Feathers as fossilized behaviour (was:Re: Function Talks at Ostrom Symposium)

[Ronald Orenstein <ornstn@home.com>]

>I was with Alan all the way until he reached this section of his talk.
>The cute little lamb in his slide may have been good for a laugh, but it
>ignored the fact that most of the larger prey animals of _Deinonychus_
>(i.e., juvenile tenontosaurs) would have had a stinkin' long tail,
>effectively preventing a rear attack. I also wondered: if _Deinonychus_
>was close enough to confuse its prey in this manner, wasn't it already
>close enough to just grab it?
>
>Brian (franczak@ntplx.net)

Brian has touched on a bee in my bonnet that I intended to write up later,
but what the heck, I might as well do it now (hi, Brian, sorry I missed you
at the symposium!)

My problem is not so much the "blinder" idea, but, to go back one step, the
idea that Deinonychus had feathers (or at least large Caudipteryx-type
remiges) on its arms at all.  Now bear with me - I am not arguing that
remiges are not basal to dromies.  I am arguing for secondary loss.

One of the remarkable things about Caudipteryx, Archaeopteryx and the
various individual fossil flight feathers that have been turned up is that
they are in good condition - the barbs neatly arranged, the barbules
interlocked.  What no one seems to have commented on (except Alan Brush,
who briefly mentioned it at the symposium during discussion) is that this
represents a very clear case of fossilized behaviour.

The point is, feathers don't stay neat by themselves (though they may be
regularly replaced in moult).  In every modern bird, they have to be
maintained, and I see no reason why this should not have been true in the
Mesozoic.  That means that the animals possessing them had to have used
some sort of maintenance behaviour, akin to modern preening.  If a bird
can't preen, its feather condition deteriorates, and modern birds spend a
lot of time doing it.  Some birds even have built-in "combs" in the form of
pectinate claws to assist in the process.  In other words, I would bet a
tidy sum that Caudipteryx preened its feathers - perhaps using its few
remaining teeth.  They would simply not have been so neatly arranged otherwise.

The corollary to this is that good feather condition was as important to
dinosaurs as to modern birds.  Studies of living birds show that good
feather condition increases mating success (in Barn Swallows, for example,
to name one well-studied species).  It probably also plays a role in
determining the winner in male-male competition for display or territory
sites - and certainly serves other functions as well.

So keeping feathers in good shape is worth the investment of time and
energy.  But what if the task is simply impossible?  In a number of cases
the result is secondary feather loss.  The best-known example of this is
the convergent loss of head and neck feathers in the new world and old
world vultures (these two groups, for those who don't know, are quite
unrelated, the new world group being allied to storks and the old world
group to eagles).  Vultures stick their heads into messy carcasses, and
keeping head feathers clean and neat under these conditions is pretty much
impossible.  There are other birds that have lost head feathers in
connection with their diet of large, juicy fruits (eg the Vulturine Parrot
of South America).

Now let's get back to Caudipteryx.  This species has short arms and quite
gracile fingers.  It was almost certainly not a predator on large animals,
and is unlikely to have used its arms to capture such beasts.  Keeping its
remiges in shape was, obviously, a doable job.

But what about Deinonychus?  Imagine such a creature grasping a large
animal - an animal that it struggling and, probably, bleeding - perhaps
profusely.  How long would remiges (which, remember, should arise right
down to or near the tip of the second finger) stay in good condition after
such a battering?  Even if they could be cleaned up, they might well be
broken - and remember that there is no way to repair a broken feather,
beyond waiting for the next moult.  The cost of cleaning them - and even
the metabolic cost of replacing them, if they could only last a short while
- might well not have been worth it.

Therefore I predict (drum roll, please) that the more maniraptorian
dinosaurs used their arms for prey capture, the greater the likelihood that
remiges on the arms would be reduced (at least distally) or lost.  I admit
the possibility that they might have been retained along with a breeding
cycle that swung into high gear immediately after moult, when feathers were
fresh, but I consider loss or reduction to be the likelier scenario.  I
would therefore not expect a "winged" Deinonychus (and perhaps I should not
be surprised that no wing feathers were preserved with Protarchaeopteryx
either, as its arms are longer and more robust than in Caudipteryx, but I'm
hesitant about that idea).  Of course Archaeopteryx had long arms too, but
it was flying with them - and besides, I do not think it was using them to
wrestle large prey items to the ground.

Whether you buy this or not - and it's rather speculative - the idea that
dinosaurs had feather maintenance behaviours  seems to me to be hard to
dispute - the proof is in the fossils of well-maintained feathers.  This
leads me to the idea that we should perhaps look closely at these animals
for adaptations to that end.  I have suggested the teeth of Caudipteryx -
and if I am right, then perhaps (and I do mean perhaps!) the more advanced
oviraptors, which had lost these teeth, had lost or reduced their remiges
and rectrices as well. 
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com