Last week I gave you this mystery object from the collection of the late Dr Don Cotton to have a go at identifying:
It led to some really interesting discussion in the comments, which converged on this being a whale vertebra. More exactly, one of the cervical (neck) vertebrae from the neck of a smallish to medium-sized whale.
Whale necks are very short and the bones are a bit odd, as in they can be fused together in the adults and sometimes in juveniles (but not always), and depending on the species they might not fuse at all. This one is not fused, but you can see facets just above the solid centrum section, where the vertebra in front of this one would have snugly nestled.
It looks like the lateral processes (bits that stick out to the side) that would have extended from the facets, but have broken off, presumably due to the action of the waves on the shore where this specimen washed up. This makes it even harder to identify which of the cervical vertebrae this is or the species that it came from. However, the squared centrum and spur-like lower processes make me think that this is probably from one of the cervicals nearer the thoracic (chest) region – my guess would be cervical number 6 (cervical 7 often lacks the lower processes while 3,4 and 5 tend have better developed lower processes).
In the comments the discussion focussed on large dolphins, like the Beluga or Narwhal, but the shape reminds me more of the cervicals I’ve seen from baleen whales like the Fin Whale, although the size is all wrong. However, there is a much smaller member of the Balaenoptera species complex that inhabits Irish waters: the Northern Minke Whale Balaenoptera acutorostrata Lacépède, 1804 – which is what I think this mystery object probably came from.
I could be wrong and this could possibly be from a large dolphin that occurs around Ireland, like an Orca or Long-finned Pilot whale, but these have extensive fusion of the neck vertebrae, so I’m going to stick my neck out with the Northern Minke.
Northern Minke Whales are well documented in the waters around Ireland, especially during the spring and summer months. Don Cotton was a founding member of the excellent Irish Whale and Dolphin Group, which is the source of much of the information we have about the occurrance of these otherwise enigmatic animals in Irish waters.
Zygoma 
O.k., that’s a possibility I hadn’t thought of! Looking around the WWWeb, I found a couple of photos of what were claimed to be (articulated series of) Minke whale cervicals: photographed from above and from below, making it a bit harder to compare…
(i) They seem to have very prominent lateral processes (that’s a description: I don’t know what the anatomical term would be), extending about as far out from the centra on either side as the centra themselves are wide. Seen from above or below, however, these look like very thin and delicate laminae: the sort of thing that could easily break off if the vertebra spent any significant time rolling around in the surf.
(ii) seen from above, there seems to be some fusion (particularly between c3-c4-c5), but little enough that the individual vertebrae are still readily distinguishable: something that is not the case in adults of some Cetacean species. A full-sized adult Minke, however, is a good deal larger than a Beluga or Narwhal, so — if fusion is something that happens over time — this is compatible with Don Cotton’s specimen being from a subadult. (It’s been a good decade plus since I last had a chance to look at Rorqual cervicals, and I don’t remember what degree of fusion they are supposed to have…)
(iii) the neural spines seem a bit big (wider in a fore-and-aft direction) compared to the vertebra Paolo has showed us, but it’s hard to be sure with this camera angle. Any chance of a photo from above?
(And… Thanks for this specimen: I feel I’ve learned from the discussion even though I’m not yet fully confident of the identification!)
On the other hand, geography: I think Belugas and Narwhals would be a lot less likely than Minke in the waters around Ireland.