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Re: Microraptor also ate fish



That bit about the colugos is your best point. It is a valid hypothesis
but implausible and not supported by the evidence.

So, although you have used this language, you aren't really saying that my
hypothesis is unscientific. You're just saying
You don't buy it, and that's fine by me. But let's not call something
untestable too hastily. And let's not put new tests on hypotheses that
aren't really required of them, like saying they must completely
reconstruct every motion.

As an example let's look at the hypothesis by Gong et al. that
Sinornithosaurus was venomous. There they did just what you've asked, Dr.
Williams. They found the jagged hole where the venom gland sat, they found
grooves in the teeth, they noted that the teeth were extra long. They even
reconstructed in detail, as you say they must, the ecology of the animal:
running around biting birds, specifically, and injecting a  venom so fast
- acting that the birds dropped dead on the ground, ready for consumption.
That hypothesis passes all your tests for anatomical detail, clear
evidence of adaptations, and detailed reconstructions.

The reasons, I think, that this hypothesis convinced no one were precisely
because the authors did not refer to living birds and other analogs
enough. They were not concerned that there are no other venomous
archosaurs at all (with the possible exception of the polyphyletic
Pithohuis), relying instead on their own biomechanical analysis. They were
not concerned with the occurrence of grooves in the teeth of a wide range
of non - venomous animals. They were confident that the venom pocket was
not just an area where the fossil was damaged, and that the teeth were not
popped out of their sockets.

In contrast, I grounded my hypothesis in the behaviors of the closest
living relatives of Microraptor and anatomical analyses done by other,
expert, teams of researchers. If you think that it is 'completely
irrelevant' that all of the most basal birds (tinamous, galliforms, and
anatids) that weigh little enough to do so have many representatives that
roost and brood chicks in trees in the same manner, and that Microraptor
has foot talons that a team of experts have measured and found to compare
to those of perching birds, then I probably can't convince you that these
things are relevant. I will just have to turn it over to our peers to
decide.

I don't call them arboreal features, Birn-Jeffrey et al. do. And
Microraptor could have roosted in trees by two methods off the top of my
head. 1) by holding on to branches with its feet, which had claws that
have been measured as within the morphological range for perching birds.
2) by climbing to a thick enough crotch in a tree that it could simply
rest its weight there, as diving petrels do. Is that exact enough for you?

And, yes, Microraptor was incapacitated by the limited range of motion in
its joints and the parasagittal range of motion of its legs, but so are
pheasants, turkeys, and all other birds that get up into trees.

I am not in the mood right now to search for this email, but didn't
someone on DML once write that raccoons are unable to descend trees head
down because of some limitation in their joints? I saw one in the park
doing just that anyway, and I choose to believe the raccoon instead.

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544





On 4/29/13 10:54 PM, "Tim Williams" <tijawi@gmail.com> wrote:

>In response to Jason, two points:
>
>(1) There is a difference between what an animal is adapted for, and
>what it is capable of.  Obviously, the latter is more expansive than
>the former.  (I can climb some trees - but I have no arboreal
>adaptations.)  However, if an animal is not morphologically adapted
>for a certain behavior, then I think it is dangerous to argue that
>this behavior was central to its ecology.
>
>You say, quite reasonably: "Thus I defend any researcher who presents
>a hypothesis about extinct animals based on observations of living
>animals."  However... unless that hypothesis is testable (e.g., by
>biomechanics, morphometrics, etc), then it is just speculation.  (BTW,
>speculation is fine - as long as it's presented as such.)
>
>
>(2) I think we agree broadly that _Microraptor_ spent much of its time
>on the ground.  As you say: "If you'll recall, my hypothesis was that
>it may have foraged on the ground and roosted in trees, as do the
>clades of living basal birds that are small enough to do so."
>
>This is a prime example of why I'm so uneasy about using living birds
>as analogs for non-avian maniraptorans.  Unless you can reconstruct
>exactly *how* _Microraptor_ roosted in trees, the comparison between
>_Microraptor_ and a roosting bird is entirely meaningless IMHO.  Yes,
>some extant birds can roost without the benefit of a perching pes
>(like certain tinamous).  But unless _Microraptor_ roosted in the same
>manner as one of these birds, what's the relevance?  This sounds like
>a hypothesis waiting to be tested.  Unless there is a methodology in
>mind, then it's just speculation.
>
>I would sum up your argument as "If small birds can roost, why not
>_Microraptor_?"  But what I want to know is "Why?" and "How?" - not
>just "Why not?"
>
>Too often, analogs based on superficial or trivial similarities are
>used to cut corners.  Someone finds a point of anatomical similarity
>between (say) _Microraptor_ and a flying lemur.  They then claim that
>_Microraptor_ behaved in the same way as a flying lemur.  There is a
>fine line between being "unrealistically constrained" and outright
>bullsh*t.
>
>The paper by Birn-Jeffery et al. (2012) corroborates the hypothesis
>that _Microraptor_ and friends might have been scansorial.  What you
>call arboreal features are actually scansorial (i.e., used for
>climbing).  But climbing up (or on) what?  Many small mammals are
>scansorial, but spend hardly any time in trees.  Because these
>furballs are small in size, walking or running over uneven terrain
>requires scansorial adaptations.  (I've wondered if this was the
>adaptive rationale behind the scansorial features in tiny
>_Epidendrosaurus_/_Scansoriopteryx_ i.e., nothing to do with
>arboreality.)
>
>
>
>
>
>
>Cheers
>
>Tim