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A few comments on a recently published paper
(Burness et al. 2001. Dinosaurs, Dragons and Dwarfs... PNAS,
28: 14516-14523) examining the relationship between bodymass in extinct
& extant species and landmass area over the last 65,000 years--
This aims of this paper are commendable, however,
there are a number of eminently valid questions with respect to
methodology. I won't bore you with a complete critique (unless asked), but as a
specialist on Australian marsupial palaeontology, there are a couple of
specific issues that I feel obliged to address. Burgess et
al. suggest that both Australia's largest marsupial carnivore
(Thylacoleo carnifex) and largest herbivore (Diprotodon
optatum) are too small, while the largest reptile (Megalania
prisca) is too big to be explained by area dependent processes alone-
proposing inherently low productivity as a compounding factor. However, the raw
data on which these conclusions are based is of dubious value and in at least
one instance, undeniably relevant published data is conspicuously
overlooked. The authors give a mean bodymass for Thylacoleo of 73 kg.
No raw data and no method, only a personal communication from a PHD student of
one of the contributors is cited. I am relieved to see that a downward spiral in
estimates, all founded in guesswork, that recently saw Thylacoleo
(an animal with a head up to 24 cm wide) estimated at 20 kg, has apparently been
halted (interestingly the lowest bodymass guesses are typically forwarded
by authors attempting to support the hypothesis that low productivity
constrained marsupial carnivore size in Australia). However, if a previous and
the only estimate determined using quantitative methodology, giving a mean
mass of 101-130 kg, is considered, then Thylacoleo is in fact
larger than would be predicted on the basis of area alone (Wroe et al.
1999. Australian Journal of Zoology, 47: 489-498).
There are no published estimates for other
Pleistocene taxa that are not the product of guesswork and Burness et
al. can hardly be blamed for resorting to such, although I'd argue that
the great uncertainty inherent in this method should have evoked very
strong qualification. At any rate- the bodymass presented for
Diprotodon of 1150 kg was taken from a published guess made by a
respected Australian expert. But soon to be published work by myself and
colleagues puts the mean for this 3.7 m long (head-body) and
hyper-robust animal at 2.7 tonnes. Again this is actually larger than would be
predicted by area. Regarding Megalania, the authors give mass of
380 kg - I am again relieved to see that a escalating hyperbole regarding this
animal, culminating in a recent estimate of "several tonnes" appears
to have subsided. However, again this figure is based on no published raw data
or clearly articulated methodology. My own estimate of average bodymass for this
giant varanid is between 90 & 160 kg (mean total length around 3.45
m).
Feel free to hit me with criticism or comment- a
number of relevant articles can be accessed in PDF on my homepage (address
below) or I will send them on request.
Cheers
Stephen Wroe
______________________________________________________
Dr Stephen Wroe
HOMEPAGE - http://www.bio.usyd.edu.au/staff/swroe/swroe.htm
Institute of Wildlife Research, School of Biological Sciences (AO8) University of Sydney NSW Australia 2006 Email: swroe@bio.usyd.edu.au; Email: thylacoleo@optusnet.com.au Ph. 02 9351 8764; Ph. 02 9702 6435 ______________________________________________________ |
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