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more debate on stems & nodes



>>While some cladists, in their youth perhaps, did name every node on their
>>cladogram, that is hardly standard practice.
>>
>Well, check out the _Marasuchus_ papers in JVP. Dinosauromorpha:
_Lagerpeton_
>+ Dinosauriformes. Dinosauriformes: _Marasuchus_ + Dinosauria. Honestly!

I never said I particularly liked those clades.  I think all that was need
was Dinosauria and Dinosauromorpha (= all taxa closer to dinos than to
pterosaurs).  In that scheme, the nondinosaurian dinosauromorphs (admittedly
a clumsy phrase) would include Lagerpeton, Marasuchus, Pseudolagosuchus, and
perhaps Eoraptor and Herrerasauridae.

[I also said 'in their youth', which I think still describes Sereno & Novas
(although they're both older than me...)].

>>As Kevin Padian & I will advocate at SVP, only robustly supported clades
>>should be named.
>
>A step in the right direction!

Thanks.

>>As deQuieroz (hope I spelled it correctly this time) and
>>Gauthier have shown, it is a simple enough (and useful) practice to name a
>>node-based clade and a stem-based clade for each robuts group.  For example,
>>for the node-based Reptilia (the most recent common ancestor of turtles,
>>lepidosaurs, and archosaurs), there is the stem-based Sauropsida.  Thus,
>>while most sauropsids are reptiles, some (e.g., mesosaurs) are not.
>
>A step backward! Now we need TWO names for each robust group? The only
>difference between node-based and stem-based definitions is the little tail
>below the common ancestor node (which never has any taxa in it anyway).

 No, no, no, the little tail often DOES have some taxa in it.

For example, mesosaurs and other traditional "anapsids" as nonreptilian
sauropsids, the 'pelycosaurs' and traditional 'therapsids' as nonmammalian
synapsids, Ouranosaurus, Iguanodon, and Probactrosaurus as nonhadrosaurid
iguanodontians, etc.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084