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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.