Its the dawn of a new day, being a palaeontologist.
Now, being a palaeontologist is lot like being a detective, but with a case millions of years old.
Some weeks ago, some fishermen up in Broome discovered a new set of dinosaur footprints
Today its our job to find out what was going on on this day millions of years ago.
The case we're going to be investigating today is based on it's based off of real-life discoveries
found in Broome, the United States, and Italy.
If we were to make this journey during the cretaceous period, then we’d be greeted
with a very different landscape.
The Gondwanan supercontinent was breaking up and towering conifer forests covered much
of Australia.
Broom was a river plane opening up into tidal deltas and brackish lagoons; conditions perfect
for dinosaurs.
It we went back 130 million years to this very spot then you’d be crushed by a 30
tonne brontosaurus.
We know that because I’m standing in its footprint.
Preserving dinosaur footprints has a lot in common with making a caramel slice.
First we need to have the right base.
If the ground is too soft, then the prints will collapse in on themselves; not preserving any sort of detail.
Whereas if its too hard then the tracks won't form at all.
Fortunately the mudflats of Broome, and my shortcrust pastry mix, have just the right consistency.
Next, we need to bake the prints to ensure that they are as hard as possible.
This doesn’t turn them into stone just yet but does prevent the next stages in preservation from
destroying the prints entirely.
For dinosaur prints in mud this can take anywhere from a couple of days to a few months.
However for my shortcrust its going to take just 20 minutes at 120 degree Celsius in my oven.
After being baked in the hot sun, we now need to preserve our tracks.
In nature that happens by covering them in a layer of
ash or mud. But for us we're going to be using some caramel.
A layer of chocolate tops it off.
Here is a cross section of the situation you can see the key layers.
As hundreds of metres of sediment builds up the pressure beneath increases;
crushing out and remaining water from the lower layers and causing dissolved minerals to recrystallise.
This forms a solid layer of rock. Over time erosion
removes the layers revealing the dinosaur footprints beneath.
This beach is a hive of dinosaur activity, so far researchers have found about 21 different
track types from a number of different families.
Our set of prints seem to come from three induviduals of two different species.
But which ones?
To find out I've come to the Melbourne Museum.
This is their dinosaur walk but for today it's going to be a police line-up for the
world's oldest crime.
Here is a photograph of one of our prints as you can see it has three large toes.
We're looking for someone with similar structures.
It could be Deinonychus, however Deinonychus literally means big claw, and as you can see
this picture doesn't have any preserved claw marks.
Tarbosaurus however, closely related to the T-Rex, is looking a bit more suspicious.
So what about this print then?
It doesn't have any obvious toes or claws so instead we're going to have to infer some
other properties based on its rather weird structure.
Modern elephant's have some very similar tracks from rounded feet used to spread their weight
over a large area.
Whatever made these prints must also be pretty huge.
From our fossils it looks it could be a brontosaurus.
Fossils can tell us what dinosaurs looked like, but only their footprints can show us
how they behaved.
These footprints must have been made by a mother brontosaurus and her calf.
We know that because we can see their footprints travelling together.
From other tracksites we know that the Tarbosaurus must have hunted alone, because their footprints
crisscross randomly along the landscape.
By measuring distances between each the prints and working out how different forces were
orientated based on how deep they go we can add another layer of understanding.
At the beginning the tracks are all the same distance apart and pretty close together;
which indicates that all the dinosaurs were walking pretty slowly.
Then the Tarbosaurus changes direction and starts to speed up.
The tracks disappear at this point.
Either all thee dinosaurs were abducted by aliens, or potentially nature herself has
removed part two of the story.
The constant ebb and flow of the second largest tide in the southern hemisphere in addition
to regular cyclones means that these footprints are constantly being eroded away.
Visitors brought in by cruse ships, or by ever more regular passenger flights
are slowly grinding them into dust.
Fortunately our tracks are actually suffering from the opposite issue; they're covered by a thin layer of rock.
A strong cyclone has torn through the area; revealing a new set of footprints.
We can see all three dinosaurs converging on the same spot of ground.
There are tracks everywhere here; perhaps there was a small lake or source of food.
That does make a lot of sense, but I still think we’re missing something important.
Rather than just waiting for another storm to reveal the final set of track prints paleontologists
might one day be able to use ground-penetrating radar to spot them even before they’re revealed
naturally.
This technique is based on the on the propagation and reflection of electromagnetic waves through
different densities of rock.
This system is more typically used to map subsurface features such as cables and pipes
but has recently been applied to archaeological sites.
Here is a depth profile from which the domed roof of a buried crypt can be seen.
This other survey shows an Italian sunflower field in which the fossilised remains of early
dugong were found.
While we’re going to need to wait some time for ground-penetrating radar to be sensitive enough to detect subtle difference
in rock densities; when we do
we might find something like this.
Interpreting these large splotches as the mother’s prints, and these smaller ones
as the daughter, we can finally reveal the true story of what happened here.
A mother Brontosaurus and her calf were walking along the banks of a river.
With a tarbosaurus following behind. Catching sight of the pair it swiftly turns and breaks out into a sprint.
This is where they get into a fight; the mother brontosaurus is fortunately able to protect her daughter by using her massive bulk
Allowing the two to escape to live another day.
If the soil properties were different perhaps we’d have discovered the crushed bones of
a Tarbosaurus but with no idea how they got there.
It is only through combining our understanding of both preservation types in which
a full image of a land before time can be constructed.
This has been James Dingley from the Atomic Frontier.
Keep Looking Up.