Last week, I gave you this devilishly difficult genuine mystery object to have a go at identifying:

At first glance, it looks like it should be the occipital (the bone at the very back of the skull) of an Ostrich, or other very large bird. The bone is thin and dense (typical for a bird) and the overall shape and size looks like it might fit. However, none of the details of the bony sutures fit that possibility, for any large bird. Also, this came in as an enquiry, and was almost certaily found in Ireland, making a big bird even less likely,

With birds ruled out, I looked into the mammals. Generally it’s helpful to start with common species, to start ruling out the more frequently encountered species. There are some unfused sutures, so I began with looking at some common large mammals, keeping in mind the developmental differences that occur, making the skulls of juveniles appear quite different to adults of the same species. This is especially the case in relation to skull shape and presence of unfused sutures that can vanish in adults.

Sticking with the occipital, since the shape looks right and several people converged on the same idea (although the species suggested varied quite considerably), for me, the nuchal crest (the area of bone where the ligaments for the neck muscles attach to the back of the head) is very similar in shape to that of a sheep:

This would have been a nice and simple way to wrap things up, but unfortunately I’m still unsure. Mainly this is because the shape doesn’t match so well from other angles:

Of course, this may simply be an artefact of comparing a juvenile animal skull to an adult – so I’ll need to check with a range of specimens of different ages to be more certain.

However, there was also a suggestion of Porpoise (or other cetacean) by Adam Yates and Kat Edmonson came up with an intriguing suggestion that I am quite taken by. It is possible that the raised region is not the nuchal region at all (in Porpoises and many other cetaceans there’s actually a depression rather than a raised ridge in that area of the back of the skull), it may actually mark the junction between two very short nasal bones, a very compressed frontal region and the occipital at the back of a cetacean skull:

Just to help clarify, check out the area labelled 1, 2 and 3 in the image below:

So it may be that I was looking at the bone upside down the whole time. I’ll need to do some more comparisons to narrow down species if that is what it is, but huge thanks to Kat for getting me to see this object from a new perspective!