Quoting "David J. Peterson" <[log in to unmask]>:

> Now, I've never actually been taught this in any linguistics class (hence,
> why I'm asking), but in Spanish, it appears that Latin long mid vowels, when
> stressed, became diphthongs with an on-glide.  Examples:

[snip examples]

> Note: I'm imagining that there was an secondary stage with "dormir" where it
> was actually /dwormo/, at one time, and then the vowel fronted, for reasons
> unknown.

Indeed, it happens in a number of Romance languages...

> My question: Does anyone have any examples of this happening in other
> languages (nat or non)?

.. and in Old High German as well, IIRC.  It is a well known
phenomenon that unmarked diphthongs have at least one element
that is [+high], but where that [+high] element goes is determined
by other factors.  For the case in Spanish, I'd suggest taking a
look at Rebecca Posner's _The Romance Languages_, pp. 157-159, in
the Cambridge Textbook series, which discusses the origin of this
process in those languages.

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