According to the Comparative Tables, the diphthongs [eo] and [iu] later became the diphthong [io] rather than becoming [jō], [jū] as they did in East Danian (PE19/25). Since the diphthong [eo] is attested in The Etymologies in Dan. beorn and meord (Ety/BER, MIZD), it seems likely that this change occurred after the period of the Wars of Beleriand. Furthermore, based on the pattern of the breaking of the vowel [i] to [eo] before [r] in the word meord, it seems likely that [iu] first merged with [eo] before becoming [io].

See Dan. [a], [e], [i] broke into diphthongs before [l], [r] clusters for further discussion.