RE: Microraptor also ate fish

[Jason Brougham <jaseb@amnh.org>]

 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.


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. 

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. But is it 
unscientific to present a hypothesis, and then discuss with one's peers 
comparative methods to test it? I must reply, with all respect, that you seem 
to have actually committed a logical fallacy by categorically calling one of 
these hypotheses impossible on a priori grounds. That is where I think 
scientifically shaky ground and woolly thinking entered into this conversation. 
If I may jokingly exaggerate to make a point, you are saying that since we 
never found Amelia Earhart's body there is no way she could be dead. Disproving 
that A = B doesn't prove if Not A then Not B. 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). Thanks to observations from 
actual Zoology, we know for certain that behaviors 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. 

You may retort that ana
gy indispensable in evolutionary theory? Didn't Darwin apply the lessons of 
Galapagos finches to apes to help understand all evolution?

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. 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.

>Unless you are arguing that _Microraptor_ could perch like a raven
>(and clearly you aren't), I would say that comparing _Microraptor_ to
>a raven is irrelevant and moot.  _Microraptor_ has no morphological
>traits that are correlated with an ability to climb out on to terminal
>branches the way ravens do.  Yes, _Microraptor_ might have done so.
>Animals often perform functions for which they are not adapted.  But
>I'm trying to keep our inferences about an animal's behavior to a
>soundly scientific footing (so to speak).  In short: What was
>_Microraptor_ actually *adapted* to do?

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. They just need to have 
feet that can grip. Do you reject the use of all analogs in comparative zoology 
and Paleontology? Or do you accept that, if a Harbor Porpoise weighing 60 kg 
can breach the water and leap into the air, that this is one line
 60 kg could perform the same maneuver?

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 morphological 
correlates, it was adapted to do nothing.

Some measurements, of feather vane asymmetry, wing length and surface area, 
sternum size, estimated pectoral muscle mass etc. place Microraptor among 
powered fliers like megachiropteran bats. Some wind tunnel tests showed that it 
was an efficient glider and that, even thought its leg feathers cut into the 
induced wind the wrong way, they still somehow produce lift. That experiment 
even suggested Microraptor was  adapted to quickly tip up to land on trunks. 
Other comparisons to living birds, like ornamental breeds of pigeons, suggest 
the leg feathers had no aerodynamic function at all, and that this little thing 
could have spent its life darting around in thickets and covering its huge egg 
clutches with its wings. I think all of these are real possiblities, and I 
don't reject any of them a priori.

>This grasping pes may have been exapted in other lineages for arboreal
> perching; but it wasn't there yet.  Not even close, IMHO.

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!

To repeat, I have never suggested that Microraptor was in the morphological 
categ
t 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 with NO halluces also 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.

If you look only at unambiguous correlates, how would you know an intermediate 
condition if you saw it? If we look at the jaw joint in Morganucodon, would you 
say that the articular and quadrate still participate in the jaw joint and 
that, lacking a purely squamosal/dentary jaw joint, Morganucodon lacks that 
correlate for being a Therian and thus has nothing to tell us about mammal 
evolution? Or can you see it in context, as a model for how the evolutionary 
stages may have progressed, even if it may not be an actual ancestor of true 
mammals?

>Regarding the manual claws, there is an issue regarding how it is
>difficult to distinguish predation from climbing ability (after all,
>both require gripping).  This leaves scope for exaptation, if a
>predatory manus was co-opted for climbing, which is possible in small
>maniraptorans.  This is an entirely scientific example of
>"uncertainty".

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. To bring the hands together a large percentage of the length of the 
primaries strikes the ground. Sullivan, C., Hone, D. W. E., Xu, X. and Zhang, 
F. The asymmetry of the carpal joint and the evolution of 
ding in maniraptoran theropod dinosaurs. Proceedings of the Royal Society B. 
Published online March 3, 2010. Figure 3

>But if we say that the manual claws or pes could be used for functions
>for which they were clearly not adapted, then we're on shaky ground.
>This is a way that "uncertainty" is mis-used.  The foot of
>_Microraptor_ was *not* adapted for perching.  No amount of discussion
>about wood ducks and ravens will convince me of otherwise.

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.

Are you suggesting that Microraptor has LESS gripping ability with the second 
toe than larger dromaeosaurs do? I am open to that possibility, has anyone 
measured that?

Now, you are right if you say that I may be wasting my time imagining the 
lifestyle scenarios of Microraptor, Archaeopteryx, Xiaotingia, Anchiornis, 
Epidexipteryx, and Epidendrosaurus, and that the real ancestral condition, and 
habits, may be revealed by as yet undiscovered animals, or may never be 
revealed. But those taxa grade pretty well into Jeholornis, Sapeornis, 
Confuciusornis so on. They seem to reflect back to the real common ancestor of 
Paraves, which was probably small, winged, and just possibly could have climbed 
into trees to roost as basal birds still do.

>I'd say the morphology of _Microraptor_ says "no way".  It has no
>adaptations that correlate with an ability to grasp narrow branches,
>either with its hands or feet (or both together).  If we are going to
>claim that _Microraptor_ engaged in behaviors for which it was *not*
>adapted, and that these behaviors were important to its life habits,
>then I think we're heading in the wrong direction.

Agreed, we must not claim this. But we must remain open - minded to plausible 
hypotheses. And we must remember that claims of what Microraptor IS adapted to 
are also speculative and must be tested. There is
 on what T. rex was adapted to do, nor Alvarezsaurs, nor sauropods, nor sabre 
toothed tigers. There are just leading and minority hypotheses.

>... let's not use uncertainty as an invitation for woolly thinking.

Agreed. Let's not claim certainty a priori either. You see, that is why I so 
often resort to real animals rather than calculations or theoretical works. If 
Sokoloff et al. hadn't finally buckled down and performed surgery on some 
Starlings, we'd still all be saying that the supracoracoideus is an 
indispensable adaptation for take off from the ground. Thanks to him we know 
that total loss of the supracoracoideus has disturbingly little effect on take 
off performance. I would have bet my savings they couldn't do it, but they did 
it with seeming ease. That humbled me, and made me leery of relying on the 
interpretation of adaptations to predict actual capabilities.

'There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy.'

- Hamlet Act 1, scene 5


>Cheers

>Tim