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Re: Yet more on pterosaur quad arm posture



Gregory S. Paul <GSP1954@aol.com> wrote:

> In every single ground dwelling theropod we have the keration sheath for,
> the toe claws II-IV are always flat. Same for all large land predators,
> except those with retractile claws. The possiblity that large dromaeosaurs had
> strongly arced toe claws is nearly zero (If they did it means that were
> climbers, like big cats).


Circular reasoning.


> This argument is an extreme stretch that is part of a
> desperate attempt to for some reason to keep the dinosaurs that are well
> adapted for arboreality on the ground.


"Well adapted for arboreality"!  Is that a joke?  There is *nothing*
in the skeletons of _Anchiornis_, _Microraptor_, _Archaeopteryx_,
_Jeholornis_ etc to suggest that they were specialized for
arboreality.  What about the mobility at the joints (or lack of it):
the highly proscribed joint mobility in theropods is a far cry from
the wide range of 3D mobility seen in arboreal quadrupeds.


There isn't even a reversed or incumbent hallux in these "arboreal"
theropods!  Bit odd for an "arboreal" dinosaur, no?  If the foot was
no longer used in terrestrial locomotion, why was the hallux so short
and so thoroughly un-reversed?


The best you can come up with for "arboreal" characters is some
tweaking of the phalangeal proportions by these theropods, and some
dodgy claw curvature data that doesn't differentiate climbers from
predators.


> It is cultish waving away of inconvenient
> evidence rather than science -- similar to the few who still deny that birds
> are dinosaurs because no dinosaur was arboreal.


Not the same thing.  Again, you're entangling two different arguments,
simply to provide a rhetorical baseball bat to hit me over the head
with.  I endorse the hypothesis that birds are dinosaurs.  Like, duh.
But that's very different to the hypothesis that certain small
theropods were arboreal.


> Because the ground is gritty and broad it will do much more foot feather
> damage than less abrasive foliage that can be more easily avoided. Breeders of
> feather footed pigeons and chickens don't let them wander about on dirt,


So if breeders didn't stop these ornamental birds from wandering about
on the ground, they would go ahead and do it...?


It's worth noting that we are not absolutely certain what the wings of
small non-avialan theropods were actually used for.  So we cannot
assume that there was an adaptive penalty incurred by damaging the
long feathers - such as inflicted by struggling prey; by snagging
feathers on branches; by courtship/territorial battles; or by just
walking around on terra firma.


Many modern birds use their wings in combat, sustaining damage to the
feathers in the process; they live to fight another day.  So I'm not
convinced by the claim that theropods with long pedal feathers were so
fastidious that they avoided the ground altogether.

http://scienceblogs.com/tetrapodzoology/2010/06/30/clubs-spurs-spikes-and-claws/


> they are allowed to roost -- narrow rods or branches keep most or all the foot
> feathers clear.


Thankfully the aforementioned pigeons and chickens are blessed with a
reversed and incumbent hallux, allowing them to perch on rods and
branches.


> Toe claws of ground animals are often worn down by the
> grit, those of climbers keep sharp tips.


So do all theropods with extensive hindwings show _Microraptor_-like
claw curvatures...?


> Tim's arguments are the sort seen out of Feduccia.


Wow, I've never been tarred with THAT brush before.


> That's not a compliment.


Yes, I got that.  Thanks for the clarification.


> Am disputing his posts just to make sure nonprofessional readers do not
> swallow them without realizing they are controversial at best.


This reminds of something to do with pots and kettles.  The notion
that _Microraptor_ was a specialized tree-living (arboreal) theropod
is hardly universally accepted.  Restoring _Microraptor_ and its kin
as primate-like arborealists (as was done in 'Dinosaurs of the Air')
is extremely controversial.  They weren't dinosaurian spider monkeys,
or colugos.







Cheers

Tim