The first part of this article investigates the distribution and emergence of front rounded vowels (FRV) in the Portuguese dialect spoken on the Azorean island of São Miguel in light of data taken from the Ethnolinguistic Atlas of the Azores (ALEAç). The analysis confirms previous findings about the distribution of FRV. Additionally, the ALEAç shows that this phenomenon spreads beyond the well-known contexts of stressed positions. FRV also occur in unstressed syllables and the mid-front rounded vowel [ø] alternates with its diphthongised counterparts [øj] and [øw]. This alternation calls for a reflection about the historical and articulatory background of [ø] in Portuguese dialects. The extensive use of FRV opens up further research perspectives in terms of the sociolinguistic significance of the phenomenon. The second part of this article focuses on the sociohistorical background of the emergence of FRV in Portuguese dialects. The concept of the feature pool provides a framework for the processes of feature selection in a situation of linguistic contacts such as those preceding the settlement period of the Azores and subsequent contact on the islands. A combination of three different concepts of markedness helps understand why a highly unusual feature like FRV emerged and persists until today.