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FW: Microraptor also ate fish



________________________________________
From: Jason Brougham
Sent: Wednesday, April 24, 2013 9:27 AM
To: Tim Williams
Subject: RE: Microraptor also ate fish

Well the good news is that we favor the same hypothesis! Microraptor spent most 
of its time on the ground and occasionally ventured into trees is the one I 
also feel is best supported.

I do still differ with you about over - interpreting what extinct animals are 
adapted to do and not adapted to do. You make categorical statements about such 
things, but there are still big arguments about what T. rex, alvarezsaurs, 
sauropods, ceratopsians, and pterosaurs were adapted to do. Skeletal morphology 
does not lead us to one clear, objective, uncomplicated answer.

What we do to figure that out is take the morphology, measure it, and compare 
it to the closest living analogs, however imperfect the comparison. Depending 
on how we design the methods we may get differing results for the same 
features. Thus, in Glen and Bennett (2007), Microraptor's claw proportions come 
out in the "Ground Bird" category, which includes ground foraging doves and 
cuckoos. Nonetheless, Microraptor's horn claw proportions come out in the "G" 
or Ga"category, one step MORE tree - adapted than birds like galliforms and 
ardeids that roost and nest, respectively, in trees.

There are other ways to measure Microraptor that make it LESS tree- adapted. 
The point is just that one cannot always say what an extinct animal is or is 
not adapted to do, because its anatomy is unique or has no perfect living 
analog. One can only test hypotheses, and different tests may get different 
results.

In any case we agree that Microraptor may have gone into trees occasionally. 
For those of us looking for the first incipient signs of theropods entering 
that realm, the trees that birds would one day master, that is one thing that 
makes Microraptor so tantalizing.

I renew my assertion that comparative morphology must draw on comparisons to 
living animals, and that ravens, turkeys, diving petrels, and so on are high
nnett et al. study because, otherwise, we wouldn't know what measurements 
correlate to what behaviors. But you seem to still dispute that.

I know you hate the goats but that may point up the problem. What morphological 
characters do goats have that show they can get up into trees, and that you 
would see as signals of this behavior even if they and let's say, all other 
artiodactyls, were extinct? You say they have certain morphological traits. 
Please be explicit, and tell us what they are.

Also, you use the word "arboreal" strictly, to mean a category involving 
foraging in trees. I use it generally, to mean any behavior involving getting 
into a tree, however briefly. That  may have been one of our biggest reasons 
for disagreement.

________________________________________
From: Tim Williams [tijawi@gmail.com]
Sent: Wednesday, April 24, 2013 2:11 AM
To: Jason Brougham
Subject: Re: Microraptor also ate fish

Jason Brougham <jaseb@amnh.org> wrote:

>  Now this is a productive debate about Paleontology.
>
> Your points are well made, well supported, succinct, and articulate. Thank 
> you. I really want
> to be as succinct but I will probably fall a little short. I apologize.


No worries.  BTW, I [snipped] a lot of your text for the sake of
brevity.  I really hope my responses don't give the impression of
cherry-picking.


Short response:  The point I'm arguing here is the distinction between
what an animal is *adapted* for and what an animal is *capable* of.
The former is a subset of the latter, of course.  For a fossil taxon,
adaptations can be inferred based on morphology, including
biomechanics.  Determining the full potential of the latter (i.e., the
full range of what an animal is capable of doing) is often impossible
to approach scientifically.


For example, what if we wanted to investigate _Archaeopteryx_'s
ecology based on its morphology.  The overall skeletal proportions and
hindlimb biomechanics indicate that it was a terrestrial cursor.  So
if our hypothesis is that _Archaeopteryx_ was a terrestrial cursor
the data support that hypothesis.


If our hypothesis is that _Archaeopteryx_ was an arboreal animal, then
the data are not supportive.  The lack of arboreal adaptations weighs
against this hypothesis.  Sure, _Archaeopteryx_ might have roosted in
trees.  As you say, many modern birds without obvious arboreal
adaptations can (and do) roost in trees, such as tinamous, petrels and
cormorants.  But I'm struggling to see how the hypothesis of roosting
behavior in _Archaeopteryx_ can be upheld scientifically in the
absence of the requisite adaptations.


Long response: Read on...


