Sea Monsters (TV series)

Sea Monsters is a 2003 BBC television trilogy which used computer-generated imagery to show past life in Earth's seas. In the U.S. it was known as Chased by Sea Monsters. It was made by Impossible Pictures, the creators of Walking with Dinosaurs, Walking with Beasts and Walking with Monsters. In the series, the British wildlife presenter Nigel Marven is shown travelling to seven past seas in the history of the Earth and scuba diving there, in order of dangerousness with the most dangerous last. He travels in a white sailboat or motorboat roughly 24 m (80 ft) long named 'The Ancient Mariner'. His time travelling device is not mentioned or shown, and the closest thing to it is his time map, showing the timeline of the seven deadliest seas and the creatures that lived at the time. He uses a scuba set with a fullface mask so he can talk underwater to produce the commentary. He performs some dives using a strong shark cage, which is spherical to make it harder for large sea creatures to bite it.

Sea Monsters
DVD cover
Created byTim Haines
Directed byJasper James
Presented byNigel Marven
Narrated byKaren Hayley
Composer(s)Ben Bartlett
Country of originUnited Kingdom
Original language(s)English
No. of episodes3
Executive producer(s)Adam Kemp
Tim Haines
Producer(s)Jasper James
Running time90 minutes
Production company(s)BBC Natural History Unit
Impossible Pictures
DistributorBBC Worldwide
Original networkBBC, Discovery Channel, ProSieben
Original release9 September (2003-09-09) 
23 September 2003 (2003-09-23)
Related showsOther shows in the Walking with... series
External links

Video release

Sea Monsters has never been released on DVD in the UK, but featured on the American Chased by Dinosaurs DVD and a similar Region 2 Dutch DVD. It was also available on Netflix in the UK and the United States, where it is referred to as Episode 2 of "Chased By Dinosaurs: Three Walking with Dinosaurs Adventures."[1]


As originally broadcast, the first episode had three segments and the second and third two each; a format later inherited by Walking with Monsters.

Ep. Title Period Time Hazards
1.1"The Seventh Most Deadly Sea"The Ordovician450 myaGiant Orthocones, Sea Scorpions

New York in the Ordovician: the day is only 21 hours long and there is more carbon dioxide than in the 21st century, forcing Nigel to don a medical-looking backpack filled with air tanks with a special oxygen mixture. To attract a Megalograptus (1 m), Nigel finds the corpse of a dead Astraspis washed up on the beach. Because there is no land life, there are no coastal scavengers to eat what the sea spits out. Before long, Nigel wades into the shallow water and the armour-plated fish attracts a large Megalograptus. The creature devours the armour-plated fish, before attacking Nigel's foot, cutting it badly.

Later on, Nigel attempts to go after a Cameroceras (9 m) by removing the eye of a dead Isotelus and replacing it with a small video camera. He then uses the inflatable raft to venture out into the deeper waters, where he throws the trilobite video camera combo overboard. However, a Megalograptus is quickly attracted to it, and Nigel immediately gets it off the trilobite. Later in the afternoon, a Cameroceras grabs and eats the trilobite, and Nigel and the cameraman plunge overboard to film it. On the dive, Nigel wears a chain mail suit, so that any marauding sea scorpion cannot harm him. He finds the Cameroceras and, after deterring it from attacking him by shining a torch in its eyes, he watches it devour two Megalograptus. The Cameroceras is agiler in the sea than Nigel, and as it attempts to swim away, Nigel grabs onto its shell. When the Cameroceras starts to dive down into the depths, Nigel swims away to the surface, almost getting attacked by another Megalograptus. When Nigel pilots the boat back to shore, he finds a surprise: there are large numbers of Megalograptus mating in the shallow waters. Nigel manages to make his way safely through the Megalograptus hordes, but a few clamber onto the inflatable boat and puncture it.

