Diadectomorphs are reptiles

["Ken Kinman" <kinman@hotmail.com>]

Dear All,
    Another classification change which I have been contemplating for a 
very very long time (especially over the last 10 years).  Namely, whether 
diadectomorphs should be regarded as early members of Amniota (and thus 
basal reptiles).
    In 1994 I decided not to do this, and stuck with a crown group Amniota, 
but strict cladists have so totally muddled the meaning of reptile (not to 
mention amphibian) that such a small expansion of Reptilia now seems tame in 
comparison, and is well supported by various lines of evidence.  And it is 
certainly preferable to the cladistic redefinitions of Cotylosauria and 
Anthracosauria (which themselves have become muddled as well).  Even 
cladists on this list (DML) were recently criticizing the revival of 
Cotylosauria.
    The diadectiforms had a breathing system much more like reptiles than 
amphibians, they almost certainly laid primitive amniotic eggs, and there 
are several morphological characters that also support this division.  The 
amphibian Family Solenodonsauridae will now be regarded as the sister group 
of Amniota (thus making Amniota equivalent to the cladistically defined 
Cotylosauria Gauthier et al., 1988 and/or Anthracosauria sensu Laurin, 
1998).
   Therefore I will no longer classify Order Diadectiformes as the 
amphibian sister group of Amniota, but as the basal order of reptiles (and 
thus also of Amniota).  Note that I am still placing turtles 
(Testudiniformes) as "incertae sedis" next to Procolophoniformes, but only 
until it is determined to which of the diapsid orders they are most closely 
related:

CLASS REPTILIA (REPTILEA)
  1  Diadectiformes
  2  Pelycosauriformes
 _a_ Therapsiformes
 _a_ {{Mammalia}}
  3  Mesosauriformes
  4  Procolophoniformes
  ?  Testudiniformes (inc. sedis)
  5  Captorhiniformes
       ...and so on.


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