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DIAPSID ICHTHYOSAURS



The latest issue of _Lethaia_ has a new ichthyosaur paper 
that I haven't seen mentioned here (apologies if it has been.. 
the search engine at the archives isn't working right now).

Maisch, M. W. & Matzke, A. T. 2002. The skull of a large 
Lower Triassic ichthyosaur from Spitsbergen and its 
implications for the origin of Ichthyosauria. _Lethaia_ 35, 
250-256.

The specimen concerned is from the Sticky Keep Fm (??) - 
this is Spathian in age - and represents the largest Triassic 
ichthyosaur yet reported (the Sikanni giant from British 
Columbia has certainly been 'reported' but not scientifically 
described). The specimen is not new; it was discovered in 
1969 and described (briefly) and figured by Mazin (1981, 
1982). 

What is most significant is that it preserves the caudoventral 
part of the cheek, demonstrating that the animal was diapsid 
in construction. Maisch and Matzke conclude that the 
evidence now favours placement of ichthyosaurs within 
Diapsida but they argue that the debate is still not over as 
there are no known diapsids that appear to be suitable 
ichthyosaur ancestors (they may or may not mention 
hupehsuchians: I haven't yet read the whole paper). This is 
significant because Maisch has previously argued strongly 
against the idea that ichthyosaurs are diapsids, favouring for 
them a basal reptile position instead. See in particular....

Maisch, M. W. 1998. The temporal region of the Middle 
Jurassic ichthyosaur _Ophthalmosaurus_ ? further evidence 
for the non-diapsid cranial architecture of the Ichthyosauria. 
_Neues Jahrbuch fur Geologie und Palaontologie, 
Monatshefte_ 1998, 401-414.

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

email: darren.naish@port.ac.uk
tel: 023 92846045