If we'd only been there to see...

You're standing at the Dinosaur Dreaming site, 120 million years ago. Imagine that instead of the sea and waves, you're looking across a broad river valley, almost as wide as the distance to the horizon. Over the horizon you can just see the tops of the high rift mountains that form the edge of Antarctica.

The valley is green and fertile, with tall pine-like trees, and thick forests of ferns and ginkgo trees below it. There are only a few trees with flowers, and almost no grasses-they have only just evolved, and pines and ferns are still the dominant plant type.

Small two-legged dinosaurs, the Hypsilophodonts, run through the ferns, some as small as chickens, others as big as a person. From time to time they stop to browse on the leaves and fruits of the plants, their forepaws and fingers reaching for and holding branches as they eat, but they are always alert for the sounds that surround them in the forests. Small lizards scuttle up the tree trunks, sunning themselves in the sunbeams that shine through the leafy canopy above.

From somewhere further along the valley comes the roar of a hunting Allosaur, a fierce hunter and cousin of Tyrannosaurus with pointed teeth longer than your hand. The small dinosaurs scatter into the undergrowth to hide in the shadows.

You move further through the forests, towards the river plains and the wide, braided rivers that carry the melting snow from the high mountains of Australia down to the coast, far away to the east, down past where Gippsland is today. On the river plains herds of small Protoceratopsid dinosaurs graze, about the size of sheep, travelling in herds. Tall Ornithomimids, the ostrich-like dinosaurs, flock this way, wheeling out of your path at the last minute, startling the turtles that were sitting on the fallen logs which plop back into the river, only their nostrils above the surface showing where they are swimming.

Also in the rivers are huge amphibian Labyrinthodonts, as big as crocodiles, waiting for a unwary dinosaur to get bogged while taking a drink at the water's edge. They nibble at the bones of other animals that died out on the plains last season; these bones now wash downriver in the flood waters, settling here and there on the banks, where they become buried in sands and mud to become fossils.

Overhead, Pterosaurs wheel and watch for the rise of fish, and lungfish in the rivers, swooping down to catch them with a 'clack' of their teeth. The head of a plesiosaur, a large swimming reptile, rises out of deeper parts of the river to look at you curiously, and then dips back into the river, ripples from its fins and tail marking its passage upriver.

Over winter, because Australia is much closer to the South Pole than it is today, the sun sinks below the horizon, and it is dark for almost a full three months from early May. Many of the dinosaurs may migrate north, to areas where the sun still shines, others may hibernate during the winter months, where the temperature drops to below freezing. Others, like the Hypsilophodonts, use their large eyes to help them see in the dark, and keep on foraging for food, surviving in the cold and dark until the sun rises again in late July.

The sun does not set between early November and late January. One long, long summer day...

Between Australia and Antarctica, in the middle of the rift valley, a chain of tall volcanoes puff out clouds of steam and ash, and fresh lava flows. Many of the sediments in the rivers are from ash falls from these volcanoes.

Since that time, Australia and Antarctica have been moving apart at about the same rate your fingernails grow, 5 cm per year. Every time you cut your fingernails, or toenails, that is how much further we have moved from Australia since the last time you cut them! It doesn't seem very fast, but 110 million years is a long time, and about 85 million years ago, the river valley got so wide that the sea slowly flooded in, turning the valley into the sea between Australia and Antarctica, stopping the dinosaurs and other animals from migrating to and from Antarctica for ever.

Since that time, the world has cooled down, and the Antarctic dinosaurs went extinct. So did the Australian dinosaurs. We don't yet know exactly why: some people think that it was because of volcanoes erupting in India, causing lots of ash to black out the sun for many months or years. Some think that it was because two large asteroids struck the Earth-one near Guatemala, and one in India-causing unbelievably huge explosions, setting off the Indian volcanoes and putting enough ash and smoke into the atmosphere to block out the sun for years. It may have been a combination of both things!

Some animals survived because they were able to move to other areas, less affected by the ash and smoke. Other animals survived because they were able to hibernate through the times of no food, until the ash and smoke settled and plants began to grow again.

Australia kept drifting northwards, towards where it is now, but about 1.6 million years ago it began to get very dry. Up until then there had been huge inland seas. Dolphins swam in them, and huge flocks of flamingoes nested around their edges. Diprotodons as big as cows, browsed on the leaves of the trees that grew in thick forests.

But then the centre of Australia dried out. It was after that time that the dunes of the Bridgewater Formation were deposited, as hot dry air blew to the coast from out of the deserts at the centre of Australia.

Now the rocks that made up the river valley are slowly eroding into the sea. The bones of the dinosaurs, the fish, turtles, plesiosaurs, amphibians, and the other animals that lived in the river valley are being found by scientists as the rocks erode, and are helping them to put together the story of what Australia was like in the time of the Dinosaurs...