Collective responsibility matters because it reflects students' collective efforts and abilities to accomplish successful collaboration. Combining a multi-faceted approach and time-line analysis, this paper aims to examine the emergence and manifestation of collective responsibility in online discourse. Twenty university students participated in online discourse within a supportive online learning environment (Knowledge Forum) while taking a 16-week research methods course. The results reveal developmental dynamics involving social and cognitive aspects of responsibility mapping onto three dimensions: social awareness, complementary contribution, and distributed engagement. Specifically, the students raised social awareness and made complementary contributions progressively in the context of question- and idea-driven collaborative inquiry. Although uneven distributed engagement was found in the responsive interactions, the students could develop cognitive responsibility by changing their involvement throughout the discourse. The present study provides new insight into how the three dimensions of collective responsibility interweave to formulate an integrated force driving productive collaboration, and how individual participatory patterns relate to this developmental process. The study has implications for learning environment designers and educators exploring approaches to incorporating technical and pedagogical adaptive strategies for capturing and fostering collective responsibility during collaboration, to allow them to tap into different levels of uptake.