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UN-DWARFED KIWIS, MONOTREMES & NZ



Hello people. More stuff on NZ..

In a recent post, I said that NZ had broken from Australia about 80 mya. Both
Ronald Orenstein and Dr. Paul Willis pointed out that I was incorrect. Paul
said..

> One probllem here is that New Zealand was never attached to Australia. It
> was attached to Antartica.

Thanks to both of you for picking up on this. Strictly speaking, I was
incorrect: however, I have noted that exactly where NZ _was_ prior to rifting
depends somewhat on the source you consult. First of all, NZ consists of at
least 13 terranes. Prior to Late Cret. rifting, they were clumped in a landmass
that reached from just east of the Antarctic Peninsula to the NE coast of
Australia: this area (biggest between late Tithonian and early Aptian), about
half the size of present Australia, is often referred to as 'Greater NZ' (see
Stevens 1989).

I shall not go into this at length (a lengthy tangential could spin), but the
paper I had read (Cooper and Millener 1993) does not really emphasise a NZ-
Antarctic link (NZ is said to have drifted from 'the Australian-Antarctic margin
of Gondwana'). Their fig. 1 in fact shows NZ rifting from east Australia as the
Tasman Sea opens. As, therefore, early Cret. 'Greater NZ' was sutured to
Australia, the NZ landmass may have shared biota with that continent. But while
NZ may have been (partially) attached to Australia, it should correctly be said
to have rifted from the eastern margin (or Australian-east Antarctic margin) of
Gondwanaland. See also Stock and Molnar 1987.

> >By the Lower Cret, Australia had _Steropodon galmani_,
>
> We also now have a second Cretaceous monotreme in _Kallikodon_.

_Kollikodon_ (nomen nudum _Hotcrossbunodon_ never accepted by ICZN). I used
_Steropodon_ as I thought it was earlier - - it's probably not: Archer et al
1985 say that _Steropodon_ is Albian, whereas, for Flannery et al 1995,
_Kollikodon_ is Middle Albian. I suspect that chronology of Lightning Ridge got
better between 1985 and 1995. Anyone have data on the Lightning Ridge
plesiosaur? (and this isn't Eric..).

> >_Tingamarra_, a basal
> >ungulate from the Eocene, is Australian.

> Basal ungulate? I thought it was a condralyth.

'Condylarths' are basal ungulates. I'm playing mammalian cladist and banishing
the term.

KIWIS, THEIR EGGS AND ALL THAT

I don't know much about kiwis, so I never bothered to comment on the fact that
kiwis lay such whopping huge eggs. But here are some thoughts. (Incidentally,
I checked, and plural of kiwi _is_ kiwis, unlike moa, where the plural is still
moa).

First of all, it is still something of a mystery why kiwis produce such large
eggs. Females lay one or two, and a 2 and-a-half kg bird will lay eggs that
weigh about 500 g each. Eggs contain high proportions of rich yolk, and young
hatch large and fully feathered. This all sounds like classic K-strategy
behaviour. The kiwis have gone down the road where investment for only one or
two young is vast, and energy losses are high. Females lose about 20% of body
weight for each breeding attempt. However, things are made a bit easier for them
as males do the incubating - and with a 3 month incubation period (longest known
for any bird), he certainly has his work cut out too.

In fact, data presented by Taborsky in 1989 shows that males put 13% _more_
energy into each clutch that do females. In other birds (like sandpipers) where
the male incubates, the female mates with another male and lays another clutch
for the 'new' male to incubate. This doesn't happen with female kiwis, even when
their ranges overlap with 'new' males, so presumably she's just too damn
exhausted to go and produce another clutch right away. This strategy, with both
sexes putting considerable investment into one or two large, well-developed
young seems to be 'K' at its most extreme. Both sexes have to work together, as
neither could raise a clutch by themselves.

So - did the kiwis evolve this method (because they were in a land with strange
rules), or did they retain it from ancestors with big eggs?

The latter view was widely supported prior to a slew of recent data. In his
classic paper on ratite evolution, Cracraft (1973) wrote: '... kiwis are
therefore secondarily small. This conclusion is supported by the fact that kiwis
have the largest egg relative to body-size amongst known birds. Supposedly,
during phylogeny the kiwi lineage became smaller in body-size but a large egg
remained advantageous.' (p. 515).

