''Neohelos'' is an extinct

diprotodontid The Diprotodontidae are an extinct family of large herbivorous marsupials, endemic to Australia and New Guinea during the Oligocene through Pleistocene periods from 28.4 million to 40,000 years ago. The family consisted of large quadrupedal te ...

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

, that lived from the early to middle-

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

. There are four species assigned to this genus, ''Neohelos tirarensis'', the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

, ''N. stirtoni'', ''N. solus'' and ''N. davidridei''. ''N. davidridei'' is the most derived species of the genus, and its premolar morphology shows that it is structurally and ancestor of the genus ''

Kolopsis ''Kolopsis'' is an extinct genus of diprotodontid marsupials from Australia and Papua New Guinea. It contains three species, although ''K. rotundus'' may be more closely related to other zygomaturines than to ''Kolopsis''. *†''Kolopsis rotu ...

''. All four species are from the Bullock Creek in the

Northern Territory The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an Australian territory in the central and central northern regions of Australia. The Northern Territory shares its borders with Western Aust ...

and Riversleigh of Australia.

Description

''Neohelos'' is known from many specimens, assigned to all the species. ''N. tirarensis'' includes a partial

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, t ...

, and

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

s; ''N. solus'' is known from a maxilla and dentary; ''N. davidridei'' includes

and a maxilla fragment; and ''N. stirtoni'' is known from a mostly complete skull, a maxilla and a dentary.

Distinguishing characteristics

A revision of ''Neohelos'' found a set of features in all the species that are absent in all other diprotodontoids. They are listed below: * four−cusped P3 with a tall, subcentral parametacone, a distinct anterior parastyle, a moderately developed protocone and a small to moderate (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 ''N. 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.

Classification

''Neohelos'' includes many species. Among them, ''N. davidridei'' is the most derived. ''N. davidridei'' shows many features that are also found in ''

'', and is thought to be the ancestor of it and its species. Together, ''Neohelos'' and ''Kolopsis'' make up

Zygomaturinae The Zygomaturinae are an extinct subfamily of marsupials. The phylogeny and taxonomy of this clade is poorly understood and problematic. Zygomaturines are currently thought to be a subfamily within Diprotodontidae The Diprotodontidae are an ...

along with '' Zygomaturus'' and other genera.

Paleoecology

''Neohelos'' lived in the early to Middle Miocene of

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , establishe ...

, Australia. It is one of a few diprotodont genera that existed in all three of Bullock Creek in the Northern Territory, Riversleigh in Queensland, and the Wipajiri Formation of South Australia.

References

* ''The Book of Life: An Illustrated History of the Evolution of Life on Earth'' by Jean-Paul Tibbles, Peter Andrews, John Barber, and Michael Benton * ''Prehistoric Mammals of Australia and New Guinea: One Hundred Million Years of Evolution'' by John A. Long, Michael Archer, Timothy Flannery, and Suzanne Hand
Number 6 Murray P et al., 2000 Morphology, systematics and evolution of the marsupial genus Neohelos Stirton (Diprotdontidae, Zygomaturinae)
{{Taxonbar, from=Q3338183 Miocene marsupials Prehistoric mammals of Australia Prehistoric vombatiforms Riversleigh fauna Prehistoric marsupial genera