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RE: Aw: RE: Arboreal Theropods: The prize at the bottom of the cracker jack box



Some on this thread have mentioned that, if an animal is using trees in its 
biology, it should show specializations.

Recent work has found an ingenious way to test the time between a behavioral 
shift and a clear morphological specialization.

In fossil proboscideans that switched from a tree leaf diet to a grass diet (as 
marked by carbon isotope ratios) the answer is 3 million years.

I bet that is a long interval but, then again, tooth crown height should 
increase faster (by shifting to the taller end of the pre-existing distribution 
of tooth crown heights in the population) than complete descent and reversal of 
a toe.

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12275.html



________________________________________
From: owner-DINOSAUR@usc.edu [owner-DINOSAUR@usc.edu] on behalf of K Kripchak 
[saurierlagen1978@gmail.com]
Sent: Tuesday, July 23, 2013 3:41 PM
To: DML
Subject: Re: Aw: RE: Arboreal Theropods: The prize at the bottom of the cracker 
jack box

Jason Brougham wrote:
>Animals that routinely entered trees without specializations would be ideal 
>candidates
>to adapt to those habitats.
>
>The reasons we could suspect this in basal paravians, as opposed to other
>dinosaurs that show no climbing adaptations (such as, say, hadrosaurs),
>are 1) they are small 2) they are comparatively agile, with long, sharply
>clawed, hands and feet 3) they actually ARE the direct ancestors of the
>animals that specialized toward arboreality: the Avialae.
>
>For any given taxon the hypothesis can be tested by biomechanical analyses.

EXACTLY what I was saying from the very start of this thread... Niche,
pressure, exaptation, adaptation... The selection of arboreal traits
occurred in the un-specialized ancestors of arboreal specialists
because those un-specialized ancestors were being arboreal.
Otherwise, arguments normally boil down to a version of;
"Paravians/Avialae were unlikely to have become arboreal specialists
without cursorial basal Paravians/Avialae possessing the capabilities,
traits, and behaviors
capabilities, traits, and behaviors for becoming arboreal weren't
selected for until after cursorial basal Paravians/Avialae became
arboreal specialists."

V/r
Kris



On Tue, Jul 23, 2013 at 5:23 PM, Jason Brougham <jaseb@amnh.org> wrote:
> Alright. To recap as succinctly as I can.
>
> There seems to be consensus here that basal paravians could have engaged
> in 'occasional' climbing behaviors.
>
> But, to go further...
>
> There are living animals that lack climbing adaptations, or that are even
> members of clades that show 'trends' away from climbing, for which trees
> are still indispensable parts of their biology. These include murrelets
> and petrels, which have secondarily lost halluces. They include chicks and
> other birds with limited or absent flight ability (Inaccessible Rail,
> Kagu, hatchling tinamous, hatchling chukar).
>
> Basal paravians, living in habitats such as the Tiaojishan Formation which
> had diverse gymnosperm trees, arborescent bennettites, and tree ferns,
> could have utilized these habitats in some similar manner. Say, scrambling
> a meter or two up them to launch on imperfect wings. Or roosting on fallen
> tree limbs. Such behaviors do not require specialized adaptations but,
> rather, they could be the precursor of those adaptations. Animals that
> routinely entered trees without specializations would be ideal candidates
> to adapt to those habitats.
>
> The reasons we could suspect this in basal paravians, as opposed to other
> dinosaurs that show no climbing adaptations (such as, say, hadrosaurs),
> are 1) they are small 2) they are comparatively agile, with long, sharply
> clawed, hands and feet 3) they actually ARE the direct ancestors of the
> animals that specialized toward arboreality: the Avialae.
>
> For any given taxon the hypothesis can be tested by biomechanical analyses.
>
> Jason Brougham
> Senior Principal Preparator
> American Museum of Natural History
> jaseb@amnh.org
> (212) 496 3544
>
>
>
>
>
> On 7/23/13 2:31 AM, "Tim Williams" <tijawi@gmail.com> wrote:
>
>>Jas
>>
>>> Well, hey, you can always say my counterexamples don't count. Strictly
>>> speaking, they don't, because we are using derived animals to see what
>>>may
>>> have been possible for primitive ones.
>>
>>
>>Excellent point, IMHO.  There are a great many extant birds that show
>>rudimentary aerial behaviors, such as WAIR or CFD (by fully volant
>>species, including juveniles) or fluttering and short glides as
>>exhibited by some secondarily flightless birds (the kagu has been
>>mentioned, but there are others).
>>
>>
>>It is possible that one of these extant non-flight aerial behaviors
>>replicates the incipient flight behavior of the theropod ancestors of
>>birds.  But they might not.  We may never know which behavior(s)
>>engendered flight in theropods.  However, I don't think we should
>>assume that it was "trees-down", despite the intuitive attraction of
>>an arboreal origin of flight.
>>
>>
>>> My goal is to stop people in this forum from saying it is impossible
>>>that
>>> basal paravians utilized trees to some limited extent. I believe I have
>>> demonstrated that it is possible, and that categorically excluding it
>>>with
>>> the current evidence is not correct.
>>
>>
>>I don't recall anyone saying that it was impossible for basal
>>paravians to use trees.  Speaking solely for myself, I would say that
>>the evidence for arboreality (i.e., spending most or all of their time
>>in trees) in microraptorines and archaeopterygids is less than
>>compelling.  To me, there is nothing in the osteology to back up
>>arboreal ecologies in these taxa.
>>
>>
>>However, occasional/opportunistic tree-climbing seems entirely
>>plausible (such as _Microraptor_ grabbing a little birdie off a tree
>>branch).  But because this is still part of a fundamentally
>>terrestrial ecology, it perhaps would not seep through into the
>>anatomy.  So it's difficult to test for.
>>
>>
>>I'm certainly intrigued by GSP's data on _Microraptor_'s claw
>>curvature.  Might highly arced pedal claws be useful for gaining
>>purchase on soft terr
>>
>>
>>
>>
>>
>>
>>Cheers
>>
>>Tim
>