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The largest land animal ever to tread the surface of the Earth
was a sauropoda.
They were enormous.
Some, like Dreadnoughtus, could grow to 85 feet
long, while others tipped the scales at 100 tons.
That's 10 times heavier than the biggest elephant.
So why were the dinosaurs so much bigger
than their modern counterparts?
There have been a lot of strange ideas about why dinosaurs
could have gotten so big.
One of my favorites was that gravity
has changed through time and maybe the gravity of the Earth
was lower in the past which have meant that the animals got
correspondingly larger.
It's an interesting idea but an idea that's
very definitely nonsense, the Earth's gravity
has not changed that much in the last few million years.
One thing we do know is that dinosaurs could grow fast.
They grew from an egg the size of a grapefruit
to an absolutely enormous animal.
And we have some evidence that they grew very,
very, very quickly throughout their early life.
Growth patterns in fossilized bones
show some sauropods got to full size in just 20 years.
That's an extraordinary 1,000 fold increase.
So how did they do it?
The sauropods were to some extent
pre-adapted to be able to let them get really, really big.
They had a metabolism that was probably
quite like that of birds which allows
them to take oxygen on the in breath
but also on the out breath.
The evidence for that is all of the holes
that we see in the vertebrae and also in their limb bones.
These holes contained air sacs crucial for extracting oxygen
to power their super efficient metabolism.
But the holes had another role.
The biggest land animal today, the elephant, has solid bones.
Its skeleton has reached the limit of what it can support.
Much bigger and it would collapse under its own weight.
But the holes in the sauropod bones
meant their skeletons were comparatively lighter
and stronger.
Their posture helped too.
Their legs are tucked very firmly under their bodies
acting as pillars.
And those pillars very efficiently
allow the holding up of weight against gravity.
These sets of features together meant
that dinosaurs had a unique opportunity
to reach these huge body sizes.
As these plant-eating sauropods got bigger and bigger,
it had an impact on the evolution of the hunters living
alongside them.
One of the reasons why gigantic carnivores may have reached
their large sizes is actually simply
because they're trying to keep up.
They're trying in an evolutionary arms race
to stay in the game, to be able to take on some
of these very large herbivores.
The predators got larger--
so the sauropods got larger, so the predators got larger still.
This helped the sauropods grow to these absolutely enormous
sizes that we haven't seen since on Earth.
It's unlikely we will ever see anything
like these prehistoric giants ever again.
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