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



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