Re: New Mesozoic bird papers (advance publication)

[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.

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 the hand claws, we might expect that the fossil 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