[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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



"T. Mike Keesey" <tmk@dinosauricon.com> wrote:
> On 24 Jun 2001 archosaur@usa.net wrote:
> 
> > > As I mentioned in another post, that "small group" is at LEAST
> > > Clade(_Sinosauropteryx_ + _Passer_), which is hardly small.
> >
> > Compared to the rest of Dinosauria, I'd call it pretty darn small.
> 
> 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).

_____________________


> > > 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.
> 
> 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).

__________________________
> 
> Nonetheless, I tend to agree -- the first animal with "protofeathers"
> probably lies somewhere between the ancestor of Clade(_Passer_ <--
> _Carnotaurus_) and the ancestor of Clade(_Sinosauropteryx_ + _Passer_),
> although that is by no means certain.

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

Fair enough

__________________


> > > Impressions showing scales all over the body are
> > > known only from certain large cerapods (ceratopsids and            > > >
hadrosaurids), a few sauropods (_Tehuelchesaurus_, ?_Camarasaurus_, > > >
embryonic titanosaurs), and two carnotaurine abelisaurs            > >
>(_Aucasaurus_ and _Carnotaurus_). Someone please let me know if I   > > >
missed anything.) For the vaaast majority of fossil dinosaurs, we  > > > have
no data about the skin.
> >
> > Tyrannosaurs too, until shown otherwise.
> 
> 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. 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)?

___________________________

 
> > As for the vast majority, is this not also true for most of the
> > animals within the clade _Sinosauropteryx_ + _Passer_. Now if we want
> > to play cladistics with it and assume that those scaled animals are
> > indicative of all the rest of the dinosaurs within those clades,
> > wouldn't that then mean that scales are basal to Dinosauria and,
> > hence, the default dinosaur skin type (at least up till maniraptors)?
> 
> No, up until Clade(_Sinosaurosauropteryx_ + _Passer_). And actually,   >
since there's no information for ANYTHING in between the base of       >
_Neotheropoda_ and the base of Clade(_Sinosauropteryx_ + _Passer_)     >
(except perhaps _Santanaraptor_), there really isn't a safe default    >
assumption yet for forms such as "megalosaurs", spinosaurs, carnosaurs, >
etc.

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

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). Meanwhile we have scale impressions from
ceratopians, ornithopods, sauropods a carnotaurine and a tyrannosaur. Even if
the tyrannosaur impressions turn out to be wrong (which I doubt) that still
gives us a wide range of dinosaurs here. 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?  
 
Jura

The Reptipage: A site devoted to the study of and education on, the reptilia:

http://reptilis.net