RE: Megalancosaurus, Longisquama & other oddballs

["T. Mike Keesey" <tmk@dinosauricon.com>]

On Fri, 16 Mar 2001, Ken Kinman wrote:

>        I take it Merck's paper will a major in-depth analysis for
> archosauromorphs, comparable to Sereno's 1991 Memoir on Basal Archosaurs.
> Is he considering possibly including turtles in his analysis?

It would be better to do so in a major analysis of _Sauropsida_. A
cladistic analysis trying to determine where _Chelonia_ falls should allow
for both possibilities -- as relatives of _Pareiasauridae_, etc., or as
_Archosauromorpha_.

>        Don't you mean a more primitive "archosauromorph" position?  And
> either way, the question is whether taxon Ornithodira will be abandoned or
> will become much more inclusive (perhaps more so than Archosauriformes).

Yes, this is an excellent example of where PhyloCode's Article 11.9
<http://www.ohiou.edu/phylocode/art11.html> might come in handy. A good
definition of _Ornithodira_ would probably be something along the lines of
"the most exclusive subclade of _Archosauria_ (Clade(_Crocodylus
niloticus_ + _Passer domesticus_)) containing _Pterodactylus antiquus_ and
_Passer domesticus_". If _Pterosauria_ were hypothesized to be
non-archosaurian, then _Ornithodira_ would be invalidated under that
hypothesis. (Although, as per Article 11.10, it would remain an eligible
name, since there may always be some who dispute the idea that
_Pterosauria_ are non-archosaurian.)

It might be a good idea to revise the definition of _Dinosauromorpha_
(currently Clade(_Dinosauria_ <-- _Pterosauria_)), too, since it would
also greatly expand if _Pterosauria_ were not included in _Archosauria_.
Clade(_Iguanodon bernissartensis_ <-- _Pterodactylus antiquus_,
_Crocodylus niloticus_) might be better. _Pterosauromorpha_ (currently
Clade(_Pterosauria_ <-- _Dinosauria)) may need revision, too, or it might
become a synonym of _Prolacertiformes_ (has this ever been defined?)
(which already might be a synonym of _Protorosauria_).

The companion volume of PhyloCode would be a good place to possibly get
rid of _Ornithosuchia_ (Clade(_Ornithodira_ <-- _Crocodylia_)). As
currently understood, it doesn't include _Ornithosuchus_, and Article 11.8
doesn't like that one bit. Wouldn't it be great irony if the name
_Avemetatarsalia_ (proposed by Benton, an opponent of PhyloCode) were
assigned to Clade(_Passer domesticus_ <-- _Crocodylus niloticus_) instead
of _Ornithosuchia_? (And it's a more appropriate name, too.) Of course, if
_Pterosauria_ are not included in _Archosauria_, this becomes a synonym of
my proposed _Dinosauromorpha_, but I don't think that's too terrible.

(Note that I'm giving PhyloCode's Recommendation 6.1A, which suggests
italicization (or, in this case, faux-underlining) of all formal taxa
(clades & species) a whirl.)

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