East Dangla and West Dangla, two dialects of the Dangla language which belongs to the Chadic language family, differ substantially in their tone systems. In numerous lexical items, entire or partial tonal inversions are observable. Earlier research has not succeeded in boiling this down to regular sound correspondences. In the meantime, data from Central Dangla as a third dialect have become available, which provide important insights into the matter. Based on all available materials, a new attempt to establish the tonal correspondences is undertaken here. This results in a reconstruction of the tone system of Proto-Dangla, the hypothetical ancestor of the modern varieties, together with a chronological elaboration of the tonal changes that occurred in the individual dialects.
A genetic subgrouping of 16 East Chadic languages is proposed in this paper. Contrary to the popular lexicostatistical approach, and in order to take into account potentially different rates of lexical evolution in the individual languages, it is attempted here to rely on the identification of common innovations. A practical method is presented how to apply the notion of common innovation when working with lexical isoglosses. This new method can also serve as a model for the subgrouping of language families other than East Chadic.