Re: Ornithischian clavicles

["Nick Gardner" <ratites637@hotmail.com>]

> From: Richard Butler <rbut02@esc.cam.ac.uk>
> Reply-To: rbut02@esc.cam.ac.uk
> To: <dinosaur@usc.edu>
> Subject: Ornithischian clavicles
> Date: Mon, 12 May 2003 17:01:20 +0100
>
> Hi all,
>
> Does anyone know of ossified clavicles being found in ornithischian
> dinosaurs other than Psittacosaurus, Protoceratops, Montanoceratops and
> Leptoceratops? I know that Sereno (1999, 2000), Chinnery and Weishampel
> (1998) and Xu et al (2002) code the loss of ossified clavicles as a derived
> state of the ceratopsids, yet if they are in fact absent elsewhere in the
> Ornithischia then their presence is actually a derived condition of some
> basal Neoceratopsians. Right?

Well, personally the following three things are important to note:

1) Basal ornithischians are not well-preserved enough to conclusively 
demonstrate the absence or presence of clavicles.  It is important to note 
that not all members of the most exclusive clade containg "Syntarsus" 
kayentakae, Allosaurus, Segisaurus, Carnotaurus, etc. preserve furculae, but 
they are presumed to have been present because of phylogenetic bracketing.  
It is possible that the absence of clavicles in ornithischians is due to 
early loss, but it's also possible that the structure was lost due to 
preservational forces.

2) The loss in ceratopsids is derived regardless of whether or not it's 
present in non-ceratopsian ornithischians, because it is a reversal, another 
dash-mark to separate them further from the stem.  Also, since it is not 
present in any taxa that have been hypothesized to belong to the same group, 
but are instead originally serially leading up to the Ceratopsidae, one can 
assume that the presence of clavicles can not be a synapomorphy of a clade 
containing Psittacosaurus, Protoceratops, Leptoceratops, and Montanoceratops 
to the exclusion of ceratopsids.

3) The loss of the interclavicle is simply the loss of the brace between the 
two clavicles, if I am not mistaken, therefore, it is possible that the 
clavicles were retained in the basalmost ornithischians.  Does anyone know 
if pterosaurs or sauropods retain clavicles?


nick gardner

 = = paleogeek
 = = paleoartist

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