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Re: Science feather strength debate



That is an important point. Zygodactyly is another big difference between
troodontids and roadrunners.

Yet, here is where I would caution all of us about drawing a priori
conclusions based on morphology alone. Sometimes our logic alone can be
too facile. If we knew modern day turkeys and tinamous only from fossil
skeletons we might never guess that they roost in trees. All are
anisodactyl. In turkeys Mt 1 is quite proximal, and the halluces don't
quite reach the foot pads. In tinamous the halluces can be extremely tiny,
medially positioned, and proximal (elevated), or even absent in some
genera. Yet both types of birds roost easily in trees and even brood
swarms of their young in trees once they hatch from ground nests. I
believe I learned from Gregory S. Paul that even goats climb trees
routinely. And, as Dr. Alan Turner said to me once "consider the minimum
number of adaptations that an animal needs to climb trees, which are
none."

None of this should be thought of as evidence that small troodontids or
basal paravians climbed trees or shrubs, it just makes me wary about
saying that they couldn't.

The Anchiornis type specimen appears to me to have an Mt 1 that is perhaps
no more elevated than in Tinamous. Microraptor, of course, has an Mt 1
that is in line with the other toes.

Your note also made me remember that Lockley et al. (Naturwissenschaften
2007 vol. 94 no. 8) described zygodactyl footbrints from lower Cretaceous
China that are the same size as modern Geococcyx and even show the same
stride length! The trace fossil is called Shandongornipes. They inferred
that the most likely track maker was a bird, but they mentioned that it
could have also been a non-avian theropod that had convereged with modern
Geococcyx. Maybe it did so for perching? Who knows.

-Jason

> Jason Brougham <jaseb@amnh.org> wrote:
>
>> I would like to see how the humerus of Geococcyx stacks up. Meinzer (The
>> Roadrunner, 1993, Texas Tech U. Press) reports that they usually ascend
>> to
>> their nests in trees by leaping upward to a series of branches, and not
>> by
>> flying. I've been imagining similar behavior in an animal like
>> Anchiornis
>> or other small troodontids - with long legs and probably somewhat
>> underpowered flight apparatus.
>
>
> The roadrunner (_Geococcyx_ spp.) has a zygodactyl foot that is
> adapted for perching, as is the case with all cuckoos (Cuculidae).
> Apparently the zygodactyl pes, with two toes pointing forward and two
> toes of almost the same length pointing back, does not interfere with
> the ability of roadrunners to run fast on the ground.  Roadrunners and
> other ground-cuckoos have shorter wings and longer distal hindlimbs
> than arboreal cuckoos, but they retain excellent perching abilities.
>
> Thus, I'm not sure it's a good idea to use roadrunners as analogs for
> troodontids.  Troodontids, as well as dromaeosaurids and
> _Archaeopteryx_, do not have a pes that is adapted to perching.
>
> It is possible that non-ornithothoracine paravians could climb trees
> using all four limbs, which obviated the need for a perching foot.
> But this is merely speculation.
>
>
>
> Cheers
>
> Tim
>


Jason Brougham
Senior Principal Preparator
Department of Exhibition
American Museum of Natural History
81st Street at Central Park West
212 496 3544
jaseb@amnh.org