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spinal cord morphology




Darren Naish - via Jerry Harris writes:


>>"Woodbury's work on spinal cord morphology in birds has rightly been
getting a lot of interest recently, and his new paper in _Proc. R.
Soc._ (Woodbury 1998) brings it all together in a very nice review.
Basically, birds have two spinal cord morphologies - the primitive
leiocerate morphology (where cutaneous nerves in the dorsal horn form
only a single map of the body surface), and the unique schizocerate
morphology (where there are two maps side by side). Leiocerate is
primitive (it's, I think, the ordinary tetrapod condition), and is
seen in palaeognaths as well as some gruiforms, pigeons, cuckoos,
piciforms (other than puffbirds and jacamars) and passerines! (The
hoatzin is not a cuckoo). Woodbury argues that these groups therefore
evolved before schizocerate birds, and therefore passerines and other
leiocerates are relatively primitive in the Aves (sensu Gauthier)
tree: as Woodbury notes, this is an accord with some molecular data
(e.g. Mindell et al. (1997)) where passerines also come out as
'primitive' birds."<<<

Having read the paper by Woodbury on spinal cord morphology - this is a
great paper, it describes in detail _one_ character that will be of use
to studies of avian phylogeny - BUT it is just that, ONE character -
this on its own does not provide any tangible evidence for the
production of an evolutionary scenario- cleary the contention that, for
example, passerines are "primitive birds" will need to be tested within
the context of a character analysis that contains more than just one
character. As such, the result produce may simply be a single incidence
of homoplasy -  

Gareth
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Gareth J. Dyke
Dept of Earth Sciences
University of Bristol
Wills Memorial Building 
Queens' Road
Bristol BS8 1RJ UK

www: http://palaeo.gly.bris.ac.uk/

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