Undocumented labor: How old fieldwork sheds new light on Tai tone system diversification

Much work on diachrony in lexical tone has focused on tonogenesis, with less focus on how systems diversify once firmly in place. This gap can lead to problematic assumptions about tone system complexity. Language documentation in non-English languages represents a large body of largely unknown and uncited work. This paper presents findings from an extensive survey of tone systems in hundreds of Tai doculects, which enables us to better examine how the tonogenetic situation played out in the Tai branch. Data gathered is both phonemic and phonetic, mapping tones to historical splits and mergers. This tone split data is also encoded as binary data for phylogenetic approaches. These untapped resources significantly improve our ability to understand how tone systems diversify.