Re: Yet more on dinosaur quad climbers

[GSP1954@aol.com]

In a message dated 7/12/13 12:27:14 AM, tijawi@gmail.com writes:

<< Even allowing for some wiggle-room (especially at the shoulder and

hip), theropods don't even come close to extant climbing quadrupeds in

terms of appendicular mobility.  Add to that, the motions at the wrist

and ankle of maniraptorans are actually highly proscribed, courtesy of

the semilunate carpal and mesotarsal ankle joint.  I find it difficult

to imagine a worse construction for quadrupedal climbing.(GP - the last 
item is the  sort of extremist expression of opinion I earlier noted TW is 
prone towards making, it being easy to imagine worse limb design for quad 
climbing.)


I'm not saying that these theropods didn't climb trees.  I'm saying

they were not adapted for it.


Yes, but those climbing quadrupeds (especially mammals) without

opposable digits have manifold other arboreal adaptations.  This has

been discussed at length on this list. >>

TW who is prone to extreme premises that are not scientific or in accord 
with make do evolutionary biology, is making the mistake of thinking that to 
be a specialized arboreal animal requires that a creature be as well adapted 
for climbing as highly modified arboreal mammals, especially derived 
primates. Nyet. All that a beast needs to be a specialized arborealist is to 
have 
the minimal adaptations needed to spend the majority of its life in 
vegetation rather than on the ground. Micraptor clearly had what was needed to 
be a 
tree specialist -- small size, long limbs for long reach between branches and 
good leaping ability, fairly long grasping fingers and toes tipped with 
big, strongly hooked, sharp tipped claws, well developed airfoils for moving 
aerially about among the trees when any limitations in its climbing abilities 
preclude further quadrupedal progress. In fact, microraptors were better 
adapted than the best climbing primates for the tree life because they had 
wings. 

Indeed, as others point out, the flight abilities of the winged dinobirds 
reduced the need for, and may have precluded, the evolution of greater 
specialization for quad climbing, since adaptations for the latter could impair 
the aerodyamic function of the wings (which benefits from arm rigidity to 
improve flight in birds). At the same time, the adaptations for climbing and 
for 
flight in Microraptor feet -- the sharp tipped, curved claws and big 
metatarsal feathers -- show that they were not specialized or even well adapted 
for living on the ground. And it is a relative matter. Only if arboreal 
adaptations were consistently low among theropods could we say they were all 
nonarboreal, but the adaptations do vary, so arboreality should have too. Along 
with some Archaeopteryx microraptors were the theropods best adapted for 
climbing, so they were the most arboreal of the bunch.  

Even if they did not have wings, microraptors could have been reasonably 
good arborealists in an age when they were not going up against primate 
competitors (such clipped dinobirds would probably not make it against primate 
level competition). But add the wings, and the arboreal dromaeosaurs may have 
been about as well adapted for living high up as primates, which lack wings 
the poor things.   

GSPaul

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