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RE: Yet more on pterosaur quad arm posture



There is a danger here that we may become convinced that basal paravians did 
not climb into trees. There is also a danger that we may become convinced that 
basal paravians were arboreal.

The danger is the same, it is overstating the evidence for and disregarding the 
evidence against our favored hypotheses. 

We all agree there was a transition at some point in the theropod lineage that 
led to perching foot morphologies in birds, whether that happened within the 
Avialae or earlier. We probably all agree that animals did not evolve perching 
feet AND THEN climb up into trees. They had to be adapting to living in trees 
when arboreal features were selected for.

I would say that Dr. Williams is right that (despite many claims) no one has 
firmly proven arboreality in Paravians below Avialae, but he uses a strict 
definition of arboreality (as foraging primarily in trees) and is only 
comfortable assigning that behavior to animals with reversed halluces. I'd say 
his reasoning there is unassailable, and conservative in the best sense of the 
word. However I think he sometimes confuses those with whom he corresponds, who 
may use a far more inclusive definition of the word 'arboreal'.

I am personally more interested in incipient tree climbing behaviors. That is 
to say, tree - climbing behaviors that occur without clear, skeletal, arboreal 
(sensu stricto) adaptations. There could have been a very long evolutionary 
transition that involved tree - exploiting behaviors among the many small - 
bodied, winged, basal paravians. It is also eminently possibler that tree - 
utilization could have been quite sudden within basal avialans, in which case 
it may have required flight to proceed.

It is true to say that several empirical studies of claw curvature and foot 
proportions are consistent with the possibility that these small, basal, 
paravians spent some time in trees and foraged primarily on the ground. Their 
measurements tend to overlap those of ground birds that roost or spend some 
small percentage of time in trees, though the co
 Glen and Bennett. (2007) Foraging Modes of Mesozoic Birds and Non-Avian 
Theropods. Birn-Jeffrey et al. (2012) Pedal Claw Curvature in Birds, lizards 
and Mesozoic Dinosaurs. 

The frustrating thing for all of us is that the inconclusive results make both 
scenarios equally likely. These little winged paravians spent their lives 
running through thickets of bennettites and cycads, maybe they also scampered 
up into trees, maybe they never did.

I, for one, would like to acknowledge the fact that the evidence is open, and 
refer to the research of those who have done the hard work of publishing papers 
on this subject. We already know what one another's inclinations are.
________________________________________
From: owner-DINOSAUR@usc.edu [owner-DINOSAUR@usc.edu] on behalf of Tim Williams 
[tijawi@gmail.com]
Sent: Wednesday, July 03, 2013 11:54 PM
To: dinosaur@usc.edu
Subject: 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 t
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 cla
> 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