[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Mongolian dinosaur inspires religion in grad student

Jonathan Wagner wrote (quoting Nino):

>>Do you know that nearly all of the teeth character states are the same for
>>Ornithomimosauria (not Ornithomimoidea; and you have to include here
>        The taxonomy is twisted because it is a work-in-progress...

Aren't they all?

>Tyrannosauroidea (here again, I doubt a taxon larger than a super-family is
>necessary to adequitely describe this group) plus Ornithomoidea.

Actually, by rules of Linnean taxonomy, the superfamily would be
"Ornithomimoidea" (Ornithomim- + -oidea).

>I disagree with Holtz (pers. com.), this taxon needs a name.  Of
>course, in the phylogeny I presented, this taxon recieves his name

Bullatosauria is the node-based taxon joining Troodon (or Stenonychosaurus,
as soon as a second distinct troodontid with the same tooth form is found in
the Judith River... :-() and Ornithomimus.

>        I am still unclear on how to handle the apparent "synonomy" of a
>stem-based clade and a node-based clade...

These will not be synonyms unless they use the same name.

In Phylogenetic Taxonomy (PT, to keep things quick), priority is given to
the first clear phylogenetic definition of the taxon name.  In practice,
these definitions can be stem-based (X and all taxa sharing a more recent
common ancestor with X than Y) or node-based (all descendants of the most
recent common ancestor of X and Y).  Although these might contain the same
known species, they describe different clades, and the total membership
(which may never be known, due to the spottiness of the fossil record) of
the stem-based taxon will always be larger than the total membership of any
node inside it.

Example (Gauthier et al. 1988 and others):
Reptilia is a node-based taxon joining Anapsida and Diapsida.  Sauropsida is
a stem-based taxon (reptiles and all taxa closer to Reptilia than to
Mammalia).  Although the contain, for the most part, the same members (i.e.,
most known sauropsids, and all living sauropsids, are reptiles), they are
not synonyms.  Some taxa (e.g., Mesosauridae) are sauropsids but seem to be
outside of Reptilia.

Sister taxon example (Gauthier et al. 1988, Rowe 198X):
Mammalia is a node-based taxon joining Monotremata and Theria.  Synapsida is
a stem-based taxon (mammals and all taxa closer to Mammalia than to
Reptilia).  Although all living synapsids are mammals, there are many
extinct forms of synapsids which were not mammals: dicynodonts, Dimetrodon,
Casea, etc.

>        Note that, in the above, I assume Ornithomimoidea to be "all animals
>more closely related to Ornithomimus than to Troodon or Tyrannosaurus."
>Presently, this gives Ornithomimisauria: "all animals more closely related
>to Ornithomimus than they are to Troodon",

I like this one, which I use informally (until I formally define it

>or "the most recent common ancestor of Tyrannosaurus and
>Ornithomimus and all of it's decendants."

This I don't like.

>  If the first is accepted, than it the Ornithomimisauria
>conveniently disappears into synonomy with Ornithomoidea (which,
>being an elevated family-rank taxon, should have priority) when the
>Bullatosauria excludes the Tyrannosauria.  In any case, if I can't
>do this, my public apologies to those who named these taxa.

No problem.

>>_Pelecanimimus_ for the teeth characters), Troodontidae and (I think)
>>Alvarezsauridae? Have you included _Pelecanimimus_ in your analysis?
>        But of course!  The D-shaped premax teeth of Pelicanomimus are
>probably what keeps making the ornithomims come out as sister to the
>        I do realize that these traits are found in troodontids,
>ornithomims, and alvarezsaurs (IMHO these are oviraptorsaurs anyway...).

Have you coded the maxillary and dentary tooth form yet?

>  I was trying to make a case both for therizinosaurs as
>oviraptorsaurs, and as coelurosaurs, hence the confusion (possibly I
>worded the post too confusingly, I'll have to be more careful).  In
>the phylogeny I presented, these characters end up scattered all
>about the coelurosaurs, yet many of them do show up as
>synapomorphies of the Oviraptorsaria in their current position as
>sister to the Maniraptoriforms.

As has been said before:  Homoplasy! Thy name is "Theropod"!

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

"There are some who call me...  Tim."
-- Tim the Enchanter, "Monty Python and Quest for the Holy Grail"

"Tim?!?  They called me TIM?!?!"
-- me, on seeing the credits to "The Ultimate Guide to T. rex"  :-)