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Re: Ceratonykus braincase described



2011/4/28 Jaime Headden <qi_leong@hotmail.com>:
>
>   I would contend, as with many herbivorous-or-not arboreal animals, any any 
> that takes to the trees will require a compliment of increased sensory 
> capabilities in the optic and potentially auditory regions of the brain as 
> well as large sense organs to make do with having to deal to increased range 
> of attention (it has to care about what is below it now, as well).

I think perhaps normal auditive powers can suffice in trees, for a
similar radius of alert around the animal. However, perhaps more
important in a three-dimensional environment is receiving the sounds
(or sights) from below as well as above, as you say, and perhaps this
relates, at least in mammals, with very movable pinnae as those of
genets and some primates. This may also have to do with more movile
eyeballs (although I can just say this for chameleons, and in these
more doing with its own predation than with protection from its
predators). Ear mobility makes me wonder if somebody linked the origin
of ears to the possibility of arboreal locomotion in some Mesozoic
ancestor of modern mammals.

>   Generalist insectivores that have similar adaptations to tamanduas exist 
> that are nearly exclusively arboreal (as a preferred habitat rather than 
> restrictive biome). That was also my point. Comparing terrestrial 
> myrmecophages to non-terrestrial "myrmecophages" is not very useful as they 
> typically invoke differential habits. And alvarezsaurs strike virtually 
> anyone as terrestrial forms. If they were in the slightest myrmecophages, 
> they would be treated with a suite of features not typically found in such 
> taxa, even if their arms were primed for tearing into hard substrates.

Good point. Interestingly regarding the hypothesis of the Russian
authors, animals with forelimb adaptations to break termiteria,
including curved claws, as pangolins and small vermilinguans (Cyclopes
and tamanduas), find themselves quite good at climibing trees,
suggesting that termiteria-breaking adaptations are good for climbing.
Many ground sloths show similarities to vermilinguans in the manus,
including the reduction of some digits, and relative increase of
ungual size in others, so perhaps arboreality of sloths may have some
adaptation in common with termiteria-destruction (whatever came
before). Tubulidentates have straighter claws, likely less fit for
climbing. With this I do not attempt supporting that alvarezsaurs came
from trees, however.

> This is where the fun begins. It might be right to conceive of a chimera, but 
> I think we're also overthinking the animal. No one says all the parts of the 
> animal have to be associated with a precise behavior, and I think some people 
> in this discussion have gotten caught up in trying to oversimplify 
> alvarezsaurs (a very human tendency, I'll admit).

I concur that the puzzles these weird animals put on us is the better
part. However, I do not know what do you mean with oversimplifying
alvarezsaurs. Viewing a particular body part as only useful for one
behaviour? Looking for just one locomotor/feeding behaviour for the
entire animal? Or deduction of lifestyle by ony seeing a body part?

I admit this is a human tendency, or at least affects me when not
checking out my biases to attempting to find adaptations to just one
particular habit. A compromise lesser adaptation for two or more
different habits, but which is not optimal for any of the two tasks,
is an option we commonly do not think about except for different needs
within a single particular habit (for example, competing needs in
flying).

Perhaps it is just that adaptations of this last kind cannot be so
easily evaluated because, let's face it, if it is difficult deciding
between alternatives of best adaptation, how more difficult may it be
trying to choose between hypotheses for compromise adaptations (with
more than two different function for a limb the possibilities may go
farther than any speculative mind can imagine).