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Yet more on dinosaur quad climbers



Somebody had to change the title of this thread.

In a message dated 7/3/13 10:54:33 PM, tijawi@gmail.com writes:
<< > GP-In every single ground dwelling theropod we have the keration 
sheath for,

> the toe claws II-IV are always flat. Same for all large land predators,

> except those with retractile claws. The possiblity that large 
dromaeosaurs had

> strongly arced toe claws is nearly zero (If they did it means that were

> climbers, like big cats).


TW-Circular reasoning.

Not circular at all, it is using specific anatomy that has a consistent 
relationship to a specific function in living animals to restore specific 
function in extinct animals. As per Tyrannosaurus has bladed teeth, so it is 
not 
a herbivore. If a sauropod turns up with bladed teeth we can conclude it was 
not a herbivore. Seems TW would call this circular, which it is not. 


> GP-This argument is an extreme stretch that is part of a

> desperate attempt to for some reason to keep the dinosaurs that are well

> adapted for arboreality on the ground.


TW- "Well adapted for arboreality"!  Is that a joke?  There is *nothing*

in the skeletons of _Anchiornis_, _Microraptor_, _Archaeopteryx_,

_Jeholornis_ etc to suggest that they were specialized for

arboreality.  What about the mobility at the joints (or lack of it):

the highly proscribed joint mobility in theropods is a far cry from

the wide range of 3D mobility seen in arboreal quadrupeds.

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



TW -There isn't even a reversed or incumbent hallux in these "arboreal"

theropods!  Bit odd for an "arboreal" dinosaur, no?  If the foot was

no longer used in terrestrial locomotion, why was the hallux so short

and so thoroughly un-reversed?

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. 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. Quadrupedal dinosaur climbers would have been very 
different from bipedal climbers, the obsession with the need for a reversed 
hallux for dinosaurs with long arms and hook clawed fingers to climb is not 
scientific. Think outside rigid boxes. 

TW -- The best you can come up with for "arboreal" characters is some

tweaking of the phalangeal proportions by these theropods, and some

dodgy claw curvature data that doesn't differentiate climbers from

predators.

Perhaps repeating it in plain English will work in this time. Every deity 
damned predatory bird that actually spends considerable time walking on the 
ground has flat toe claws. As per secretary bird, caracara, burrowing owl, 
roadrunner. No predatory bird with strongly arced, sharp tipped central toe 
claws walks or runs on the ground much. TW has yet to cite a single predatory 
ground bird that is a regular terrestrial walker and runner that has 
strongly arced toe claws. No land predator of any kind has strongly arced and 
sharp 
tipped toe claws unless they can be retracted to avoid abrasion. It is 
entirely possible to distinguish among predatory ground birds and predatory 
nonground birds via toe curvature. 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. 

TW seems fixated on the idea that there were ground dwelling predatory 
dinosaurs that evolved strongly curved, sharp tipped talons on toes 2 & 3 for 
predation. It is dubious that this would happen in dinosaurs that still had 
tooth filled jaws and long fingered hands, and in the case of dromaeosaurs 
sickle toe claws to dispatch prey with. Adding more hook claws to toes 2 & 3 is 
overkill as it were. And impractical. If the claws are so ventrally 
projecting because of strong curvature that they can impale hapless victims, 
they 
will quickly lose the sharp tips from ground abrasion as in secretary birds, 
so they cannot impale hapless victims (secretary birds instead pummel prey 
with their small and blunt clawed feet to stun them). Check out the talons on 
an eagle or hawk foot, the tips of the claws are so below the level of the 
axis of the toe that they strongly impact the ground when standing and 
walking, they will not stay sharp if the raptors walk and run a lot. If the 
claws 
tips are set on the toe tips to be carried clear of the ground to avoid tip 
erosion, then they cannot contribute to increasing the grip with the ground 
during running & when on sloping ground and so on, and would be hard 
pressed to impale victims when the toes are flexed, so they are pretty useless. 
The bone cores of toe claws 2 & 3 in Deinonychus (figured in the good old 
Ostrom monograph -- which I get a fresh copy of when at Yale recently you all 
eat your hearts out) show no adaptations for being talons. They have small 
basal tubers, are short, fairly flat, and have an inverted T shape with a flat 
bottom rather than the blade shape of the sickle claw and the finger claws. 
They could be long and strongly hooked only if they had very long keratin 
sheathes. Not impossible, but the lack of bony support would have made the 
distal half of the claw suspiciously weak for a weapon, again unlike the sickle 
and finger claws in which the bone clearly reinforced most of the claw's 
length. The small basal tubers also indicate weak flexion power for impaling, 
yet again unlike the sickle and finger claws. The possibility that big 
dromaeosaurs had sharp hooked talons on toes 2 & 3 similar to Microraptor as TW 
fantasizes is essentially zero, so using the flightless dromaeosaurs has 
possible examples of terrestrial predators with hooked toe claws starts as wild 
nonscientific speculative pleading and ends as nonsensical in every way it 
can be. The long, strongly arced 2 & 3 toe claws with big basal tubers of 
Microraptor are dramatically different, would have been worn down like the big 
foot feathers if regularly used on the ground, and are therefore for 
climbing rather than terrestrial predation.   


