The History of Australia Podcast

Episode 3 - Dinosaurs

October 04, 2020 Jasmin O'Connor Season 1 Episode 4
The History of Australia Podcast
Episode 3 - Dinosaurs
Show Notes Transcript

By the Jurassic Period,  the supercontinent Pangea had schismed into Laurasia and Gondwanaland. Dinosaurs reigned supreme.

The History of Australia Podcast

Transcript - Episode 3 Dinosaurs


Welcome to the History of Australia Podcast, Episode 3, Dinosaurs. So in Episode 1 we’ve done the Permian and the Triassic. Now to go onto the period that really needs no introduction, the Jurassic. 

By the Jurassic Period, starting 200 million years ago, the supercontinent Pangea had schismed into Laurasia in the North and Gondwanaland in the south. The climate was still warm and tropical. There were no polar ice caps and carbon dioxide levels were about seven times higher than today. Ferns, cycads and conifers dominated the landscape. Fish and amphibians multiplied as did dinosaurs and mammals. 

The proliferation of dinosaurs and mammals seems to have been aided by another mass extinction that occurred at the Triassic/Jurassic juncture. This was not as large as the extinction event that occurred during the Permian that we spoke about in episode 1, but nevertheless large enough that it created this opportunity for the evolution of new forms of life. 

By the early Jurassic, placental mammals and marsupials had already diverged. Marsupials are mammals from the Americas and Australia that give birth to live but somewhat under-cooked young, and these then live in a pouch until they are able to look after themselves. Also in the Australian region of Gondwanaland, there was the formation of monotremes. For those who aren’t familiar with monotremes, they are primitive mammals that lay eggs (like a bird). Monotremes are found exclusively in Australia and New Guinea, which are islands to the north of Australia. Despite this growth in the variety of mammals, there wasn’t much growth in size. Mammals remained small, never tipping more than one kilogram.It was the dinosaurs that reigned supreme. 

During the Jurassic, there was the emergence of some pretty significant dinosaurs including the diplodocus, and brachiosaurus. Both are these colossal, giraffe-like herbivores from North America. 

That said, the fossil record of dinosaurs during this period in Australia in particular is pretty scant. There is a scarcity of fossils in the Australian Jurassic strata, particularly across the eastern half of the continent. 

The fossil record in Australia is far more abundant for the period after the Jurassic, the Cretaceous, for reasons that will soon become apparent.

During the Cretaceous Period, starting 146 million years ago, Gondwanaland, including Australia, India, South Africa and Antarctica, was breaking apart. Still, Australia remained joined to Antarctica, New Zealand and South America. Southern Australia lay within the Antarctic Circle. Australia’s climate was cooling with icy polar winters. Still the land was covered by towering conifers with ferns and cycads in the under-storey. There were also now flowering plants.

An inland sea called the Eromanga covered about a third to a half of the landmass.  The Eromanga Sea covered much of Queensland in the north and at one point extended all the way down into South Australia. The sea was shallow, cold, poorly connected to the open ocean, muddy and stagnant, with rivers draining into the basin rather than out to the ocean. This created much more ideal conditions for the preservation of fossils. Many of the large fossils that survive from this period are found in areas once covered by the Eromanga Sea. 

These would have been plants and animals living around the basin that, when they died, were washed by the rivers into the inland sea, where the stagnant waters allowed sediment to be deposited on top of them. The inland sea also gave rise to a range of marine fossils as well, some of which would really surprise you in terms of their scale. 

One of the excellent things about the fossils found in the Eromanga basin is that they are actually opalised. For reference, opals are gemstones often used to create beautiful jewellery and about 95% of them globally are actually Australian, cretaceous rock. 

Opals formed in the sandstones and mudstones, the sedimentary rocks, that were washed into the Eromanga Sea. Silica from these rocks leached into the water and this silica-rich solution would seep into and harden in any spaces or cavities between the remaining rocks. The pattern of silica spheres and water that results defract the light, breaking it into all the colours of the rainbow. So there are these eye-popping flashes of blue, green and purple. If the space was there because an animal or plant had died and been buried in sediment, then the opal formed a fossil replica of the object that was buried. This isn’t a common phenomenon. Australia is the only part of the world where opalised animal and plant fossils have been found. 

