Episode 50 – Australia

Listen to Episode 50 on PodBean, iTunes, YouTube, or wherever you find your podcasts.

This episode, we’re exploring the largest “island” in the world. We’re discussing the long geologic history of how this landmass came to be the way it is now, and what fascinating ecosystems have come and gone along the way. Join us on a trip Down Under, to Australia.

In the news
Two species of peccary identified at the Gray Fossil Site, TN.
Newly analyzed ichthyosaur specimen reveals signs of counter shading and blubber.
Fungus remains have been identified at the (you guessed it!) Gray Fossil Site, TN.
An opalized dinosaur jaw described from Australia.

Australia

Australia is both a country and a continent. As a continent it includes Australia the country and the islands of Tasmania and New Guinea. It is centered on the Indo-Australian tectonic plate which includes the subcontinent of India and reaches to the edge of Antarctica. It is the smallest continent and sixth largest country in the world. It is also the flattest and lowest land mass on Earth, its flattest points characterized by an extremely dry and arid environment with slow-flowing rivers and salt rich lakes.

Australia-climate-map_MJC01
Australia’s arid interior is known for its red color. This is due to build ups of iron in the soil from long-lasting erosion. Image by Martyman from Wikimedia Commons.

The only things stranger than the land are its inhabitants. The majority of taxa found there are endemic to Australia, meaning they are found nowhere else. Most notably, placental mammals (the dominant mammal group in the rest of the world) have been out-competed by marsupials and monotremes there.

Kangur.rudy.drs
Though marsupials are also found in South America, the macropods are only found in Australia. This group includes kangaroos, wallabies and quokkas. Pictured here is a red kangaroo (Macropus rufus). Image by Drs from Wikimedia Commons.

An Old Continent

Australia is also home to the oldest dated materials in the world. Zircon crystals found in Western Australia have been radiometrically dated to 4.374 billion years (+6 million years). This places them just 160 million years after the formation of the solar system.

Zircon-249203
Zircon crystals, or zirconium silicate, are commonly formed within igneous and metamorphic rocks. The zircon crystals in Australia likely formed about the same time Earth’s moon was formed from a planetary body impacting the Earth. Image by Robert M. Lavinsky from Wikimedia Commons.

Over the next 4 billion years, the sections of Australia formed roughly from east to west, gradually constructing the landmass we know today. But it didn’t look quite like this until much more recently.

Ausgeolbasic
Geologically speaking, Australia is very stable. Situated in the middle of its tectonic plate, it experiences few earthquakes and has almost no volcanic activity. Image by Rolinator from Wikimedia Commons.

A Trip Through Gondwana

Australia first starts to take shape when it is crushed together in the super-continent Rodinia, just over 1 billion years ago. When Rodinia broke up, between 830 to 745 million years ago, Australia was a part of the eastern chunk which included what would eventually be India and Antarctica. By the Cambrian, starting just before 500 million years ago, Africa and South America join this landmass to form the famous southern supercontinent of Gondwana.

Snider-Pellegrini_Wegener_fossil_map
Gondwana connected four of Earth’s continents and allowed animals and plants to migrate across it’s expanse for hundreds of millions of years. Its history is told through the fossils found on the now separate continents today. Image jmwatson@usgs.gov form Wikimedia Commons.

Throughout the Paleozoic Era, Australia is covered by a long history of shallow seas, and as they start to receded, the continent sees some of the earliest land-dwelling vertebrates and plants. The first amphibians in Australia are known from track-ways in the southeast of the country.

Toward the end of the Era, Gondwana joins up with the northern landmasses of Laurussia and Siberia, and Australia finds itself at the southeastern tip of the new super-continent of Pangaea.

509px-Pangaea_continents.svg.png
By far the most famous of all the super-continents that have existed so far, Pangaea formed a “C”-shaped landmass. The interior sea become known as the Tethys Sea. Image by Kieff from Wikimedia Commons.

Throughout the Mesozoic Era, as the world warms and Australia shifts to the north, the island-continent becomes more temperate and lush. This trend more or less continues in the Cenozoic Era as the continents gradually pull apart, eventually leaving Australia isolated by the Eocene, around 40 million years ago, and takes on the warm and dry climate we know today.

To this day Australia continues to move north-east at about 7 cm/year, a rather quick pace for a continent.

481px-Pangaea_to_present
Watch Australia on its eons-long trip around the world. Image by Kious, Jacquelyne; Tilling, Robert I.; Kiger, Martha, Russel, Jane form Wikimedia Commons.

Fossil Australia

The fossil record in Australia is full of oddities.

Very few dinosaurs have been identified there, fewer than 20 species so far. We don’t see horned dinosaurs or hadrosaurs, but we do find a diverse array of sauropods, armored ankylosaurs, and small bipedal ornithopods, as well as a few predatory theropods.

The most well-preserved dinosaur is the famous Muttaburrasaurus, an iguanpdontid that grew to 8 meters long.

Muttaburrasaurus_skel_QM_email
Muttaburrasaurus (pictured above is a specimen from the Queensland Museum) is known from the most complete dinosaur skeleton ever found in Australia. Image by Cas Liber from Wikimedia Commons.

Australia is famous for marsupials today, but these mammals actually appear to have originated in North America, traveling across the Gondwanan continents and only hitting it big in Australia fairly recently. Starting in the Miocene, we see the development of some of Australia’s famous marsupial megafauna, including such stars as DiprotodonThylacoleoMegalania, Wonambi, Quinkana, Dromornis, and Genyornis. Many of these are now known from the Naracoorte Caves in South Australia.

 

Palorchestes_BW.jpg
Palorchestes is sometimes called the “marsupial tapir” due to the likeliness that is possessed a proboscis. This strange marsupial grew to about 2.5 meters long.  Image by Nobu Tamura from Wikimedia Commons.

The earliest monotremes in Australia are known from way back in the Cretaceous. Currently the oldest monotreme is Steropodon galmani.

Zaglossus_hacketti
Zaglossus hacketti is the largest monotreme ever discovered. Known from Pleistocene material in Western Australia, it measured about 1 meter long. Image by Dixi from Wikimedia Commons.

The history and geology of Australia is incredibly complex. This is but a glimpse. If you’d like an even more snapshot look here’s a poster of Australia through time that might help.

 

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2 thoughts on “Episode 50 – Australia

  1. Ed Culver December 27, 2018 / 4:32 pm

    I know it’s something of a meme, but Australia has a reputation for a disproportionately large number of species that are toxic or venomous, such as the pretty little blue-ringed octopus. Is this just hyperbole or does Australia actually have more toxic and venomous species than, say, Africa?

    Like

    • commondescentpc January 1, 2019 / 1:06 pm

      As far as we know, Australia doesn’t really have more toxic species in general, just very famous ones. Snakes are sort of an exception – there are a high number of venomous snakes (though not necessarily dangerous snakes) on the continent, and this is probably less related to Australia being dangerous, and more to do with the fact that Australia is isolated, and only certain groups of animals have made it there. Just like only a few groups of mammals, birds, and insects have really been successful on Australia, elapid snakes (which happen to be venomous) are among the main groups of snakes to make it big in Australia.

      Liked by 1 person

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