A diminutive species of emu (Casuariidae: Dromaiinae) from the late Miocene of the Northern Territory, Australia

A new, diminutive species of dromaiine casuariid, <i>Dromaius arleyekweke</i>, is described from dispersed skeletal elements from the late Miocene Waite Formation of the Northern Territory, Australia. Remains of <i>D. arleyekweke</i>, sp. nov., have been found from the Ongeva Local Fauna in the Alcoota Scientific Reserve, but most remains come from the stratigraphically lower Alcoota Local Fauna where they form part of a densely fossiliferous series of mingled bone beds. Previously, remains of the new species had been referred to the basal dromaiine genus, <i>Emuarius</i>, but phylogenetic appraisal of new specimens indicates that the species shared a more recent common ancestor with the extant <i>Dromaius novaehollandiae</i> than it did with the type species of <i>Emuarius</i>, <i>E. gidju</i>. Consequently, the new species is placed in the genus <i>Dromaius</i> as its oldest known member. Derived characters of <i>D. arleyekweke</i> that are shared with <i>D. novaehollandiae</i> to the exclusion of <i>E. gidju</i> include a distally flattened external condyle of the distal end of the tibiotarsus and a more elongate tarsometatarsus, with marked transverse compression of the midshaft and a weakly impressed median sulcus on trochlea metatarsi II. Casuariid evolution shows a trend of increasingly cursorial hind limb proportions on the emu lineage, but <i>D. arleyekweke</i> has a tarsometatarsus that is more elongate than that of <i>D. novaehollandiae</i>. This implies nonlinear evolution of cursoriality in dromaiines and that <i>D. arleyekweke</i> evolved extreme cursorial proportions independently of <i>D. novaehollandiae</i>, or that a high degree of cursoriality evolved early in <i>Dromaius</i> and was reversed in the Pliocene <i>D. ocypus</i>.