RE: New paper on Neoaves

[Christopher Taylor <gerarus@westnet.com.au>]

>>Or maybe Amphioxus isn't a chordate.

>That's a tough sell.  Notochord, pharyngeal slits, myotomes...?

    These characters may be ancestral for deuterostomes - as
demonstrated by the fossil record and morphology of modern taxa. The
notochord of chordates may be homologous with the stomochord of
hemichordates and even the hydrocoel of echinoderms (Heinzeller & Welch,
1999). The 'tail' of homalozoans has a central canal which some authors
have interpreted as housing a notochord. Hemichordates possess
pharyngeal slits (multiple slits for enteropneusts, one pair for
_Cephalodiscus_ and a single unpaired slit for _Rhabdopleura_). Muscle
blocks are present in fossil Vetulicolia and Yunnanozoa, which may lie
outside the deuterostome crown group (Shu, Conway Morris et al., 2001).
    True, these points are contentious. Some would see the central canal
of the homalozoan appendage as an ambulacrum, not a notochord. The
'muscle blocks' of Vetulicolia may be arthropod like segments. But my
point is that supposed 'chordate' features being plesiomorphic for
deuterostomes as a whole is not irreconcilable with morphology at
present.

    Cheers,

        Christopher Taylor

PS. You know, I wrote a lot more on this subject on Palaeos, but the
website appears to have finally been taken down and I don't have a
backup copy of my pages there. Grumble....

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