Australia: The Land Where Time Began

A biography of the Australian continent 

The Marsupial Fauna 

The biological integrity of Gondwana is indicated by the very limited Early Cretaceous mammals found in fossil deposits of central northern New South Wales, but provides no evidence of the habitats the animals occupied. The deposits from southeast Queensland, of Early Eocene age, that is better known, but still limited, is believed to suggest the presence of complex forests that were rich in fruit-bearing plants and insects. There does appear to have been, at least regionally, diverse lowland rainforests, such as the Riversleigh Deposits of northwest Queensland, from the Late Oligocene to the Middle Miocene.

It is believed bats dispersed to Australia from Eurasia, via an archipelago the probably linked Australia to Asia, as a stepping-stone for flying animals, birds and bats, since about the Early Eocene. Between the Middle Miocene and the Early Pliocene the Australian continent appears to have suffered 1 or more climatic crises, most of which involved the decline or extinction of animal groups that would have been forest inhabitants, such as ringtail possums, and increase of animal groups of more open habitats, such as the grazing kangaroos, which became abundant for the first time in the Early Pliocene. The forest specialised species appear to have been largely restricted to refuge areas such as small areas in the wet tropics of northeast Australia and New Guinea. During the late Tertiary, Middle-Late Miocene, the forests were opened up as the climate dried. This is believed to have led to a triple convergence in which 3 lines of Australian possums evolved gliding forms, apparently to move among trees that were now further apart, their canopies no longer being close enough for the possums to move from one tree to the next without descending to the forest floor, which would have exposed them to increased danger of predation.

Rodents appear to have reached Australia from Asia some time in the latest Miocene and earliest Pliocene, probably by way of a relatively dry corridor of islands of an archipelago, possibly rafting from island to island (Hill, 1994).

One unique feature of the Australian marsupial fauna is that Australia never seems to have developed large mammalian carnivores. At the time when the other continents were populated by their placental megafauna such as mammoths and sabre-tooth cats, Australia had a marsupial megafauna. There were diprotodonts as large as a hippo and giant kangaroos and wombats but the carnivorous marsupials consisted of the thylacine and marsupial lions, the largest being about the size of a modern leopard. The largest mammalian predator, in height at least, seems to have been a 2-metre tall carnivorous kangaroo. These kangaroos, 2 of which were Propleopus in the Pliocene and Pleistocene and the Ekaltadeta from the middle Tertiary. They appear to have had the speed of cheetahs and the crushing powers of hyenas. Their molars had flanges on their margins that could protect their gums from splinters if they crushed bone, as do the crushing teeth of modern carnivores such as dogs.

Marsupial origins
Marsupial Reproductive Pattern Classification
Defining characters of marsupials
Anatomy based relationships - teeth
Foot Structure
Ankle bones
Brain anatomy
Sperm morphology and anatomy
Sex chromosomes
X-chromosome inactivation
Sources & Further reading
  1. Chris Johnson, Australia's Mammal Extinctions, a 50,000 year history, Cambridge University Press, 2006
  2. M.Archer, S.J. Hand & H. Godthelp in Hill, Robert S., (ed.), 1994, History of the Australian Vegetation, Cambridge University Press.
  3. Tyndale-Biscoe, Hugh, 2005, Life of Marsupials, CSIRO Publishing.

Links

Miocene mammal reveals a Mesozoic ghost lineage on insular New Zealand, southwest Pacific

 

Author: M. H. Monroe
Email:  admin@austhrutime.com
Last Updated 26/05/2012

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading