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More on Moser and prosauropod sacrals



Following the recent brief discussion of Marcus' paper on 
plateosaur dorsosacrals, Adam Yates has asked me to fwd 
the following to the DML....

On the presence/absence of prosauropod dorsosacrals, 
Marcus wrote...

----------------------
I don't think that Adam Yates and Peter Galton will 
maintain their view.
----------------------

In response, Adam writes...

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I admire Marcus's optimism, but for the moment I'm not 
persuaded by his arguments and maintain that a dorsosacral 
is the basal condition for Prosauropoda + Sauropoda. The 
presence of a caudosacral is an unusual synapomorphy of 
Plateosaurus (and as far as I can tell Plateosaurus alone). A 
dorsosacral is most definitely present in Massospondylus (I 
am in the fortunate position of having a number of Masso. 
specimens at my disposal). Most are undescribed or 
unfigured but Cecilio Vasconcelos is working hard to 
rectify this problem (at least postcranially). Marcus himself 
has shown that the last sacral vertebra of Masso. is the 
second primordial but argues upon the basis of Cooper's 
illustrations (of a sacrum not in contact with the ilium) that 
there were only two sacral vertebrae (ie. the two primordial 
sacrals and no dorsosacral). Much better specimens at the 
BPI and SAM show very clearly that this is not the case. So 
I guess the argument will be how much of the Prosauropoda 
has a Plateosaurus-like arrangement and how much has the 
Massospondylus-like arrangement. Based on my 
observations of Coloradisaurus, Riojasaurus (there are 
better specimens than the one illustrated by Bonaparte), 
Anchisaurus and Efraasia I'd say most had dorsosacrals. 
Most of these sacra are extremely similar to that of 
Massospondylus (Anchisaurus is the odd one out with an 
unusual sacrum and consequently I'm rather less certain 
about its homologies). 

Anyway my heartiest congratulations to Marcus on a very 
thorough and valuable monograph. It contains a trove of 
information and lots of food for thought.

Cheers

Adam  
----------------------


-- 
Darren Naish
School of Earth & Environmental Sciences
University of Portsmouth UK, PO1 3QL

email: darren.naish@port.ac.uk
tel: 023 92846045
Darren Naish
School of Earth & Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road                           email: 
darren.naish@port.ac.uk
Portsmouth UK                          tel: 023 92846045                   
PO1 3QL                                www.palaeobiology.co.uk