This dissertation presents a comprehensive analysis of the complex case-marking patterns as found in the Ecuadorian variety of Siona language, a Tukanoan language belonging to the western branch. This endangered language is spoken today by roughly 350 individuals in the Upper Napo-Aguarico watershed in northwestern Amazonia.
The aim of this work is to investigate the mechanisms of differential case-marking (DCM), the phenomenon whereby not all subject, object, or certain spatial arguments bear the same morphological case-markers. To characterize these patterns, this dissertation employs a range of methodological approaches, including a comparative typological survey of case-marking in the region, a quantitative corpus study of DCM in narratives, and a rigorous elicitation-based research program. The corroborating evidence indicates a principled system where the distribution of surface case-marking is conditioned primarily by the interplay of animacy classes and information structure. Ultimately Siona DCM is characterized by an admixture of typologically common properties and unique, language-particular nuances, making this an important contribution to the theory and the typology of DCM in Tukanoan languages, in Amazonia, and in the broader literature.
