Any idea of the likely cetaecea this disc comes from? My son found it on the same beach as the two much smaller ones posted on this site before. This one is much bigger at 11cm diameter - it may have been stained brown from the peaty water that drains onto the beach in places.
Given the other two discs were identified as likely white sided dolphins - this one must surely be whale - but which one?
Interestingly I have recently gone back to all the descriptions of whale skeletons, may of them from the 1860-1890's and virtually none of them include the diameter of the vertebra or the disc plates. However, all is not lost, a juvenile minke whale has discs of between 7.5 and 11cm for the round ones (some are oval). What I cannot find out is what size pilot whale, killer whale and bottlenose whale would be; I expect them to be in this ball park.