 It was said to differ from "S. dongi" mainly in its smaller size (only about half the size of "S. dongi") and the presence of a notarium, though this was later disproved.Some later studies found "S. gui" to simply represent a younger specimen of "S. dongi", though one large analysis in 2014 found it to be a more primitive tapejarid closely related to "Nemicolopterus".A third species was referred to "Sinopterus" in 2007, "S. jii".