Message 2003-02-0011: Re: Therizinosaur Nature

Sun, 02 Feb 2003 17:42:36 -0800 (PST)

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Date: Sun, 02 Feb 2003 17:42:36 -0800 (PST)
From: "Jaime A. Headden" <>
To: List PhyloCode <>
Cc: Stephan Pickering <>
Subject: Re: Therizinosaur Nature

Stephan Pickering ( wrote:

<In particular, the "therizinosaurs" are long-necked, poorly known
theropods of uncertain taxonomic position within the converted clade name
Coelurosuria. Thomas Holtz's 2000 and 2001 theropod taxonomies were unable
to resolve their synapomorphies (Therizinosaurus itself is barely
diagnostic if one ignores the suite of characters found in other, more
complete taxa).>

   This ignores about 10 years of phylogenetic analysis. Holtz's work had
placement problems by one node or two, buyt always within
Maniraptoriformes. Sereno found them to be ornithomimosaur relatives (as
Ornithomimoidea) and thus arctometatarsalians along with alvarezsaurs
(though they lack the features which unite alvarezsaurs and
ornithomimosaurs) and Xu et al. always found them as the sister group of
oviraptorosaurs. This is hardly "poorly known theropods of uncertain
taxonomic position within the converted clade name Coelurosuria."

   Holtz had difficulty diagnosing the clade aside from its autapomorphies
on the basis of variability of its position and an admittedly brief,
Theropoda mainly set matrix. That of Sereno was the first to explicitly
look for shared features with other coelurosaurs, and most of these were
with ornithomimosaurs, though some have criticized Paul for "looking too
hard at ornithomimosaurs." I don't entirely agree. However, only the
recent work with the Theropod Group Working Matrix (people at Yale, the
AMNH and the IVPP, along with the LACMNH all contributing) has included
many features of both ornithomimosaur similarity and maniraptoran
similarity. The diagnosis of Therizinosauria (or Segnosauria) is rather
extensive, and depends largely on the basal features of *Beipiaosaurus*
known in all other segnosaurs for which the anatomy is known. This is
primarily found in the ankle (which Stephan should be well familiar with)
and the wrist. Though some avetheropods, such as *Acrocanthosaurus*, have
similar wrists and metacarpal proportions, the humerus is diagnostic to
segnosaurs, as are the gross claw morphology, and some of the features of
the arm and leg are seen also almost exclusively in oviraptorosaurs.
Discovery of *Incisivosaurus* increases the features into the jaw.


   Jaime A. Headden

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.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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