From the introduction: "In this paper [...] I will be arguing for a direction of change in Cariban languages from systems that are purely ergative in both nominal case marking and verb agreement patterns (and which are probably of considerable antiquity) to mixed systems where in main clauses the core nominals are not marked at all and the verb agreement patterns are a mixture of nominative and absolutive, based on an agentivity-person hierarchy. Subordinate clauses take the form of nominalizations that retain characteristics of the older pure ergative system."
Derbyshire, Desmond C.
"Are Cariban languages moving away from or towards ergative systems?,"
Work Papers of the Summer Institute of Linguistics, University of North Dakota Session: Vol. 35
, Article 6.
Available at: https://commons.und.edu/sil-work-papers/vol35/iss1/6