Proto - Lolo - Burmese velar clusters and the origin of Lisu palatal sibilants

Standard Northern Lisu has two series of palatal sibilants: (alveolo-)palatals [t ̊ t ̊æ d ̊ ] and palato-alveolars [t∆ t∆æ dÔ ∆ Ô]. The phonemic status of the latter is questionable, since they are in complementary distribution with the former, occurring only before vowels [u] and [Ω]. The vowel [Ω] is itself in complemetary distribution with [i], occurring only after the palatoalveolars. Thus the contrasting minimal pair [t ̊æi££] ‘to arrive’ and [t∆æΩ££] ‘Muntjac deer’, from a synchronic viewpoint, can be phonemicized either as /t ̊æi££/ and /t ̊æΩ££/ (treating the palato-alveolars as allophones of the palatals and /i/, /Ω/ as distinct phonemes) or as /t ̊æi££/ and /t∆æi££/ (treating [Ω] as an allophone of /i/, and the two sibilant series as phonemically distinct). While synchronically either approach is possible, the question arises as to how this “overlapping complementary distribution” phenomenon arose historically. What is the origin of the two contrasting syllable types [t ̊æi] and [t∆æΩ]? The Lisu palatals have multiple origins. One source is the Proto-LoloBurmese palatal initials. Another is Proto-Lolo-Burmese velar clusters with *r or *y. Analysis reveals that the original Lolo-Burmese distinction between clusters such as *kr and *ky, although lost in most environments, is still maintained before high front vowels, resulting in the distinction between [t ̊æi] and [t∆æΩ]-type syllables.