I was reading through the Chronicle of Ireland and came across an interesting story in the entry for 744:
A strange sign was revealed in Bairrche in the time of Fiachna son of Áed Rón, king of the Ulaid, and in the time of Eochu son of Bresal, king of Uí Echach, that is a whale which the sea deposited on the land, and there were three gold teeth in its head, and 50 ounces [of silver] was the value of each tooth, and one of the teeth was taken and remained upon the altar of Bangor for a long time.
The surviving Irish annals (such as the Annals of Ulster) are thought to have derived from a common source, the so-called ‘Chronicle of Ireland’. The annal was kept first on Iona, an island off the west coast of Scotland, then moved to Brega in eastern Ireland. After 911 it split into several daughter annals. Thomas Charles-Edwards has reconstructed the Chronicle of Ireland based off of these other chronicles.
This entry, however, does not appear in all of these daughter annals – only in the set of annals known as the Clonmacnoise group. Clonmacnoise was another important monastery in early medieval Ireland. The chronicle at Clonmacnoise dates from the 10th century, so it is possible that this entry was added retrospectively, with someone calculating back from a legend about the tooth’s age. However, a similar story appears in the Annals of Ulster in 753, so the original date may have been miscopied, and the story may have been recorded contemporaneously in the 8th, rather than in the 10th century.