More on therizinosaurs

[gpb6845@msu.oscs.montana.edu]

Two more points I'd like to put in.

Where the heck is the parasphenoid?  Again, Clark et al state that about five 
different braincase bones are totally fused and their sutures totally 
unrecognizable, the parasphenoid and basisphenoid among them.  In the section 
on the braincase they talk about the cultriform process of the parasphenoid.  
In the accompanying photograph, their is a palatal view of Erlikosaurus' 
skull showing the fused braincase and the cultriform process (The cultriform 
process is that spike-like projection in the front of the braincase going 
between the vomers) with a "break line".  Now, this can mean a couple of things:
1. The entire paraspenoid has been reduced to the cultriform process and is 
        unfused to the rest of the braincase.
Unlikely.  This is unlike any other dinosaurian braincase and is illogical.  
Why would you have a rock-solid braincase and then a spike shaped thing 
wiggling around in your head.
2. The parashenoid has migrated somewhere that it can't be seen and the 
        basisphenoid has developed a process that is remarkably similar if not 
        identical to the cultriform process on the parasphenoid and the 
        "break line" was caused after death.
Unlikely.  The amount of convergence required is unreal.
3. The parasphenoid is part of, if not most of, the bulbous fused braincase 
        and the "break line" was caused after death.
Likely.  This makes the braincase remarkably similar to the condition seen in 
bullatosaurs.

The foot thing.  I am not pretending to offer an explanation as to why 
therizinosaurs got their four toed feet, but I can try to explain why they 
look so much like prosauropods'.  Take a look at a small or juvenile 
prosauropod's foot.  It is remarkably similar to Herrerasaurus'.  Perhaps the 
similarity to prosauropod feet has to do with reverting to a Herrerasaur 
style foot and then getting heavier (Alxasaurus, although small, is still a 
great deal larger than Herrerasaurus) making their feet more similar to those 
of bigger prosauropods.

Peter Buchholz
gpb6845@msu.oscs.montana.edu

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