Casuariidae Casuariidae The bird family Casuariidae has four surviving members: the three species of cassowary and the emu. All living members of the family are very large flightless birds native to Australia-New Guinea, though the extinct potential member "Hypselornis" was native to India. The characteristics of the family are those of its members. The fossil record of casuariforms is interesting, but not very extensive. 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. A Pliocene Indian ratite, "Hypselornis", has
Flightless bird the lineage. This indicates that the distinctive flightless nature of ratites is the result of convergent evolution. Two key differences between flying and flightless birds are the smaller wing bones of flightless birds and the absent (or greatly reduced) keel on their breastbone. (The keel anchors muscles needed for wing movement.) Adapting to a cursorial lifestyle causes two inverse morphological changes to occur in the skeleto-muscular system: the pectoral apparatus used to power flight is paedorphically reduced while peramorphosis leads to enlargement of the pelvic girdle for running. Repeated selection for cursorial traits across ratites suggests these adaptions comprise a