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



"T. Mike Keesey" <tmk@dinosauricon.com> wrote:
> On 25 Jun 2001 archosaur@usa.net wrote:
>
> > > It's over (possibly well over) 120 Mesozoic species and counting. (And
that's not including about 9,000 Cenozoic species....) And remember,
> > > Clade(_Sinosauropteryx_ + _Passer_) is only the *smallest* clade which
feathery integument might be a synapomorphy of.
> > Compared to the 6 or 700 other dinosaur species known (don't know what the
official dino count is up to now), it still ranks as pretty small (and yes,
this is obviously not counting Aves itself).
>
> *At least* 20% of all Mesozoic dinosaurs. I guess it's subjective, but I
> wouldn't call that small. And there's about 100 more that could have had
> feathery integument as well (tetanurans outside or possibly outside
> Clade(_Sinosauropteryx_ + _Passer_)), so it may be over 30%. (Again, not
> including Cenozoic neornitheans.)
+++++++++++++++++++++++++

Actually I get about 15% (assuming 800 known dino species. The examples above
were sans 120 "fuzzy" maniraptorans).

It's a moot point anyway; as you already mentioned, this is probably
subjective.

______________________

> > And the group may be as large as _Tetanurae_, or even larger if
> > certain all-scaled large forms are secondarily so.
> > Again, unless scutes are derived feathers, I don't see any reason to
> > believe that a group of animals that were feathered, would do a      > >
complete reversal instead of just losing the feathers and sticking   > > with
skin.

> I tend to doubt it, too, but I wouldn't discount it.

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

Nor do I discount the possible presence of feathers in a crocodylomorph or
sauropod, but that doesn't mean that I'm going to give it any serious thought
until further evidence is found for it though.

___________________________

> > > No feathered animal ever completely lost scales/scutes, TMK. (Snow owls,
maybe?)
> >
> > Likewise; no secondarily featherless bird has ever re-evolved a scaly > >
covering (or even went so far as to become truly featherless, but    > >
that's another story).
>
> True, but it *may* be that when feathery integument had just evolved, it
> was easier to lose.

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

Perhaps; sorta in the vein of BCF regarding secondary flightlessness.

_________________________


> [Tyrannosaurs]
> > > A few small patches don't necessarily indicate scaliness for the   > > >
whole body. (I've seen some interesting speculative restorations  showing
> > > feathers only on the arms, used for display. And, of course, we all know
the "elephants aren't hairy; why should an elephant-sized coelurosaur be
fuzzy?" argument.)
> >
> > The inherent problem with the elephant argument, is that elephants never
evolved (or re-evolved) a new (or old) form of integument in place of
feathers.
>
> Well, what old form would that be? Is there one for mammals?

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

Beats me; up until about two years ago I would've said scales. Now apparently
that's not even considered true.

Do we even have any skin imprints of synapsids (pelycosaurian or older would
be preferred). From what I've read, it seems that one would be better off
drawing a skeleton than bare skin or scales.

Oh and an addendum to my above post. That should have said in place of hair,
not feathers.

________________________
>
> > If _T.rex_ really was secondarily featherless, then it re-evolved
> > scales to cover its body. To me, that seems to be stretching it. Why
evolve scales again ,when one can just remain bare skinned (it works for the
elephant sized animals)?
>
> But no feathered animal ever lost scales entirely (TMK), so the genes   >
are obviously still present.

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

That doesn't necessarily mean that re-evolution of scales would happen. Many
mammals have forsaken their tails, yet not completely lost them (barring a few
exceptions), and I've never seen tail re-evolvment in bob-tailed lineages
(e.g. apes; who seem to be fine just brachiating without a tail).

Well, it might not be the best example (probably could have come up with a
better one), but I'm sure you get my point.

_______________________
>
> > > > As for the vast majority, is this not also true for most of the
> > Wait a minute; why is _Sinosauropteryx_ + _Passer_ all of a sudden exempt
from this. We don't know the skin type of most of the animals between these
two either, yet you seem to be stating, that it is safe to assume that they
were all feathery (or protofeathery).
>
> It stands to reason, unless
> A) You don't consider _Sinosauropteryx_' integument to be homologous > with
avian feathers, or
> B) You think some of these forms may have been secondarily featherless
> (and you don't appear to).
>
> If the structures of _Sinosauropteryx_ and fully-feathered animals such as
_Caudipteryx_, _Protarchaeopteryx_, and avians are homologous, then it
> means the ancestor of Clade(_Sinosauropteryx_ + _Passer_) had feathery
> integument, and every one of its descendants had it as well, unless they
> lost it.

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

Yeah, I follow you there; what I don't understand is what you had said after
that.

______________________

> > Meanwhile we have scale impressions from
> > ceratopians, ornithopods, sauropods a carnotaurine and a tyrannosaur.
>
> And, indeed, all dinosaurs probably do have scales somewhere.

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





> > Even if the tyrannosaur impressions turn out to be wrong (which I
> > doubt) that still gives us a wide range of dinosaurs here.
>
> Even if they are not wrong, they only tell us about the tail of adults. >
small piece of the tail, even.

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

And near the pelvis (at least the ilia where an apparent impression was made)

For clarification:

http://www.cmnh.org/fun/dinosaur-archive/1996Feb/0497.html

____________________________

> > Their last common ancestor would *at least* be between the divide
> > between ornithischia and saurischia, which makes for practically all
> > dinosaurs.
> >
> > Are you saying that all these dinosaurs just evolved scaly coverings
> > convergently?
>
> No, of course not. Scutes were present in the ancestral dinosaur (and
> further back), and feathery integument *probably* was not. No dinosaur
> (AFAIK) ever lost scutes, but one clade (probably something within
> Clade(_Passer_ <-- _Carnotaurus_)  and including Clade(_Sinosauropteryx_ +
> _Passer_)) exhibits feathery integument in addition to scutes.

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

Alright then; so why did you say that it would not be valid to consider scales
to be plesiomorphic to dinosauria in my previous post (i.e. where I stated
that it would be the default condition)?

Jura


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