Deinocheirus Again

["Jaime A. Headden" <qilongia@yahoo.com>]

Ken Kinman (kinman@hotmail.com) wrote:

<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.>

  It would be easy to test, actually, using some forms of
phylogenetic analysis, including cladistics. However, in gross
anatomy, there is no relative similarity between *Deinocheirus*
and *Therizinosaurus*. Barsbold proposed in 1976 the name
Deinocheirosauria to include *Deinocheirus* and
*Therizinosaurus* (or to be exact, their "families", but they
were both monotypic, as Segnosauria was held separately.
Barsbold's diagnosis was related to three characteristics of the
taxa: gigantic size; unreduced shoulder region; and large claws.

  It is clear the first is not useful phylogenetically; the
second is true for both ornithomimids, whereas *Pelecanimimus*
and *Anserimimus* have more maniraptoran-like shoulders, and
therizinosauroides, though they too are basally
maniraptoran-like, both groups trending from shallow
supraglenoid scapulae with cranially oriented acromion
processes, rectangular coracoids, and moderately lateroventrally
facing glenoids to ventrally facing glenoids,
triangular/dorsally elongate rectangular coracoids, acromion
process reduced and facing dorsally or absent, tall triangular
scapulocoracoid contact, and elongated scapular shaft.

  It is also more likely that *Deinocheirus* is an
ornithomimosaur more closely related to *Ornithomimus* than even
*Pelecanimimus* is, based on features of the shoulder that Pele
lacks and the lack of complete appression of all metacarpals to
each other, and that *Therizinosaurus* in comparison with
*Segnosaurus* and *Erlikosaurus* in the forelimb, is more
closely related to them, thus synonymizing Segnosauridae with
Therizinosauridae.

  There is no real way these two are any more closely related
than *Ornithomimus* and *Oviraptor* or birds are, which forms
the distinction between Maniraptora and Maniraptoriformes.

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