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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."

and

"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 
dromaeosaurids."

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 
restoration.

Mickey Mortimer


----------------------------------------
> Date: Tue, 22 Nov 2011 17:13:31 +1100
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: Microraptor preyed on birds (official paper in PNAS)
>
> Mickey Mortimer <mickey_mortimer111@msn.com> 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.
>
>
>
>
>
>
> Cheers
>
> Tim