[Taxacom] Class Amphibia (classification)

Ken Kinman kinman at hotmail.com
Wed May 23 22:23:06 CDT 2007


Dear All,
     I have been meaning to update my classification of Class Amphibia, but 
never got around to polishing it up.  I'm sure I will want to do some 
further "tweaking" of the particulars, but in celebration of the birthday of 
Linnaeus, here is a preliminary version.  A very good reason to end my 
procrastination and get me motivated to delve into it more deeply.

     Although it has been called a "fish" and a "fishapod", I regard genus 
Tiktaalik as the earliest tetrapod and amphibian.  It no doubt did most of 
its "crawling" in shallow water (perhaps rarely onto land to escape 
predators), but it exhibits the beginnings of amphibian life (particularly 
in the morphology of the head).  As I have noted before, the loss of the 
bony gill cover (beginnings of a mobile neck) is a very important 
development that Tiktaalik displays which seems to be an excellent 
synapomorphy for separating sarcopterygian fish from amphibians (primitive 
tetrapods).  I regard the "upper" limit of Class Amphibia to be the 
development of the amniotic egg, and as I have noted here previously (2004), 
I now regard Diadectiformes as the most basal group of Class Reptilia for 
this and other reasons.  Amphibians are simply tetrapods that have not yet 
evolved the amniotic egg, and Class Amphibia is a singly paraphyletic taxon 
(truncated clade) which equals Tetrapoda minus Amniota.  Anyway, here is how 
my updated classification presently looks:

           CLASS AMPHIBIA%

1  Ichthyostegiformes%
          1  Plesion Tiktaalik
          2  Elginerpetonidae
          3  Pl. Densignathus
          4  Acanthostegidae
          5  Ichythostegidae
          6  Pl. Hynerpeton
          7  Whatcheeridae
          8  Crassigyrinidae
          9  Loxommatidae (baphetoids)
         10  {{Temnospondyliformes + "Reptiliomorpha"}}

_1_  Temnospondyliformes
  2  Embolomeriformes (anthracosaurs)
  3  Seymouriformes
  4  Pl. Solenodonsaurus
  5  Pl. Westlothiana
  B  {{Amniota}} (= Reptilia, thence to Mammalia and Aves)
  6  Aistopodiformes
  7  Nectriformes
  8  Microsauriformes%
_1_ Lysorophiformes
  2  Gymnophioniformes
  3  Urodeliformes
  4  Anuriformes
********************************
NOTES:  Two of the above Orders could well turn out to be paraphyletic:  
Embolomeriformes (Gephyrostegids and/or Chroniosuchids could render it 
paraphyletic); and also Urodeliformes (Albanerpetonids could rend it 
paraphyletic).

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