Re: New Mesozoic bird papers (advance publication)

[Denver Fowler <df9465@yahoo.co.uk>]

----- Original Message ----

From: Jason Brougham <jaseb@amnh.org>

>The new Burnham et al. paper presents puzzling methods and unsupported 
>statements. It also fails to address criticisms of the authors' assumptions 
>that 
>>are now about a decade old.

I couldn't agree more. Feduccia's (1993) measurement method is flawed: and was 
pointed out as such by Glen and Bennett (2007) -which isn't cited at all. They 
don't survey any non-paravian theropods, and while I realise this is due to 
lack 
of keratin preservation, comparison of bony cores of taxa like Allosaurus or 
Baryonyx with paravians would be revealing, or at least test their hypotheses 
(a 
criticism I think Kevin Padian leveled at some of the earlier papers). Some 
critical statements are unjustified (as noted below). They also suggest that 
reconstructing keratin sheath lengths by measuring bony cores has problems, and 
cite our paper (fowler et al 2009), but I don't recall any detailed discussion 
we made of bony core issues, just that we measured an eagle foot that had 
removable keratin sheaths, hence we were able to compare keratin sheaths with 
their bony cores. I don't see any attempt to do this (nor quantify it) in this 
paper. They measured just the fossil sheaths, yet they had the bony core 
sitting 
there right next to them! why not measure those and make comparisons? You can 
only assume that they did not do this becuse the data did not support their 
view.

And of course, where are the extant raptors in their dataset? Nowhere. Curved 
claws clearly have predatory functions in extant birds, but this is ignored 
(indeed, specifically excluded in Feduccia 1993).

Really, you have to question the reviewers' / editor's decision here. We had 
problems getting our 2009 paper through review at a couple places, mainly for 
lack of statistical analysis (fair enough, which was consequently added for 
PLoS), but this (which has no statistics at all) apparently sailed through. I 
can forgive the fact that the authors have their own views, and want to pres
 of the pertinent literature 
(only the papers that support their own view), and there isn't statistical 
testing. Should the reviewers / editor pick up on this? Should we expect any 
differently? 



 ----------------------------------
Denver Fowler
df9465@yahoo.co.uk
http://www.denverfowler.com
-----------------------------------


The ones that stood out, in my mind are:

1) from page 3: "The manual claws of Microraptor ... were surely used only for 
climbing, as prey held at the tips of the long fingers could not be reached by 
the mouth." The authors present no evidence at all that this is true, nor do 
they inform the reader of the methods they used to determine this. To test it, 
I 
took out my articulated skeletal restoration of Microraptor and found that the 
longest fingertips can be easily brought to the mouth.

2) from page 3 "The earliest ornithurine birds resemble shorebirds and 
presumably occupied an ecological niche with few trees". The problems with 
these 
unsupported hypotheses were discussed 8 years ago by Clarke and Norell 
(Morphology and Phylogenetic position of Apsaravis ukhaana from the Late 
Cretaceous of Mongolia, AM Novitates, Dec. 27 2002). They include Livezey's 
caution that the morphological correlates of a shorebird habit are not well 
defined, and may be pelsiomorphic in modern Charadriiformes. The discovery of a 
very basal Ornithurine, Apsaravis, in the continental interior of Mongolia, 
also 
calls the shorebird hypothesis into question.

3) the one graph presented as evidence indexes degree of curvature only to the 
number of specimens. Thus, the visual separation on the graph between fossil 
and 
modern taxa is produced by the relatively smaller number of  fossils sampled. 
If 
we eliminate this axis on the graph we find that the fossil taxa group right on 
top of the modern ones, with only a slightly higher degree of curvature for the 
fossils. Moreover, the graph lumps together hand and foot claws into one data 
set. Since the fossil taxa are almost exclusively the ones with t
 group would automatically have a higher average 
degree of curvature.

Thus I don't really see any support for the hypothesis that early birds were 
adapted to climbing trees in this paper.

Also, just to nitpick, they forgot to capitalize the genus name "Microraptor" 
in 
figure 1. They wrote "a microraptor", but I learned that one should always 
write 
"a specimen of Microraptor" or else just "Microraptor".

-Jason

On Dec 17, 2010, at 1:00 AM, Mickey Mortimer wrote:

> 
> Brad McFeeters wrote-
> 
>> If the claws were used for something other than climbing, why were they lost 
>> at 
>>the same time birds developed the ability to ascend without climbing?  It's 
>>obviously not an airtight deduction, but still an interesting observation to 
>>think about, especially if the correlated claw reduction + improved 
>>backstroke 
>>evolved more than once in different bird clades (did it?  I haven't read the 
>>paper yet either).
> 
> Simply put, claws weren't lost at that point.  Compare Sapeornis' claws to 
>Eoenantiornis' and you'll see no great difference.  Both are strongly curved 
>with large flexor tubercles, yet I think the consensus is that 
>enantiornithines 
>could take off from the ground while omnivoropterygids were worse off than 
>confuciusornithids (unossified sternum, often short coracoid, etc.).  Even 
>basal 
>euornithines like Jianchangornis and Yixianornis had well developed (albeit 
>less 
>curved and smaller) claws, despite having a pectoral apparatus extremely 
>similar 
>to Aves.  In general, the claws do reduce going from Archaeopteryx to Aves but 
>there was a lot happening on that lineage besides improving the takeoff.  For 
>instance, the second digit was becoming more robust and stiffer to support the 
>primaries and the first digit was becoming reduced in size and developing an 
>alula.
> 
> Mickey Mortimer
>                           

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