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Therizinosaurs (was Vorona...)
Jaime, BJ Strata, et al.,
Yes, there is evidence of a Therizinosaur-Ornithomimid group. As a
matter of fact, Paul Sereno places them (along with Alvarezsaurids) in his
clade Ornithomimosauria. I don't like Alvarezsaurids in there with them
however (as is shown below).
Therefore Deinocheirus could be closest to ornithomimids and yet still
be fairly close to therizinosaurs as well. The similarities between
Deinocheirus and Therizinosaurus could be a form of "parallelism"
(convergence in two fairly closely-related lineages). I would think that
this "convergence" was probably due to similar feeding strategies, but one
could perhaps speculate that one of these forms was mimicking the other form
for some reason (maybe similar to viceroy butterflies mimicking
monarchs---which is a predator evasion strategy). But mimicking doesn't
seem terribly likely, and would be extremely difficult to test (but fun to
think about). Who knows.
Anyway, I like Jaime's cladistic definition of Oviraptorosauria. Shows
that he is trying to avoid the kinds of mistakes that have been made by
Sereno and others. I just hope he and Mike Keesey will continue to be a
moderating influence in the PhyloCode process, and come up with definitions
that will not have to be changed later on.
As for therizinosaurs, if Mickey's upcoming analysis shows that they
might be paraphyletic (or even polyphyletic?), I suppose cladistically
defining such a single "clade" would be premature at best. If they do form
a clade (and obviously I think that's a big "if"), I believe therizinosaurs
will end up branching off between ornithomimids and oviraptorosaurs (or even
before both of them---see below). Placing therizinosaurs and
oviraptorosaurs as sister groups just doesn't feel right to me (I tried
classifying them as sisters, and ended up going back to splitting off
therizinosaurs earlier in the tree). We shall see. Here is the topology I
am trying at the present time:
_1_ Therizinosauridae (paraphyletic??)***
3 Plesion Bagaraatan
4 Plesion Protarcheopteryx
? Troodontidae (position very uncertain)
7 Dromaeosauridae (= Deinonychosauria)
8 Plesion Rahonavis
***NOTE: If therizinosaurs are not holophyletic, some of them may move
closer to oviraptorosaurs (clade 5), and others may move closer to the base
of coelurosaurs (perhaps before Tyrannosaurids). We'll have to wait and see
if Mickey's analysis (experiment) shakes things up or not.
From: "BJ Strata" <firstname.lastname@example.org>
Subject: RE: Vorona and Sickle Claws
Date: Sun, 01 Jul 2001 00:44:30 -0600
Tracy Ford wrote:
It wouldn't surprise me that Deinocheirus was a large Therizinosaur.
IIRC, before Therizinosaurus was grouped with Segnosaurus and before
Deinocheirus with ornithomimids, these two (Deinocheirus and
Therizinosaurus) were often tentatively grouped together as strange, large
forelimbed theropods. In other words, it wouldn't surprise me either.
Related question: Is there any evidence for a ornithomimosaur +
therizinosaur group - Why/Why Not?
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