Remains attributed to the species are generally around the size of the living dwarf cassowary (Casuarius bennetti).

Remains attributed to C. lydekkeri differ from living cassowaries in a number of morphological characters, including "a shallower, narrower pelvis, more gracile femur and a narrower proximal [closer to hip] end to the tarsometatarsus".

[1] The species was originally described by Walter Rothschild based on a partial right tibiotarsus of probable Pleistocene age.

[2][3] The exact provenance is unknown, and was originally reported as coming from cave deposits near Wellington in New South Wales,[4] though this is now considered unlikely.

[6] The taxonomy of the species has been described as "problematic", and it has been said that there "is no indication of close affinity between these fossil forms [attributed to C. lydekkeri] and living cassowaries", and it has been suggested that all living cassowaries are more closely related to each other than to forms attributed to C.