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Re: Quo vadis, T. rex? [long]
On Thu, 8 Feb 1996, Jeffrey Martz wrote:
> > The same argument could just as easily be
> > used to separate bats or whales from the rest of the Mammalia, if all
> > terrestrial mammals were to die off and all we had were their fossils.
> > Yet that is not the way we classify them. Bats and whales are merely
> > two examples of the broad spectrum of mammalian adaptation, just as birds
> > are merely an example of the broad spectrum of dinosaurian adaptation.
> We have living, breathing bats and whales. We don't have living
> breathing dinosaurs to compare to birds,
Right. So we have to go on the bones. Based on their osteology, whales
and bats are mammals; and based on their osteology, birds are dinosaurs.
> so determining with certainty
> that birds and dinosaurs shared a physiology is not possible.
> Pinpointing the point at which endothermy evolved in the bird
> lineage is no more possible at this point that pinpointing when
> feathers evolved.
We'll see; but, again, this is irrelevant.
> There is at least some indication that there were
> differences. Birds occupy a size range that extends below that of the
> smallest dinosaur.
Birds can hop and perch, while other dinosaurs could not. Their limbs
were fairly stiff, with restricted planes of motion unsuited for small,
walking or climbing animals.
Also, there may have been many dinosaurs in the small range (although not
as small as some birds), but the likelihood that they would be preserved
is much less than that for the larger types.
The smallest birds, by the way, are mostly hummingbirds and songbirds,
the most derived and latest to evolve in the entire bird clade. members
of less derived clades (galliforms, anseriforms, ciconiiforms, and
particularly ratites) can be quite large.
Finally, as you are fond of pointing out, birds fly, and flying usually
works best for comparatively small animals.
> Birds survived the K-T extinction, while dinosaurs did
So what? Crocodiles survived, too. eutherians survived, but not
> Feathers are known for birds, while scales are known for at least
> some dinosaurs.
Well, not scales exactly. bumps, tubercles, and wrinkles, yes; plates
and spikes, yes; scales, not really.
> Endothermy is known for birds, while the indications of
> endothermy (or at least what we would call endotermy in modern birds and
> mammals) for dinosaurs is questionable.
Again, we'll see.
> Uncertainties are great, and
> there are at least slight indications of important differences.
> Separating them is the safest bet given what is known.
No, it is not. Birds are known to be deeply nested (no pun intended)
within the dinosaur clade. Trying to extricate them therefrom on the
basis of speculations about physiology and obscure notions of
typological distance makes no sense at all.
> LN Jeff
Pacific Lutheran University
Tacoma, WA 98447
"If you can't convince them, confuse them." -- Harry S Truman