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Re: feather tracts (and spiny tails?)



Jaime,
     I don't need to make a mechanical model to know that a theropod could
use its muscles to shift its weight enough to compensate (were not talking
about tinker-toys here).  And I am certainly not talking about Velociraptor
or Oviraptor, which are Cretaceous (way too late), too large, and dependent
on running to make a living.  They certainly are not the kind of theropod I
was talking about----Triassic, small, not obligately bipedal (but not
necessarily obligately quadripedal either).
     And being small, they probably could climb (making toppling less of a
problem) and may have been herbivores (leaves can't run away from a crippled
animal) or insectivores.  Most your arguments seem to be based on a
Cretaceous world, not the Triassic world of primitive dinosaurs.
     We know almost nothing about small Triassic dinosaurs, their
diversity, way of life, ecological interactions, or anything else.
Extrapolating Cretaceous patterns back into the Triassic, separated by lots
of evolution (and two sizeable extinction events) just closes off so many
possibilities (or even probabilities), and if one does not speculate about
them, one is more likely to fail to seek evidence for or against such
possibilities (or worse yet, overlook or misinterpret evidence that might
already be available in some museum drawer).
     I think Darwin was quite right in observing that without speculation
there is no good and original science (or something to that effect).
Brainstorming and speculation is a very important scientific tool, as long
as one keeps in mind that it is speculation until hard evidence is found to
corroborate it.
     If there was a quill stage, most traces of it may have been gone by
Cretaceous times.  And scales, scutes, quills, feathers, and bare skin may
not be the only possibilities.  There could well be all kinds of
intermediate structures that we have yet to find in the dinosaur fauna of
the Triassic.  And whether or not Longisquama had true feather homologs, it
is important evidence, no matter where they end up falling cladistically.
If you want to make unexpected discoveries, you have to be on the look out
for the unexpected when that lucky piece of evidence comes your way.
                       ------Ken
*********************************************************

From: "Jaime A. Headden" <qilongia@yahoo.com>
To: dinosaur@usc.edu
CC: kinman@hotmail.com
Subject: Re: feather tracts (and spiny tails?)
Date: Sun, 15 Jul 2001 19:16:17 -0700 (PDT)

Ken Kinman (kinman@hotmail.com) wrote:

<As I said before, better to be a theropod with a balancing
problem than a dead theropod.>

  Heh ... a theropod with a balancing problem is a dead
theropod.
It;s not like a quadruped who can walk on three legs if need be.
If a theropod was tripping over, or couldn't run properly, or
escape fast enough, then it's not likely to survive really well.
Thus, pressure NOT to have such a tail adaptation, irrelevant of
how glass snakes and *Uromastix* can do this, as they either hug
the ground, or are quadrupedal, and do not require the tail to
keep them from toppling over.

<The small forms which developed early protofeathers wouldn't
necessarily have been obligate bipeds in the first place, and
even if they were, the animal could often compensate enough to
get by if the section of tail lost wasn't too massive.>

  Based on what evidence? This is speculationb rampant to
suggest that there were feathered quadrupedal dinosaurs before
there were bipedal animals. This has been discussed _to death_,
and whole herds of dead horses have been whipped.

<Since the vast majority of the mass is in the proximal part of
the tail, the loss of 20 or 30% of the distal tail length would
not be a huge loss in mass (5-10% or less, maybe a lot less if
the animal tail was long and skinny distally, but still "meaty"
proximally).>

  Okay, make a mechanical model to support how loosing 5-10% of
the tail will make an animal like *Velociraptor* or *Oviraptor*
_not_ topple over. The shortening of the tail is always
correlated with a shift in the form of the hip and mass between
the knees, so any abrupt shortening of the tail _will_ be
demonstrable.

<And finally, why would they have to necessarily be herbivores,
as opposed to insectivores or even meat-eaters.>

  Insectivores (possibly, troodontids) tend to have effective
defense strategies in the form of large claws, sickle-claws on
the feet, great capability for speed, etc.; *Microraptor* may be
another insectivore with arboreal capabilities, thus staying
away from the likely predators (only true birds now may be
effective competition). We're not talking mammals here. Other
carnivores are evenly defensive, or smaller and swifter, and
have various other means of evasion. Only the larger, slower
animals would need a defense strategy for one on one encounters
with an animal that could kill it. Herbivores either develop
armor, great size, speed, small size, social groups, or unique
defences to retard predator effectiveness. Only hadrosaurs seem
to be utterly without anatomical defenses, but have the social
group which may have been year-round.

<There is no rule that a bigger meat-eater can't pursue smaller
meat-eaters.>

  No, there's not, and I was replying to this assumption. The
statement here is that the only known "fuzzy" theropods are all
possible small carnivores or larger herbivores, omnivores,
insectivores. The majority have no indication that any form of
integument was quilly (see *Sinornithosaurus,* *Microraptor,*
*Beipiaosaurus*) or that there were feathers on the tail
(*Caudipteryx,* *Protarchaopteryx,* birds) that suggest if
quills were anywhere along the line, it was ill-supported
sideline. We need more data to support the theory.

=====
Jaime A. Headden

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

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