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ROB MORRISON: Ben Kear is a palaeontologist, a scientist who studies extinct plants and animals. He helps to build displays in the South Australian Museum but he also works in the field, locating and retrieving ancient fossils.

BEN KEAR: I work mainly on vertebrates, Mesozoic vertebrates which means vertebrates from the age of dinosaurs, particularly marine animals such as sea turtles, ichthyosaurs and plesiosaurs.

ROB MORRISON: The opal is Australia's own gem stone and much of it is mined at Coober Pedy but this outback town produces riches of another kind. Every now and again the opal miners turn up not opals but mysterious bones.

BEN KEAR: Where we find ancient sea reptiles strangely enough is in the desert of central Australia. This is effectively now what was 120 million years ago the bottom of the sea. The mud under your feet is literally mud from this ancient sea floor. Walk along and you pick up fossils. It's that easy.

Much of the animals that were alive in the oceans in the age of dinosaurs are the same types of things you find in the ocean today, for example, clams, shellfish of all different kinds: cockles; snails; all these things were around. Many of them have very close relationships to modern groups.

Over millions of years the fossils that are preserved in these rocks have been replaced by opal, the gem stone that Australia is famous for and what this can sometimes do is turn what was once a clam living at the bottom of the ocean into a fantastic piece of opal.

Another example would be this kind of odd bullet shaped structure. This is actually the internal skeleton of a squid-like animal called a belemnite. This is only the very end of the body and the whole thing is probably about that long, looking much like a modern squid, but this is only the very tip of the shell.

We're looking at about 120 million years ago so this is somewhere around the middle end part of the age of dinosaurs.

ROB MORRISON: But not all ancient reptiles were dinosaurs. Others that swam in the early oceans included ichthyosaurs.

BEN KEAR: Imagine an animal which looked something like a giant reptilian dolphin. They were effectively the dolphins of the Mesozoic. They hunted fish, squid, this sort of thing and they also include some of the biggest marine reptiles of all time.

ROB MORRISON: And some of the largest fossil vertebrates are plesiosaurs.

BEN KEAR: The classic body shape is something that looks a bit like the Loch Ness Monster, a huge long swan-like neck, four flippers, a short turtle-like body. Some of the biggest ones, and certainly the biggest animals we get in Australia is an animal called kronosaurus, and this is like a giant saltwater crocodile with flippers. It's the killer whale equivalent of the Cretaceous.

ROB MORRISON: Like dinosaurs ichthyosaurs and plesiosaurs are extinct, but other types of reptiles that are even older still survive.

BEN KEAR: Well, certainly turtles are something of an evolutionary success story. They have been virtually unchanged since dinosaurs were running around. You would imagine an animal which looks like a sea turtle today. These animals are feeding on the bottom. They're eating shells and shellfish and we know this because we can find the remains as gut contents.

Imagine you can open the skeleton up and you find this white phosphatic mass and within the mass is broken up fragments of shells so they're actually swallowing these things, breaking them up and processing them and we actually find the remains of the droppings.

There's many different ways we can extract fossils from rocks. The most obvious is to use physical methods, things like pneumatic hammers, even dental picks, and slowly remove the rock from around the bone. However a slightly more interesting way we can do it, it's slow, but has beautiful results, is to use acid.

Here you can see something that has only been in the acid for a very few days but is effectively the emerging fingerbones of an ichthyosaur. This is part of a paddle of one of these giant marine reptiles.

The end result of literally dissolving away something like this can be something like this. So this is the skull of a 100 million year old turtle. It is in fact one of the earliest representatives we have of sea turtles.

Soft tissue generally doesn't fossilise although sometimes we do get remnants of it in terms of skin impressions, even sometimes bits of the skin itself.

One of the techniques that we can luckily now use is cat scanning or computerised scanning. If we end up with something like an ichthyosaur we can prepare the skull out, put it through a cat scanner and then send it off to a computer guy who will reconstruct these animals in three dimensions. You can look at the bones and start to put muscles, skin, eyes, all these sort of things and reconstruct these animals from the bones up. It's kind of like building your own monster.

ROB MORRISON: The reconstructions end up in museum displays where they are a constant source of fascination to the public which never tires of dinosaurs and their interesting relatives.

BEN KEAR: Certainly wandering around in the desert and finding a complete skeleton under your feet is a breathtaking experience but then that's only the beginning of the process. Putting this animal together after 120, 130, even sometimes 200 or more million years is an experience you just can't match.
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