Phalacrocorax Skulls, lack a foramen?

 I'm working on developing the extent of how much an observation I made is true; that Phalacrocorax skulls lack a foramen that other cormorants tend to have. Some individual specimen of non-Phalacrocorax species also lack this opening, so it wouldn't be true that the lack of a pronounced foramen confirms that a skull is Phalacrocorax, only that the presence of a forman excludes Phalacrocorax. 

(from https://www.flickr.com/photos/jrochester/15996283568/in/album-72157651043869057/)

The European Shag is now classified as Gulosus aristotelis. It has a very pronounced foraman, where the Great Cormorant does not. 

Phalacrocorax skulls:

Phalacrocorax auritus:

From https://collections.nmnh.si.edu/search/birds/?ark=ark:/65665/30edc701b00174dc28a138d9f41032441

From https://virtual.imnh.iri.isu.edu/Osteo/View/Double_crested_Cormorant/570

From http://shearwater.nl/index.php%3Ffile=kop83.php.html

Phlalacrocorax carbo:

From https://www.biolib.cz/en/image/id32230/

And... oh...

I had a lot more for this planned, but this seems to of quickly warped things up:

From https://www.flickr.com/photos/wessexarchaeology/24975074255/

A nice great cormorant with a huge foramen. Turns out I was totally wrong. I was sort of researching this as I was making it. This post was kind of useless but I'm going to keep it up for personal reference.