

Sharovipteryx an ornithodiran??

T. Michael Keesey wrote:
CMIIW, but don't both the ornithodiran archosaur and the
prolacertiform hypotheses advocate _Sharovipteryx mirabilis_ as a
pterosaur sister taxon?

Tim Williams wrote:
You know, I'm not sure. I don't even know if _Sharovipteryx_ is an ornithodiran.


There are no 'Ornithodirans.'  

There are dinosaurs and there are crocodiliforms (Scleromochlus nests here) and 
together they comprise the sum total of the Archosauria (birds + crocs). 
Pterosaurs and Sharovipteryx are way off yonder in lizard land where the 
lateral digits are not reduced, there is a big sternum, the pubis and ischium 
are fused and short (Cosesaurus and succeeding taxa), the hemal arches are 
reduced and the legs are always bowed. Lots of convergence, including the 
antorbital fenestra and elongated ilium (phylogenetically way before the same 
shows up in dinosaurs, by the way) -- but basically different. 

No one has done a cladistic analysis of Scleromochlus and included 
crocodiliforms before. Sclero turns out to be close to Gracilisuchus, just a 
step away from the most basal crocs -- and therefore very close to the most 
basal dinos.

Only Benton 1985 tested pteros with lizards and dinos and found the first two 
to be sister taxa a few branches away from _any_ archosaurs. Everyone since, 
including Benton, has stopped looking at lizards. I don't know why. Perhaps 
it's the influence of Gauthier 1986. That's the problem with following, rather 
than testing, the literature.

Taxon exclusion is the biggest source of problems with reptile phylogeny. The 
average of 40 cladograms in amniote studies has about 14 taxa. So you can see 
the problem. Lots of nestings by default (because PAUP nests everything). In 
summary, we've seen the metaphorical trunks, tail and ears, but we have yet to 
see the whole dang thing at once. A big cladogram would solve that problem. 

David Peters
St. Louis

PS If anyone is interested in the other half of Longisquama, plus detailed 
drawings of the skull and forelimbs, plus a hypothetical answer to the origin 
of flapping flight based on a _series_ of real taxa (not Rupert Wild's 
imaginary colugo-lizard), it's in the latest Prehistoric Times --  where color 
doesn't cost extra. Next issue includes the skull and forelimbs of 
Sharovipteryx. The skull was there all along, and I overlooked it a hundred 
times. It's extremely thin and diagonally smashed into the matrix. Even the 
pineal opening is preserved. But it's all there.