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



I gotta say: "Duh".

But good to see it published.

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com

-----Original Message-----
From: tijawi@yahoo.com
To: dinosaur@usc.edu
Cc: tijawi@yahoo.com
Sent: Wed, 29 Apr 2009 8:05 pm
Subject: New paper: Theropod forelimb evolution & Archie is not a "Rosetta stone"








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