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MOA & TUATARA (AGAIN)



Hope no-one's *too* bored with this thread. Tough in any case.

Adam Yates bought up the following points..

> Infact the fossil record of Sphenodon only goes back as far as the 
>  Late Pleistocene (if that).

One of the reasons that tuatara aren't 'living fossils' is that they have,
strictly speaking, NO FOSSIL RECORD. Remains go back about 1000 years, and I
don't know if you can even call that *subfossil*.

> The lack of a Cainozoic fossil record of tuataras in New Zealand is
> puzzling, especially since it was probably present in NZ before it
> broke away from Gondwana (Cretaceous?).

NZ, with its cargo of dinosaurs, (probably) early moa, tuatara, and ancestors
of just about all other extant NZ biota, broke from the Australo-Antarctic
margin of Gondwana 82 mya as part of a crustal raft which also includes New
Caledonia, the Lord Howe Rise and the Campbell Plateau. This was initiated by
sea floor spreading centres in the Tasman Sea and the south Pacific, both of
which became extinct shortly after (about 60 mya). Prior to this divergence,
there was a 10-20 mya history of crustal thinning and rifting.

> Even more puzzling is the extremely short fossil record of those
> other NZ gondwanan endemics, the Moas.

1 moa, 2 moa, 50,000 moa. 

> Now I know that terrestrial deposits may be few and far between but
> surely one or two bones of the Tertiary moas would done a bit of a
> nodosaur and ended up in the superb tertiary marine sequences of NZ?
> I don't know what this means if anything!

One of the great unresolved anomalies of the NZ terrestrial fauna (the plant
macrofossil and palynomorph record is good) is the near total absence of a
fossil record. Though molecular data suggest antiquity of about 80 mya, the
oldest moa fossils are only 2 million years old! We have seen how tuatara lack
a fossil record: similarly the giant gecko _Hoplodactylus delcourti_ is
presently known (bar the type specimen) only from 2 recent (c. 1000 A.D.) bone
fragments (a cloacal bone and a mandibular ramus [Bauer & Russell 1988]). Cooper
and Millener (1993) suggest that the paucity of fossil terrestrial fauna may be
'due, in part, to high acidity of the terrestrial sediments (but, probably, in
part, to lack of searching)' (p. 430). 

Adam's speculations are interesting. We can only guess that moa remains did not
ever, in their entire NZ history, end up on beaches. That seems unlikely to me.
It is even odder when we consider the absence of tuatara fossils - animals that
often nest on coastal cliffs! In contrast to the terrestrial record, NZ does
have superb marine sequences, and with a very rich record of marine fossil
vertebrates. It was a haven throughout the Cainozoic for penguins and whales (as
it is still, with over 40% of extant cetaceans recorded from its shores), and
was a focal point in the evolution of both groups (and it was great for marine
reptiles too, but then that's another story..). 

One more thing - I should have said that the very high tuatara densities on
Stephens Island (up to 2000 per hectare) are probably the result of a human-
managed habitat: sheep-grazed grassland. Stephens Island tuatara lay their eggs
in these grasslands, having found that temperatures here (with cooler forest as
alternative) result in greater clutch success. Paradoxically, therefore, the
biggest tuatara population in the world is the result of a man-made environment.
There are plans to restore Stephens Island, and in the interests of weta,
_Leiopelma_, and rare geckos, this would mean replanting of native shrubs across
the grassland. Cree and Daugherty (1990) therefore predicted that such a change
would reduce the Stephens Island tuatara population across time. 

_References_

BAUER, A.M. & RUSSELL. A.P. 1986. _Hoplodactylus delcourti_ n. sp. (Reptilia:
Gekkonidae), the largest known gecko. _New Zealand Journal of Zoology_ 13: 141-
148. Description of the Marseille specimen with detailed figures of all the
material.

--------------------------. 1988. Osteological evidence for the prior occurrence
of a giant gecko in Otaga, New Zealand. _Cryptozoology_ 7: 22-37. Reviews and
describes two bones fragments, establishing the presence of _Hoplodactylus
delcourti_ in the Earnscleugh Cave deposits. Includes a pretty spooky photo of
a tuatara biting a stick. Of several papers on the giant gecko, another must is
BAUER & RUSSELL 1986.

COOPER, R.A. & MILLENER, P.R. 1993. The New Zealand Biota: Historical Background
and New Research. _Trends in Ecology & Evolution_ 8: 429-433. Comprehensive
overview of the tectonic evolution of NZ, its biogeography and climatic history.

CREE, A. & DAUGHERTY, C. 1990. Tuatara sheds its fossil image. _New Scientist_
128 (1739): 30-34. Go here to find out about the complex courtship and nest-
guarding behaviours in the tuatara. Also very good historic review of ideas
about mating in this animal.

For penguins, check out:

SIMPSON, G.G. 1975. Fossil Penguins. _IN_ STONEHOUSE, B. (ed). _The Biology of
Penguins_. Macmillan Press Ltd (London): 19-41. Zusi's paper 'An interpretation
of skull structure in penguins' (ch. 4 in same book) is great too.

An update on fossil penguins, co-authored by Ewan Fordyce, is in the recent
Biology of Penguins volume.

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DARREN NAISH