[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
More on therizinosaurs
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
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.