This hypothesis is logical, but is not supported by other data that suggest that
kiwis have plesiomorphically retained the small body size of primitive ratites.
Cracraft's proposed kiwi-moa affinity was in fact based only on four characters
that are either plesiomorphic (e.g. distal projection of middle trochlea), or
easily evolved convergently, and not convincing in determining a relationship
(e.g. two short ridges on hypotarsus). Kiwis are not descended from moa (Cooper
et al 1992, 1993), and there is no reason to suspect that they are dwarfed.

So, it's obviously hard to find a tetrapod that has really been dwarfed. Island
endemics and the cross-taxon dwarfism that occurred after the Pleistocene
(Guthrie 1989) notwithstanding, are there really any examples? I was interested
to find that G.G. Simpson considered this very area in his 1949 book _The
Meaning of Evolution_:

'There is increasing evidence that mammals in general, especially some of the
relatively large forms, have tended to decrease in average size since the
Pleistocene ice age. In itself this negates any invariability in the rule of
increase in size, and it certainly strongly suggests adaptive response to
climatic conditions as opposed to size control by some inner tendency or life
urge within the organisms alone. We know that climates have tended to become
warmer since the Pleistocene. We also know that closely related living mammals
show the adaptive phenomenon of being, on an average, relatively smaller in
warmer climates. It is certainly reasonable to suppose that this is the same
sort of phenomenon involved in size decrease from Pleistocene to Recent.

'In this connection, it is known that many large animals of the past became
extinct and are not the ancestors of their smaller living relatives.....
[mammoths and living elephants, ground and tree sloths and dinosaurs and living
lizards discussed as examples]... But this does not mean that forms that _were_
the ancestors of living animals were not also somewhat larger than the latter
at one time or another, and such does appear to be the case for some of them.

'Some paleontologists [sic] have been so impressed by the frequent trend for
animals to become larger as time goes on that they have tried to work it the
other way round. If they find, say, a Pleistocene bison that is somewhat larger
than a Recent bison (so-called _Bison taylori_, associate and prey of early man
in America, is a good example), then they conclude that it is not ancestral to
later bison _because_ it is larger. You can establish any "rule" you like if you
start with the rule and then interpret the evidence accordingly.' (pp. 136-7).

_REFERENCES_

ARCHER, M., FLANNERY, T.F., RITCHIE, A. & MOLNAR, R.E. 1985. First Mesozoic
mammal from Australia - an early Cretaceous monotreme. _Nature_ 318: 363-366

COOPER, A. et al. 1992. _Proc. Natl. Acad. Sci._ 89: 8741-8744. Sorry, don't
have the complete ref with me. Looks at mitochondrial DNA I think.

---------., ATKINSON, I.A.E., LEE, W.G. and WORTHY, T.H. 1993. Evolution of the
Moa and their Effect on the NZ Flora. _Trends in Ecology & Evolution_ 12: 433-
437

COOPER, R.A. & MILLENER, P. 1993. The NZ Biota: Historical Background and New
Research. _TREE_ 12: 429-433

CRACRAFT, J. 1973. Phylogeny and Evolution of the Ratite Birds. _Ibis_ 116: 494-
521

FLANNERY, T.F., ARCHER, M., RICH, T.H. & JONES, R. 1995. A new family of
monotremes from the Cretaceous of Australia. _Nature_ 377: 418-420

GUTHRIE, R.D. 1989. Mosaics, allelochemics and nutrients. IN MARTIN, P.S. &
KLEIN, R.G. _Quaternary Extinctions: A Prehistoric Revolution_ Uni. of Arizona
Press (Tucson), pp. 259-298

SIMPSON, G.G. 1949. _The Meaning of Evolution._ Yale Uni. Press (New Haven), pp.
364

STEVENS, G.R. 1989. The nature and timing of biotic links between NZ and
Antarctica in Mesozoic and early Cenozoic times. IN CRAME, J.A. (ed) _Origins
and Evolution of the Antarctic Biota_. The Geological Society (London), pp. 141-
166

STOCK, J. & MOLNAR, P. 1987. Revised history of early Tertiary plate motion in
the south-west Pacific. _Nature_ 325: 495-499

TABORSKY, M. 1989. Talk given at _International Ethological Conference_ held at
Utrecht, The Netherlands.

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DARREN NAISH