Technically it’s a ‘microfossil’, but you get the idea.

The extinction event at the boundary between the Cretaceous and Palaeogene periods is popularly known as the time when the dinosaurs died out. What is less commonly appreciated, however, is the extinction of a broad variety of other lifeforms at the same time. Among these are numerous species of planktonic foraminifera. These tiny plankton formed an important part of the marine food-web, and their loss is likely to have caused the extinction of larger fishes, cephalopods and marine reptiles.