0:00:02 > 0:00:06If you thought you knew all there was to know about dinosaurs,
0:00:06 > 0:00:08think again.
0:00:08 > 0:00:10This is Planet Dinosaur Files,
0:00:10 > 0:00:13the series that rewrites the pre-history books.
0:00:13 > 0:00:16We're bringing to life
0:00:16 > 0:00:20the most awesome beasts ever to walk the Earth,
0:00:20 > 0:00:23with state of the art CGI technology that makes you feel
0:00:23 > 0:00:25like you're right there.
0:00:25 > 0:00:27And I'll be discovering
0:00:27 > 0:00:32what made these massive, lethal and, frankly, bizarre beasts tick.
0:00:32 > 0:00:38I'll be taking the plunge to devise demos in my watery workshop,
0:00:38 > 0:00:42where I'll be using fin power, backed up with a bit of muscle.
0:00:42 > 0:00:46And I'll even be turning myself into a human crocodile.
0:00:48 > 0:00:52In the last 20 years, scientists have discovered more dinosaurs
0:00:52 > 0:00:55than in all the centuries that have gone before.
0:00:55 > 0:00:58Amazing new discoveries.
0:01:00 > 0:01:04They reveal a jaw-dropping cast list of creatures.
0:01:05 > 0:01:07Bigger...
0:01:07 > 0:01:08weirder...
0:01:08 > 0:01:12deadlier, than we'd ever imagined.
0:01:12 > 0:01:15This time on Planet Dinosaur Files,
0:01:15 > 0:01:16we're asking the question,
0:01:16 > 0:01:20which creature was king of the prehistoric water world?
0:01:29 > 0:01:32You might think you know about prehistoric creatures...
0:01:33 > 0:01:36..like the huge, 12-tonne plant-eater,
0:01:36 > 0:01:37Diplodocus...
0:01:40 > 0:01:43..or the mighty Tyrannosaurus Rex,
0:01:43 > 0:01:49a savage predator who dominated on land for almost five million years.
0:01:50 > 0:01:55But who ruled our planet's rivers and seas?
0:01:55 > 0:01:59Prepare to meet some new watery wonders from the age before man.
0:02:01 > 0:02:03Kimmerosaurus -
0:02:03 > 0:02:05as long as a killer whale,
0:02:05 > 0:02:07agile as a dolphin.
0:02:07 > 0:02:09He ate sharks for breakfast.
0:02:09 > 0:02:11Sarchosuchus -
0:02:11 > 0:02:13a super-crocodile,
0:02:13 > 0:02:15a terrifying reptile.
0:02:15 > 0:02:18King of the prehistoric rivers.
0:02:18 > 0:02:21And Predator X -
0:02:21 > 0:02:24heavier than 20 hippos.
0:02:24 > 0:02:26His jaws were stronger
0:02:26 > 0:02:29than any dinosaur that has ever lived.
0:02:29 > 0:02:35Three amazing creatures from the prehistoric waterworld.
0:02:40 > 0:02:43But first, let's get something straight.
0:02:43 > 0:02:46These creatures were gigantic reptiles,
0:02:46 > 0:02:50with the weaponry and power to match many top dinosaurs,
0:02:50 > 0:02:53but none of them were actually dinosaurs.
0:02:53 > 0:02:56That's because a dinosaur stands upright on legs.
0:02:57 > 0:03:01So prehistoric creatures that swam using fins or a tail
0:03:01 > 0:03:04are not dinosaurs.
0:03:04 > 0:03:07They're best described as marine reptiles.
0:03:07 > 0:03:11But they lived at the same time as the dinosaurs,
0:03:11 > 0:03:15and I'm going to look at what made these creatures so special.
0:03:18 > 0:03:21First, how well do they swim through the water?
0:03:21 > 0:03:26What equipment do they have to speed them through their watery world?
0:03:26 > 0:03:28Next, size.
