The Casuariiformes is an order of large flightless birds that has four surviving members: the three

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

cassowary Cassowaries (; Biak: ''man suar'' ; ; Papuan: ''kasu weri'' ) are flightless birds of the genus ''Casuarius'', in the order Casuariiformes. They are classified as ratites, flightless birds without a keel on their sternum bones. Cassowaries a ...

, and the only remaining species of

emu The emu (; ''Dromaius novaehollandiae'') is a species of flightless bird endemism, endemic to Australia, where it is the Tallest extant birds, tallest native bird. It is the only extant taxon, extant member of the genus ''Dromaius'' and the ...

. They are divided into either a single family, Casuariidae, or occasionally two, with the emu splitting off into its own family, Dromaiidae. The

IOC World Bird List ''Birds of the World: Recommended English Names'' is a paperback book written by Frank Gill and Minturn Wright on behalf of the International Ornithologists' Union. The book is an attempt to produce a standardized set of English names for all bi ...

and

Cornell Lab of Ornithology The Cornell Lab of Ornithology is a member-supported unit of Cornell University in Ithaca, New York, which studies birds and other wildlife. It is housed in the Imogene Powers Johnson Center for Birds and Biodiversity in Sapsucker Woods Sanctuar ...

's Birds of the World both do not recognize Dromaiidae, placing the emu in the family Casuariidae. All four living members are native to Australia-New Guinea,Clements, J (2007) but some possible extinct taxa occurred in other landmasses.

Systematics and evolution

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 In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...

or none at all. The fossil record of casuariforms is interesting, but not very extensive. Regarding fossil species of ''

Dromaius ''Dromaius'' (from greek language, greek δρομαίυς "runner") is a genus of ratite present in Australia. There is one extant species, ''Dromaius novaehollandiae,'' commonly known as the emu. In his original 1816 description of the emu, Lou ...

'' and '' Casuarius'', see their genus pages. As with all

ratite Ratites () are a polyphyletic group consisting of all birds within the infraclass Palaeognathae that lack keels and cannot fly. They are mostly large, long-necked, and long-legged, the exception being the kiwi, which is also the only nocturnal ...

s, there are several contested theories concerning their evolution and relationships. Some Australian fossils initially believed to be from emus were recognized to represent a distinct genus, ''Emuarius'',"Emuarius" is from "Emu" + "''Casuarius''". Describer W.E. Boles commonly refers to the genus as "emuwaries" or "cassomus". which had a cassowary-like skull and

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

and an emu-like lower leg and foot. In addition, the first fossils of mihirungs were initially believed to be from giant emus,The vernacular name "mihirung" is derived from ''mihirung paringmal'', which means "giant emu" in the Chaap Wuurong language. but these birds were completely unrelated. It has been suggested that the

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

n 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 The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

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. An especially interesting 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 A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

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 Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

Taxonomy

Casuariiformes Mikko's Phylogeny Archiv

Paleofile.com (net, info) .
*?†'' Diogenornis'' (Paleocene of

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

) **†''Diogenornis fragilis'' * Casuariidae (emus and cassowaries) **†'' Emuarius'' (emuwaries) (Late Oligocene – Late Miocene) ***†''Emuarius gidju'' ***†''Emuarius guljaruba'' **'' Casuarius'' (cassowary) ***†'' Casuarius lydekkeri'' (Pygmy cassowary) ***'' Casuarius casuarius'' (Southern cassowary) ***'' Casuarius unappendiculatus'' (Northern cassowary) ***'' Casuarius bennetti'' (Dwarf cassowary) **''

'' (modern emus) (Middle Miocene – Recent) ***†'' Dromaius arleyekweke ***†'' Dromaius ocypus'' ***''

Dromaius novaehollandiae The emu (; ''Dromaius novaehollandiae'') is a species of flightless bird endemism, endemic to Australia, where it is the Tallest extant birds, tallest native bird. It is the only extant taxon, extant member of the genus ''Dromaius'' and the ...

'' (emu) ****†'' D. n. minor'' (King Island/black emu) ****†'' D. n. baudinianus'' (Kangaroo Island/dwarf emu) ****†'' D. n. diemenensis'' (Tasmanian emu) ****'' D. n. novaehollandiae'' (Australian emu)

Footnotes

References

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External links

{{Authority control Novaeratitae Taxa named by Philip Sclater Bird orders Ratites Flightless birds Extant Miocene first appearances Miocene taxonomic orders Pliocene taxonomic orders Pleistocene taxonomic orders Holocene taxonomic orders