Casuariiformes

The emus form a distinct branch, characterized by legs adapted for running. The total number of cassowary species described, based on minor differences in casque shape and color variations, formerly reached nine. Now, however, only three species are recognized, and most authorities only acknowledge few subspecies or none at all.

Some Australian fossils initially believed to be from emus were recognized to represent a distinct genus, Emuarius, which had a cassowary-like skull and femur and an emu-like lower leg and foot. In addition, the first fossils of mihirungs were initially believed to be from giant emus, but these birds were completely unrelated.

It has been suggested that the South American genus Diogenornis was a casuariiform bird, instead of a member of the rheas, the current South American lineage of giant ground birds. 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. 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.

A question regarding this order is whether emus or cassowaries are the more primitive form, if either. 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. The casuariiform fossil record is ambiguous, and the present knowledge of their genome is insufficient for comprehensive analysis. Resolving the cladistic issues will require combination of all these approaches, with at least the additional consideration of plate tectonics.

Casuariiformes (Sclater, 1880) Forbes 1884

• ?†Diogenornis Alvarenga, 1983 (Paleocene of Brazil)
  • †Diogenornis fragilis Alvarenga, 1983
• Casuariidae Kaup, 1847 (emus and cassowaries)
  • †Emuarius Boles, 1992 (emuwaries) (Late Oligocene, Late Miocene)
    • †Emuarius gidju (Patterson & Rich 1987) Boles, 1992
    • †Emuarius guljaruba Boles, 2001
  • Casuarius (Linnaeus 1758) Brisson, 1760 (cassowary)
    • †Casuarius lydekkeri Rothschild, 1911 (Pygmy cassowary)
    • Casuarius casuarius (Linnaeus, 1758) Brisson, 1760 (Southern cassowary)
    • Casuarius unappendiculatus Blyth 1860 (Northern cassowary)
    • Casuarius bennetti Gould, 1857 (Dwarf cassowary)
  • Dromaius Vieillot, 1816 (modern emus) (Middle Miocene, Recent)
    • †Dromaius arleyekweke Yates & Worthy, 2019
    • †Dromaius ocypus Miller, 1963
    • Dromaius novaehollandiae (Latham, 1790) Vieillot 1816 (emu)
      • †D. n. minor Spencer, 1906 (King Island/black emu)
      • †D. n. baudinianus Parker, 1984 (Kangaroo Island/dwarf emu)
      • †D. n. diemenensis (Jennings, 1827) Le Souef, 1907 (Tasmanian emu)
      • D. n. novaehollandiae (Latham, 1790) (Australian emu)

The IOC World Bird List (version 15.1) recognizes 4 species of Casuariiformes. As of December 2025, IUCN/BirdLife International has assessed all species within the order, and three of four have population estimates.