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



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.

> > 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?)

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.

> > 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.)

> 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.

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