Animals: Cameroceras (identified as giant orthocone)  · Megalograptus (identified as sea scorpion)  · Astraspis (identified as an armor-plated fish)  · Isotelus (identified as a trilobite)  · Graptolite  · Tarbosaurus (in intro)  · Giganotosaurus (in intro)  · Velociraptor (in intro)

1.2"The Sixth Most Deadly Sea"The Triassic230 myaNothosaurs, Cymbospondylus

As Nigel walks along the tropical coastlines of Triassic Switzerland, he explains that the reptiles are taking over the surface of the earth from the skies to the land. But of course, he is here to see the earliest sea reptiles.

From the deck of the Ancient Mariner, Nigel and crew watch as a Nothosaurus (3 m) comes up for air. When he sees one, Nigel dives into the seas, pursuing the elusive sea reptile.

Before long, Nigel finds a pair of Nothosaurus. The Nothosaurus circle him, and Nigel has his prod ready to put off any Nothosaurus that comes too close. One of the Nothosaurus moves in closer, so Nigel grabs it around its head to swim with it, explaining that although the Nothosaurus would be able to close its jaws with tremendous force, the muscles that open its jaws are very weak. He lets the Nothosaurus go discovers another bizarre sea reptile: a Tanystropheus (4 m).

Nigel follows the female Tanystropheus, and attempts to get a closer look at her by grabbing onto her tail, impeding her movement. The Tanystropheus struggles with all of her might, but Nigel still had a grip on her tail. However, the Tanystropheus loses her tail, similar to the modern day leopard gecko. Nigel can hold onto the tail only with difficulty because it is thrashing around (intended as a predator decoy). Suddenly the tail is snatched up and then eaten by a Cymbospondylus (9 m).

The Cymbospondylus begins to circle Nigel, and he explains that its slow movement is designed to deceive prey, and it can move very quickly when it is needed to. After he pokes it with the prod several times, the Cymbospondylus swims away, and Nigel returns to the relative safety of the Ancient Mariner.

Animals: Cymbospondylus  · Coelurosaur[2]  · Nothosaurus (identified as nothosaur)  · Tanystropheus  · Peteinosaurus (identified as pterosaur)  · Placodus (appears in book)  · Neusticosaurus (appears in book)  · Mastodonsaurus (appears in book)  · Cynodont (appears in book)  · Prestosuchus (appears in book)

1.3/2.1"The Fifth Most Deadly Sea"The Devonian360 myaDunkleosteus

On a preliminary dive, another crew member of the Mariner (Mike) films a huge female Dunkleosteus (9 m), swimming around the shallow reefs near the Ancient Mariner. The crew springs into action, and Nigel goes fishing for Bothriolepis (30cm). Nigel places a bet with one of the other crew members that the Dunkleosteus will be able to slice through the Bothriolepis wrapped in chain mail. When the round shark cage is fully assembled, Nigel descends into it. The smell of the dead Bothriolepis begins to attract a young Stethacanthus (70cm). Eventually, the monstrous Dunkleosteus is sighted, which scares away the Stethacanthus, and the agitated fish repeatedly bashes the cage with its thick head. The episode ends on a cliffhanger as the Dunkleosteus comes straight at the cage.

In the next episode, "Into the Jaws of Death", the Dunkleosteus indeed rams the cage, heavily denting the bars. Eventually, the Dunkleosteus snatches the Bothriolepis out of the cage (and almost rips Nigel's arm off in doing so), and slices through the bait, chainmail and all. A young Dunkleosteus (1 m) feeds on the remains, but the huge adult turns cannibal and devours the young Dunkleosteus. She then regurgitates the indigestible parts of its meal (the armour plating and the chainmail).

Before all this, Nigel explains that the placoderms as a whole have a grim future ahead of them. After thriving for fifty million years, the entire Class of placoderms will disappear, much to the other Devonian fish's relief.

