Re: Ornithischian clavicles

[Richard Butler <rbut02@esc.cam.ac.uk>]

Points taken. 

However how is it possible to be certain that the absence of ossified
clavicles in ceratopsids is not just a preservational feature as well? I
assume that they have been coded as absent based on the fact that many of
the ceratopsid taxa are known from very complete material. If this is the
case should it not be possible to code them as absent for other very well
known taxa such as Iguanodon and Hypsilophodon? The phylogenetic bracket
would then imply absence of ossified clavicles as the basal condition for
Neornithischia at least and probably for Ornithischia (clavicles are unknown
in Thyreophora). Thus presence of ossified clavicles would be a synapomorphy
of a clade including Psittacosaurus, Protoceratops, Leptoceratops and
Montanoceratops (i.e. Ceratopsia), regardless of the fact that derived
members of that clade, the Ceratopsidae, then reverse the condition.


Rich Butler


On 5/13/03 3:27 AM, "Nick Gardner" <ratites637@hotmail.com> wrote:

>> 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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