Re: feather tracts (and spiny tails?)

["Jaime A. Headden" <qilongia@yahoo.com>]

Ken Kinman (kinman@hotmail.com) wrote:

<And if such filaments became barbed and painful to the mouth of
predators, their color would then serve to frighten off any
predator that had a previous painful experience (and then
spreading up the spine of the animal would become an effective
strategy). But this kind of strategy would only work if it began
on an relatively expendable tail, not a critical area like the
head, neck or spine.

I will think about quills starting on head and necks and then
spreading down the back, but right now I prefer a "tail
deception" strategy which was exapted and then spread up the
back. Quills and spines could have easily been exapted from such
filaments, and even if spines were the original function, they
could have begun on the tail (as in spiny-tailed lizards like
Uromastix).>

  All bipedal dinosaurs have a need for a long, balancing organ
in the tail. Any loss of this organ, in anyway, even by a few
inches, may interrupt the function and effectiveness of the
organ. To have spine prongs on the tail to prevent predators
from biting it would only work if the animal was quadrupedal and
did not require as much of a balancing function for the caudal
organ. They could afford possibly loose a few inches. This is
true even if the animal had detachable quills the predator would
obviously go for.

<In any case, I think predatory evasion (of some sort) preceded
exaptation for thermoregulation (which in turn apparently
preceded the exaptation for aerodynamics).>

  But this scenario only works if the bipeds were herbivores,
and possibly quadrupedal. One could possibly see this in
"hypsilophodontians" and other basal ornithischians or
ornithopods or marginocephalians. We see derived caudal scutes
in thyreophore taxa like *Scelidosaurus* and *Scutellosaurus*,
but these are bony in nature, and scute-shaped, not
spine-shaped.

  That theropods (those known to have developed feathery
structures in the integument) would have any sort of tail
structures first adapted into "quills" suggests that this
important organ of locomotion would have been constantly bitten
at to drive such a structure in an evolutionary paradigm. As
theropods are prdators with the possible exception of a very
few, and these being advanced, very bird-like animals
(ornithomimosaurs, oviraptorosaurs, segnosaurs, etc.), it is
unlikely most of them would ever have been under the pressure to
develop a defence they did not already have: ornithomimosaurs
have a body adapted to speed and foraging, so were probably
based in the brush, as environments fron the Judith River and
Edmonton suggest, and the Nemegt; similarly, oviraptorosaurs had
among them some impressive claw equipage and a powerful bite,
and very strong feet: I can imagine these animals being kickers
and fighters in the style Paul has popularized with
dromaeosaurs; and finally, segnosaurs had even more powerful
arms, claws, and legs, reached great size, averaging 20+ feet in
length, and the biggest, ~40ft *Therizinosaurus* shared its
habitat with *Tarbosaurus* but was impressively larger in mass
and likely could have defended itself easily.

  Similarly, defense is not reasonable in the eye of the
evolution of the caudal, hindlimb, and pevic evolution among
coelurosaurs, in which the tail is increasingly separated from
the hindlimb as its own functioning locomotor organ, as in
birds. In advanced theropods outside of birds, the tail is
almost fully separated from the hindlimb and the end bears
feathers. There was an aerodynamic, locomotory function implicit
from early on (see papers by Gatesy, by Gatesy and Middleton,
etc.).

  On the other hand:

  *Sinosauropteryx* appears to have had an alternating pattern
of long and short rachi on the tail, looking like a horse-tail
frond from a distance, and it is possible this tail was
"quilled." The structure of the tail in both types of porcupines
is similar, and has a sharp quill and a guard hair arising from
the same folicle, not with quills interspersed. Only on the tail
are these quills detachable, but they are a primary defense, and
as animals large and juicy of meat (I'm told) they are often
attacked by the typical predator method of behind and to the
side -- hence quills orient caudally. Only in *Sinosauropteryx*
is the appearance approximated, but as the form of the tail
structures in the fossil theropod are currently unpublished
(Currie, in prep) except for an abstract (Currie, 1997 at SVP,
_JVP_ 17(3)) it is unwise to speculate further. But I do offer
the possibility their function may have been similar.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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