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Re: Most dinosaurs were scaly
> From: "Thomas R. Holtz, Jr." <email@example.com>
> Actually, Mickey's objection wasn't. His objection was that if you only
> coded small-bodied animals. The presence of large-bodied animals with fuzz
> is a different issue.
I don't think that size is quite the problematic factor that Mickey is
portraying it to be. Again I cite Yutyrannus as an example of why, but one can
also look at the general patterns of integument we see in extant taxa too. It's
just that Yutyrannus shows no loss of filaments with its large size,
it's that it shows no scales on its hide either. A common misconception that I
see on this list and elsewhere is that scales are not a form of
integument, but are instead equivalent to bare skin. Yes large
extant mammals show hair loss (or rather skin area outpacing hair formation)
body size, but they DON'T replace their hairless regions with scales.
Similarly, ostriches lose leg and neck feathers as they reach adult
size, but they NEVER replace these bare areas with scales. There are no
scales in the apteric regions of birds. Scales only ever occur on the
tarsometatarsus in birds. There is now an abundance of evo-devo
literature out there that suggests that there is a strong developmental
constraint behind this, and that even these small scaled areas of birds
are a relatively recent development (compared to feathers). The point
is: no extant animal today swaps one form of integument for another. Not
with ontogeny, and only rarely, with phylogeny (i.e., it has to evolve
at some point). Even then, mixing and matching of integument doesn't seem to
So if we see scales on the non-metatarsal/feet regions of tyrannosaurids and
allosaurids (and we do), it means that it was most likely that these animals
were entirely scaly animals. If tyrannosaurids preserved bare skin like
Pelecanimimus seems to, then we could argue that filaments were reduced in
these taxa due to their large body size.
> And another issue ignored in this is that NOT ALL SEDIMENTS ARE EQUAL!
> Optimize the same data for only lacustrine/lagoonal vs. coarser seds and
> you get additionally different pictures.
> Furthermore, a point I have made elsewhere: how well does fuzz/hair
> fossilize in non-shale anyway? When we have skin impressions of larger
> bodied Cenozoic mammals, how often do they show fur or hair?
I'm not sure how often hair is preserved in these sediments, but even so, naked
skin is not scaly skin. It is what is found underneath/between scales, hair,
and feathers. We are comparing apples and oranges here.
That said, I am in agreement with you, Matt, and others in that a better
understanding of how sedimentology affects integument preservation would prove
most useful. It is something that is sorely needed now that preserved soft
tissue has become more prevalent in the fossil record.