It has been proposed that the fullerene formation mechanism involves either a top-down or bottom-up pathway. Despite of different starting points, either mechanism approved that particular fullerenes or metallofullerenes are formed through a consecutive stepwise process involving Stone-Wales transformations (SWTs) and C2 insertion or extrusion. However, the formation pathway has been seldom defined at the molecular level due to the missing link fullerenes. Herein, we present a series of previously missing species, including Sc2O@C2v(24107)-C78 and Sc2O@D3h(24109)-C78, Sc2O@C2(7892)-C70 and Sc2C2@D3h(14246)-C74. Each of them can be converted to other isomers or larger or smaller species via a simple conversion route involving Stone-Wales (SW) transformation and C2 insertion or extrusion. Thus, this study might provide molecular structural evidence for the less confirmed fullerene formation mechanism.