Neohelos Stirton, 1967

Black, Karen H., Archer, Michael, Hand, Suzanne J. & Godthelp, Henk, 2013, Revision in the diprotodontid marsupial genus Neohelos: Systematics and biostratigraphy, Acta Palaeontologica Polonica 58 (4), pp. 679-706 : 680-681

Genus Neohelos Stirton, 1967

Type species: Neohelos tirarensis Stirton, 1967 ; Leaf Locality ( UCMP Locality V 6213), Kutjamarpu LF, Wipajiri Formation, Lake Ngapakaldi , South Australia; Early Miocene .

Species included.— Neohelos stirtoni Murray, Megirian, Plane, and Vickers−Rich, 2000a ; Neohelos solus sp. nov.; Neohelos davidridei sp. nov.

Revised diagnosis.—Species of Neohelos are characterized by the following combination of features: four−cusped P3 with a tall, subcentral parametacone, a distinct anterior parastyle, a moderately developed protocone and a small to moderate (though sometimes absent) hypocone; tendency to develop a mesostyle on P3; M1 with well−developed stylar cusp A, stylar cusp E and postmetacrista; M1 with a square occlusal outline (except Ne. solus ); large interproximal contact between P3 and M1; broad, lanceolate i1 with a ventrobuccal groove and longitudinal lingual crest; and moderate epitympanic fenestra in the postglenoid cavity.

Species of Neohelos differ from species of Silvabestius in being larger, and in having a distinct parastyle on P3. They differ from species of Silvabestius and Nimbadon , in having: a broader i1; an increasing posterior molar gradient; a reduced epitympanic fenestra; a moderately inflated postglenoid process; and an obliquely orientated glenoid fossa.

Species of Neohelos differ from Alkwertatherium webbi in having: a hypocone developed on P3; less oblique molar lophs; a more distinct paracristid on m1; a reduced postparaconal crest on the upper molars; an unconstricted upper diastema; a horizontally aligned basicranial axis; a diastema that does not decline from p3 to i1; and a masseteric foramen developed on the dentary.

Species of Neohelos differ from Plaisiodon centralis in being smaller and in having: a transverse parametacone crest on P3; a proportionately smaller parastyle on P3; a posteriorly narrow zygomatic arch; and a more open tympanic floor.

Species of Neohelos differ from species of Kolopsis , Zygomaturus , and Maokopia in having: an undivided parametacone on P3; a weak digastric fossa and digastric process on the dentary; an open tympanic cavity with a moderately developed epitympanic fenestra; and a shorter, less inflated postglenoid process.

Species of Neohelos differ from species of Hulitherium , Maokopia , and Zygomaturus in lacking: divergent I1s; a buccally positioned paracone and metacone on P3; a P3 that is significantly reduced relative to the length of M1; highly inflated frontals and strong frontal crests; a highly flexed basicranial axis; large, elongate, posterior recurved masseteric processes; and a strongly curved, posteriorly deep zygomatic arch.

Species of Neohelos differ from Kolopsoides cultridens in: having a proportionately shorter P3 relative to M1; having an undivided parametacone on P3; having a weaker parastyle and hypocone on P3; lacking the longitudinal crest linking the apices of the parastyle and paracone on P3; and lacking pointed, recumbent lower incisors.

Geographic and stratigraphic range.— Species of Neohelos are recorded from: the Early Miocene Kutjamarpu LF of the Wipajiri Formation, Lake Ngapakaldi , South Australia ; the Late Oligocene Kangaroo Well LF of the Ulta Limestone, northwestern Lake Eyre Basin , Northern Territory ; the Middle Miocene Bullock Creek LF of the Camfield Beds , Northern Territory ; and numerous Late Oligocene to Middle Miocene (FZs A–C) deposits of the Riversleigh WHA, northwestern Queensland . Neohelos material is also known from FZs D–E of the Etadunna Formation, central lake Eyre Basin , South Australia , but has yet to be identified to species level.