> One reason we are all so interested in Microraptor is that, thanks to its 
> anatomy, its
> phylogenetic position, and its similarities to other paravian relatives,  it 
> may retain some of
> the ancestral characters of the ancestors of birds. If so, it may be a useful 
> model for
> understanding the transitional forms between the non-flying and flying 
> dinosaurs, in any
> number of aspects of its biology.


Definitely.


> As you note, I never said I could prove Microraptor could climb into a tree, 
> I said we can't
> rule it out. You are probably annoyed with me for raising hypothetical 
> functional possibilities
> without unambiguous evidence.


"Annoyed" is perhaps overstating my reaction.  I don't really have any
emotional investment in this thread, just an intellectual one.  ;-)


> Just because birds with strong halluces often nest in trees doesn't mean 
> diving petrels,
> which do not have halluces, can't nest in trees (in fact they do).


Yes, I don't doubt that.  But again, it's irrelevant to _Microraptor_.
 Unless you can demonstrate (a) which morphological traits allow
petrels to perch in trees, and (b) that _Microraptor_ had these same
morphological traits.


Yes I know I'm being harsh here.  But I'm trying to avoid rampant
speculation about _Microraptor_ behavior simply because this-or-that
bird can do it.  Same for any other non-avialan maniraptoran or basal
avialan.  They weren't crown birds.


> Thanks to observations from actual Zoolog
viors without
> skeletal correlates are real possibilities we need to acknowledge in 
> evolutionary theory. I am
> not saying that, if diving petrels were extinct, I could just somehow tell 
> they climbed trees.
> But I never claimed certainty, you did. You feel that you can say "no way" if 
> the animals are
> "not adapted for" it without testing that conclusion, while I do not.


If diving petrels were extinct, I would say that the pedal morphology
suggests they weren't arboreal.  I'd be right.


> You may retort that analogs are speculative wastes of time.


That's not really what I said - but it's not far off.  :-)   I think
some people too readily resort to modern analogs to explain the
behavior of fossil taxa.  As examples, comparing _Microraptor_ to the
colugo, or _Archaeopteryx_ to a magpie, or _Epidendrosaurus_ to an
aye-aye...  all these "analogs" have the potential to mislead w.r.t.
the ecologies of these maniraptorans.


> But isn't analogy indispensable in evolutionary theory? Didn't Darwin apply 
> the lessons of
> Galapagos finches to apes to help understand all evolution?


In broad terms, yes. Again, I'm not rejecting the use of analogs
outright.  I'm just saying we should be *very* judicious about our
choice of analogs.


> Moreover, if we are considering evolutionary sequences, inference from 
> context will be
> relevant. In order for such highly evolved traits as opposed halluces to 
> evolve, a feedback
> loop must be established where slight improvements in the structure have real 
> survival
> benefits to the inheritors. Far from there being no way, it is in fact 
> indisputable that the
> behaviors must often precede the adaptations, or else there must be 
> exaptations.


The trouble is that there is a whole lot of small non-pygostylian
maniraptorans that clearly weren't adapted for arboreality -
_Microraptor_, _Archaeopteryx_ and _Jeholornis_ included.  If all
these non-avialan maniraptorans were spending so much time in the
trees, why did it take so long for maniraptorans to develop any
arboreal characters?  M
spend much time in trees at all.  Yes, they might have roosted.  But
how would we know?


> As you concede, the gripping of prey by the second digit which, according to 
> dromaeosaur
> anatomy could probably flex enough to pierce its own foot pad, could be just 
> such an
> exaptation. The fact that, unlike Denonychus, Microraptor weighs the same as 
> birds like
> ravens, pheasants, and tinamous that roost in trees seems to me highly 
> relevant.


I may have given the wrong impression on this one.  I think it's
reasonable that _Microraptor_ ventured in trees, and used its hands
and feet to grasp trunks and branches.  The second toe may indeed have
been useful in this context.  But this is unrelated to an ability to
roost, because none of the birds you mention uses this kind of pedal
arrangement for roosting.


> You say that Microraptor might have done so, but also that this is irrelevant 
> and moot? If two
> animals weigh the same, and the question is whether terminal branches can 
> support them,
> you don't see any relevance? Two animals do not have to have THE SAME feet in 
> order to
> hold on to branches.


