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

Re: Senter et al. 2004 impressions



Tim Williams wrote-

> >While I'm not sure if I agree Incisivosaurus and Protarchaeopteryx are
> >sister taxa, note that they were run as a single OTU, and relevant taxa
> >like
> >Avimimus and Nomingia were not included.
>
> Therizinosaurs are also not included, and these could be important since
the
> skull of _Incisivosaurus_ in many ways looks like a cross between
> _Erlikosaurus_ and _Caudipteryx_.

True.  Senter et al.'s dissertation includes Avimimus and three segnosaurs
however, and (though with a different character set) segnosaurs are basal
arctometatarsalians and Avimimus the sister clade to Oviraptoridae.  The
topology of mutually shared taxa is the same.

> >Senter et al. also have a discussion of support for neoflightless
> >dromaeosaurids.  Of the five characters they examine, at least three seem
> >ill-suited for a judgement based on parsimony when other characters are
not
> >taken into account.  These are asymmetrical remiges, enlarged humeral
> >diameter and elongate penultimate pedal phalanges.
>
> Something I had overlooked: The distal displacement of metatarsal I, a
> character associated with climbing (scansoriality), is also seen in
> _Bambiraptor_, as well as microraptorians and birds.

Senter et al. discuss that character too, and find it equally parsimonious
as a symplesiomorphy lost in dromaeosaurids or a convergence in
microraptorians and birds.  I didn't mention it because at least some
neoflightless birds retain the distally placed hallux, so it may indeed be
well suited for independent judgements of parsimony.

> I wonder how many extra steps is required to put _Bambiraptor_ in the
> Dromaeosauridae (sensu Senter et al.) and remove it from the
Microraptoria?
> I mention this because the phylogeny of Senter et al. (2004) regards
certain
> features associated with aerial locomotion evolving *twice* as the most
> parsimonious explanation for the distribution of these features.  But if
> _Bambiraptor_ were to jump over to the Dromaeosauridae, then the most
> parsimonious explanation would be that these characters would be primitive
> (plesiomorphous) for Paraves, and secondarily lost in the dromaeosaurids.

So do I.  Unfortunately, I haven't constructed a NEXUS file from their data
yet to test such things.  A small nit-pick- Senter et al.'s Dromaeosauridae
is Padian et al.'s (1999), so would exclude Bambiraptor if the topology was
(Micro(Bambi(Veloci,Drom))).  Good observation though.  Parsimony is a
fickle mistress... or something to that effect.

> One potential complication is that the holotype for _Bambiraptor_ is an
> immature individual, and this may be pulling this taxon into the
> Microraptoria - especially if (and this is a big "if") certain
> microraptorian characters are pedomorphic.

Very true.  Just think of how juvenile tyrannosaurids differ from adults
(Carr, 1999; Currie, 2003) and how much this could screw with matrices.  You
can't even purposely exclude immature individuals, since we usually don't
know the ontogenetic stage of any given specimen.

> The Jiufotang microraptorians appear ripe for a morphometric study, along
> the lines of the allometric analyses done for the _Archaeopteryx_
specimens
> (e.g., Houck et al., 1990; Senter and Robins, 2003).

Sounds interesting, though one would want access to the unillustrated M. gui
specimens to increase the sample size.  Then there's the lack of many
measurements for Cryptovolans, and the difficulty in using Czerkas et al.'s
figures for such.  But assuming these problems could be overcome, it would
be a great project.

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html