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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 for becoming arboreal.  However, the
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:
>
>>Jason Brougham <jaseb@amnh.org> wrote:
>>
>>> 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 terrain, such as a forest floor, or soft mud?
>>
>>
>>
>>
>>
>>
>>Cheers
>>
>>Tim
>