Animals: Dunkleosteus  · Bothriolepis (identified as placoderm)  · Stethacanthus  · Onychodus (appears in book)  · Cladoselache (appears in book)  · Cheirolepis (appears in book)  · Graptolite (appears in book)  · Coelacanth (appears in book)

2.2"The Fourth Most Deadly Sea"The Eocene36 myaBasilosaurus

While walking in the mangrove swamps of Egypt, Nigel comes across some mysterious footprints and a mound of fresh dung, by smelling the manure, he proves that the owner is a fruit-eater. Following the tracks, Nigel comes across an Arsinoitherium (3 m) migrating overland. Nigel takes a calculated risk and offers the huge fruit-eater an apple, but apparently, this upsets the Arsinotherium and it charges at Nigel. Only by making a break into the thicker forests does Nigel escape from the mammal. Nigel watches from the forest as the Arsinoitherium plunges into the water, and follows it. In the water, Nigel watches as a trio of Dorudon, a species of ancient whale, pass by, and he explains that whales are the reason he came: not for the Dorudon (4 m), but a far bigger and meaner whale, Basilosaurus (15/24 m) who eats Dorudon for a meal.

The Ancient Mariner sails offshore, where the crew tries a tactic to attract whales that have been used with mixed success: record a Basilosaurus call and play it back via a huge speaker that is lowered from the boat. After playing it for a while, an enraged Basilosaurus (15 m) rams into the boat before diving again. Wasting no time, Nigel suits up and dives. However, the whale could attack from any direction, so Nigel stays close to the hull of the Mariner, using the boat as a shield to ward off the Basilosaurus. The Basilosaurus is evidently distressed by the calls, and attacks and disables the speaker (which is explained as a territorial response).

As the Ancient Mariner sails off forward through time, the narrator explains that the tropical Eocene is a world on the brink of great climatic change. As the Oligocene dawns, Basilosaurus, Arsinoitherium and Dorudon will all vanish, victims of the climatic shifts that ended the Eocene, changing the warm sea into a cold ocean and causing the Tethys Sea to disappear.

Animals: Basilosaurus  · Arsinoitherium  · Dorudon  · Palaeomastodon (appears in book)  · Physogaleus (appears in book)  · Sarkastodon (appears in book)

2.3/3.1"The Third Most Deadly Sea"The Pliocene4 myaMegalodon

In the coast of Peru, the crew of the Mariner come to an agreement. Before diving in offshore waters with the adult Megalodon (15 m), Nigel will dive in the coastal waters, with the juveniles.

Before very long, Nigel finds an Odobenocetops (2 m) foraging for oysters in the mud, and it is being hunted by an adolescent Megalodon (6 m). Only by taking cover in the thick underwater foliage do Nigel and the Odobenocetops manage to escape the huge shark.

On the next dive (with the adults), Nigel uses the round shark cage that he previously used in the Devonian era against Dunkleosteus. This time, Nigel hopes to fire a small video camera into the dorsal fin of the shark from the relative safety of the cage. Eventually, a Megalodon (15 m) is spotted, and Nigel quickly gets into the cage, while the crew sets up bait (a bag of chum), which quickly attracts the shark. As it attempts to attack the cage, Nigel tries to fire the camera.

However, Nigel panics, and never fires it. Later, he tries again, this time from the surface of the Mariner, as the dorsal fin of the Megalodon was much too high to aim at. The shark is drawn again to the boat via liberal amounts of chum. The shark tries to grab the chum but Nigel is nowhere to be seen, ending the second episode on another cliffhanger.

In the final episode, "To Hell..... and Back?", it is revealed that Nigel has been knocked off the boat by the shark and when he swims back, he finally managed to land a hit with the shark-camera, and the Megalodon grabs and swallows the chum. In a few days, they find the camera floating in the sea, and when they load it into the onboard television, they watch the Megalodon in question attack a Cetotherium.

When the crew of the Ancient Mariner head backward in time, the narrator says that as the Ice Age begins, the whales that Megalodon preyed on migrated to colder waters, where Megalodon could not follow. Megalodon is doomed to extinction, by hunger.

Animals: Megalodon  · Odobenocetops  · Cetotherium (identified as whale)  · Thalassocnus (appears in book)  · Great white shark (appears in book)

3.2"The Second Most Deadly Sea"The Jurassic155 myaLiopleurodon

Set around England, which was then largely underwater. This is the second most dangerous sea. Hazards include Liopleurodon (25/28 m), the largest carnivorous animal of all time. Nigel spies a school of migrating Leedsichthys (25/28 m). One weaker one is lagging behind the school, and a native Metriorhynchus (3 m) and a foreign Hybodus (2 m) shark launch a joint attack. Using sonar, Nigel discovers that a huge Liopleurodon (28 m) is heading toward the injured and dying Leedsichthys (28 m). The camera spots it circling the Leedsichthys which is already dead, though the Liopleurodon is eventually spooked away by the camera.

