Nimiokoala
| Nimiokoala | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Oligocene to Miocene | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Nimiokoala | ||||||||||||
| Black & Archer , 1997 | ||||||||||||
Nimiokoala is a genus of koala from the late Oligocene to early Miocene.
features
Nimiokoala was a genus of koala, but achieved significantly smaller dimensions than other members of this family of Beutler and was only about half the size of today's koalas , the head-torso length is calculated to be 25 to 30 cm. However, it is only known from a partially preserved skull, further skull fragments and some teeth. The skull, which was about 8 cm long, was flat and had a pronounced crest . The rostrum was less extensive than in today's koala. Only a few finds of lower jaws have survived, but these show that there was no closed symphysis , which is a rather primitive feature. The incisors were short and pointed, as was the canine , which was nail-shaped. However noteworthy appear molars , of which Riversleigh Rainforest Koala Like most marsupials four had ever pine bough, which were less rounded and more clearly hochkronig than other koala species and on the Kauoberfläche had a fine gerippelte structure by several enamel hump, it that the already known features of Koalas were significantly overdeveloped.
Paleobiology
Today's koalas are characterized by their specialization in eucalyptus and a way of chewing on only one side of the teeth with strong lateral movements of the lower jaw, which is seen as an adaptation to the hard plant food. The non-closed symphysis of the lower jaw and the differently shaped anterior skull, especially in the palate area, show that Nimiokoala did not yet have as strong a bite as today's koalas and has also used both rows of jaw teeth, whereby the food was rather crushed and there was hardly any lateral chewing movements . This is also shown by the molars, which have no horizontal grinding marks. The climate at that time was much more humid and Australia was covered by dense forests. The anatomical features suggest that the early koalas in this biotope preferred rather soft plants and were not extreme specialists. It was not until the continent dried up that it adapted to eucalyptus, which experts associate with the formation of the genus Phascolarctos .
Furthermore, the temporal bone shows a clearly enlarged middle ear , which allowed Nimiokoala to perceive sounds in the lower frequency range. Low-frequency sounds penetrate dense vegetation cover, while high frequencies are reflected, making directional localization hardly possible. However, this also suggests that early koala representatives had a similarly high level of vocal ability to communicate in the dense tropical rainforest, obviously an old characteristic of this group, which developed very early. Modern koalas have an even larger middle ear, which can be related to the decline in vegetation, as infrasound spreads over long distances in open landscapes and this was probably necessary in order to detect predators in time while migrating to the individual food sources.
Systematics
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Internal systematics of the Phascolarctidae family according to Black and Archer 1997
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Two types are known. Nimiokoala greystanesi Black & Archer, 1997 (holotype copy number QMF 30382), represents the type species and lived in the early and middle Miocene. It is known from several partial skulls and lower jaw fragments, which were found, among other things, in the local fauna of the Neville's-Garden site, System B near Riversleigh ( Queensland ). Another lower jaw fragment from the South Prospect B local fauna near Lake Namba in South Australia is a species not yet named ( Nimiokoala sp.Black & Archer, 1997; specimen number SAMP 19952) and dates to the late Oligocene to the middle Miocene. The closest related genera are Litokoala and today's koala , which represent the sister group of Nimiokoala . Possibly it evolved from perikoala .
The generic name is derived from the Latin word nimius and means “excessive”, “excessive”, while “koala” refers to the close relationship with the koalas living today . Overall, the name Nimiokoala refers to the much more complex tooth morphology than other koala relatives.
literature
- Long, Archer, Flannery, Hand: Prehistoric Mammals of Australia and New Guinea, one hundred million years of evolution . Johns Hopkins University Press, Baltimore / London 2002, ISBN 0-8018-7223-5
Individual evidence
- ↑ Australian Museum: Riversleigh Rainforest Koala greystanesi. ( australianmuseum.net.au )
- ↑ a b c d K. Black, M. Archer: Nimiokoala gen. Nov. (Marsurpalia, Phasicolarctidae) from Riversleigh, Northwestern Queensland with a revision of Litokoala. In: Memoirs of The Queensland Museum , 41, 1997, pp. 209-228
- ↑ a b c Julien Louys, Ken Aplin, Robin MD Beck, Michael Archer: Cranial Anatomy of Oligo-Miocene Koalas (Diprotodontia: Phascolarctidae): Stages in the Evolution of an Extreme Leaf-Eating Specialization. In: Journal of Vertebrate Paleontology , 29 (4), 2009, pp. 981-992.