Re: ACROCORACOIDS AND REPTILE PHYLOGENY

["Matthew Troutman" <m_troutman@hotmail.com>]

<<You`re sure you want to stick with this one??? I`ve heard that the AM 
ankle was a defining Characteristic of the Ornithodirans, (ie.  
Dinosaurs, Pterosaurs, Birds, Lagosuchus, Herrerasauridae). Never heard 
of Lepidosaurs being in that group!>>

Lepidosauromorphs have an Advanced Mesotarsal ankle joint and it is a 
synapomorphy of that group according to Olivier Rieppel.  Turtles also 
show the AM joint (this is one of the characters linking turtles to 
lepidosauromorphs).  I can't remember whether or not it is of a similiar 
construction to the ornithodiran kind but if memory serves, they are an 
awful lot alike.  And nobody has ever said that lepidosaurs are in the 
ornithodiran group, everybody thinks that it is a convergence.  Whoever 
said that homoplasy is rampant sure did know what they are talking 
about.  

Anyway, on to acrocoracoids...

In the other reply to my previous post, Larry said that the presense and 
elevation of the acrocoracoid process is a sure way to tell whether or 
not various maniraptoriforms are secondarily flightless.  Fair enough, 
although I guess that _Sphenosuchus_, which is one step away from being 
a crocodile, is secondarily flightless!  The _Sphenosuchus_ coracoid not 
only shows a biceps tubercle in the theropod position, the coracoid is 
elongate in the manner of the various maniraptoriforms.  Walker (1972) 
regarded the shoulder of _Sphenosuchus_ to be very birdlike, possibly 
more so than _Archaeopteryx_!  

Secondarily flightless sphenosuchids?  Keep it coming...

Matt Troutman 
m_troutman@hotmail.com

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