''Nimiokoala greystanesi'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

, closely related to the

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

koala The koala (''Phascolarctos cinereus''), sometimes inaccurately called the koala bear, is an arboreal herbivorous marsupial native to Australia. It is the only Extant taxon, extant representative of the Family (biology), family ''Phascolar ...

, that inhabited northwestern

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

in the early-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 ...

(23–16 million years ago). It is the only species assigned to the genus ''Nimiokoala''. Along with

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

sister A sister is a woman or a girl who shares parents or a parent with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a familial relationship, it is sometimes used endearingly to ref ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

'' Litokoala'', it is the smallest representative of

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Phascolarctidae The Phascolarctidae (''φάσκωλος (phaskolos)'' - pouch or bag, ''ἄρκτος (arktos)'' - bear, from the Greek ''phascolos'' + ''arctos'' meaning pouched bear) is a family of marsupials of the order Diprotodontia, consisting of only one ...

. Based on

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

analysis, ''Nimiokoala'' is one of the more basal genera of Phascolarctide. It died out due to

climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

rendering the environment more arid. It probably had a more generalized diet than that of the modern species, but its exact food preferences are unknown.

Etymology

The generic name, ''Nimiokoala,'' is derived from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word ''Nimio'' "excessive" referring to its complex molar morphology relative to other koala species. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

, ''greystanesi,'' honors Greystanes High School.

History of research

As of 2013, the fossil record of extinct koalas consists of 163 specimens across 58 deposits in Riversleigh; 55 specimens are attributed to ''N. greystanesi''. To date, a partial

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

has been found along with several lower jaws and isolated teeth. On the basis of these fossils, the dental apparatus of the animal has been completely restored. The species was named in 1997 with

Queensland Museum The Queensland Museum Kurilpa is the state museum of Queensland, funded by the government, and dedicated to natural history, cultural heritage, science and human achievement. The museum currently operates from its headquarters and general museu ...

specimen "QMF30482" being designated the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

; with the specimens used by the type description being part of the Queensland Museum collections.

Description

In the absence of postcranial fossils, the size of ''Nimiokoala'' has been estimated from measurements of its surviving teeth. It is estimated to have body length of about 25–30 cm (9.8-11.8 in), and a weight of about 3.5 kg (7.7 lb), one third the size of modern koalas and more than 10 times smaller than the largest known representative of Phascolarctidae ('' Phascolarctos yorkensis''). Its muzzle was more prominent than that of modern koalas, resembling the

possum Possum may refer to: Animals * Didelphimorphia, or (o)possums, an order of marsupials native to the Americas ** Didelphis, a genus of marsupials within Didelphimorphia *** Common opossum, native to Central and South America *** Virginia opossum ...

snout. The teeth of the Riversleigh rainforest koala are selenodontal (crescent-shaped), with a numerous cusps and accessory shearing blades. The fossilized skull contains large

orbits In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...

and very large auditory bulliae relative to its size.

Ecology and behavior

In the early-middle Miocene, Riversleigh was covered with

tropical forests Tropical forests are forested ecoregions with tropical climates – that is, land areas approximately bounded by the tropics of Cancer and Capricorn, but possibly affected by other factors such as prevailing winds. Some tropical forest types ...

. More open areas, with

karst Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...

soil, occurred at forest edges or freshwater streams and lakes. As the climate became more arid, with a more pronounced change of seasons, small species of koalas died out, including the Riversleigh rainforest koala. The small size of ''Nimiokoala'', which requires a proportionately more intensive diet, and large eye sockets, which indicate good night vision, suggest that this animal was much more mobile than the modern koala. The structure of the ear of ''Nimikoala'' corresponds to that which can be observed in modern koalas; in conjunction with the large auditory bulliae, it can be concluded that the Riversleigh rainforest koala was sensitive to and used low-frequency sounds for communication, including to attract mates.

References

Works cited

* * * * * * {{Taxonbar, from1=Q1189148, from2=Q42602605 Pleistocene mammals of Australia Prehistoric vombatiforms Pleistocene marsupials Koalas Riversleigh fauna Fossil taxa described in 1997