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RE: FEATHERS FOR T-REX?
Ken Kinman (firstname.lastname@example.org) wrote:
<It is astounding how much new diversity has been discovered in just that
small part of the tree in just 8-9 years (confuciusornithids, Protopteryx,
Longipterygids, Jibeina, Hulsanpes, even if you don't yet believe all of
those "oviraptorosaurs" go in there as well).>
Restructuring of oviraptorid facial and palatal anatomy from the
plesiomorphic condition includings tons of features that are known in
numerous other completely unrelated animals (dicynodonts, several
_advanced_ neoavian birds, mammals proper, diplodocids, etc.) indicates
that structure anatomy in relation to particular diets may force
particular anatomical correlates. For instance, read "Savitsky, A.H. 1983.
Coadapted character complexes among snakes: Fossoriality, piscivory, and
durophagy. _American Zoologist_ 23: 397-409." Few of the particular snakes
in question are effectively related more closely because of the convergent
adaptation of dietary function of the jaws, leading doubt as to the
phylogenetic effectiveness of these types of features.
It was for these mostly functional qualities that led Novas in 1992 and
Holtz in 1994 to reclassify tyrannosaurs as coelurosaurs, even though they
were so large, because only size-related features classified the
Carnosauria. Many of these were rather distinct, including shape of the
infratemporal, and so forth. Tyrannosaurs and allosaurines are,
essentially, mesopubic in form, though intermediate coelurosaurs
(*Aristosuchus* and ornithomimosaurs) are not. Thus one should take any
set of functional complexes with many grains of salt.
<In any case, if you want to group Alvarezsaurus and mononykiforms
together, it would be better to call them alvarezsaurians. Putting them
all into one alvarezsaurid family was a mistake, and that is a bad habit
that should probably be broken as soon as possible.>
This view point will only add to the illusion that "family" means
anything phylogenetically. Problem is, Alvarezsauria is a monotypic taxon
that included only Alvarezsauridae, to begin with. Before their ancestry
was hypothesized as being of recent common descent, *Mononykus* and
*Alvarezsaurus* were each included in their own monotypic families. The
minimalist approach of the researchers in question (Novas and Chiappe
prominent among them) was to reduce this monotypy to one while still
retaining a significant onclusive taxon that could be used to "stem" the
included taxa from other such suprafamilial taxa. Hence, Alvarezsauridae
and Alvarezsauria was used for both, and Novas added *Patagonykus* between
them (phylogenetically, that is) and Karhu and Rautian created
*Parvicursor* (within Parvicursoridae) and allied it with *Mononykus*. At
this point, both Novas and Chiappe were hard at work developing analyses
testing the relationships of the group as a whole, and found through an
overwhelming complex of vertebral and even appendicular features, that
*Alvarezsaurus* was the most basal member of a clade that included
*Mononykus* to the exclusion of other sets of dinosaurs, including birds.
Chiappe et al, in 1998, added *Shuvuuia*, but this taxon only demonstrated
the following phylogeny through its inclusion:
Based on derived conditions of the tarsus, *Parvicursor* _may_ be closer
to *Mononykus* than *Shuvuuia* is to either, but this is hypothetical as
of yet, and I've not tried to test it. For such a derived group, one will
_expect_ that the most basal mameber will look less like the most advanced
and have many features of the outgroups that are _plesiomorphic_ and
effectively _root_ the group to ancestry. This is the power of cladistic
machines. They do not tell us how relationships are, they give a framework
in which to employ certain protocols of research. That's all. No one has
ever tried to say they are the final word.
But one will observe that in such a dynamic phylogeny, one must look at
ever progressively more primitive taxa to find possible outgroups and
lines of descent. In this manner, *Alvarezsaurus* is hypothesized to be
the most primitive known alvarezsaur, a group which includes *Mononykus*
as well. Without any data to the contrary, there is nothing to refute
this, and in fact this relationship has been tested in such a manner as to
be devoid of "alvarezsaur" characters (as in Xu et al., 2002, the
*Sinovenator* analysis) and still finds them group together.
Jaime A. Headden
Little steps are often the hardest to take. We are too used to making leaps
in the face of adversity, that a simple skip is so hard to do. We should all
learn to walk soft, walk small, see the world around us rather than zoom by it.
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