0:03:29 > 0:03:33Is being big a great advantage for these marine reptiles?
0:03:33 > 0:03:35And hunting.
0:03:35 > 0:03:40What cunning ways do these predators have of catching their prey?
0:03:45 > 0:03:48Let's meet our first contender.
0:03:48 > 0:03:51Their home was these warm, tropical oceans
0:03:51 > 0:03:54that once covered the continent of Europe.
0:03:56 > 0:03:59This is Kimmerosaurus.
0:04:01 > 0:04:06It's a type of prehistoric sea creature called a Plesiosaur.
0:04:07 > 0:04:09Kimmerosaurus was six metres long,
0:04:09 > 0:04:12the length of a killer whale,
0:04:12 > 0:04:15and lived 150 million years ago.
0:04:17 > 0:04:19They may look alien to us now,
0:04:19 > 0:04:23but they shared the ocean with some very familiar fishy hunters.
0:04:23 > 0:04:25Sharks!
0:04:25 > 0:04:27This one's called a Squatina
0:04:27 > 0:04:29and it looks similar to Angel Sharks
0:04:29 > 0:04:32which can be found in the sea today.
0:04:32 > 0:04:37The Squatina blends itself in with the sea floor,
0:04:37 > 0:04:39so it can ambush passing fish.
0:04:41 > 0:04:44But Kimmerosaurus has other ideas.
0:04:44 > 0:04:46The hunter Squatina
0:04:46 > 0:04:49is about to become the hunted.
0:04:59 > 0:05:02Kimmerosaurs had a special way of hunting,
0:05:02 > 0:05:05scraping the sea bed with their snouts
0:05:05 > 0:05:08in search of prey hiding in the sand.
0:05:08 > 0:05:14But how do we know this? By examining the evidence, that's how.
0:05:17 > 0:05:20Check out this cliff in Switzerland.
0:05:20 > 0:05:22It holds an amazing secret.
0:05:24 > 0:05:28In 1998, these mysterious grooves were discovered
0:05:28 > 0:05:30carved into this cliff face.
0:05:30 > 0:05:33It's actually one giant fossil.
0:05:35 > 0:05:38Rewind 150 million years.
0:05:38 > 0:05:44That same cliff face, which is today 700 metres above sea level,
0:05:44 > 0:05:47was then the bottom of the ocean.
0:05:47 > 0:05:49And not only that,
0:05:49 > 0:05:54those grooves could have been left by a hunting Kimmerosaurus.
0:05:58 > 0:06:00This was a skilful hunter,
0:06:00 > 0:06:04relying on speed and agility to fill its belly.
0:06:05 > 0:06:07Look at those fins.
0:06:07 > 0:06:10Perfectly suited to moving quickly in the water.
0:06:12 > 0:06:16And there are creatures in our oceans today
0:06:16 > 0:06:19that swim in a very similar way to Kimmerosaurus.
0:06:23 > 0:06:28These sea lions have four fins, like Kimmerosaurus,
0:06:28 > 0:06:31and a very similar swimming technique.
0:06:33 > 0:06:36And look at these penguins.
0:06:36 > 0:06:39We all know those stubby wings don't get them airborne,
0:06:39 > 0:06:43but once they go underwater, it's almost like they're flying.
0:06:43 > 0:06:45Look how nippy they are.
0:06:56 > 0:07:00Time to head off to the Planet Dinosaur Files workshop,
0:07:00 > 0:07:02which this week has moved to my local swimming pool.
0:07:06 > 0:07:09So how good was a Kimmerosaurus's swimming technique?
0:07:09 > 0:07:13Well, I'm going to try and find out in this swimming pool.
0:07:13 > 0:07:17Now I can swim backstroke and front crawl and things like that,
0:07:17 > 0:07:20but I haven't got the equipment to swim like a Kimmerosaurus.
0:07:20 > 0:07:22So we've built this.
