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Diadectomorphs are reptiles



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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