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Re: ... vs energy deficient gigantothermy (boo hiss)



> On Mon, 7 May 2001, David Marjanovic wrote:
>
> > > and they have IMHO not yet had a chance to grow
> > > to gigantic sizes.
>
> How much time are you willing to give them?  They've been around for about
> a hundred million years already.  Maybe something is preventing them from
> being multi-tonne birds.

Time alone is not enough, of course. The biggest known mammal of all first
165 or so million years of mammal history was the 1 m long platypus
*Steropodon galmani*. For becoming gigantic a taxon needs to dominate an
ecological niche that allows for gigantism. This has rarely been the case
for birds. Biggest were the carnivores (Gastornithidae = "Diatrymidae",
Phorusrhacidae, Dromornithidae), that lived off rather small prey -- there
is no need for *T. rex* sizes if no hadrosaur-sized prey is available -- and
the herbivorous aepyornithids and moas, which have a very short fossil
(rather subfossil) record AFAIK. So far, there has indeed always been
something preventing birds from weighing tonnes, but this has not been the
birds themselves.