WHERE ICHTHYOSAURS GO

[<darren.naish@port.ac.uk>]

After days and days of hard slog the final proofs for the Pal. Ass. Isle 
of Wight book are finally done... watch this space for further info. 

Jaime wrote...

>   Ichthyosaurs are like turtles, they jump around the reptilian
> tree too much, even outside it. 

To the best of my knowledge this isn't true - of the relatively few 
studies that have included ichthyopterygians (Ichthyosauria + 
Hupehsuchia) in an analysis together with other reptiles, ichthyosaurs 
are diapsids, usually neodiapsids, and either lepidosauromorphs or 
archosauromorphs (John Merck has published abstracts on the latter 
position and I hope he's working on the paper that will present the 
data). Huene, Maisch, Osborn and others have famously argued that 
ichthyosaurs are not diapsids, or even not reptiles, but these 
conclusions are not based on parsimony analyses, rather on 
consideration of a few aberrant features that are probably 
ichthyosaurian autapomorphies (e.g. robust suspensorium, infolded 
dentine). 

Likewise Nichols et al's suggestion that ichthyosaurs might be closest 
to younginiforms was based on simple comparison with the character 
lists given in Mike Benton's papers on diapsid phylogeny.

There is a nice quotation that sums up this sort of controversy in 
Farlow et al's recent _American Zoologist_ theropod locomotion 
paper. It is....

'Is it reasonable to let a phylogeny based on a large number of 
characters [to] be 'trumped' by one or a few characters seemingly at 
variance with it?' (p. 643).

DARREN NAISH 
PALAEOBIOLOGY RESEARCH GROUP
School of Earth & Environmental Sciences
UNIVERSITY OF PORTSMOUTH
Burnaby Building
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