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Re: Yet more on dinosaur quad climbers



Briefly...

Gregory S. Paul <GSP1954@aol.com> wrote:

> It appears to be TW who is joking. I do not claim that Anchiornis or
> Jeholornis are arboreal, althought the first may well be. No keratin sheaths 
> to
> assess the first, toe claws too flat in the second. Latter also true for
> Aurornis, Eosinopteryx, and Pedopenna. Situation for Archaeopteryx is 
> complicated
> (realized today more complicated than I realized). Recent publications show
> joint action in living animals often exceeds that indicated by dry bone
> manipulation.


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.

I'm not saying that these theropods didn't climb trees.  I'm saying
they were not adapted for it.


> Climbing theropods would not have had primate competition, and
> had aerial abilities to aid in arboreality not seen in most primates.


Again, this is an assumption on your part that aerial abilities
complemented arboreal abilities in basal winged theropods.  You may be
right.  But this isn't the only hypothesis.  The inception of aerial
abilities may be completely decoupled from arboreality in the
evolution of winged theropods.


> Classic example of limited thinking. As I have said so many times,
> quadrupedal climbing dinosaurs may not have needed the reversed hallux 
> arboreal
> bipedal birds need. Might have even been a disadvantage for quadrupedal
> climbers. There are lots of climbing quadrupeds without opposable digits.


Yes, but those climbing quadrupeds (especially mammals) without
opposable digits have manifold other arboreal adaptations.  This has
been discussed at length on this list.


>  The very
> basal Sapeornis lacks well developed finger claws and has a well developed
> reverse hallux, indicating that the opposable hallux is linked to bipedal
> arboreality in dinosaurs.


I agree that it is tempting to associate the retention of claws in
winged theropods (including basal-most avialans and microraptorines)
to tree-climbing.  You might be right here.  But without a grasping
hallux, the theropod has to use both its fore- and hindlimbs to gain
purchase when roosting - or initiating an aerial launch.


> No predatory bird with strongly arced, sharp tipped central toe
> claws walks or runs on the ground much.


I'm betting they don't climb trees very much either.


> All Microraptors are fully in the arboreal
> range in toe claw curvature. Ergo, they were specialized for arboreality.
> Basic logic, it's called comparative anatomical functional morphology.


One swallow doesn't make a summer.  And one claw curvature datum
doesn't make an arboreal theropod.

BTW, are you claiming that constantly climbing trees doesn't wear down
the claws?  This is where your argument is a bit woolly, because
although your arboreal theropods didn't spend much time on the ground,
they couldn't fly from ground-level up to the trees either, or from
one branch to a higher branch.  As quadrupedal climbers, the claws
would be abraded by climbing trunks and boughs all the time...
wouldn't they?


> Note how TW uses extreme lanquage when inappropriate but he thinks it
> serves his purposes. Such as "absolutely certain." What we do know is that the
> distal foot feathers of Microraptors were highly asymmetrical, so they were
> for flight, and they are preserved in good shape rather than beat up as they
> would be from being dragged on the ground all the time.


What you have here is an inverted pyramid of assumptions.  We don't
know exactly how the metatarsal feathers were arranged, so we can't be
certain they would have been dragged along the ground during
terrestrial progression.  (Maybe the feathers were held off the
ground?)  And we don't know exactly how the metatarsal feathers were
arranged because we don't know exactly what they were used for.  Some
aerodynamic purpose seems likely, but it may not necessarily have been
flight.


> Why have such big spectacular feathers evolved for flight
> and then live a lifestyle that will maximize damage to them? Does not make
> sense. Evolution is not that stupid.


Again, "big spectacular feathers evolved for flight" is an assumption.
 You seem certain on this point, but your certainty alone does not
turn opinion into fact.


> Guess I will have to do something about all that claw curvature data I'm
> sitting on. Dang it. Real work.


I look forward to the paper.







Cheers

Tim