''Litokoala'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

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 ...

s, and along with '' Nimiokoala'', is closely related to the modern

koala The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family Phascolarctidae and its closest living relatives are the w ...

. The three genera may have diverged at an earlier date, although the drying of the continent and the expansion of ''

Eucalyptus ''Eucalyptus'' () is a genus of over seven hundred species of flowering trees, shrubs or mallees in the myrtle family, Myrtaceae. Along with several other genera in the tribe Eucalypteae, including '' Corymbia'', they are commonly known as e ...

'' forests towards the late Miocene may have delayed the evolution of cranial features unique to the modern genera. This indicates that either fossil genus could be an ancestor of the modern genus, or the modern genus has a common ancestor to both. More material needs collection to improve their taxonomical relationships. The genus lived about 10–16 million years ago in the middle Miocene Riversleigh of Queensland. This area is described as a rainforest habitat at time of sediment deposition. It had a different diet to the modern species, with the dental

symphysis A symphysis (, pl. symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing togethe ...

unfused, indicating a diet that was properly varied in nature, unlike the specialised nature of ''Phascolarctos''. The size is estimated to be only half of the modern genus. Cranial adaptations are intermediate between the extant

common brushtail possum The common brushtail possum (''Trichosurus vulpecula'', from the Greek for "furry tailed" and the Latin for "little fox", previously in the genus ''Phalangista'') is a nocturnal, semiarboreal marsupial of the family Phalangeridae, native to Aus ...

and koala, with minor divergence from either. This genus and ''Nimiokoala'' are similar in most anatomical features so far as is known, except ''Litokoala'' possessed a superficial messateric process, while ''Nimiokoala'' had "more marked basio

occipital The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cereb ...

-basi sphenoid flexion and a more extensive posterior attachment of the

pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Medi ...

",(Louys et al., 2009, p. 989) which make these features basal in their taxonomical position in relation to the ''Phascolarctos''. The basiocranial (back of skull) features are similar to ''Phascolarctos'', while anterior (facial) features exhibit similarities with the genus ''

Trichosurus The brushtail possums are the members of the genus ''Trichosurus'' in the Phalangeridae, a family of marsupials. They are native to Australia (including Tasmania) and some small nearby islands. Unique among marsupials, they have shifted the hyp ...

''. Only partial fragments are known, with only the posterior section of the

zygomatic process The zygomatic processes are three processes (protrusions) from other bones of the skull which each articulate with the zygomatic bone. The three processes are: * Zygomatic process of frontal bone from the frontal bone * Zygomatic process of max ...

known from the ''L. kutjamarpensis'' skull.

References

{{Taxonbar, from=Q6648651 Miocene mammals of Australia Prehistoric vombatiforms Miocene marsupials Koalas Prehistoric marsupial genera Riversleigh fauna Fossil taxa described in 1967