0:07:22 > 0:07:25Now, it may look a bit big and bulky,
0:07:25 > 0:07:29but actually it's only about half the size of the real thing.
0:07:29 > 0:07:33And the Kimmerosaurus, he didn't swim front crawl like that.
0:07:34 > 0:07:37The Kimmerosaurus used wings.
0:07:37 > 0:07:40What they used to do was, sort of, flap these wings in the water,
0:07:40 > 0:07:44to propel themselves at great speed underwater.
0:07:44 > 0:07:47Now, Jim and I, the muscles of the Kimmerosaurus,
0:07:47 > 0:07:50can't spend much time underwater, because of our lungs,
0:07:50 > 0:07:53but we can operate these wings.
0:07:55 > 0:07:57- Ready, Jim?- Yeah.- Let's go!
0:07:57 > 0:08:01'We're timing how long it takes our Kimmerosaurus swimming model
0:08:01 > 0:08:05'to get down this 25-metre pool.
0:08:05 > 0:08:07'Just how good are those underwater wings?'
0:08:30 > 0:08:33That's pretty astonishing.
0:08:33 > 0:08:35I mean, just these four flapping fins
0:08:35 > 0:08:39have managed to get well over a quarter of a ton of boat and rider
0:08:39 > 0:08:44down a swimming pool in less than 45 seconds.
0:08:44 > 0:08:48And obviously a real Kimmerosaur would be a lot smoother,
0:08:48 > 0:08:50because they swam under the water.
0:08:50 > 0:08:53They didn't have a big bulky boat with them.
0:08:53 > 0:08:57I think it is a very effective swimming technique.
0:09:02 > 0:09:07That's Kimmerosaurus. A weird, but wonderful, ocean creature.
0:09:09 > 0:09:12For swimming, it was nearly twice as fast as an Olympic swimmer,
0:09:12 > 0:09:15and agile with it.
0:09:15 > 0:09:21Size? This predator was as big as a killer whale, at six metres long.
0:09:21 > 0:09:22And hunting?
0:09:22 > 0:09:26Remember, it had that clever way of flushing out prey from the sea bed.
0:09:27 > 0:09:31But my search for a prehistoric king of the water world
0:09:31 > 0:09:34isn't just limited to creatures from the sea.
0:09:41 > 0:09:47This is a river in North Africa more than 95 million years ago.
0:09:51 > 0:09:54A herd of massive Paralititans
0:09:54 > 0:09:56is coming for a drink at the water's edge.
0:09:58 > 0:10:01These were some of the biggest dinosaurs that ever lived.
0:10:01 > 0:10:04And there's something about this river
0:10:04 > 0:10:07that's making these plant-eating giants uneasy...
0:10:08 > 0:10:10..crocodiles!
0:10:10 > 0:10:13They may be dwarfed by the Paralititans,
0:10:13 > 0:10:15but they're still dangerous.
0:10:20 > 0:10:25And now this young Paralititan has got stuck in some mud.
0:10:25 > 0:10:28The crocodiles smell dinner.
0:10:31 > 0:10:35But what that young herbivore doesn't know is that there's a much,
0:10:35 > 0:10:38much bigger threat lurking in these waters.
0:10:44 > 0:10:49Meet the king of the crocodiles, Sarchosuchus.
0:10:49 > 0:10:55Its name means "flesh crocodile." And this one's hungry.
0:10:58 > 0:11:01An enormous 12 metres long -
0:11:01 > 0:11:05that's the length of a whole railway carriage -
0:11:05 > 0:11:07heavier than a fully-grown elephant,
0:11:07 > 0:11:11weighing an astonishing eight tonnes.
0:11:11 > 0:11:15Twice the size of any crocodile in the world today.
0:11:15 > 0:11:17This is a super-crocodile.
0:11:19 > 0:11:24But how can we be sure that a crocodile this big actually existed?
0:11:24 > 0:11:27By taking a look at the evidence, that's how.
