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



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

> 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. 
> 
> 
>