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RE: Sinocalliopteryx (Theropoda: Compsognathidae) ate confuciusornithids and dromaeosaurids



Thank you for conceding that, if basal paravians could elevate the humerus just 
a bit above the dorsum, they could have engaged in flapping flight. 

However, as I mentioned before, pinning down the exact position, geometry, and 
range of motion in the shoulders of extinct animals known only from fossils - 
to a certainty good enough to settle this matter - may be impossible.

I agree with your observations about the advanced features of the flight 
apparatus in modern birds, but I noticed you did not mention my reference on 
bats. Bats may be useful analogs for early stages of flight evolution, as 
animals that achieved powered flight with fewer radical modifications of the 
basic tetrapod pectoral anatomy. 

I am afraid I cannot agree with your certainty in this statement:

"But it's safe to say that an inability to raise
the humerus above the dorsum precludes powered flight, and therefore
indicates flightlessness."

as nature has a way of providing counter examples to almost all a priori rules 
we may try to impose on it.

Rotation in the humerus, for example, could produce elevation of the wingtip 
that could be sufficient for weak flapping. 

But it's good to see we have developed a pretty good consensus here, and good 
reasoning is prevailing.

-Jason
________________________________________
From: owner-DINOSAUR@usc.edu [owner-DINOSAUR@usc.edu] on behalf of Tim Williams 
[tijawi@gmail.com]
Sent: Tuesday, September 04, 2012 8:30 PM
To: dinosaur@usc.edu
Subject: Re: Sinocalliopteryx (Theropoda: Compsognathidae) ate 
confuciusornithids and dromaeosaurids

GS Paul <GSP1954@aol.com> wrote:

> I went on and on about this in a book I published back in 1988, and another
> in 2002, and a reply to a notoriously defective Science paper in 2010.


I have in my possession both the 1988 and 2002 books, and have read
both of them.  I just happen to disagree with both books on this
issue.  I'm not converted.  ;-)


> To glide merely requires the ability to spread out an airfoil.


No, not really.  Gliding is "passive" only in the sense that there is
no thrust generation.  Modern gliding mammals actively modulate
aerodynamic forces during the glide.  They just don't stick their arms
and legs out and hope for the best.  Gliding is a lot harder than it
looks.


> Archeopteryx and
> sinornithosaurs and all basal birds with large wings had way too many
> additional flight adaptations to merely glide, they were powered fliers of
> some sort or another using a basal system for flapping their arm wings. Quite
> possibly not very well, but we might be surprised what they could do.


You may well be right that _Archaeopteryx_ and microraptorines could
flap, and were therefore capable of some sort of powered flight.
However, the "additional flight adaptations" that you allude to may
not originally have been used for powered flight.  Instead, they could
have been subsequently drawn into the flight apparatus after being
used for non-flight functions.  We know that features such as
postcranial pneumaticity and the furcula did not originally evolve for
powered flight, and the same may be true for small body size, vaned
feathers, and the pygostyle.  These are exaptations.  The same may be
true for these so-called "additional flight adaptations" featured in
DA.


Jason Brougham <jaseb@amnh.org> wrote:


> I agree that basal paravians probably could not elevate their humeri to the 
> vertical.
>
> But I hope that all readers will recall that experimental evidence shows that 
> bats and surgically altered starlings can take off and fly well even when 
> elevating their
> humeri only to a maximum of 50 degrees above horizontal (Sokoloff et al. 
> 2001, and Bullen and McKenzie 2002).


Starlings have highly advanced flight abilities.  So I don't think
it's fair to compare the surgically altered flight apparatus of a
modern passerine with the incipient flight apparatus of an
archaeopterygid.


In the same vein, many modern flighted birds lack a furcula (e.g.,
some parrots, toucans, and owls).  They still fly extremely well.  So
the furcula is not essential for flapping flight in all modern birds.
But I would bet that a furcula was essential for flight in the first
flying birds.  I'm very wary of using the flight abilities of modern
birds (including surgically compromised ones) as analogs for the
behavior of basal avialans like _Archaeopteryx_.


> Thus the lack of a glenoid with the range of motion of
> modern birds should not be assumed by any reader to imply proof of 
> flightlessness.


Yes, even low-amplitude flapping is sufficient to generate thrust
during fast flight.  But it's safe to say that an inability to raise
the humerus above the dorsum precludes powered flight, and therefore
indicates flightlessness.


What we're debating here boils down to a relatively small number of
degrees.  If the humerus of _Archaeopteryx_ and other
non-ornithothoracean avialans could be raised even slightly above the
dorsum, allowing execution of an upstroke, then we have the
possibility of thrust generation and powered flight.







Cheers

Tim