Re: Microraptor also ate fish

[Tim Williams <tijawi@gmail.com>]

Mickey Mortimer <mickey_mortimer111@msn.com>

> But as I argued, by limiting "arboreal trait" to "traits only found in taxa 
> which are arboreal
> and can't serve another purpose", you're probably going to be blind to many 
> arboreal taxa.


I never said arboreal features can't serve other purposes.  Many birds
of prey use their feet for both prey capture and perching, for
example.


I doubt if we would find taxa that are arboreal (sensu stricto) that
lack arboreal characters. I also understand that arboreal vs
terrestrial is not a dichotomy, but a spectrum.  Glen and Bennett's
paper makes this clear; and Van Valkenburgh's definitions of arboreal
and terrestrial don't apply to birds.  For example, some birds forage
and nest on the ground, but shelter in trees - like turkeys.  Maybe
_Microraptor_ did too.  But I'd like to know exactly *how*
_Microraptor_ did this, rather than just assume it could.


> If  the latter percentage is high enough (e.g. a third of arboreal taxa don't 
> have such strictly
> arboreal traits), then saying Microraptor lacks such strictly arboreal traits 
> isn't going to tell
> us much about its actual habits.


You seem to be arguing that there may be a lot of "slop" in the data,
and that arboreality isn't always tightly correlated with morphology.
You may be right.  But to argue that _Microraptor_ was arboreal, and
its arboreal characters fall within the "slop", strikes me as dodgy.
We might as well argue that _Coelophysis_ was arboreal too.  Or even
that _Deinocheirus_ was arboreal, as Rozhdestvensky proposed in the
1970's - and the forelimbs do indeed show certain tree-sloth-like
features.


> We need to know that percentage before we can say anything substantive.


I disagree.  _Microraptor_ was not arboreal - that much is clear.
Note that I'm using arboreal in the strict sense.  I'm not denying
that _Microraptor_ could have ventured into trees or other vegetation,
though.


> But we still don't know how "strictly arboreal characters" are distributed in 
> arboreal taxa.


I think I see the misunderstanding here.  By "strictly arboreal" I
don't mean "arboreal and nothing else".  I mean "used for an arboreal
lifestyle" not for opportunistic forays into trees.  The traits that
goats use to get into trees (mentioned by David M.) are *not* arboreal
characters.


> I meant the fingers and toes could curl inward to hook narrow objects.  This 
> is a trait which
> would be useful to an arboreal taxon, while our example the blue whale lacks 
> this ability,
> one aspect of it being very poorly built for an arboreal lifestyle.


Fingers and toes that can curl inward during flexion could certainly
be useful in an arboreal taxon.  But arboreal mammals have more than
this - specific phalangeal proportions and articular/trochleate
morphologies, increased ranges of motion at the joints, etc etc,
consistent with a life spent mostly in the trees.  Birds that spend
most of their time in trees, and forage and/or nest in trees have
specialized pedal morphologies.


> But it doesn't mean they're not used for an arboreal lifestyle either, which 
> seems to be your
> default.


You seem to be using a very broad definition of "arboreal".  Every
arboreal mammal and bird I can think of has arboreal characters.


But in essence I agree with your point.  Theropods were/are
plesiomorphically terrestrial bipeds.  Any deviation from this
"default" requires strong evidence, in my book.  I don't see any
compelling evidence for arboreality in any theropod more basal than
sapeornithids or confuciusornithids.  (Maybe _Epidendrosaurus.... but
it's a tricky one.)


> Birds only have two grasping appendages (except hoatzins; three if you count 
> parrots).
> Monkeys lack an aerodynamic surface, so will be injured or killed more often 
> if they fall.
> Sloths lack a safe way to travel between trees.


All these tetrapods have arboreal adaptations.  They may not have all
possible adaptations - but enough for a life spent mostly in trees (=
arboreal).  Hoatzins have a highly specialized perching foot; monkeys
have appendages specialized for moving rapidly through trees; and tree
sloths have limbs specialized for suspensory behavior; and so on.


Jason Brougham <jaseb@amnh.org> wrote:

> Well I'm sorry but you did say that. You said that, if we consider two 1kg 
> animals, one
> extinct and the other a raven, and they both have grasping feet, unless they 
> have the same
> EXACT type of grasping foot (unless both are ravens, basically) no comparison 
> can be
> made and no inference of function. Indeed you said that there is no relevance 
> at all. Your
> words.


Yes, lots of 1 kg animals can roost in trees.  But unless you can
infer that _Microraptor_ used the same mechanism for roosting as one
of these animals, then I maintain that it has no bearing on whether
_Microraptor_ could roost or not.

There are many different types of grasping feet.  The feet of many
ornithurans and enantiornitheans are adapted for anisodactyl perching.
 The grasping feet of fruit bats are adapted for suspending from thick
tree branches.  The grasping feet of dromaeosaurs are different to
both (though more similar to birds than to bats).


So my point is that comparing the raven's foot to _Microraptor_'s foot
is a poor analogy.  _Microraptor_ did not perch like a raven.  There
may indeed be individual points of similarity between the two, and
from that standpoint you could argue that the foot of _Microraptor_
could be used for roosting or perching.  But I'd like to see that
particular notion framed as an explicit hypothesis that can be tested.
 In a previous post you mentioned reconstructing the pes of
_Microraptor_ using the musculoskeletal anatomy of modern birds as a
template, to investigate if the foot of _Microraptor_ was
biomechanically capable of grasping a branch.  I think this is a great
idea.  This kind of hypothesis-driven research would be invaluable.
It's far superior to the hand-waving that often goes on to explain why
_Microraptor_ was (allegedly) arboreal.










Cheers

Tim