr. Falla (1935) records a specimen which lived in a shell pit at Motiti Island and was said to have been known to the Maoris for 300 years.

The association of tuataras with one or other of the petrels in the same burrow has frequently been mentioned, as the commensalism of such dissimilar vertebrates is a rare occurrence. Probably the only closely comparable case is the association of the burrowing owl and the vizacacha (a large rodent) in the pampas of Argentine. There has been much discussion as to whether the tuatara or the petrel does the original burrowing. It seems clear that both make burrows. There is no possible doubt about the tunnelling of petrels in many localities uni-habited by tuataras, and it is equally clear that the very small well hidden burrows of the younger tuataras have been made by themselves. Older animals carry on excavation for egg laying and some writers state that they have observed adults burrowing. No doubt they also frequently occupy burrows constructed originally by the several species of petrel which breed in great numbers on the same islets. For much of the year tuataras can remain in undisputed possession, but in the summer months the petrels return for breeding. At this time tuataras have been found in company with the flesh-footed shearwater (Puffinus carneipes), the mutton-bird (P. griseus), the fluttering shearwater (P. gavia), and other petrels. In most cases this association is apparently without ill effects to either of the dissimilar occupants except for page 95 the few occasions when tuataras may devour a chick. It seems reasonably clear, however, that the association of bird and reptile is fortuitous, due to their proximity and similar needs for burrows, rather than to a particular preference.

While the habits of tuataras show many unusual points of general interest, it is the more fundamental problems that especially attracted the attention of zoologists. The pioneer studies, specially by Dr. Gunther, quickly showed that in spite of its external appearance the tuatara was not a lizard. Although most of its internal organs closely resemble those of a lizard, certain notable differences especially in the skeleton showed that it belonged to a different order for which the name Rhynchocephalia was proposed. This name means beaked head, and all its members possessed a small overhanging beak on the upper jaw. Other members of the group had become extinct long previously in other parts of the world, and the tuatara is the sole remaining survivor. One well known characteristic is the presence of a well developed pineal eye, the “third eye,” in the centre of the forehead. It is better developed in the tuatara than in any other living animal. Originally this eye was probably paired as the intensives studies by Prof. Dendy (1910) and other have shown that it is derived from the left side in tuataras, and the right in lizards. This suggests a more or less equally developed pair in their common ancestors. Although the pineal eye has a well developed retina and lens, anatomical studies showed that certain structures would prevent the formation of an image on the retina. It was believed that it might still retain the power of distinguishing differences in light intensity, but experiments by Dendy failed to show this, and there is evidence that the nerve supply to the pineal eye degenerates during life. In the skull there are two apertures or fossae completely bounded by bony bars in the outer layer of the hind region of the skull. This feature is found only in the Crocodilia among other living reptiles, but was quite common in many extinct reptiles including the numerous dinasours. Although there have been studies of many aspects of the anatomy and development of the tuatara carried out in many parts of the world from N.Z. material, there are related problems urgently needing study. In particular the physiology of this last survivor of a very ancient group of reptiles needs close study. The fact that Milligan (1923) found a lower metabolic rate in tuataras than that of any other vertebrate studied, shows that other very interesting findings might be expected from further work. It is fortunate that some at least of the present island colonies of tuataras are in a thriving state and should maintain the animal as a source of interest for biologists in the future.

Selected References.

Buller, W. L., 1877. Notes on Tuatara lizard; with description of supposed new species. T.N.Z. Inst. Vol IX. P. 317.

Dendy, A., 1899. The Life History of the Tuatara (Sphenodon punctatus). T.N.Z. Inst. Vol. 31. P. 249-55.

Dendy, A., 1910. On the structure, development and morphological interpretation of the pineal organs and adjacent parts of the brain in the Tuatara. (Sphenodon punctatus). Phil. Trans. R. Soc. Lond. B. 201. P. 227-331.

Falla, R. A., 1935. The Tuatara (Sphenodon punctatus). Bull. Auck. Zool. Soc. No. 2.

Flower, S. S., 1925. On the Duration of Life in Vertebrate Animals. III. Reptiles. Proc. Zool. Soc. (Lond.). 911.

Gunther, A., 1867. Anatomy of Hatteria. (Rhyncocephalus, Owen). Phil. Trans. Pt. II. P. 1-35.

Howes, G. B. & Swinnerton, H. H., 1901. On the Development of the Skeleton of the Tuatara, Sphenodon punctatus; with remarks on the egg, on the hatching and on the hatched young. Trans. Zool. Soc. Vol. XVI. P. 1-86.

Milligan, R. R. D., 1924. The Respiration and Metabolism of the Tuatara. Rept. Aust. Adv. Sc. Vol. 16 P. 404-6.

Newman, A. K., 1878. Notes on the Physiology and Anatomy of Tuatara. T.N.Z. Inst. Vol. 10. P. 222.

Sladden, B., and Falla, R. A., 1927. Alderman Islands. NZ Jour. Sc. & Tech. Vol. 9. P. 193.

Thomas, A. P. W., 1890. Preliminary Note on Development of Tuatara. Proc. R. Soc. Lond. Vol. 48. P. 152.