Irritator and Spinosaurids

[Adam Yates <zooamy@zoo.latrobe.edu.au>]

I'd like to fly an highly speculative kite for the troops to take shots at.
I've just got hold of the description of Irritator and a few points 
strikeme as very interesting. The authors note that there is a similarity 
between the teeth of Irritator and those of Spinosaurids. I was also 
struck by the similarity of Irritator to Baryonyx in gross skull shape, 
mostly the long low shape, the placement of the nostrils far back from 
the snout tip and the strong postero-lateral inclination of the ramus of 
the lacrimal that forms the preorbital bar. Perhaps Irritator is indeed a 
spinosaurid and spinosaurids are infact coelurosaurs (bullatosaurs even?) 
rather than megalosauroids.This may help explain the Baryonyx-like 
features seen in the jaw of the coelurosaur, Archaeornithoides. In the 
Irritator paper it is also noted that saggital crest on the frontals and 
parietals may have been an attachment site for an enlaged dorsal neck 
musculature designed to pull the head back sharply (as a fisheater would 
do when a fish had been caught). Might the unusal, derived necks of 
spinosaurids be adapted for the same purpose? I would further speculate 
that the small saggital eminance on the nasal of Baryonyx is part of a 
larger Irritator-like crest. Under my scheme then the Spinosaurids 
would be a Gondwanan radiation (with some incursions into Laurasia) of 
large piscivorous coelurosaurs , possibly bullatosaurs, characterised 
by long low heads, strong necks for pulling the head backwards and 
conical unserrated teeth. 
Of course the similarities between Irritator and Spinosaurids may be 
due to convergence caused by a similar piscivorous lifestyle. 
Hopefully the new Spinosaurus material will provide the answers.

Adam Yates