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Re: Microraptor also ate fish

Mickey Mortimer <mickey_mortimer111@msn.com>

> As paleontologists, it seems to me we often assume a behavior was not normal 
> without
> some obvious adaptation to it.  But is this a realistic view of how 
> adaptation and behavior
> work in living animals?  I'm not talking about rare but possible behaviors 
> like goats climbing
> trees, but about behaviors that living animals actually perform on a regular 
> basis.  For
> instance, are there any studies demonstrating species that spend a certain 
> amount of time
> in trees have a certain amount of arboreal adaptations?  Or is it 
> possible/likely that say,
> 20% of species that spend >30% of their time in trees can't be statistically 
> separated
> based on skeletal morphology from 20% of species that spend <5% of their time 
> in trees?
>  If the error bars and overlap are large enough, it would seem the right 
> answer would just be
> to say "I don't know".

This is an excellent point.  Often phylogeny can muddy the waters.
For example, the roadrunner (_Geococcyx_ spp.) forages on the ground,
and runs fast.  So it has cursorial hindlimbs to suit.  But the feet
retain the zygodactyl configuration of its arboreal cuckoo ancestors,
and are not highly adapted for cursoriality.  (One suggestion is that
the flat, desert environment is more forgiving of the roadrunner's
distinctly un-cursorial toes.)  The zygodactyl pes does come in handy
during perching and nesting above ground.

> This is especially true for taxa like Microraptor that fall outside the range 
> of living taxa in
> their basic anatomy.

Yes.  Which is why I'm so unenthusiastic about using any modern
tetrapod as an analog for _Microraptor_.  It may well have individual
characters in common with certain extant tetrapods - but nothing
approaching an entire bauplan.

> This all boils down to whether we're actually justified in using the tiny 
> amount of information
> we have on extinct animal behavior to say anything significantly likely to be 
> true.  Without
> some broader study on the kinds and frequencies of arboreal adaptations 
> today, and the
> influence of novel variables such as Microraptor's clawed wings and solid 
> mobile tail make,
> can we even make a useful statement about its arboreality?

I think we can.  For _Microraptor_, the lack of *any* arboreal traits
is telling.  Motion at the joints is very limited or highly
proscribed, as it is in all theropods.  (Although there is evidence of
increased range of motion at the acetabulum, this is found in larger
and incontrovertibly terrestrial dromaeosaurs too.)  The manus and pes
of _Microraptor_ lack any apparent adaptations for branch-grasping -
apart from those that possibly have a raptorial function (as well?).

Thus, traits characteristic of arboreal quadrupeds and/or perching
bipeds are absent from _Microraptor_.  The best we can do is argue
that the claw curvature might be compatible with tree-climbing, and
the grasping pes might have been used for gripping branches - in both
cases, these are likely exaptations of ancestrally predatory
characters.  This (combined with small body size) might be enough to
get _Microraptor_ into a tree.  I tend to think so.  But I'm doubtful
that _Microraptor_ could sit, roost or perch in a tree.

If _Microraptor_ routinely roosted in trees, I would expect it to have
a pes that was adapted for roosting.  Anatomically speaking, it
doesn't take much.  Push the hallux down, twist the first metatarsal a
bit, and enlarge the pedal claws.  Even _Epidendrosaurus_ managed the
first one (fully descended hallux), though I'm not sure why.  But
arguing that _Microraptor_ was arboreal in the absence of arboreal
characters strikes me as special pleading.  Yes, _Microraptor_ might
have been exceptional in this regard.  But probably not.  My
impression is that _Microraptor_ did what it was adapted to do, and
not much else.