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Re: Dinosaur temperature paper
The Gillooly et al. paper seems to work on the presumption that the dinosaurs
under investigation were bradyenergetic like reptiles. Therefore their
argument is circular. In order to estimate dinosaur metabolic rates from growth
rates it would be necessary to show that the two factors are closely
It is true that no demonstated bradyenergetic continental animal grows rapidly,
so any extinct terrestrial form that exceeds the maximum reptilian growth
rate at a given size is probably tachyenergetic like birds and mammals.
tachyenergetic animals can grow slowly, and growth rates vary tremendously
within mammals. As you can see in Append Fig 13A in your copy of DA, girl red
kangaroos grow at a rate similar to that of crocodilians. Yet the marsupials
far more energetic than the crocs. Equally interesting is that boy red
kangaroos are much larger than the females and grow a lot faster. There is
difference in the metabolics of the boys and girls roos. That some small
dinosaurs grew as slowly as reptiles and female kangaroos does not tell us
about their energy production.
I say some small dinosaurs because it looks like some small ornithopods grew
fast. A number of small ornithopods have extensive fibro-lamellar bone matrix
which indicates rapid growth, and no deep bone growth rings. The only good
explanation for this is that they grew up within a year before the dry season
winter came along, like similar sized birds. This point has been ignored by
Erickson et al., who have concluded that all observed small dinosaurs grew
slowly. But their methodology, in which only specimens with growth rings are
measured for growth rates, automatically excludes any examples that lack growth
rings. This too is circular reasoning.
That Gillooly et al. excluded alvarezsaurs up front is telling. They grew
slowly like the other small dinosaurs examined in the paper, but since they
feathered they should have had high metabolic rates. Had Gillooly et al. run
an alvarezsaur through their process it would have turned out bradyenergetic
like a reptile. That would have been awkward.
The widely reported claim by Gillooly et al. that they found direct evidence
for low metabolic rates in dinosaurs is silly since all they seem to have done
is assumed that they had reptilian MRS, and following that assumption
calculated reptilian level body temperatures at different body sizes. The
have produced direct evidence for body temperatures in dinosaurs are the likes
of Barrick and most recently Amiot et al. 06 Earth & Planet. Sci. Letters
246: 41 who use bone isotopes. They find that dinosaurs of all sizes ran at
pretty much the same high, constant temperature, and are distinctive from the
temp., heterothermic herps found in the same deposits.