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RE: Yet more on pterosaur quad arm posture



Very good, thank you.

We agree that animals that are not scansorial do roost in trees.


________________________________________
From: owner-DINOSAUR@usc.edu [owner-DINOSAUR@usc.edu] on behalf of Tim Williams 
[tijawi@gmail.com]
Sent: Wednesday, July 10, 2013 11:24 PM
To: dinosaur@usc.edu
Subject: Re: Yet more on pterosaur quad arm posture

Jason Brougham <jaseb@amnh.org> wrote:

> Is the Great Tinamou (Tinamus major) scansorial?


Not that I'm aware of.  Then again, if a tinamou wants to get from the
ground on to a tree branch, it can fly up there.  They don't need to
climb a trunk to access the tree crown.  (Tinamous can also perform
WAIR, but I'm not aware if they use this behavior to scale tree
trunks.)


> It perches when roosting with chicks, so that is important in its biology, 
> yet it forages and nests exclusively on
> the ground. I think its foot, by most standards, would be placed on the 
> cursorial end of the spectrum of living
> birds,


Yes, tinamous are predominantly terrestrial birds.  The hind toe
(hallux) is either small and raised high on the foot or missing
altogether, depending on the genus.


Apparently _Tinamus_ species are capable of roosting in trees with the
aid of their specially modified tarsi.  These have rough scales that
enable the tinamou to cling to branches; so these birds rest on their
tarsi, rather than use their toes.  (Wikipedia also mentions this -
"Tinamous prefer thick branches on which to roost as they do not
clutch the branch with their toes, but rest on it with folded legs" -
and provides a link.)


>  though not AS cursorial as, say, the Ostrich.


Agreed.  The ostrich is an extreme example of cursorial adaptation.
For example, it has only two toes.


> T. major, I would think, would clearly go into the terrestrial, or 'Ground 
> Based' category of Glen and Bennett,
> were they to include tinamiforms.


The tinamou would probably go in to the 'Ground Based' or 'Ground'
categories of Glen and Bennett.  These catagories are where the
Mesozoic paravians Glen and Bennett examine
_Microraptor_, _Archaeopteryx_, _Jeholornis_, confuciusornithids),
with the possible exception of _Sapeornis_.  GSP has (unpublished)
pedal claw curvature data for _Microraptor_ that would presumably put
it in a more arboreal category... but we'll have to wait and see.


The hindtoe characters of tinamous (see above) are consistent with
being predominantly terrestrial birds.  Thus, if any basal paravian
was predominantly arboreal (including microraptorines or
archaeopterygids), we might expect to see a larger and/or much lower
hindtoe (as we see in _Sapeornis_).


The overall body proportions of tinamous are more similar to
gallinaceous birds than to ratites, or to any basal paravian (or
avialan).  I apologize if this statement comes across as provocative
(I'm just stating my interpretation, and don't mean to offend anyone
with a different view), but tinamous make a poor analog for critters
like _Microraptor_ or _Archaeopteryx_, at least in terms of putative
perching or roosting ability.






Cheers

Tim