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Helen Thompson: This is an amazing fossil, can you tell us a bit about Eric the plesiosaur?
Robert Jones: Eric is an opalised pliosaur, his bones are completely replaced by opal. He was found in the opal fields of Coober Pedy in South Australia.
He was bought by a private collector and then he was offered to us to prepare it - clean up all the bones and reassembling.
So after many hours of work cleaning up all the bones we get what we have here behind us, a near complete skeleton of an opalised pliosaur.
Helen: I notice there are gizzard stones from the stomach of Eric. What is the function of these?
Robert: Eric had teeth for catching fish but he didn't have any teeth for grinding up the fish, so he would swallow the fish pretty much whole and the gizzard stones were used to grind up the fish,
so the food in his stomach, to allow the digestion to take place.
Helen: What do the gizzard stones tell us about the diet of Eric?
Robert: Well, basically what it tells us that whatever it ate had to be ground up in the stomach and they didn't use their teeth to chew it up like many other herbivorous dinosaurs ...
and other dinosaurs that ate meat might have done.
Helen: Are there any modern day animals that have gizzard stones?
Robert: Yes, there are, crocodiles have gizzard stones and also so do birds have some stones in what we call a 'crop' to help them with digestion.
Summary:
What do dinosaur teeth tell us about their diet?
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Helen Thompson: So Robert, looking at the fossil's teeth, what does this tell you about the diet?
Robert Jones: Teeth in animals usually tell you what the animal ate. For carnivorous animals, the ones that ate meat, they had nice sharp teeth, conical sharp teeth for slicing up meat.
The herbivorous or the plant-eating animals including plant eating dinosaurs had teeth for crunching up plants and for breaking up all the bits of vegetation ...
so that's the main thing they tell you is what they ate. So the carnivorous ones had sharp teeth and the herbivorous ones, the crushing teeth.
Helen: And were they effective?
Robert: Generally effective, to a lesser and greater extent. Some of the animals just bit off meat like the carnivorous ones and swallowed it as large chunks but with the herbivorous ...
or plant-eating dinosaurs, some of them actually crushed up the vegetation with their teeth alot.
Others just ripped off the vegetation and swallowed it and then it was crushed up in their stomachs.
Helen: What other information would help you in determining the diet of the fossil?
Robert: I suppose one of the best indicators of what an animal ate is what came out the other end. So the fossilised faeces or what we call coprolites or fossilised poo.
You can have a look at that when you find it, it's not all that common but it is found and you can actually see the remains of what the animal ate in that.
So you can definitely see bits of plant, or see bits of bones from the carnivorous animals. That tells you what the animal ate.
Helen: What sort of plants did the herbivores eat?
Robert: They probably ate a varied number of plants; it depends on what was available.
During the time of the dinosaurs, there was no grass but there was a lot of ferns, cycads and pine trees so these are the things we think that they ate.
Some of them ate the soft sort of ferns which would have been easy to chew up and digest.
Others ate the harsher vegetation which probably needed a lot more munching up and chewing and crunching before they could swallow it.
Summary:
What does the femur tell us about dinosaurs?
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Helen Thompson: Looking at this fossil dinosaur here of the Muttaburrasaurus, what information do we get from the femur of it?
Robert: I suppose there's two things you get from the femur of most four-legged animals is the actual overall size of the animal. A bigger femur belongs to a larger animal and the other thing you get from it,
is using a mathematical formula applied to the circumference of the femur, you can determine the actual mass or the weight of the animal.
Helen: If we were to find the front legs and hind legs of a fossil animal, what other evidence do you need to conclude it walked on two legs or four legs?
Robert: Well basically I suppose, with all four-legged animals the front and the hind legs are roughly the same size.
So if the bones of the hind legs are matched up in size to the bones of the front legs then you say it walked on four legs and as you can see from this dinosaur here ...
the front legs are smaller than the hind legs so therefore you just compare the size of the front leg bones to the rear leg bones will tell you if its two- or four- legged walking.
Helen: What about these two femur here? What can you tell us about the animals that these came from?
Robert: Righty oh, we have here two femora, singular is femur and femora for plural. They're both femora right, they look quite different.
This one here in my left hand is lightly built but roughly the same length therefore we expect these two animals were roughly the same size in height but this one's more heavily built.
So this one probably weighed a lot more. I expect the one with the lightly built bone was a faster runner,
this actually belonged to a carnivorous dinosaur and probably used the speed of its running, to pursue prey, to eat.
While this one here is a more heavily built herbivorous dinosaur and it only had to run to escape other dinosaurs.
It might have had other things it could do to help escape too. So it probably didn't run as fast, was heavier and more solidly built.