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RE: New basal dinosauriform



First- YAY Nyasasaurus is finally official!  I fondly remember 
http://dml.cmnh.org/2001Aug/msg00695.html However...

Tim Williams wrote-

> _Thecodontosaurus alophos_ (named by Haughton, 1932) is referred by
> Nesbitt et al. to their new taxon _Nyasasaurus parringtoni_. So
> shouldn't the name be _Nyasasaurus alophos_...? (Unless _T. alophos_
> is a nomen nudum.)

Of course not.  Didn't Ichthyornis anceps teach you anything?  Valid names are 
those associated with more complete specimens, not those specimens which were 
named first.  The Principle of Priority is dead, which I thought you were 
pleased with. ;)

Though seriously, in this case we have a taxon diagnosed by a unique 
combination of characters, which I think is fine.  Yet of that listed 
combination, only one (hyposphene–hypantrum intervertebral articulations in the 
presacral vertebrae) is preserved in the alophos holotype.  This is because the 
only overlapping elements are poorly preserved posterior dorsals.  So we have 
two choices-

1. There are actually more recognized but unlisted characters that, in 
combination, make Nyasasaurus dorsals diagnostic, and thus it should be 
Nyasasaurus alophos.  Nesbitt et al. do state "Both share a 
hyposphene-hypantrum intervertebral articulation, and all other features of the 
vertebrae are consistent", so maybe we need to add those "other features".

2. We actually couldn't refer alophos to Nyasasaurus based on morphological 
data alone.  Nesbitt et al. state "We also argue that both the holotype and 
referred specimens of Nyasasaurus parringtoni have a similar placement near or 
within Dinosauria. Each specimen was placed into the early archosaur phylogeny 
of Nesbitt [11] and even though each specimen did not fall out in the same 
location in the resulting trees, both fell near or within Dinosauria."  The 
exact placements were Nyasasaurus was "found as the sister taxon of Dinosauria, 
as the earliest divergence of ornithischians, or as a theropod" [the latter 
actually as sister to Dilophosaurus] while alophos was "found as the sister 
taxon of Tawa hallae + Neotheropoda".  So maybe they're different.  We have 
tons of examples of contemporaneous taxa which have extremely similar e.g. 
dorsals but are distinct (e.g. many hadrosaurids, ceratopsids...).

I'm going with #2 for now, pending further study of the dorsal similarities.  
alophos is just a potential synonym of Nyasasaurus parringtoni then, much like 
explanatus and laevifrons are for Saurornitholestes langstoni.
http://home.comcast.net/~eoraptor/Dromaeosaurs.htm#Saurornitholesteslangstoni

Mickey Mortimer