Agreed.  But if the two animals don't have the "same feet", you can't
use them as analogs for how they could have used their feet to grasp
terminal branches.


Show me a modern example of an animal with _Microraptor_-like pedal
morphology that perches or roosts on narrow branches.  If you can't,
then there's no point in citing this animal as an analog for how
_Microraptor_ did it.  Yes, I understand petrels, wood ducks, tinamous
etc can roost without the aid of a long hallux.  But that argument
alone doesn't cut any ice with me.


> What was Microraptor actually adapted to do? What is your answer? No one 
> knows what
> Microraptor is adapted to do because there are no four - winged animals with 
> functional,
> unfused, finger and toe claws, long bony tails, and feathered integuments 
> alive today for us
> to calibrate any correlates. This is why we are all so fascinated by the 
> animal. If you rely
> solely on modern morphologic



_Microraptor_ has the proportions of a terrestrial cursor.  It also
has a few putative scansorial characters.  It has a plumage suggestive
of aerial descents.  This leads me to hypothesize that it was an
animal that spent most of its time on the ground, and occasionally
ventured into trees.


> I have photos of two different grouse chicks perching in trees by pinching  
> branches -
> between the 2nd and 3rd toe with the left foot, and 3rd and fourth, on the 
> left, in both cases.
> I have photos of turkeys in trees where the halluces do not touch the branch. 
> We have often
> discussed the goats climbing trees. If all goats were extinct you would say 
> there was no
> way they could climb trees, because they lack all skeletal correlates for 
> climbing, like
> thumbs. But since they are alive we know that one correlate for climbing is 
> being a nimble
> goat!


Ah, it always comes back to "But goats can climb trees!"  :-)  Yes,
goats have certain morphological traits that allow them to climb trees
(many of these traits are associated with negotiating narrow and/or
3-dimensional substrates).  But unless you can identify these same
traits in _Microraptor_, goats are utterly irrelevant to how
_Microraptor_ might have climbed trees.


Nevertheless, goats don't roost in trees.  They are not arboreal.  If
all goats were extinct I would say that, based on morphology, that
goats were not arboreal, and that tree-climbing was not essential to
their ecology.  I'd be right on both accounts.  Whether they did climb
trees or not is unimportant to me, because it's outside the scope of
what fossil evidence can tell us.


> To repeat, I have never suggested that Microraptor was in the morphological 
> category of
> "perching" or "arboreal" birds. That is obvious, and those last two 
> categories are highly
> derived states in true bird evolution. Instead, I observed that basal birds 
> with body masses
> low enough (tinamous, galliforms, anatids) all have many representatives that 
> roost in trees,
> often at night and when brooding young. Some birds 
nest in trees,
> such as In some cases (tinamous with vestigial halluces and wild turkeys with 
> elevated
> halluces) where their feet are even degenerate for perching, so that, if they 
> were extinct, you
> could go on the DML and argue that there was "no way" they could get into a 
> tree, let alone
> with their chicks, since their morphology shows they were going in the other 
> direction
> entirely, of being strictly ground birds.


Excellent point.  I wouldn't say there is "no way" they could get into
a tree.  I would say that the morphologies of these birds tell me that
they are/were terrestrial.  In other words, they spent most of their
time on the ground.  I could not rule out roosting; but I can't rule
out other behaviors too for which there are no apparent adaptations.


Apparently tinamous "roost" in trees by sitting on their tarsi using
highly modified scales on the plantar tarsal surface.   In any case,
tinamous and turkeys nest on the ground, don't they?


> Actually David Hone suggested in his paper that the hands of Microraptor 
> could not be
> brought together to grasp prey because of the primary feathers. I was 
> skeptical, so I tested
> it in my precise scale model, and found that he was right.


This only applies to small objects, correct?  A _Microraptor_ could
grasp a tree trunk two-handedly.  Trunk-climbing would require the use
of all four limbs.


> Agreed. The foot of Microraptor does not have the adaptations of modern 
> perching birds. But
> its anatomy is tantalizing precisely because we can't exclude the possibility 
> that it could
> climb into trees. Not perch, but start on that sequence.


I agree with you here.  And so I'll end this voluminous response on a
positive note.






Cheers

Tim