Probably the most famous opalised fossil is Eric the plesiosaur who was found at Coober Pedy by opal miners and now forms part of the Australian Museum collection.  Not only is the opalised skeleton of this animal preserved, but also the stomach contents of its last fish meal. Which isn’t it amazing that palaeontologists are able to work out something as intimate as a last meal for a being living 120 million years ago. And I’m wondering how it would go down if something happened to me, and I ended up a fossil being studied in hundreds of millions of years, what would that say about me, and about the human race? 

Anyway, Eric, being a plesiosaur,  was one of the four main reptiles that dominated the inland sea. There were Ichthyosaurs (a dolphin-like predator with four flippers), sea turtles (getting as big as 4 metres long), mosasaurs, a predator related to snakes and monitor lizards, and plesiosaurs, of which there are two main types, pliosaurs, like Eric, and elasmosaurs. 

Both pliosaurs and elasmosaurs are a snake/turtle/whale hybrid looking predator. They were something of a real life Loch Ness Monster. For those not familiar with Nessie, it has a small head, really long thin neck, wide flat body and four flippers. This prehistoric marine reptile came in at up to 12 metres long and would have been one of the apex predators of its time. 

Eric was on the smaller side of the plesiosaur/pliosaur spectrum, only about 2.5 metres long, so about the size of a seal. He was a unique breed of pliosaur with a comparatively long neck and a proportionately small head (other pliosaurs tended to have shorter necks and larger heads compared to other plesiosaurs). A keel on the snout suggests that Eric may have had a crest and also thin ridges of bone over the eye sockets.

These crests may have been used for either species recognition or decoratively as part of mating behaviours. That said, the function of the cranial crests remains speculative. They do appear too fragile for use in skull reinforcement, defence or male to male combat. 

Like other small pliosaurs, 'Eric' probably subsisted mainly on a diet of fish. Fish bones and gastroliths (small stones to help regulate buoyancy and aid digestion) and were found in the region of Eric's stomach. 

'Eric' lived in the Eromanga Sea about 115 million years ago. There is evidence that during winters the water would have gotten to near freezing. Which is unusual for reptiles, being cold-blooded, as it doesn’t really present much of an opportunity to get heat from their environment. So these marine reptiles might have possessed adaptations for example heightened or more stable metabolic levels, kind of like we see in large turtles today, or behavioural strategies like seasonal migration.

Eric was probably something of a fossil, even in his day. He was actually quite a primitive in his broader family of pliosaurs and plesiosaurs, but he was around relatively recently. Later evolved (derived) species were much bigger and had either diverged into the long neck/small head elasmosaurs or the short neck/big head plesiosaurs. But Eric was in the middle of those. I mentioned in Episode 1 how it is thought that even in Jurassic/Cretaceous Australia was already a relatively isolated place, a far flung corner of Gondwanaland, and so you see the survival of some ancient species surviving much longer than in other parts of the world. And you generally also begin to see the evolution of more distinctly Australian fauna. 

So I’m going to take a look now at two of those more distinctly Australian animals that were evolving during the Cretaceous. 

The first is the Muttaburrasaurus. I’ve chosen the Muttaburrasaurus because I love saying muttaburrasaurus. It’s really up there in the Excellent Words category. Muttaburrasaurus was a large, 7 metre long, 2 ⅕ metre high, plant-eating dinosaur living in eastern Australia. 

If you have a look at a physical depiction of it, it has a fairly standard herbivorous dinosaur look. The Australian museum gives it a dewy green colour. It has a large thick tail, about the length of its body. It has four legs, the front two are a little short and useless looking, not quite as bad as a T-Rex or Kangaroo, but in that vein. it has a thick, llama-length neck and a parrot-esque beak/snout. Given it’s sort of dumpy front legs, it's thought it could probably have gotten around on either two legs or four legs, so again I’m imagining something similar to a kangaroo here, though it has bird-like hips, so it would be running, not jumping on two legs. Its teeth suggest a plant-based diet. The strong beak would be used to snip plant matter, that would then be ground down by sizeable teeth. It may have eaten the ferns and cycads that were growing plentifully at the time, though that’s just conjecture. 

