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RE: Microraptor preyed on birds (official paper in PNAS)
Thanks to Tim Williams for a copy of the paper. I can now finally say that
nothing in the paper changes my opinion. The only quote which argues the bird
was killed instead of scavenged is-
"What is preserved of the ingested enantiornithine skeleton is still in
articulation with the feet located in the proximal end of the stomach,
suggesting that the meal was not scavenged, but captured and swallowed nearly
whole and proximal end first, as in most living predatory birds."
First, the "skeleton still in articulation" is a partial wing and two feet
lying parallel to each other. Sure they're positioned right if we insert the
rest of the body between them, but it could also be chance. Yet that doesn't
even matter since O'Connor et al. never even bring up the possibility that
scavenged prey can be articulated and eaten head first as well. Plenty of
birds die while whole, and even more die with two legs and a wing still
connected. Nor is there any reason it wouldn't be eaten head first if found
dead. But that doesn't even matter either, since we all know living arboreal
birds often spend time and are killed on the ground. O'Connor et al.'s only
statement defending Microraptor killing it in a tree is-
"The predation of an arboreal enantiornithine suggests Microraptor hunted in an
arboreal environment (Fig. 3)."
Wow. That's.... completely untrue. Sure it might have killed the bird in a
tree, but it might have killed it on the ground, or eaten it after finding it
dead on the ground, or dead hanging from a tree branch for all we know. What's
especially amusing is that O'Connor et al. note two other cases of fossil
diets. One is a mammal skeleton found in another Microraptor, as described by
Larsson et al. (2010)-
"The morphology of the foot is most similar to Eomaia and Sinodelphys, although
this specimen lacks the level of arboreal adaptations seen in those taxa. The
foot is relatively long, with a shortened first metatarsal and elongate
phalanges possessing a phalangeal ratio of around 1. The preserved unguals are
moderately recurved, the phalanges are straight and the ratio of proximal to
distal phalanges does not indicate a dedicated arboreal lifestyle but suggests
the animal was most likely scansorial."
The other is an enantiornithine tibiotarsus found in an ichthyosaur as
described by Kear et al. (2003). Maybe it was scavenged, but maybe the
ichthyosaur killed it. Sharks kill birds today after all. O'Connor et al.
argue the bird's incompleteness indicates scavenging, but the turtles preserved
in that ichthyosaur are also incomplete.
So here we have a Microraptor that ate a non-arboreal animal, and a definitely
non-arboreal animal that ate an enantiornithine. If these two cases don't
eliminate the importance of O'Connor et al.'s specimen in regard to
Microraptor's arboreality, what would? And yet we get statements like-
"This new specimen indicates that M. gui fed on arboreal birds, lending further
support to interpretations that M. gui was spending a substantial amount of
time in the trees."
"Further, because Jehol enantiornithines were distinctly arboreal, in contrast
to their cursorial ornithurine counterparts, this fossil suggests that
Microraptor hunted in trees thereby supporting inferences that this taxon was
also an arborealist, and provides further support for the arboreality of basal
My basic issue with this paper isn't that it's wrong, since maybe Microraptor
was arboreal and maybe this specimen did kill that bird in a tree. It's that
the paper doesn't even try to support the various arguments it takes to get to
that point. Where's the data showing scavenged birds are usually
disarticulated? Where's the data showing modern predatory birds usually don't
swallow carcasses head first? Where's the data showing arboreal birds are
usually killed in trees? Nowhere. It's a neat specimen, but to infer anything
more than "Microraptor sometimes ate at least partially articulated
enantiornithines head first" is story-telling instead of science, at least at
the level of O'Connor et al.'s analysis.
Taxonomy-wise, O'Connor et al. refer the specimen to M. gui based on "its large
size (relative to Microraptor zhaoianus), the proportions of its manual digits,
curvature of the pubis, and slight bowing of the tibia", which were all
convincingly shown to be problematic by Senter et al. (2004). They also refer
the bird to Cathayornithiformes, a group which has never been supported by an
analysis or defended by synapomorphies.
Finally, I do want to end on a positive note and praise Brian Choo's excellent
> Date: Tue, 22 Nov 2011 17:13:31 +1100
> From: firstname.lastname@example.org
> To: email@example.com
> Subject: Re: Microraptor preyed on birds (official paper in PNAS)
> Mickey Mortimer <firstname.lastname@example.org> wrote:
> > Well, since it's not open access I can't say anything about the paper
> > itself (though I could access it for 2 days for the low low price of $10),
> > but the
> > Discover article implies the bird wasn't scavenged because it's articulated
> > and facing headfirst. This doesn't address the obvious argument made
> > on the DML that the enantiornithine could have been caught on the ground,
> > since that's the case for many modern predators attacking arboreal
> > birds. Indeed, I don't see why a predator wouldn't eat a scavenged bird
> > the same way it eats a recently killed bird, since the animal still goes
> > down
> > the throat more smoothly head first. So while I still technically reserve
> > final judgement until I read the paper, I stand by my earlier statement
> > that it's
> > impossible to infer arboreality from one Microraptor eating one arboreal
> > bird.
> I'm prepared to cut the authors some slack here. Here we have a small
> theropod (_Microraptor_) that previous studies have inferred to be at
> last partly arboreal. And what turns up in the stomach of one of
> these theropods? An arboreal bird.
> Yeah, there is no reason to assume that the little bird was
> necessarily in a tree when the _Microraptor_ snapped it up. Modern
> specialist perching birds often forage on the ground. _Microraptor_
> might have pounced on the bird while it was on the ground. Or the
> bird might have already been dead when _Microraptor_ gobbled it up.
> But the behavior depicted for _Microraptor_ in Fig. 3 is at least
> consistent with the skeletal (and integumental) anatomy of this
> theropod: the hindlimbs 'walk' up the tree, the hands grip the tree on
> either side to provide support, and the jaws catch the prey.
> _Microraptor_'s 'wings' could then be deployed to return the animal
> to the ground. No perching (or roosting) is required - so
> _Microraptor_ doesn't require a perching pes or prehensile manus.