Labialized velar stops have become velar stops. Tripartite split of the A tone A1-23-4 Merger of A23 and B4 The low vowels /ɛ/ and /ɔ/ have merged with /e/ and /o/, respectively. *ʔb > m Luo (2001) Luo Yongxian (2001) also recognizes the uniqueness of Dehong Tai (Tai Nuea), but argues for that it should be placed in a separate Northwestern Tai branch with Southwestern Tai as a sister branch. Luo claims that the Northwestern Tai branch has many Northern Tai and Central Tai features that are not found in Southwestern Tai. His proposed tree for the Tai branch is as follows. Tai Northern Central Southwestern Northwestern Pittayaporn (2009) According to Pittayaporn (2009:301), Southwestern Tai (his subgroup Q) is defined by a phonological shift of *kr- → *ʰr-. Pittayaporn (2014) also suggests that Southwestern Tai began to disperse southward after the 7th century C.E. but before the 11th century C.E. (between 700 and 1000 C.E., during the late Tang dynasty or early Song dynasty), as evidenced by loanwords from Late Middle Chinese. Pittayaporn (2018) recognizes two branches within Southwestern Tai, namely Eastern and Western. The Eastern branch consists of the closely related languages Black Tai, White Tai, and Red Tai, while the Western branch is much more internally diverse. The Western branch also contains a Southern group consisting of Thai and Lao. Southwestern Tai Eastern branch: Black Tai, White Tai, Red Tai Western branch: Shan varieties, Lue, Yuan, Lao, Thai (defining innovation: *kʰr- > kʰ-) Southern sub-branch: Thai, Lao, etc. (defining innovations: *ɓl- > ɗ- and *ʰr > h-) Pittayaporn, et al. (2018) note that following sound changes from Proto-Southwestern Tai (PSWT) to the Tai varieties represented in the Sukhothai and Ayutthaya inscriptions, and conclude that the Sukhothai and Ayutthaya inscriptions in fact represent the same language. the merger of dorsal obstruents the merger of PSWT *aɯ and *aj the merger of PSWT *ɲ-, *j- and *ʔj- the loss of voicing distinction in sonorants *ɓl- > d- *kʰr- > kʰ- *ʰr- > h- Dialects Southern Thai (Pak Thai) is often posited to be the most divergent; it seems to retain regular reflexes of early tonal developments that were obscured in the other (Central–Eastern) languages. The reconstructed language is called Proto-Thai; cf. Proto-Tai, which is the ancestor of all of the Tai languages. The following tree follows that of Ethnologue Southern Thai (Pak Thai) (Thailand) Chiang Saen dialects (10) Tai Dam