RE: Campbell's even crazier than a MANIAC? (archeopteryx climbing)

[Tim Williams <twilliams_alpha@hotmail.com>]

Augusto Haro wrote:


> It seems that many things without clear adaptations to climb can climb trees, 
> but it is more difficult to 
> prove that they were always on trees, except for such specialized climbers 
> such as Megalancosaurus.


Exactly.  There are two separate questions here, which occasionally get 
conflated...

(1) Given the right motivation, what kind of behavior(s) is an animal capable 
of?

(2) Based on the animal's anatomy, what kind of behavior(s) is the animal best 
adapted for?

The second question can be approached far more rigorously than the first 
question, which tends to become the subject of a great deal of arm-waving.  


Getting back to _Archaeopteryx_, there is no way that its functional anatomy 
supports the interpretation that it was a specialized arboreal animal.  For 
(2), there is some indication of a shift to scansorial/climbing behavior in 
some of its pedal characters (also seen in microraptorines and _Pedopenna_).  
But no aspect of its anatomy is consistent with a predominantly arboreal 
animal.  Unless its weak scansorial/arboreal abilities are derived (= 
secondary), there's nothing to indicate that it evolved directly from a 
specialized gliding animal (e.g., "tetrapteryx"")


As for (1), this is a little 'warm-and-fuzzy': _Archaeopteryx_ could probably 
climb, and maybe even perch (although only on large branches, if at all).  
However, there's nothing about its anatomy to suggest that it was specialized 
for either.  Similarly, there's no reason why _Archaeopteryx_ couldn't swim.  
But this doesn't make _Archaeopteryx_ a natatorial animal.


> From my ignorance, I guess it would be hard to tell from just bones why 
> Iguana is so arboreal while 
> other large Caribbean iguanids are not, or why some cats (except for the 
> specialized margay) are more
>  arboreal than others (putting aside the reason of a tree-less habitat).


Yes, when it comes to iguanas, I'm mostly ignorant too.  However, you mention 
the margay, which is a felid that is specialized for arboreality.  The margay 
spends most (if not all) of its life in the trees (it even hunts there), and it 
has specialized adaptations to suit.  The margay's tarsus is highly adapted to 
suspensory behavior, and it can fully reverse its feet when descending trees 
head-first.  If the margay were a fossil mammal, and we didn't have living 
margays that we could observe first-hand, we could probably infer that the 
margay is specialized for arboreality based on (among other things) the 
functional anatomy of the ankle, which looks more like that of an arboreal 
lemur or kinkajou than a 'typical' felid.


The leoapard is often cited as an example of the limits of inferring function 
from morphology alone.  For the big cats, leopards and lions have very similar 
skeletons, and if we were to infer the behavior of a leopard based solely on 
its skeletal anatomy, we might infer that it's probably terrestrial like a 
lion.  However, leopards are accomplished climbers, and do spend a lot of time 
in trees (mostly resting, and eating their kills).  But they only hunt on the 
ground, and (AFAIK) they don't leap between trees.  So, leopards are only 
"arboreal" in a very limited sense.



Cheers

Tim


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