Class Scorpionea (was: Megarachne reclassified)

Ken Kinman kinman2 at YAHOO.COM
Thu Feb 17 22:27:11 CST 2005


Dear Victor,
      Yes, I am sure many do still think that way, due to Shultz, 1990, and his so-called cladistic analysis.  Even in 1994, it was apparent to me that it was riddled with homoplasies (and/or plesiomorphies) masquerading as synapomorphies.  The requirements for terrestrialization clearly led to a number of major convergences (or call them parallelisms if that makes you feel better) in the scorpions and arachnids.  Due to terrestrial-induced homoplasy, even Arachnida without the scorpions could be polyphyletic (although I personally doubt it).

      Shultz also didn't have access (nor did I in 1994) to a lot of new fossil data discovered in the late 1990's.  The case for a Class Scorpionea (eurypterids plus scorpions) continues to get stronger, and the analysis of Shultz (1990) looks more like a homoplastic mess as time passes.  A good place to start is Dunlop and Webster, 1999 (Journal of Arachnology, 27:86-93).  Scorpions are NOT derived arachnids, and the absolute best you could hope for is that they are basal arachnids (but that would almost certainly make Eurypterida paraphyletic).  Either way, strict cladists are fighting a losing battle on this one.          ---- Ken Kinman
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Victor Fet wrote:
No, it should not...
Class Eurypterida is usually believed to be a sister group of Class Arachnida in Subphylum Chelicerata.  The relationship of Eurypterida and the arachnid order Scorpiones is a controversial subject, the jury is still out on it.  Many think that scorpions are a derived arachnid group, and have little to do with extinct "sea-scorpions" (Eurypterida).




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