Although soon abandoned, Burke and Wills had started their expedition with a wagon that could be converted to a boat. They planned to use it to cross rivers and the inland sea that was still rumoured to exist.

They may have walked past evidence of the existence of such a sea, albeit one that had existed long ago. An ammonite fossil preserved in the rock can clearly be seen in the limestone riverbed of the Flinders River near where Burke and Wills passed.

Ben Beeton explains about the sea that existed in this area between 90 and 130 million years ago. He describes what the ammonite was like and some of the other fossils that could be found in the Eromanga Sea.

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TRANSCRIPT

-We're on the Flinders River about 50 kilometers from the gulf. And we have found something absolutely amazing. Now, we know that, say, about between 130 million years ago to say about 90 million years ago, there was an inland sea in Australia.

It started to flow through into Australia from the gulf approximately 130 million years ago. Now, I'm standing on a piece of limestone that has been exposed as the river has flowed this way over potentially thousands of years. If we look to the banks, we can't see the limestone.

So it's only here at the dried base of this river that we're able to see something as fascinating as this. It's an ammonite. Which means it's a cephalopod. Cephalopods are groups of animals such as the octopuses, the squids, the pearl nautilus is another. And the way that this animal grew, you can see it would have started quite small.

Each one of these is a chamber. And the actual creature lived in each one of these chambers as it grew into adulthood. It existed at this size probably in this area here. And it used the rest of its shell for buoyancy.

Traveling with the currents, to get food, it will have filled this area with air. And using that, it created a buoyancy. And it probably traveled in groups as well. Now, it's difficult to tell when this ammonite actually existed.

As I've said, the inland sea lasted a long time. 130 million years ago to about 90 or so million years ago. And because this is one of the first areas to be flooded by the inland sea, it's actually called the Eromanga Sea.

It could be at the beginning of the sea. It could be at the end. It's hard to say. There's so much that we don't know. Perhaps if we had the correct scientific tools with us now, we could give you an exact age. But I want you to think about an environment perhaps similar to the Great Barrier Reef in a way.

You can imagine. This is a fascinating, colored-- all sorts of multi colors here. Corals of all sorts. But there would have been other animals, too. There were things such as Kronosaurus queenslandicus, which is a Pliosaur, a huge marine reptiles similar to a crocodile, but with flippers and a lot bigger.

There were Plesiosaurs, those ones with the long necks and flippers. There were Ichthyosaurs. Ichthyosaurs looked similar to dolphins. Now, the ammonites were a huge group of animals. They all died off at the end of the Cretaceous period along with the dinosaurs when an asteroid collided with the Gulf of Mexico.

An interesting thing about that collision is that the Gulf of Mexico was a shallow sea, such as the inland sea in Australia. But when the asteroid hit, it was actually shallow and there was a limestone at the base of it, just like this limestone.

When the asteroid impacted, powdered limestone went up into the atmosphere. And perhaps if the asteroid had hit a deeper area of the ocean, the extinction wouldn't have occurred with the violence that it did and I wouldn't be here talking about the ammonite right now.

Now, the last thing I'd like to add is that ammonites grew to all different sizes. Up to the size of tractor tires. So here at the Flinders River, we are seeing absolute proof that there was an inland sea in Australia. And compared to the history of this planet, it actually only happened yesterday.

There were many inland seas in Australia. There was once an inland sea in which over 400 million years ago, nautiloids the size of semi trailer trucks used swim in that kind of ocean. So the sea has come in and out many, many times in the ancient past.

This is an ammonite from the Eromanga Sea. We're currently in the Eromanga Basin. And it's a fascinating example of deep time and our ability to look back and imagine an incredible, ancient world just as fascinating as the world around us now.

What I'm doing at the moment is drawing in the fleshy element of the animal. Now, a fossil as it is is only part of the story. Obviously, the shell is the only part that's fossilized. But in drawing in the rest of the animal, what I'll be able to show you is something of a sketch of what this creature actually looked like.

What I'm drawing here is actually the fleshy element of the ammonite. Now, the ammonite was a cephalopod. It was similar in many respects to the pearl nautilis, which exists today. It had these tentacles and it most likely swam backwards.

This element of the animal's fascinating as well. It probably started quite small. And as it grew, these different chambers grew with it. It only existed in probably about this part of its shell. The rest of it it used for buoyancy. It was able to float up and down moving with the currents.

And potentially lived as part of a larger group. You can see it's probably got quite large eyes. Such is the pearl nautilis today. And one of the fascinating things about the ammonites is the size to which they grew. You could imagine something like this but the size of a tire tractor.

They died out with the dinosaurs at the end of the Cretaceous period. It's a fascinating creature of a very different time in the inland sea of Australia that we call the Eromanga Sea.