0:11:29 > 0:11:34In Niger, Africa, in 2001, an amazing discovery was made.
0:11:35 > 0:11:37A massive crocodile fossil.
0:11:37 > 0:11:42A staggering total of 250 different bones.
0:11:44 > 0:11:48Amongst all these bones was a huge skull.
0:11:48 > 0:11:53Dinosaur experts measured it at a whopping two metres in length.
0:11:53 > 0:11:57That's taller than most dinosaur experts!
0:11:58 > 0:12:02Back on the prehistoric river bank, Sarchosuchus' enormous size
0:12:02 > 0:12:07and massive jaws are a terrifying sight to this young Paralititan.
0:12:09 > 0:12:13I don't fancy the chances of this youngster surviving.
0:12:22 > 0:12:25Now, the prehistoric Sarchosuchus, although much bigger,
0:12:25 > 0:12:27is very similar to crocodiles today.
0:12:29 > 0:12:33Dinosaurs have long gone, but crocodiles have survived
0:12:33 > 0:12:36and thrived for millions of years.
0:12:36 > 0:12:39These ones are in the Nile river in East Africa.
0:12:43 > 0:12:46A herd of wildebeest approach the water's edge.
0:12:49 > 0:12:53The crocodiles get ready to spring a surprise attack.
0:12:55 > 0:13:00Their tactic is to suddenly grab their prey in a vice-like grip,
0:13:00 > 0:13:04and drown them in the water, where they have a deadly advantage.
0:13:07 > 0:13:13Rewind 95 million years, and we find that even other big predators
0:13:13 > 0:13:16had to take care when they entered the patch
0:13:16 > 0:13:18of our super-croc Sarchosuchus.
0:13:20 > 0:13:25Here the mighty Spinosaurus is looking for a meal nearby.
0:13:27 > 0:13:30This normal-sized crocodile isn't really a threat.
0:13:30 > 0:13:34But then Sarchosuchus emerges from the water.
0:13:37 > 0:13:40Even though Sarcho is barely half its size,
0:13:40 > 0:13:46Spinosaurus knows those powerful jaws could drag it underwater.
0:13:46 > 0:13:49Taking him on is just not worth it.
0:13:49 > 0:13:51You've got to hand it to Sarchosuchus,
0:13:51 > 0:13:53when a terrifying dinosaur
0:13:53 > 0:13:57like Spinosaurus decides to give it a wide berth.
0:14:02 > 0:14:05Sarchosuchus, like all crocodiles,
0:14:05 > 0:14:09was perfectly adapted to living in water.
0:14:09 > 0:14:13True, crocodiles do have to come to the surface to breathe.
0:14:13 > 0:14:16But they've evolved, to be able to spend
0:14:16 > 0:14:18staggering lengths of time underwater.
0:14:18 > 0:14:22If they're not moving, they can spend several hours
0:14:22 > 0:14:25beneath the surface, without needing to come up for air.
0:14:25 > 0:14:29They also have a special way of swimming,
0:14:29 > 0:14:31that's different to sea lions or Kimmerosaurus,
0:14:31 > 0:14:33the plesiosaur we've already met.
0:14:35 > 0:14:39A crocodile's body and tail moves in a sideways action,
0:14:39 > 0:14:42making a kind of S-shape through the water.
0:14:51 > 0:14:53'It's time to find out
0:14:53 > 0:14:56'just how effective that method was in practice.'
0:15:00 > 0:15:05OK, now let's see how quick it is swimming like a Sarchosuchus.
0:15:05 > 0:15:08First, I need a very long tail.
0:15:10 > 0:15:15Next, I want to make myself look as frightening and sleek as possible.
0:15:19 > 0:15:21And, finally, to be a top predator,
0:15:21 > 0:15:24you need to be able to see underwater.
0:15:26 > 0:15:28That's it. A Sarchosuchus!
