New paper: Theropod forelimb evolution & Archie is not a "Rosetta stone"

[tijawi@yahoo.com]

Dececchi, TA and Larsson, HCE. (2009) Patristic evolutionary rates suggest a 
punctuated pattern in forelimb evolution before and after the origin of birds. 
Paleobiology 35: 1-12 


Abstract: "The evolution of powered flight has traditionally been associated 
with the origin of birds, the most successful clade of modern tetrapods, as 
exemplified by the nearly 10,000 species alive today. Flight requires a suite 
of morphological changes to skeletal anatomy to create a light vet resistant 
framework for an airfoil and advanced nervous motor control. Given the level of 
morphological integration necessary to create a suitable aerofoil, the origin 
of flight may be intuitively assumed to be coupled with high evolutionary rates 
of wing-related morphologies. Here we show that the origin of birds is 
associated with little or no evolutionary change to the skeletal anatomy of the 
forelimb, and thus _Archaeopteryx_ is unlikely to be the "Rosetta Stone" for 
the origin of flight it was once believed to be. Using comparative statistics 
and time-series analyses on a data set constructed from all known forelimb 
skeletal anatomy of non-avian theropod
 dinosaurs and a diverse assemblage of early birds, we demonstrate three 
focused peaks of rapid forelimb evolution at Tetanurae, Eumaniraptora, and 
Ornithothoraces. The peaks are not associated with missing data and remain 
stable tinder multiple perturbations to the phylogenctic arrangements. 
Different regions of the forelimbs are demonstrated to have undergone 
asynchronous periods of evolutionary peaks and stasis. Our results evince a 
more complicated stepwise mode of forelimb evolution before and after the 
origin of Aves than previously supposed."


The paper pours cold water on the centrality of _Archaeopteryx_ to the 
evolution of flight, but offers oblique support for non-avian eumaniraptorans 
being secondarily flightless.  However, I'm not exactly sure how the clades 
'Paraves' and 'Eumaniraptora' are defined here: the former is treated as more 
inclusive than the latter, and the Supplementary Material link (which the main 
text suggests might contain this info) takes me to the wrong site.

Among other things, the authors argue that the number of shared derived 
characters between small deinonychosaurs (microraptorines) and _Archaeopteryx_ 
are not so much due to flight capability but to similar prey-capture behaviors. 
 Nevertheless, the authors also claim that non-avian eumaniraptorans had 
"facultative" flight ability, which was refined later in Ornithothoraces, when 
powered light became "central" to the ecomorphology of birds.  I think this is 
the point, anyway.    


Cheers

Tim