[Taxacom] Recoding diapsid reptiles (revised placement of turtles)

[Kenneth Kinman]

Dear All, 
      Since I last updated my classification of Class
Reptilia in 2007, a couple of relevant papers have been published which
indicate some coding changes are needed in my phylogeny of Subclass
Lepidosauria. Also note that I have now added three problematic genera
(Plesia Galesphyrus, Claudiosaurus, and Heliosaurus) between Apsisaurus
and Younginiformes. 
      The far more important (and cladistic) change is that
the turtles (Order Testudiniformes) are most likely a sister group of
Order Sauropterygiformes. This is supported by the analysis in a
November 2008 paper (in the journal Nature) which described a primitive
Triassic "toothed" turtle named Odontochelys. Then there is a very
recent paper by Werneburg and Sanchez-Villagra, 2009, entitled "Timing
of organogenesis support basal position of turtles in the amniote tree
of life". It indicates that turtles split off before the tuatara-lizard
clade. 
       The latter finding conflicts with the paper by
Shedlock et al., 2007 (in Proc. Natl. Acad. Sci.), in which molecular
data indicated turtles were closer to Archosauria than the
tuatara-lizard clade. However, there is other morphological data in the
literature which agrees with Werneburg and Sanchez-Villagra's
conclusion, so I am now thinking that Shedlock's molecular analysis must
have had some problems (such as long branch attraction?).                 
     Therefore, I am now coding a revived euryapsid clade (Clade
7 below) including ichthyosaurs, sauropterygians, and turtles. This
would mean that the ancestors of turtles had already lost one of the
temporal fenestrae (thus euryapsid), and turtles just simply lost the
other one.  One could argue that the Werneburg paper also supports the
hypothesis that turtles are true anapsids (my Subclass Cotylosauria)
after all.  However, I still lean toward the hypothesis that turtles are
indeed diapsids that are secondarily anapsid (evolving from
intermediate, euryapsid ancestors).            
        ---------Cheers,
                        Ken
Kinman        


    LEPIDOSAURIA% (basal diapsids)
           1 Araeosceliformes
           2 Plesion Coelurosauravidae
           3 Plesion Apsisaurus
           ? Plesion Galesphyrus
           4 Plesion Claudiosaurus
           5 Plesion Heliosaurus
           6 Younginiformes
           7 Ichthyosauriformes
           ? Thalattosauriformes
           B Sauropterygiformes
           C Testudiniformes (turtles)
           8 Eolacertiliformes 
           B Sphenodontiformes (tuatara)
     
           C Squamatiformes (lizards, etc.)   
       
           9 Choristoderiformes
          10 Trilophosauriformes
           B Rhynchosauriformes 
          11 Protorosauriformes (prolacertiforms)  
          12 Proterosuchiformes% 
         _a_ {{Archosauria}}