0:15:31 > 0:15:34'Kimmerosaurus took 45 seconds.
0:15:34 > 0:15:38'But Sarchosuchus swims in a very different style.
0:15:38 > 0:15:42'Will it be any quicker over one length of this pool?'
0:16:00 > 0:16:05That, that is astonishingly quick! That is twice
0:16:05 > 0:16:06the speed of a Kimmerosaurus.
0:16:06 > 0:16:10And the thing is, once you get one of these big crocodile tails on,
0:16:10 > 0:16:13you can feel the power in the water.
0:16:13 > 0:16:17You can use every muscle in your body to propel yourself along.
0:16:17 > 0:16:21And that's why the Sarchosuchus must have been
0:16:21 > 0:16:25one of the most feared predators in prehistoric waters.
0:16:33 > 0:16:40That's Sarchosuchus. A giant grandparent of the modern crocodile.
0:16:40 > 0:16:43For swimming, that powerful tail made Sarcho
0:16:43 > 0:16:45really fast through the water.
0:16:45 > 0:16:47Size-wise?
0:16:47 > 0:16:51Well, this beast makes a truly massive splash.
0:16:51 > 0:16:54Eight tonnes and 12 metres long.
0:16:55 > 0:16:57And hunting?
0:16:57 > 0:17:00This killer could just as easily get its dinner on land
0:17:00 > 0:17:02as in the water.
0:17:05 > 0:17:10But was Sarcho the most fearsome beast in the prehistoric water?
0:17:10 > 0:17:13Well, as it happens, far from it.
0:17:14 > 0:17:18Because recently, dinosaur detectives have discovered
0:17:18 > 0:17:21an even more gruesome killer.
0:17:21 > 0:17:26It's so fearsome that even its name is terrifying.
0:17:26 > 0:17:30This is Predator X.
0:17:30 > 0:17:32A truly enormous monster.
0:17:34 > 0:17:40More than 15 metres long and a massive 45 tonnes -
0:17:40 > 0:17:45nearly five times the weight of the largest-known killer whale.
0:17:45 > 0:17:49It had jaws more powerful than any dinosaur.
0:17:51 > 0:17:55But how can we be sure that a creature this massive
0:17:55 > 0:17:58once swam in our oceans?
0:17:58 > 0:18:02By taking a look at the evidence, that's how.
0:18:07 > 0:18:12These are very special prehistoric bones found in 2008.
0:18:12 > 0:18:16They come from the island of Svalbard in the Arctic Ocean.
0:18:18 > 0:18:23Here, a huge fossil was discovered. This was Predator X.
0:18:25 > 0:18:28Its skull was found to be nearly twice the size
0:18:28 > 0:18:30of a Tyrannosaurus Rex's.
0:18:31 > 0:18:33Predator X was a monster.
0:18:35 > 0:18:39If you were to put one on a set of weighing scales today,
0:18:39 > 0:18:43it would take five double-decker buses to tip the balance.
0:18:45 > 0:18:51So what exactly did this giant sea predator eat to get so big?
0:18:51 > 0:18:53And how did it catch its prey?
0:18:58 > 0:19:03Well, this predator hunted other smaller predators.
0:19:03 > 0:19:06In fact, there's evidence that Kimmerosaurus could have been
0:19:06 > 0:19:09top of the menu for this ocean monster.
0:19:11 > 0:19:14Predator X hunted mainly by smell.
0:19:14 > 0:19:18By passing water through special nostrils
0:19:18 > 0:19:22inside its massive snout, it picked up the scent of nearby prey.
0:19:28 > 0:19:33Now, often in the water, smaller can seem faster.
0:19:33 > 0:19:37And as Predator X is three times bigger than Kimmerosaurus,
0:19:37 > 0:19:39you might think that Kimmerosaurus
0:19:39 > 0:19:42would be able to outswim this huge hunter.
0:19:43 > 0:19:45Let's find out if that really is the case.
0:19:54 > 0:19:59'Back to the pool, where I'm doing a spot of underwater engineering.'
0:20:03 > 0:20:06Time to bring a bit of Predator X to the local swimming pool.
0:20:06 > 0:20:11Now, in swimming style he's pretty much the same as Kimmerosaurus,
0:20:11 > 0:20:14four large fins flying through the water.
0:20:14 > 0:20:18The significant difference, he's much, much bigger.
0:20:18 > 0:20:23There's the little old Kimmerosaurus one. Here's the big Predator X one.
0:20:23 > 0:20:26Now, whereas Kimmerosaurus was about the size of a killer whale,
0:20:26 > 0:20:28this thing, in real life, would have been
0:20:28 > 0:20:31about the size of this swimming pool.
0:20:31 > 0:20:36'Now, remember, our Kimmerosaurus swam a length in 45 seconds.
0:20:36 > 0:20:40'But Sarchosuchus did the same distance twice as fast,
0:20:40 > 0:20:42'just 22 seconds.
0:20:44 > 0:20:47'How will Predator X get on?
0:20:52 > 0:20:56'Once we get those massive fins into a rhythm,
0:20:56 > 0:20:59'Predator X eats up the water.'
0:21:15 > 0:21:19Just over 30 seconds! This thing's quick.
0:21:19 > 0:21:21It's not quite as quick as Sarchosuchus,
0:21:21 > 0:21:23which was very swift off the mark,
0:21:23 > 0:21:25but noticeably faster than Kimmerosaurus.
0:21:25 > 0:21:28And the fact is, the way it felt here,
0:21:28 > 0:21:33Jim and I just don't have the power for waterwings this big.
0:21:33 > 0:21:38And the difference is, real-life Predator X was a veritable monster.
0:21:38 > 0:21:41He was like a 45-tonne torpedo.
0:21:41 > 0:21:45And it had all the strength it needed to drive its massive wings
0:21:45 > 0:21:47through the water, giving it the ability
0:21:47 > 0:21:50to devour just about anything it wanted.
0:21:57 > 0:21:59So, Predator X was no slow-coach.
0:22:00 > 0:22:04In fact, dinosaur experts have worked out
0:22:04 > 0:22:06that Predator X's muscle power and huge fins
0:22:06 > 0:22:11gave it a maximum speed of five metres per second.
0:22:11 > 0:22:14Crucially, and our demo backs this up,
0:22:14 > 0:22:18that's faster than Kimmerosaurus.
0:22:18 > 0:22:21And that could mean the difference between life and death.
0:22:22 > 0:22:25But don't write off Kimmerosaurus.
0:22:25 > 0:22:29It wasn't completely defenceless against an attack from Predator X.
0:22:29 > 0:22:33Sometimes, being a lot smaller than the creature that's hunting you
0:22:33 > 0:22:36can be an unexpected advantage.
0:22:43 > 0:22:46These Kimmerosaurs have swum into the much shallower water
0:22:46 > 0:22:50of this lagoon. This is a clever tactic,
0:22:50 > 0:22:54because Predator X is just too big to get in here.
0:22:57 > 0:23:01Now, you can see this kind of thing happening with sea creatures today.
0:23:01 > 0:23:06These killer whales are hunting seals.
0:23:06 > 0:23:10But the seals know that if they stay in water near the beach,
0:23:10 > 0:23:14the whales won't be able to get them.
0:23:14 > 0:23:18That's one hungry whale that's staying hungry a while longer.
0:23:21 > 0:23:24Rewind again 150 million years,
0:23:24 > 0:23:28and the tide is rising in the Kimmerosaurs' lagoon.
0:23:28 > 0:23:30They think they're safe here,
0:23:30 > 0:23:34but now it's become deep enough for Predator X to swim in.
0:23:44 > 0:23:50However, the water's still too shallow for its big power advantage
0:23:50 > 0:23:53to count against these more agile Kimmerosaurs.
