Riversleigh rainforest koala
- Lake Namba, Riversleigh, Australia
Nimiokoala is a genus of late Oligocene Koala to early Miocene.
Features
Nimiokoala was a Koala genus, but reached significantly smaller extent than other members of this family Beutler and was only about half as large as today's koalas, the head-body length is calculated to be 25 to 30 cm. However, it is known only by a partially preserved skull, skull fragments and some more teeth. The skull, which was about 8 inches long, was flat and had a strikingly distinctive head crest. The rostrum was less extensive than at present Koala. Finds of mandibles are preserved only a few, this show, however, that no closed symphysis was present, which is a more primordial feature. The incisors were short and sharp, as is the canine, which had a nail-like shape. However noteworthy appear the molars, of which Nimiokoala like most marsupials four had ever pine bough, which were less rounded and clearly hochkronig than other Koala genera and on the Kauobefläche by several enamel hump had a fine gerippelte structure so that they are already known features of the koalas were significantly over-developed.
Paleobiology
Today's koalas are characterized by their specialization in eucalyptus and a Kauweise on only one side of the dentition with strong lateral movements of the mandible, which is considered as an adaptation to the harsh plant food. Held the unclosed symphysis of the mandible and the differently shaped front skull, showing mainly in the mouth area that Nimiokoala do not yet have such a strong bite decreed as today's koalas and also has used both jaw tooth rows, the food was rather crushed and hardly any lateral chewing movements. This is also the molars, which have no horizontal grinding marks. The climate at that time was much more humid and Australia by dense forests. The anatomical features suggest that the early koalas in this biotope rather soft plant preferred and no extreme specialists were. Only the drying of the continent led to the adaptation of eucalyptus, which bring experts with the training of the genus Phascolarctos in conjunction.
Furthermore, the perspective on temporal bone a significantly expanded middle ear, the Nimiokoala allowed to perceive sounds in the low frequency range. Low-frequency sounds penetrate dense vegetation cover, while high frequencies are reflected and makes such a direction locating hardly possible. However, this also suggests that early Koala representatives possessed a similarly high volume capacity to communicate in the dense tropical rain forest, obviously an old characteristic of this group, which developed very early. Modern koalas have an even bigger middle ear, which may be associated with the decline in vegetation, as infrasound propagates in open landscapes over long distances and this was probably necessary to timely detect predators during the pilgrimage to the individual food sources.
System
Koobor
Madakoala
Perikoala
Nimiokoala
Litokoala
Phascolarctos
There are known two types. Nimiokoala greystanesi Black & Archer, 1997 ( holotype specimen number QMF 30382 ), represents the type species and lived in the early and middle Miocene. You sit known reference to several partial skull and mandible fragments B were found near Riversleigh (Queensland ), among others, in local fauna of the reference Neville's - Garden system. Another lower jaw fragment from the South - Prospect B local fauna near Lake Namba in South Australia is an as yet unnamed species ( Nimiokoala sp Black & Archer, 1997;. Specimen number SAMP 19952 ) and dated to the late Oligocene to middle Miocene. The most closely related genera are Litokoala and the present Koala, which are the sister group of Nimiokoala. Maybe he grew out Perikoala.
The genus name is derived from the Latin word Nimius and means " excessively ", " excessive", are "koala " refers to the close relationship with the living today koalas. Overall, the name Nimiokoala refers to the significantly more complex dental morphology than other Koala relatives.