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




On Tue, Jul 23, 2013 5:17 PM EDT Allan Edels wrote:

>Just a quick question inspired by Don's post (esp. "the hallux leaves no 
>impression when turkeys walk on firm sand")  -  
>
>Don't we have some mud/sand footprint impressions of dromeosaurids, which 
>shows the claws (including the raised one) being pulled out of the mud/wet 
>sand?
>
>Allan Edels

I don't doubt it -- and turkeys leave definite impressions of the posterior toe 
when on soft ground -- but am not sure I take your point.

Could you expand?

>
>> Date: Tue, 23 Jul 2013 14:12:55 -0700
>> From: d_ohmes@yahoo.com
>> To: dinosaur@usc.edu
>> Subject: Re: Aw: RE: Arboreal Theropods: The prize at the bottom of the 
>> cracker jack box
>> 
>> 
>> 
>> On Tue, Jul 23, 2013 11:23 AM EDT Jason Brougham 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).
>> 
>> And M gallopavo. I note that the hallux leaves no impression when turkeys 
>> walk on firm sand, and the claw tip does not extend to the rearward edge of 
>> the weight-bearing pad. Indeed, if memory serves, it has the gestalt of a 
>> dewclaw...
>> 
>> That said, it may indeed have function when hens are crouching on branches 
>> in brooding position.
>> 
>>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 habi
>>
>>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.
>> 
>> True. And I add that the iconic perching foot is most excellent gear for 
>> landing on a 'branch, or even grasping prey in hawk-like fashion, but what 
>> advantage would it grant to a flightless quadrupedal climber? 
>> 
>> Especially one that forages on the ground...
>> 
>> It would follow that the perching foot is a lagging indicator of flight, not 
>> a precursor. 
>> 
>> 
>>