The total number of cassowary species described, based on minor differences in casque shape and color variations, formerly reached nine.

Some Australian fossils initially believed to be from emus were recognized to represent a distinct genus, Emuarius,[a] which had a cassowary-like skull and femur and an emu-like lower leg and foot.

If this were the case, not only would it extend the fossil range of this lineage to a wider region, but to a broader time span as well, since Diogenornis occurs in the late Paleocene and is among the earliest known ratites.

[5] In the late 19th century, a fossil casuariid (Hypselornis) was named from India based on a single toe bone, however it was later shown to belong to a crocodilian.

Emus are generally assumed to retain more ancestral features, in part because of their more modest coloration, but this does not necessarily have to be the case.