IRRITATOR SKULL AGAIN

[darren.naish@port.ac.uk]

Jaime Headden made some interesting observations on spinosauroid 
skulls. Thought you might be interested in some of my comments.

I've personally examined the holotype specimen of _Irritator_ (as 
well as the type specimen of _Baryonyx walkeri_ and various 
_Spinosaurus_ material in private collections), and I'm sitting here 
with a load of high-quality close-up photos of the specimen. 

Before I start, I would like to point something out: of the many 
artistic restorations I have seen of the skull of _Irritator_, pretty 
much all of them make it look like _Irritator_ was a small animal. 
Look at the size of the eye in restorations by Pete Buchholz, Brian 
Choo and others: _Irritator_ seems to be drawn as if its head was 
about 15 cm long. I presume this is because of Martill et al.'s 
incorrect early classification of _Irritator_ as a bullatosaur: the 
temptation may then be to make _Irritator_'s head of about the same 
size as that of most troodontids and ornithomimosaurs. Well, the news 
is IRRITATOR IS HUGE. It's skull is actually about 80 cm long, and 
may have been even longer (as the snout tip is unknown).

It's a shame photos of the skull as it looked when first discovered 
have not been published: with its elongate, laterally compressed 
snout-tip the skull looked even more bizarre than it is (and 
strikingly pterosaurian:)).

Jaime writes...

> Nonetheless, *Irritator*'s skull appears to have been crushed
> posteriorly, making the rear of the skull very
> fragmentary, even the quadratojugal is missing, and
> the quadrate is anteriorly displaced, being upswept
> into the orbital space. 

The skull is currently being prepped, and the back of it is actually 
not in bad shape at all. The quadratojugal is not missing (at least 
not on the left side): it is just that in the published photos it is 
obscured by matrix. Neither quadrate is 'upswept into the [orbit]', 
I'm not sure why you say this. 

> there's a process posterior to the orbit and crest that is
> probably the paroccipital process or squamosal, and
> this suggests the skull is much longer than Martill et
> al. illustrated. 

The skull does not extend caudally beyond what has already been 
figured. The big lump caudal to the orbit (in Martill et al. 1996) is 
probably the squamosal. It has some interesting features.. you'll 
have to wait till publication of the new monograph.

"Then you will know that you can call the girls round"

DARREN NAISH
darren.naish@port.ac.uk