> GP - Because the ground is gritty and broad it will do much more foot 
feather

> damage than less abrasive foliage that can be more easily avoided. 
Breeders of

> feather footed pigeons and chickens don't let them wander about on dirt,


TW- So if breeders didn't stop these ornamental birds from wandering about

on the ground, they would go ahead and do it...?

Not sure what TW means. Pigeons and chickens are flat toe clawed ground 
walkers, and those articifically bred with big foot feathers are not adapted to 
care for them, so if breeders allowed them to then they would ruin their 
foot feathers if allowed to wander about on the ground. 


TW - It's worth noting that we are not absolutely certain what the wings of

small non-avialan theropods were actually used for.  So we cannot

assume that there was an adaptive penalty incurred by damaging the

long feathers.

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. By far best 
conclusion, they were arboreal as their toe claws show they were, not living on 
the 
ground as their sharp tipped strong curved toe claws show they were not, and 
where the big foot feathers would tend to be in the way and would get badly 
beat up, degrading their flight performance. 


TW - Many modern birds use their wings in combat, sustaining damage to the

feathers in the process; they live to fight another day.  So I'm not

convinced by the claim that theropods with long pedal feathers were so

fastidious that they avoided the ground altogether.

Again the use of extreme lanquage when inappropriate. Never said that 
Microraptors "were so fastidious that they avoided the ground altogether." But 
they were not idiots. Occasional use of wings in combat is not the same as 
constantly abrading flight feathers by chronic contact with gritty ground. What 
bird does that? 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. 

TW - So do all theropods with extensive hindwings show _Microraptor_-like

claw curvatures...?

No. And no other theropods have such enormous, asymmetrical, high quality 
flight feathers on their footsies. What is informative is that dinobirds that 
combine flat toe claws that indicate lots of ground time with large foot 
feathers show that the latter are irregular and probably damaged by ground 
abrasion, such as Pedopenna. 


> GP - Tim's arguments are the sort seen out of Feduccia.


TW - Wow, I've never been tarred with THAT brush before.


If you don't like getting tarred like that then do not push arguments that 
qualify for the charge. 


TW -- This reminds of something to do with pots and kettles.  The notion

that _Microraptor_ was a specialized tree-living (arboreal) theropod

is hardly universally accepted.  Restoring _Microraptor_ and its kin

as primate-like arborealists (as was done in 'Dinosaurs of the Air')

is extremely controversial.  They weren't dinosaurian spider monkeys,

or colugos. >>

The best data on claw curvature on various critical types has not been 
published yet. The 07 Glen & Bennett data on Microraptor is spurious because it 
was based only on the inadequate figures in the original notice of the type 
specimen. Microraptor, and probably sinornithosaurs in general, as well as 
some Archaeopteryx probably were the most long limbed primate like known 
climbers in the Mesozoic. 

TW - Yes, certain papers have drawn attention to derived characters 
associated with pedal phalangeal proportions, claw curvatures, and femoral 
insertion into the acetabulum - all supposedly "arboreal" characters.  But 
since 
some other (much larger) dromaeosaurs like _Deinonychus_ have these too, I'm 
reluctant to accept these as evidence of arboreality.

Dromaeosaurs like Deinonychus had normal cylinderical femoral heads of the 
type I have never seen in a sinornithosaur (if someone can point me to a 
clearly preserved cylinderical femoral head on a sinornithosaur please let me 
know - no one has so far). There is of course no evidence that big 
dromaeosaurs had climbing toe claws like sinornithosaurs. 

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

GSPaul


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