Planktic Foraminifera are an extremely abundant, important and successful group of marine protists. They are particularly useful in reconstructing past environments and for biostratigraphic dating. Despite their importance, the origin of the group is uncertain. Previous work has suggested that they evolved from a benthic ancestor during the Triassic or, perhaps, the Mid-Jurassic (?Bajocian), but a reason for their origination has remained unclear. Here, we present evidence from the Toarcian (early Jurassic) of NW Europe that the origin of the planktic Foraminifera may have been one of the results of the early Toarcian oceanic anoxic event. This event appears to have been associated with a massive dissociation of gas hydrates and other, perhaps related, water chemistry changes.