Nigel equips his and the cameraman's diving suit with a chemical system that will spray a cloud of Putrescene at the huge pliosaur should they get too close (experiments with juveniles showed that shark repellent wouldn't work). The crew uses huge waterproof lights when they descend to the corpse of the Leedsichthys because it is nighttime. A pair of Liopleurodon (every 18 m and 20 m) are feasting on the carcass, and Nigel starts to move closer toward them. When one turns its head towards him, Nigel panics and ejects the chemical, which works on the huge predator.

Animals: Liopleurodon  · Leedsichthys  · Metriorhynchus  · Hybodus  · Cryptoclidus (appears in book)  · Ophthalmosaurus (appears in book)  · Eustreptospondylus (appears in book)  · Rhamphorhynchus (appears in book)

3.3"The Most Deadly Sea Ever"The Cretaceous75 myaXiphactinus, Sharks, Giant Mosasaurs

Nigel is now entering his final sea mission in "Hell's Aquarium" as he calls it. On the land, there's Tyrannosaurus (12m), but even it can't compare to what's in the water. After viewing a colony of Hesperornis (2 m) on the coastline, Nigel and another member of the Mariner pause for a second to view a huge underwater bloodbath. As far as Nigel (using a periscope) can figure out, an elderly Hesperornis was killed, and the resulting carnage has attracted many sea animals, such as Squalicorax (5 m), and Xiphactinus (6 m). However, Nigel noticed another predator around: a mosasaur known as Halisaurus (5 m). Nigel and the crew head out to deeper water in search of Tylosaurus (14 m). But Nigel explains that this sea is far too dangerous to go diving in because of mosasaurs and other huge carnivores like Xiphactinus. Instead, the crew of the Ancient Mariner has rigged an ROV to dive for them, while the sonar and cameras on the side of the boat would give them early warning if any mosasaurs are nearby. While sailing they see a Tyrannosaurus roaring on land.

The next morning, Nigel discovers that they have hit a dead Archelon (2 m), which was mauled by some other predator before being hit by the boat. Later, after managing to domesticate a Pteranodon (6 m), the sonar picks up some creatures right beneath the boat. This was a good time for them to use the ROV, and when they send it down, the crew finds that it's a small pod of Elasmosaurus (10.3 m) riding their wake like 21st century dolphins, but soon they depart due to the risk that they may provoke the herd. Some of them knocked the ROV when they were investigating it, and an Archelon (4 m) is also spotted. Having done the same thing with present-day leatherback turtles, Nigel risks his personal safety to track down the Archelon and ride it. He and the cameraman ride off in the small inflatable raft.

Before long, Nigel finds the Archelon when it comes up to the surface for air. He dives, grabbing onto the huge turtle's shell. But not long after, the sonar picked up something nearby: a Xiphactinus was circling Nigel and the Archelon. He quickly makes his escape back up to the raft, but disaster strikes. A family pod of Tylosaurus attack and completely overturn the raft, plunging the crew into the sea. Fortunately for Nigel, the Tylosaurus seem more interested in the boat than the humans, and they quickly escape back to the Mariner. However, that night, as the men sleep, a large group of Tylosaurus and Halisaurus appear, apparently attracted to the Mariner, and rush straight to the boat, leaving the crew's fate unknown.

Animals: Tylosaurus (identified as a giant mosasaur)  · Hesperornis  · Squalicorax (identified as (shark)  · Xiphactinus  · Halisaurus (identified as mosasaur)  · Daspletosaurus (identified as Tyrannosaurus)  · Pteranodon  · Elasmosaurus  · Archelon  · Claosaurus (appears in book)  · Niobrarasaurus (appears in book)  · Hainosaurus (appears in book)  · Platecarpus (appears in book)



  1. "IMDB".
  2. "Coelurosaur". Sea Monsters. BBC. Retrieved 15 July 2019.
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