0:24:02 > 0:24:06But Predator X knows it will get its chance.
0:24:06 > 0:24:09Eventually, the Kimmerosaurs will have to leave the shallows
0:24:09 > 0:24:12so they can feed in deeper water.
0:24:14 > 0:24:18And in the deep ocean, the odds swing back in his favour.
0:24:18 > 0:24:20He just needs to wait.
0:24:23 > 0:24:27Big sea predators come into their own in the deep ocean.
0:24:28 > 0:24:32This Great White shark is searching for seals on the surface.
0:24:32 > 0:24:37It can stay out of sight down in the murky depths
0:24:37 > 0:24:38and then spring an ambush.
0:24:39 > 0:24:42This amazing slow-motion film shows how,
0:24:42 > 0:24:44by attacking the seal from below,
0:24:44 > 0:24:47the Great White can use its maximum speed and power
0:24:47 > 0:24:49to surprise its prey.
0:24:53 > 0:24:54Just like the seal,
0:24:54 > 0:24:57this Kimmerosaurus is hunting for food in deep water.
0:25:02 > 0:25:06But that also means it's vulnerable to attack.
0:25:06 > 0:25:09Predator X spots its prey from below.
0:25:09 > 0:25:13Now it can use all its power and speed.
0:25:13 > 0:25:15Just like the Great White shark,
0:25:15 > 0:25:19it's all about a surprise attack from the depths.
0:25:22 > 0:25:28That first incredible blow stuns the Kimmerosaurus and slows it down.
0:25:28 > 0:25:31Now Predator X can finish the job.
0:25:39 > 0:25:44Those jaws are an astonishing four times as powerful as T-Rex.
0:25:47 > 0:25:50Kimmerosaurus is history.
0:26:07 > 0:26:10So that's Predator X, a huge ocean hunter.
0:26:12 > 0:26:15But how does this mega-monster from the deep
0:26:15 > 0:26:20compare with our other amazing marine reptiles?
0:26:22 > 0:26:26There was Kimmerosaurus. Sharks were its favourite food.
0:26:28 > 0:26:33For swimming, it was rapid underwater and agile, as well.
0:26:33 > 0:26:38Size-wise, it weighed one tonne and was six metres long.
0:26:38 > 0:26:39And hunting?
0:26:39 > 0:26:42It had a clever way of flushing out prey from the sea floor.
0:26:44 > 0:26:50Then the massive Sarchosuchus, a very powerful super-crocodile.
0:26:51 > 0:26:56Swimming? It was faster than Kimmerosaurus and Predator X.
0:26:56 > 0:27:01For size, it was impressive - eight tonnes and 12 metres long.
0:27:01 > 0:27:06Hunting? Well, it could take prey on land and in water.
0:27:07 > 0:27:11And finally, the incredible Predator X,
0:27:11 > 0:27:13with jaws stronger than any dinosaur.
0:27:15 > 0:27:20For swimming, its huge bulk didn't stop it being frighteningly fast.
0:27:20 > 0:27:25Size? Well, it was stunning - 45 tonnes and 15 metres long.
0:27:27 > 0:27:28And hunting?
0:27:28 > 0:27:30It was like a massive Great White shark,
0:27:30 > 0:27:33using the surprise attack.
0:27:34 > 0:27:37Predator X was truly astonishing -
0:27:37 > 0:27:43a mighty monster that ruled the seas for 100 million years.
0:27:44 > 0:27:50So, my pre-historic king of the waterworld is Predator X.
0:27:50 > 0:27:53And by a distance.
0:27:57 > 0:27:59Next time on Planet Dinosaur Files,
0:27:59 > 0:28:03we meet the prehistoric super-heavyweights.
0:28:05 > 0:28:10And find out just how much damage all that weight can do.
0:28:10 > 0:28:13Subtitles by Red Bee Media Ltd