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Re: Ah ha! That's where therizinosaurs came from



Thomas R. Holtz, Jr. <tholtz@umd.edu> wrote:

> Not uncommon at all in big galliforms. Peacocks actually go up into the trees 
> in order to roost at night, too.



Peafowl (_Pavo_) can (and do) roost in trees.  But it's my
understanding that peafowl forage mostly on the ground.  The hallux is
relatively higher than in related phasianids that have a more arboreal
lifestyle.  The related Congo peafowl (_Afropavo_) not only roosts in
trees, but forages within the canopy on fruits and arboreal prey
(insects and small vertebrates).  _Afropavo_ has a more elongated
hallux than _Pavo_.  Differences in the degree of elevation of the
hallux are also evident in the related Argus pheasants (the more
terrestrial _Argusianus_ has a higher hallux than the more arboreal
_Rheinardia_).



The degree of elevation of the hallux varies within the Galliformes in
general, and within the Phasianidae in particular, depending on the
bird's habits.  A short/elevated hallux does not prevent a bird from
perching.  But it does tend to limit them to thicker branches.  Within
the Galliformes, the length and proportions of the hallux gives some
indication of how much time the bird spends on the ground, and how
predisposed it is to run in response to danger (rather than take to
the air).  The key feature is that the hallux is reversed
(retroverted), allowing it to oppose the front three toes.  This is
why comparisons between fossil paravians like _Archaeopteryx_ and
_Microraptor_ (which retained a medially-directed hallux) and
gallinaceous birds like turkeys or peafowl are so inapt, IMHO







Cheers

Tim