Proto-Samoyedic vowel system has been studied for more than a hundred years, since the relation between the Samoyedic languages was discovered. The first, as far as we know, publication of this system was in [12].
This is what it looked like:
*i *ü *i̮ *u
*e *ö *ə̑ *e̮ *o
*ä *å
Later, after analyzing modern Nganasan data, E. Helimski [7] proposed adding two more phonemes to the system (see analysis of these addings for relevance in [1]):
*i *ü *i̮ *u
*e *ö *ə *ə̑ *e̮ *o
*ä *a *å
On the base of the analyses of the Taz-Selkup vocalism system and Narym, Ket and Middle-Ob’ dialects’ field and archival audio materials was noticed some additional series of regular correspondences between the Selkup dialects and Northern Samoyedic languages such as Nenets, Enets and Nganasan. Further analysis of these series showed correspondences in Kamassian, which reliably denotes their Proto-Samoyedic nature, as well as in the Finno-Ugric languages:
1. Proto-Selkup *о/*ō < Proto-Samoyedic *å
(> Kamassian а) < Proto-Uralic *а // *o (> Saami N oa)
2. Proto-Selkup *uə/*uə̅ < Proto-Samoyedic *ɐ
(> Kamassian u, o) < Proto-Uralic *а (> Saami N uo)
3. Proto-Selkup *u/*ū < Proto-Samoyedic *ʌ (> Kamassian u, o, ш) < Proto-Uralic *o, *u.