NIZAR IBRAHIM: Spinosaurus is probably the most enigmatic dinosaur out there.
VOICE OVER: For decades, paleontologists have disagreed on how Spinosaurus aegyptiacus,
a huge Cretaceous predator, might have lived and hunted.
Now a new skeleton, discovered in Morocco,
has revealed an unexpected surprise in the tail of this enormous hunter.
NIZAR: We’re digging up a caudal, a tail bone of Spinosaurus.
And this is one of the most bizarre tailbones you can imagine.
I’ve never seen anything like this before.
VOICE OVER: The new bones suggest that Spinosaurus swam through the water propelled by a powerful tail -
a lifestyle apparently unique among dinosaurs.
NIZAR: We can finally flesh out this bizarre, mysterious dinosaur
and it turns out it was even stranger than we expected.
NIZAR: So what you see here is the Sahara,
one of the driest places on Earth.
But 100 million years ago this was a huge river system.
VOICE OVER: Nizar Ibrahim wanted to be a paleontologist since he was five.
So a trip to the Sahara to uncover a new Spinosaurus skeleton was a dream come true -
especially given the scarcity of Spinosaurus bones.
NIZAR: We were finding bone after bone after bone and I couldn’t believe it,
it was like being a five-year old all over again.
The only other Spinosaurus skeleton that had ever been found was destroyed in World War II.
And so we had these tantalising clues.
We knew that Spinosaurus looked really strange. It had a giant sail on its back and narrow
jaws like a crocodile, and we knew that it was very big, probably even bigger than T-rex.
But that was about it. We really didn’t know anything about the lifestyle of Spinosaurus
and its detailed anatomy.
VOICE OVER: A particular mystery was the tail of a Spinosaurus -
a part of its body only known from a few fragmentary bones.
Previous reconstructions showed a long thin tail,
similar to other therapod dinosaurs.
But when Nizar and his team started excavating the tail of the new specimen,
they knew they had found something special.
NIZAR: So we’re excavating caudal vertebrae, the tail vertebrae, and there’s a spine
at the top, right, the neural spine.
The spine goes on and on and on and on and we still haven’t reached the end!
And we thought, that’s really weird, this is a tailbone at the end of the tail,
why on earth does it have such a long spine?
Yeah, 52cm, almost 53 actually.
No other dinosaur has tailbones like this.
And that’s when we realised that the tail was basically like a giant fin.
VOICE OVER: Nizar suspected that this fin would have made Spinosaurus an adept swimmer.
To test the idea, he sent the reconstructed shape to colleagues at Harvard University
where they crafted plastic tails representing Spinosaurus,
two other therapod dinosaurs, a crocodile and a newt.
They then measured the thrust and efficiency of each tail shape as it moved in the water.
NIZAR: The Spinosaurus tail really outperforms the other dinosaur tails.
And it is comparable in many ways with the tails of crocodiles and newts.
So what the experiments showed was that this was a clear advantage
for an animal pursuing prey in the water.
VOICE OVER: Spinosaurus’s aquatic lifestyle has been the subject of decades of debate.
While there were several other large aquatic reptiles in this period, none were dinosaurs.
NIZAR: For a very very long time, paleontologists assumed the one thing dinosaurs never did
was invade the watery world - aquatic ecosystems.
VOICE OVER: There were already several pieces of evidence
pointing towards Spinosaurus being adapted for water:
Crocodile-like teeth for grasping fish, dense bones for buoyancy control,
and short hind legs unsuited to running.
Still, researchers disagreed on just how reliant Spinosaurus was on aquatic prey
and whether it swam or just waded in the shallows.
Nizar believes this new find could settle the debate.
NIZAR: The big thing we were missing was a propulsive structure,
because you can’t really be an aquatic predator unless you have
some way to catch prey in the water and move through the water.
And so that’s what we’ve now found.
We know now that this dinosaur had a fin-like tail that propelled it through this river system.
So this was a river monster and it was a dinosaur that did things that no other dinosaur did.
VOICE OVER: Paleontologists knew that dinosaurs went on to conquer the skies,
but this is the strongest evidence yet that at least one of them also conquered the waters.
It could be that Spinosaurus is unique.
Or it could show just how much there is left to learn
about the age of dinosaurs.