[Taxacom] Homalozoan classification (still stem-group echinoderms?)

Ken Kinman kinman at hotmail.com
Wed May 2 22:33:33 CDT 2007


Dear All,
      Today I have done some additional reading on recent research in 
echinoderm paleontology, and there seems to be a possibility that Class 
Edrioasteroidea split off before (not after) Class Crinoidea.  In other 
words, edrioasteroids would not be eleutherozoans or even within crown group 
echinoderms.

      If I find this idea to be probable after delving into it further, I 
might well expand Class Homalozoea to include edrioasteroids as well.  This 
would almost certainly also bring Order Arkaruida (of the Upper PreCambrian) 
into this stem-group taxon, and this would make more sense 
chronologically----Homalozoea beginning in the Upper PreCambrian, and crown 
group echinoderms arising from them around the time of the 
PreCambrian-Cambrian boundary.  Very interesting that both stylophorans and 
edrioasteroids lasted until the Carboniferous, and I can't help but wonder 
if one or both of these groups may have made it into the Permian.  Anyway, 
stay tuned for a possible further expansion of Class Homalozoea.
     ------Cheers,
              Ken Kinman
**********************************
>From: "Ken Kinman" <kinman at hotmail.com>
>To: taxacom at mailman.nhm.ku.edu
>Subject: [Taxacom] Homalozoan classification (still stem-group 
>echinoderms?)
>Date: Wed, 02 May 2007 02:23:56 +0000
>
>Dear All,
>      Due to the continued bitter controversy over homalozoans (early
>echinoderms or early "carpoid" chordates?), I haven't really been inclined
>to attempt an updated classification since my 1994 book.  However, I have
>seen nothing since that changes my mind about them being stem-group
>echinoderms.
>
>      Among those who do regard them as stem-echinoderms, there is a 
>growing
>consensus that homalozoans are a paraphyletic taxon.  In 1994 I classified
>Class Homalozoea (sensu stricto) as separate from Class Helicoplacoidea, 
>but
>it is now pretty clear that even Class Homalozoea (sensu stricto) is still
>paraphyletic, so I am going to now formally recognize (and code) them as
>such (including helicoplacoids as derived members that are sister group to
>crown group echinoderms).
>
>      I am also adding the more recently discovered Order Vetulocystida at
>the base of Class Homalozoea.  I am still including Cambroclavida (incertae
>sedis) even though some workers now place them near acanthocephalans (not
>echinoderms).  I don't think anyone really knows where cambroclaves will 
>end
>up.  However, I am going to now omit the problematic Order Cymbionitida
>(haplozoans), because they probably fit better in with my broad Class
>Crinoidea (including blastozoans).  Whether a broad Class Crinoidea is
>holophyletic is something I will have to tackle next.  Anyway, here is my
>updated and recoded classification of Class Homalozoea (including
>helicoplacoids, but excluding haplozoans):
>
>           PHYLUM ECHINODERMATA
>
>1  Homalozoea% (Cambrian-Carboniferous)
>       1  Vetulocystida
>       ?  Cambroclavida (affinities very uncertain)
>       2  Stylophorida
>       3  Solutida
>       4  Cinctida
>       5  Ctenocystida
>       6  Helicoplacida
>       B  Polyplacida
>       7  {{crown group echinoderms}}
>
>_1_ Crinoidea
>2  Edrioasteroidea
>3  Asteroidea, etc.
>-----------------------------------
>NOTES:  Cinctida and Solutida are here no longer considered sister taxa,
>although they are closely related and still form an informal paraphyletic
>grouping.  Also note that "Heterostelea" might belong in Homalozoea, but I
>am still betting that they will end up in one of the crown group classes.
>As always, I am open to suggestions, especially relating to such
>controversial fossil problematica.
>       ----Ken Kinman
>
>_________________________________________________________________

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