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Re: [Re: Feathered/scaly theropods: trying to make the point.]



"T. Mike Keesey" <tmk@dinosauricon.com> wrote:
> Information on theropod skin impressions is only available for a little
> over half a dozen taxa. These include two scaly forms (the abelisaurid
> ceratosaurs _Carnotaurus_ and _Aucasaurus_) and a bunch of feathered or
> proto-feathered forms (coelurosaurs such as _Sinosauropteryx_,
> _Protarchaeopteryx_, _Caudipteryx_, _Beipiaosaurus_, _Microraptor_,
> _Sinornithosaurus_, and avians).

++++++++++++++++++++++++++

Don't forget those two (three?) tyrannosaur scale impressions that have been
found as well. Yeah, Currie says that they found skin, but until I see some
photos of this, supposed, find, I'm placing it right up there with
Archaeoraptor and his pack hunting _Giganotosaurus_ statements.

It should also be noted that these bunch of "feathered" dinos all came from
the exact same location; which is more than just a little suspicion if you ask
me.


___________________________

> 
> The most parsimonious explanation, based on these data and the most
> commonly accepted phylogenies, is that feathery integument was present in
all members of Clade(_Sinosauropteryx_ + _Passer_*), and possibly
> originated earlier, as far back as basal _Tetanurae_ (Clade(_Passer_ <--
> _Ceratosaurus_)).

+++++++++++++++++++++

But if it originated earlier, then how does one explain the scale impressions
of tyrannosaurs?

______________________

> 
> It is currently ambiguous as to whether such taxa as _Tyrannosauroidea_,
> _Ornithomimosauria_, _Coelurus_, _Ornitholestes_, _Scipionyx_, etc. are
> inside Clade(_Sinosauropteryx_ + _Passer_) or not. However, since feathery
integument may well be a feature of a wider clade, it is quite likely to have
occurred in these forms.

++++++++++++++++++++++++++

Operative word being "if." So far, impressions from these various animals seem
to indicate that their origin was inside Sino +_Passer_, if that.

_________________________

> It is also possible that feathery integument extends even further than
> _Neotheropoda_ (Clade(_Ceratosaurus_ + _Passer_)), and the             >
aforementioned carnotaurines are secondarily featherless. At the other > end
of the range of possibilities, it may be that feathery integument  > is
restricted to Clade (_Sinosauropteryx_ + _Passer_), and that certain > members
of that clade may have been secondarily featherless, either    > during part
or all of their lives.

+++++++++++++++++++++++++

The only evidence I have seen for the former would be Zhou & Niswander's
scutes = feathers discovery. And since no one has done any follow up work on
it (AFAIK), this seems to be the extent of any evidence for BCF type
feathering.

As for secondary featherlessness, I don't buy it. What people seem to be
forgetting is that scales aren't simple little structures, but another form of
integument. In order for the secondarily featherless _Carnotaurus_ scenario to
work, the animal would have had to have lost one form of integument (feathers,
fuzz or what have you) and replaced it with another form (scales). Afterall we
don't find scales on the skin of plucked chickens do we? And the secondary
featherlessness on the legs of ostriches shows skin, not scales. So it would
seem more parsimonious to assume that if the animal is found with scales, then
it probably always had scales and didn't evolve them later on; unless, of
course, the aforementioned experiment with scutes proves to be true.

Why noone has tried making fuzzy crocodiles, I'll never know :)

___________________________________

> Apparently there are some new discoveries of non-avian theropod        >
integument being written up. Perhaps we'll know more soon.

+++++++++++++++++++++++

No doubt; these Yixian "fuzzballs" have been the hottest topic in dino
paleontology since the whole "birds are dinosaurs descendants" thing took
off.


Jura - who believes all dinosaurs are scaly, until proven otherwise.



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