FREE ESSAY ON RIVERSLEIGH

RIVERSLEIGH

"65 MILLION YEARS OF CONTINENTAL WALKABOUT"
The Riversleigh excavation site provides views of life in Australia at chronologically
different periods. These different periods are what lead Australia to its unique
environment and habitats of today. This modern appearance developed in the Eocene time.
The initial conditions of the early Paleocene and Eocene periods the land masses where
experiencing tropical weather conditions. Lush vibrant rainforest developed in these
conditions. Comparisons between leaves characteristics can be viewed at Maslin bay here
leafs from the Eocene period are similar to modern notophyll forests. However, Eocene
leaves still retained a distinctive quality because of Nothofagus and conifers. 
The continents of Australia and South America were still coupled by way of Antarctica.
Through this positioning it was possible for rainforests to extend between the
continents. Routes were established due to the connections; however, there were sporadic
breaks in the route. The breaks were cause by archipelagos and etc. Finally the eastern
part was closed when Australia separated somewhere between 45 and 38 million years ago. 
However, the continents of Australia and Antarctica separating brought previously
isolated types of forests that included numerous types of trees, including Nothofagus.
The fact that it was commonly associated with South America accounts for some
similarities with forests of today in Tasmania. Discoveries of various fossilized animals
also suggest the once connection of the continents. 
Since the separation of Australia it has been heading in a northern direction. This
northern movement is about 11 cm each year. Thus, around 25 million years ago the
continent was actually ten degrees further south. The southerly positioning suggests that
Australia was infested with rainforest. The Riversleigh's findings show that Australia's
northern region once had a rich rainforest. Deposits found at the Simposn desert suggest
central Australia had a closed forest. Yet, potentially less diverse than forest
jacketing the northern regions. 
Modern Rainforest offer a complex history of the Australasian regions rainforest. The
'palaeoaustral' rainforest have taken refuge in northeastern QLD and the mountains of New
Guinea. The origins of New Guinea's forest have Gondwanan origins. Nonetheless, the
rainforest of the region had to be created by "…drifting micro continental
fragments…" that produced forests origins in Gondwanan, India, and etc. 
15 million years ago landmasses from southeastern Asian plates and the Australian crustal
plates collided and were respectively "…shoved down each other's throats." Thus a
decline of Australia's rainforest in the central and northern regions due to build up of
mountains. Now, weather would be affected and possibly productive rainfall would be lost
to the highlands of New Guinea. Increasing problems were permanent polar icecaps, and
cooler oceanic temperatures. Thus, effectively reducing the amount of precipitation and a
stage of cooling and drying occurred. 
Migration of animals and plants (rainforests) were increased with the contact of Asian
land. Various groups could make beneficial advances by using the migration routes. These
migration routes, which allowed reptiles, frogs, birds, bats, and rats migrate into
Australia. Before colliding with Asia and its separation with Antarctica Australia might
have supported biota, which included Eurasian and Gondwanan clusters. The evidence for
this comes from rich fossil deposits at Riversleigh. 
"Riversleigh's fossil deposits indicate that a number of vertebrate groups probably first
entered Australia from south eastern Asia more than 30 million years ago." There is no
relating evidence of Asian taxa within Australian plants since the last 15 million years.
Thus, they had already invaded before the collisions. Ice sheets lead to a increase
destruction of Rainforest. Now, pockets and patches of forest were left. The remaining
forests were just basic enough to preserve examples of archaic rainforest groups. 
The devastated rainforests were replaced by alternating forests of wet and dry types.
Variation in the world's climate proved difficult for animals trying to pass back and
forth. Now, grasslands and woodlands followed which led to kangaroos beginning to
diversify. Australia was not effected glaciations during the Pleistocene Epoch (ice age).
Nonetheless, it had a impact on the development of Australia's biota.