Re: Taxonomy (was Re: Fixing dinosaurian carnivour question)

[Stanley Friesen <sarima@ix.netcom.com>]

At 10:36 PM 6/5/99 -0400, T. Mike Keesey wrote:
>On Sat, 5 Jun 1999, Stanley Friesen wrote:
>
>> At 01:14 AM 6/2/99 -0400, Dinogeorge@aol.com wrote:
>> >As >orders< I would make the basic groups of dinosaurian discourse,
namely, 
>> >Theropoda, Sauropoda, Ankylosauria, Ceratopia, Ornithopoda, Stegosauria, 
>and 
>> >such.
>
>What happens to pachycephalosaurs,

These might be an order of their own, or be a suborder in an inclusive
Marginocaphalia.

> heterodontosaurids, basal
>marginocephalians,

Depending on where the partition is made, these would  go in a paraphyletic
Ornithopoda, or a paraphyletic Fabrosauria (erected to receive basal
ornithischians) or I might actually make Marginocephalia the order, and
treat Ceratopsia, Pachycephalosauria, and maybe Heterodontosauria as
suborders within that order.

[On my Web page I am currently using a mixture: I have a Fabrosauria for
the basal ornithischians, and I also treat Marginocephalia as a single
ordinal level group].

> _Scutellosaurus_, _Scelidosaurus_, _Emausaurus_,

I would either treat them as basal ornithischians (Fabrosauria or an
enlarged Ornithopoda), or I would put them in Stegosauria/Ankylosauria.
[Currently on my Web site I place the first and third of these as basal
ornithischians, and I place Scelidosaurus with the armored dinosaurs.

>non-genasaurian ornithischians ("fabrosaurs"),

Same place as all other basal ornithischians, either in their own order, or
in Ornithopoda.

> "prosauropods", and others
>not included in the above six?

Prosauropods are a suborder of the Sauropoda sensu lato (maybe called
Sauropodomorpha).


One of the basic requirements of a "linnaean" system is that one subtaxon
of each higher taxon be designated as containing the basal members of the
higher group.  

Currently I treat Theropoda as including basal dinosaurs and basal members
of Clade Saurischia (and within that, I use Herrerasauria for the basal
members).

I use Fabrosauria for basal ornithischians, and Prosauropoda for basal
sauropodomorphs, and so on.

[I do not currently have a well-defined taxon for basal marginocaphalians,
since if found they would likely not fit well within either basal
Ceratopsia (Psittacosauridae) or basal Pachycephalosaura
("Chaoyoungosauridae" or Homalocephaleridae)].
>
>> >These would be grouped into superorders and so forth at one's 
>> >discretion.
>> 
>> Yep.  That is indeed why I would make Saurischia/Ornithischia superorders.
>
>There go Genasauria, Thyreophora, Cerapoda, and Marginocephalia.

Perhaps.  The exact relative ranking is a bit tricky.  I currently use
Marginocephalia and Thyreophora as basic taxa.


One of the keys to this sort of classification is to choose to formalize
those taxa that are most *informative*, and leave other clades out of the
system (though still having names for them as *clades*).

It was in measuring the informativeness of a given taxon that Ashlock's
work was pioneering.

--------------
May the peace of God be with you.         sarima@ix.netcom.com