Victoria’s southern Bass Coast around Inverloch is not only a lovely place to spend Summer at the beach and explore the surrounds, but it is also a walk into the past.
The sandstone rock platforms date to around 120 million years ago (mya) which was during the Cretaceous Period and it is fascinating to try to consider what these times were like.
To do so requires a bit of an understanding of Australia’s place in the world then and its climate.
Southern Australia with it’s connection to Antarctica intact had moved from the northern Hemisphere where it had been some 550 mya, to close to the South Pole as part of the Pangaea super-continent.
During this migration south, around 360mya, during the Carboniferous Period when ferns, seed ferns, horsetails and gymnosperms evolved, conditions were warm and tropical which resulted in massive “Coal forests” dominating the land until the Permian Ice Age 280mya which resulted in ice glaciers covering most of south-eastern Australia (as demonstrated in Werribee Gorge and around Heathcote). These “Coal forests” became buried and are now the massive coal (as well as oil and gas) deposits which are being mined in various parts of Australia including the Bass Coast.
After the Permian Extinction event of 252mya, Australia became warmer and more monsoonal with the Triassic and Jurassic Periods, and much of Australia became large sedimentary basins with little evidence of Jurassic Period dinosaurs.
By 120mya the Australian craton had started migrating northwards but this time AWAY from the Antarctica craton creating a massive Rift Valley (similar to what is occurring in East Africa today). Africa had separated from South America (c140mya) which was still connected at its southern tip to Antarctica. Tasmania was at the South Pole.
This rifting created subsidence including the land between Tasmania and Victoria forming a massive flood plain with large rivers and many small rivulets at a time before the Ice Ages and well before Antarctica had become covered with ice and well before Australia had become an arid inland region.
120mya, the climate in this region was more of a cool temperate climate with snow on the alpine areas, long polar winters without sun and the rivers covered in ice. This was well BEFORE Australia had been populated by monotremes, marsupials, snakes or goannas but there were a range of Cretaceous dinosaurs and other animals.
Walking on these 120mya sandstone rock platforms, one can easily see today remnant fossilized trees which had fallen in the silt, and each year researchers come to dig the coast line looking for small dinosaur fragments amongst the conglomerate rocks remaining from the rivulets.
This leads us on to how Australia’s unique animals evolved and came to be in Australia.
The first monotremes evolved c110mya and whilst the first marsupials (early opossums) evolved c100mya in North America, they had to migrate to South America and then across the Antarctic (before the trans-Antarctic mountains were pushed up c50mya) arriving in Australia c55mya where they then evolved into kangaroos, koalas and wombats.
40mya, whales evolved from the hippopotamus and would eventually travel to Australian waters.
Australia is well known for having the most venomous snakes on earth, and it is interesting how these evolved.
Snakes evolved from lizards around 120mya, with the “Old World” snakes being the pythons which have residual lizard features.
The elapids evolved c38mya and arrived in Australia c25mya from the north perhaps from a close ancestor of the semi-aquatic Sea Kraits which had evolved at the same time.
It was around this time that Australia’s climate dramatically changed. Australia had already become much drier c38mya when the Antarctic started to develop ice sheets and duracrusts started to form across Australia. This arid climate accelerated when South America and Tasmania both had separated from Antarctica allowing the circum-polar ocean currents to form c27mya which would result in a freezing of Antarctica
Australian terrestrial Elapid venomous snakes then evolved over time into a range of closely related species including Eastern Brown and Taipan with their tolerance to the new arid inland conditions, the Copperhead and Tiger snakes, but also the Australian elapids evolved into vivaporous sea snakes (c16mya).
The Australian goannas (monitor lizards) and pythons arrived in Australia from the north c15mya, although the pythons may have arrived somewhat later around 8mya.
Presumably the ice ages of the Pleistocene (the last 2.8 million years) were a trigger for the evolution of Australia’s megafauna which tend to cope better in cold conditions. Yes, it is better to be shorter and smaller when there is global warming!
Homo sapiens evolved some 300,000 yrs ago, and around 45,000 yrs ago, Australia’s indigenous peoples migrated to Australia from Sri Lanka. In contrast, the Polynesians migrated much later, starting around 3000BC and migrated from Taiwan region to eventually cover most of the Pacific Islands, New Zealand and to Hawaii.
Bass Strait did not become the sea way that it is today until the end of the last Ice Age resulted in sea levels rising c8000 yrs ago which cut off Tasmania from the mainland.
More details on how Australia evolved is on my wiki page here.