Aside from dumpy arms and a large beak, another notable physical attribute is a 15 centimetre long spiked thumb on each hand. This may have been used defensively in case of attack. 

The muttaburrasaurus is relatively well-known in Australia because along with Eric, it is one of the most complete fossil finds in a country where that is fairly uncommon. It was discovered in the northern state of Queensland, near the town of Muttaburra. There have also been fossil finds in other parts of Queensland and as far south as Lighting Ridge in New South Wales. 

Another animal that came about during the cretaceous that was more distinctly Australian is the Steropodon Galmani. This one is a cute little 35 centimetre long, platypus-like monotreme. 

So if I was to describe Galmani to you, it’s very much like a platypus, but less well adapted to an aquatic environment. It has a duck-like bill, little black eyes and a fat sausage-like body. So it’s a bit of a beefy platypus, not so hydrodynamic. Also it’s tail is like a rabbit’s, whereas a platypus has a large flat rudder-like tail. 

A chunky platypus may not sound very impressive but it's actually a really large mammal for the early Cretaceous. In fact, it’s the largest known mammal from this time. 

Not a lot is known about Galmani because the fossil record is fairly scant. The only known fossil is a partial jaw bone that comes from Lightning Ridge in New South Wales. Actually the naming of the fossil reflects this origin. Sterope is Greek for ‘flash of lightning’ and odon is Greek for tooth. So it’s lightning tooth, reflecting the opalised nature of the fossil. 

By analysing a single jaw bone fragment and three teeth, palaeontologists and mammalogists have placed this specimen in its family tree. They’ve then extrapolated about it’s behaviour from its closest living and deceased relatives. It was probably a monotreme, laying eggs and it might have spent its days hunting for insects, crayfish and little aquatic animals to eat. 

So you can see that during the cretaceous there is this diversification and flourishing of life and we have this proliferation of plesiousaurs, dinosaurs and mammals. Unfortunately another mass extinction event put an end to all of that. 

About 65 million years ago, a sudden change in the earth’s atmosphere, probably caused by a meteorite though that’s up for debate, wiped out the dinosaurs and plesiosaurs amongst other species.

Reptiles such as crocodiles and snakes survived, as did some birds and mammals. The types of animals that were around afterwards looked a lot more like what we see today with frogs, turtles, birds, snakes and mammals. 

So this was the heralding of the end of the cretaceous and the beginning of the Eocene Epoch starting 56 million years ago. The climate was warming again and coniferous forests were being replaced more by rainforest, including beech trees. Australia, Antarctica and South America remained hanging together by a thread in the remnants of Gondwanaland but by 23 million years ago, Australia had wrenched its independence from Antarctica and South America. 

As Australia drifted northwards away from Antarctica and South America, rainforests covered  the warmer, northern parts of the continent and there is a real explosion in the diversity of flora and fauna, as you would see in rainforests today. During this period of separation, Australia now developed a lot of it’s quintessential and unique fauna. I’m talking the forerunners of kangaroos, possums and koalas. There were also some fairly epic animals, like marsupial lions, which I’m going to talk about in more detail in a later episode when we get up to the megafauna. 

By about 10 million years ago, Australia was again cooling, the rainforest retreating and being replaced by grasslands with beautiful wildflowers. Gums and wattle trees began to emerge and take over. Australia also collided with South East Asia about 5 million years ago, facilitating the migration of animals from that land mass, including rats and mice for the first time. 

This takes us up to the Pleistocene Epoch (1.6 million - 10,000 years ago). The time of the Megafauna and the arrival of humans on the Australian continent. So we are going to leave it there for today. Next time, we are going to look at the origin and expansion of humans and that’s going to take us right up to the doorstep of Australia. 

I would love to hear what you think of the podcast, so please reach out at historyofaustraliapodcast@gmail.com. Until next episode, keep safe and I’ll see you soon!


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