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Re: 11th specimen of Archaeopteryx



I also would like to report on what I've found about perching in tinamous.

The Great Tinamou roosts in trees and broods its chicks there. It is a
ground bird with a  small elevated hallux. However there is a derived
clade within tinamous that has lost the hallux altogether.

I've looked into it only with internet searches, but I could not find a
single image nor mention of any animal in this hallux - less subgroup of
tinamous either being found in trees.

This suggests that the possession of a hallux correlates with tree
climbing behaviors in tinamous.
 I did find one odd image, though, where a father tinamou is spreading his
wings over five of his hatchlings on a  narrow branch, and none of his
toes seem to be clutching the branch. His tarsometatarsi rest on the
branch but his feet are dangling over the edge. He seems to be crowd
surfing his brood. Ornithological stage diving analog!?



>> Scott Selberg wrote:
>>
>>> Isn't it possible that the sickle claw could have allowed basal
>>> deinonychosaurs to perch?
>>
>> Tim Williams wrote:
>>
>> I doubt it.  There is no evidence that this digit (or its claw)
>> allowed the pes to better grip branches.
>
> Manning et al. (2006, "Dinosaur killer claws or climbing crampons?", does
> conclude that the second toe claw of Deinonychus has a curvature
> measurement consistent with climbing animals. Xu found similar results for
> Microraptor.
>
> Briefly, though, we don't need to picture small paravians grasping
> branches of small diameter in order to achieve elevated positions in
> trees. Large boughs and crotches in trees, such as are found today in
> older ginkgos and redwoods, can provide broad surfaces for roosting
> without any need of perching adaptations. Redwood canopies develop
> crotches so large that the canopies hold tons of soil and even secondary
> communities of plants that are not specialized epiphytes, like huckleberry
> bushes.
>
> But to your precise point - gripping branches, one reason there may not be
> any such evidence is that I can find little investigation of this question
> in the literature. How strongly could non avian paravians, let's say
> dromaeosaurs, flex the toes? Much has been made of the hyperextensiblity
> of toe II but, taking Deinonychus as a well - preserved but improbably
> large example, there is also a deep arc of the trochlea of Mt II ventral
> to the shaft, suggesting a great range of flexion as well. In Ostrom's
> figure 76 in his 1969 monograph on Deninonychus he diagrams the range of
> flexion of the toe, but keeps the 1st joint extended. If we move the
> flexed toe to a flexed position relative to the Mt we find that the point
> of ungual II points toward the heel of the foot. This could allow a branch
> to be pinched between the heel of the foot and the point of the ungual.
> The strong flexor processes of the ungual and second phalanx are already
> well documented, and provide evidence for a strong grasping capability
> which likely exceeded that in a  hallux.
>
> My observation would have to be tested with actual 3d fossil specimens,
> the role of soft tissues would have to be estimated,  and limits on the
> ranges of motion would have to be considered, for this to be valid as
> "evidence", but the possibility certainly has not been excluded.
>
>


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