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TUATARAS



Norm King asked a bunch of questions recently, one of which is concerned with
tuatara - there has also been mention here and there of them on the list: it's
a good time to post this I guess.

First off, phylogeny.

Extant tuatara (_Sphenodon_) are part of the (mostly Trias-Juras) Sphenodontida,
a clade whose only close relatives are squamates (lizards, amphisbaenians,
snakes and a few monotypic taxa) - these two groups together are the
Lepidosauria. Lepidosaurs, perhaps the most successful of all reptile groups (in
numeric terms), have the younginiforms as their closest relatives -
younginiforms are superficially lizard-like mostly Permian forms. Together,
lepidosaurs and younginiforms form the Lepidosauromorpha - and this is the
sister group to the Archosauromorpha, the group we are mostly interested in,
as it includes archosaurs and all their relatives. 

Lizards or tuatara are *not* therefore close to archosaurs, but are very distant
relatives. On different branches of the tree, if you like.

Lepidosauromorphs and archosauromorphs are, together, the Neodiapsida - the
greatest vertebrate radiation of all time.

I think I'm right in that overlapping scales are one of the synapomorphies for
lepidosaurs. The chemistry of these scales is unique. Right?

> 2.  Did the tuatara inhabit more of New Zealand than it does now (just 
> small islands) immediately prior to the arrival of Europeans, or even of 
> the native New Zealanders?

Yes. Tuatara today are restricted to (last I heard) 28 offshore islands
(Daugherty, Cree, Hay & Thompson 1990 say 'approx. 30'), both in Cook Strait and
to the north of North Island, in the Hauraki Gulf and the Bay of Plenty, but
have been far more widespread in historic times. 

40 populations existed in the 19th century, but 25% of these (10 populations)
are now extinct. Cree and Daugherty 1990 state: 'About 30 populations are
thought to survive, but one of these may already be extinct and a further seven
are vulnerable or endangered because of the presence of an introduced rat (the
kiore, _Rattus exulans_)'. 

Extinction of these populations has been blamed on taxonomic neglect: in 1989
it was realised that the population on North Brother island (Cook Straits) did
deserve specific status after all (Barton 1989) - it had already been given this
in 1877 (but was synonymised with the nominal species in the 1930s), and was
resurrected in 1990: _Sphenodon guntheri_. Of the two currently recognised
subsp. of the better known, larger species _S. punctatus_, one - _S.p.
reischeki_ of Little Barrier Island (Hauraki Gulf) - may be extinct. Daugherty
et al. 1990 reported that it had not been seen for the last 12 years.

Confusion over whether or not tuatara populations deserve conservation is
serious in that taxa are/have been lost while the importance of individual
populations gets considered. Failures and taxonomic loss are therefore
inevitable (see May 1990 and Daugherty et al. 1990). This is in marked contrast
to the extraordinary success New Zealand has had in rescuing bird species by
maintaining pest-free, ecologically restored offshore islands (Vietmeyer 1992).
We hope for similar projects that will restore tuatara populations.

It is possible that higher taxonomic diversity existed in tuatara prior to their
extinction on the mainland, for they _were_ widespread across both North and
South Island, as recently as 150 years ago in fact. The invasion of Polynesians
about 1000 years ago resulted in massive devastation and species loss. By 1840
burning of forests reduced cover from 78 to 53% of land surface (King 1990),
with 32% of the known landbirds pushed to extinction. Successful introduction
of only 2 mammal species - the dog and the kiore - occurred, and are mostly
responsible for the loss of birds, bats, lizards, numerous invertebrates and
tuatara from the mainland (Atkinson & Cameron 1993). A secondary, more recent
invasion of European mammals had less of an impact (despite the introduction of
mustelids), but this is probably because the better part of the damage had
already been done.

Tuatara are remarkable animals with complex courtship rituals (see Cree and
Daugherty 1990). Males display to rivals and potential mates by raising their
crests and heads, and will fight if necessary: broken jaws, lost tails and
facial wounds are not uncommon in males. Males perform a ritualised stiff-
legged walk to court females, and if she does not retreat he will copulate.
Behaviourally, tuatara are as complex as, say, some iguana species - lizards
often thought of as markedly advanced with regard to social behaviour. Tuatara
lack an intromittent organ - unlike all other lepidosaurs - and 19th century
workers therefore thought them to be ineffectual lovers. Males are now known to
distend their cloacas, in a similar fashion to most birds. 

Their slow metabolism (adaptation to climate) is partially responsible for their
longevity - up to 60 years or more (locals guess up to 300 years!), this
combined with the productivity of the islets they live on can result in very
high population densities - Towns and Ballantine 1993 reported 2000 per hectare
(optimal habitat on Stephens Island), and apparently it can be hard to walk at
night without treading on them. 

It is not known if nocturnality in tuatara is secondary - it seems not to be -
 but is it somewhat unusual in a land supposedly devoid of predators. Cryptic
behaviour and morphology in other New Zealand animals, including many birds, is
probably evidence that these animals were once predated upon by animals now
extinct. These include two raptors, and possibly other animals as yet
undiscovered (there is a slim possibility that NZ *has* had native land mammals
after all). Tuatara themselves feed mostly on beetles but have also been
reported eating seabirds. At up to 60 cm in length and with robust, bulky jaws,
this is evidently a possibility.

Tuatara are certainly not 'living fossils', and anyone that say they are
deserves to be shot. Sorry.

_References_

ATKINSON, I.A.E. & CAMERON, E.K. 1993. Human Influence on the Terrestrial Biota
and Biotic Communities of New Zealand. _TREE_ 8: 447-451

BARTON, M. 1989. Brother's cousins. BBC Wildlife 7 (12): 790

CREE, A. & DAUGHERTY, C. 1990. Tuatara sheds its fossil image. _New Scientist_
128 (1739): 30-34

DAUGHERTY, C.H., CREE, A., HAY, J.M. & THOMPSON, M.B. 1990. Neglected taxonomy
and continuing extinctions of tuatara (_Sphenodon_). _Nature_ 347: 177-9

KING, C.M. (ed) 1990. _The Handbook of New Zealand Mammals_. Oxford Uni Press

MAY, R.M. 1990. Taxonomy as destiny. _Nature_ 347: 129-30

TOWNS, D.R. & BALLANTINE, W.J. 1993. Conservation and Restoration of New Zealand
Ecosystems. _TREE_ 8: 452-7

VIETMEYER, N.D. 1992. The Salvation Islands. In CALHOUN, D. (ed) _1993 Yearbook
of Science and the Future_. Ency. Britt. Inc.

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DARREN NAISH