[Taxacom] Dawn of Birds (addendum)
kennethkinman at webtv.net
Tue Jul 28 20:00:33 CDT 2009
I just found a recently published paper (in Proc.
Natl. Acad. Sci.) which adds even more evidence to the primitive nature
of therizinosaurs among the maniraptoran theropods. Xu, Zheng and You,
2009. "A new feather type in a nonavian theropod and the early
evolution of feathers." They not only lack vaned (pennaceous) feathers
of my Class Aves, but this paper shows that they also retain an
extremely primitive, monofilamentous, type of feather.
Actually this type of feather (perhaps better called a
proto-feather) is so primitive that some researchers believe it to be
homologous with the "dinofuzz" of not only non-theropod dinosaurs
(perhaps including the common ancestor of all dinosaurs), but also
similar structures are found in pterosaurs (which are non-dinosaurs).
This feather evidence (and other lines of evidence) clearly contradicts
the widely held view among many dinosaurologists that therizinosaurs and
oviraptorosaurs form a clade "Enigmosauria".
Anyway, here is the abstract from Xu, Zheng, and You, 2009:
Abstract. All described feathers in nonavian theropods are composite
structures formed by multiple filaments. They closely resemble
relatively advanced stages predicted by developmental models of the
origin of feathers, but not the earliest stage. Here, we report a
feather type in two specimens of the basal therizinosaur Beipiaosaurus,
in which each individual feather is represented by a single broad
filament. This morphotype is congruent with the stage I morphology
predicted by developmental models, and all major predicted morphotypes
have now been documented in the fossil record. This congruence between
the full range of paleontological and developmental data strongly
supports the hypothesis that feathers evolved and initially diversified
in nonavian theropods before the origin of birds and the evolution of
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