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RE: "Dinos of a Feather" (ABC Science News On-Line); HUMOR, SORT OF...

A few quick comments:
Not only did the "Peabody (Mass.)" error get into the Peter N. Spotts
article in question, but Paul Sereno had his affiliation changed (from U
Chicago to the Field Museum), and of course the ever-present typo
"Protoarchaeopteryx" for _Protarchaeopteryx_.

At 11:37 PM 2/26/99 -0800, George J. Leonard wrote:
>A hand goes up in the back of the room-- it's one of those non-majors 
>that sit against the back wall. "If T Rex had feathers...." he stammers 
>out, as the majors who sit in the front row turn to stare at him with 
>little smiles, "could we just take a second... what can we infer? Downy 
>fuzz? quills? or just filaments? Like an emu? And where?"

Okay, remember that the presence of feathers or feather-homologues in tyrant
dinosaurs is inferred because of the phylogeny:

_Sinosauropteryx_ + (Tyrannosaurs + ((Oviraptorosaurs + _Caudipteryx_) +
(Dromaeosaurids + birds))).

_Sino._ has filaments, _Caudipteryx_ has arm and tail feathers, as do birds.
We don't have integument preserved for oviraptorosaurs other than _Caudi._
nor for dromaeosaurids, and only a piece of skin inferred to come from (but
not attached to) the tail of a tyrannosaur.

We can infer that the most recent common ancestor of _Caudi._ and birds had
wing feathers and tail feathers.  Thus, oviraptorosaurs and dromaeosaurids
would be descendants of animals with such integument, and would be presumed
to have such unless lost secondarily (for which we have not direct evidence).

Using this phylogeny, however, we cannot say how much further out this
pattern goes.

_Sino._'s integumentary fibres are interpreted as feather-homologues (or
protofeathers or basal feathers... difficult to determine the best name for
these).  We can infer that the most recent common ancestor of _Sino._ and
(_Caudi._ + birds) had these structures.  Since tyrannosaurids seem to be
closer to birds than to _Sino._, they would be presumed to have these
structures ancestrally.

So, tyrant "plumage" would probably be fibres.  Where on the body?  Good
question: _Sino._ seems to have it over much of the body, but it is only
clear where mud meets mud in the specimen (i.e., as a halo around the body).

The tyrant "tail skin" patch shows typical dinoaurian tubercle scales.  Some
possibilities: tyrants actually lie outside the _Sino._ + maniraptoran
group; tyrants didn't have fuzzy tails; tyrants had fuzz ancestrally and
lost it; tyrants had fuzz as hatchlings and lost it during ontogeny.  We do
not at present have the data to sort this out.

>He fumbles with 
>his notes. "Not on the arms because 
>he couldn't keep them clean?

Well, he couldn't keep them clean with his teeth, sure, but maybe with his
other arms?  Also, see below about "keeping clean".

>and not on the back in case he wanted to 
>roll on his back wrestling with prey?

YIKES!!  Now I love tyrant dinos more than the most people, but I don't see
adult tyrannosaurids (at least) rolling around wrestling with prey.
Grappling with the jaws, sure; tearing and yanking with the powerful neck,
sure; but rolling around with a 4 tonne _Edmontosaurus_ or 6 tonne
_Triceratops_ or whatever is a good route for getting your rib
cage/skull/limbs crushed.

>Probably not on the head because 
>he'd sometimes have to stick it inside the carcass, on the bald eagle 
>model. And would he preen the things? How? How does that head reach 
>anywhere?? Those teeth, the chisels in the front, the recurved serrated 
>guys on the side? Preen with what? The first feathered animal that never 
>preened?  Could we just take a second away from rahona and caudi and the 
>hip dinos and ask about T Rex? Thanks," he mumbles, subsiding. :> (Off 
>list advice would be welcome if we can't spare bandwidth for this.) 

Okay, preening is a good thing, yes.  So is keeping your scales clean if you
are a scaly reptile.

Still, how do owls keep the backs of their heads preened?  How do kiwis keep
their back feathers preened?  Pedal claws, in many cases, certainly.  For a
juvenile tyrannosaurid, preening with the hindclaws wouldn't be that much
more difficult than it is in some of the bigger ground birds today or of the
recent geologic past.

Also, how much would an adult tyrant need to keep its plumage clean, even if
it retained it into adulthood?  As insulation it would be less important, as
surface area/volume ratios greatly decrease with body size.  I don't see
these structures as particularly useful for streamlining the adult _T. rex_.
A good dustbath for parasites would still be useful (it is for almost any
terrestrial amniote, scaly, hairy or feathered).

Interesting questions, but ones which are exceedingly difficult to test
without a better knowledge of the tyrant integument (in both ontogenetic and
phylogenetic terms), and more generalized coelurosaur behaviors (difficult
to determine without a good working time machine...).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661