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The show's host, a real British zoologist who travels in time to visit the 7 most dangerous seas of Earth's history. For tropes related to "Chased by Dinosaurs", see Walking with Dinosaurs.
- The Ace: He continues to do everything himself here, despite having an on-camera supporting crew. And he seems to be even more or an expert at everything.
- Actionized Sequel: Continuing the trend established by "Chased by Dinosaurs". He interacts with, and get chased by a lot of creatures, and even gets injured onscreen by some of them.
- Attention Deficit Oh Shiny: He is adamant that the Cretaceous sea is too dangeorus to dive in, then disregards it for a chance to swim with a giant sea turtle. The Stinger implies he got everyone killed by doing this. But don't worry, he shows up alive with no explanation in Prehistoric Park.
- Casual Time Travel: Now extended to a whole ship and its crew.
- Cool Boat: One with a cool name, the Ancient Mariner. It also travels back and forth in time. Somehow.
- Crazy-Prepared: Every segment has Nigel pull out a new gadget to interact with the creature of choice.
- Cliffhanger: His life is at stake at the end of every episode.
- Distressed Dude: He gets in danger all the time, although he usually gets out of it himself. In the most dangerous sea, however, he has to be saved by the crew.
- From Bad to Worse: Invoked both by the prologue and the show's premise. In the former, Nigel is chased subsequently by a Velociraptor pack, a (small) Giganotosaurus and a (large) Tarbosaurus. The narrator says that he is about to learn that he should never jump in the water while time travelling. He does, and is immediately surrounded by a giant Cretaceous piranha, Xiphactinus. In the latter case, Nigel visits seven seas, one of which is more dangerous than the former (and labeled as such).
- Sequel Escalation: More people, more locations, more time periods, more animals, more gadgets than in "Chased by Dinosaurs". Pity it is only one episode more.
- Took a Level in Badass: He now goes face to face with prehistoric monsters.
- Took a Level in Jerkass: He calls a crewman an "idiot" and blames him for a failed attempt to put the "shark cam" on a megalodon. He apologizes immediately, but it is still an unwelcome, weirdly out of place surprise.
- Unwitting Instigator of Doom: He disregards all safety rules to swim with an Archelon. A Xiphactinus shows up and he has to get rescued by a lifeboat. A pack of Tylosaurus is then attracted by the general scene and they destroy the lifeboat, but all three occupants can swim to safety on the ship. Which is later attacked en masse by Tylosaurus, presumably alerted or attracted by the earlier attack.
The first large marine predator on Earth, from a whopping 450 million years ago.
- All There in the Manual: The actual genus is Cameroceras. Only called orthocone or giant orthocone in the show.
- Camera Abuse: Hits the camera with a tentacle during the encounter with Nigel.
- Combat Tentacles: Its weapon of choice.
- Everything's Squishier with Cephalopods: A large cephalopod with a conical shell.
- Kraken and Leviathan: The Kraken type, due to being a cephalopod.
- Lightning Bruiser: Its jet propulsion system gives it much better mobility than the sea scorpions.
- Weaksauce Weakness: It doesn't like flashing lights, and if you grab the tip of its shell it is incapable of reaching you.
- The Worf Effect: Shown casually feeding on a sea scorpion after they have been established several times as a threat.
A grotesque sea invertebrate.
- All There in the Manual: This genus is called Megalograptus.
- Big Creepy-Crawlies: VERY creepy crawlies. Looks more live a Lovecraftian horror than a scorpion.
- Blood Is Squicker in Water: When one scratches Nigel's leg.
- Demonic Spiders: They are everywhere and a constant menace.
- Eats Babies: Of their own kind.
- Graceful in Their Element: They can walk on land, but they have no reason to run. In water, they can both swim quickly or walk over the sea floor.
- Lightning Bruiser: Fairly swift and vicious, with massive claws.
- Names to Run Away from Really Fast: Would you dip your toes in a sea with "sea scorpions" in it?
- Power Pincers: Their Weapon of Choice.
- The Precursors: Believe it or not, these critters are the first sea animals to venture on land.
- Scary Scorpions: Although they don't sting with their tail.
- What Measure Is a Non-Cute?: Can you imagine Nigel rushing another animal's mating grounds, picking one of them and casually throwing it away?
- The Worf Effect: One injures Nigel, setting the "danger" premise of the series straight.
- Zerg Rush: They rush and deflate Nigel's inflatable boat when he runs over their breeding grounds.
A large trilobite used by Nigel to bait the orthocone.
- All There in the Manual: Not named onscreen.
- The Bait: You don't say.
- Big Creepy-Crawlies: Another massive arthropod.
- Bigger Is Better: Justified, because Nigel wants to bait a large animal.
- Gentle Giant: Despite its size, it is a bottom feeder and would never endanger Nigel when it was alive.
- Living Prop: Though it mostly appears as dead prop, a living one can be seen briefly on the sea floor when Nigel is heading to meet the orthocone.
- Monster Munch: Enforced. Its only role is to be eaten by the orthocone. So much that Nigel gets annoyed when a sea scorpion tries to eat it first.
- Posthumous Character: The one used by Nigel is already dead when he picks it.
- Squick: Nigel plucks out one of its eyes to put the camera. He even warns the cameraman and advices him to turn away.
A primitive jawless fish used by Nigel to bait sea scorpions.
A large primitive ichthyosaur and the largest reptile of its time, 230 million years ago.
- Always a Bigger Fish: It surprises Nigel by eating the severed tail of the Tanystropheus.
- Mix-and-Match Critters: It looks like a cross between later ichthyosaurs (like Ophthalmosaurus in Walking with Dinosaurs) and the even later mosasaurs, who are unrelated.
- Science Marches On: In 2012, a much larger and better-armed relative, Thalattoarchon (Or "Ruler of the Seas"), specialized in killing big sharks and other marine reptiles, dethroned it as the ultimate Triassic badass.
An inquisitive, human-sized sea reptile.
- Deleted Scene: In the book, Nigel observes them as they lay eggs on the beach, at night. There is a photo of Nigel with the eggs, so it was almost certainly filmed. By being cut, the show unwittingly avoided a case of Science Marches On, as it is now believed that all sea reptiles bar sea turtles had live birth.
- From Nobody to Nightmare: Same stock from which plesiosaurs and pliosaurs will evolve from.
- Mix-and-Match Critters: Half crocodile, half monitor lizard, with anglerfish teeth. And the book has them reproducing like sea turtles.
- No Sense of Personal Space: They cheerfully swim up to Nigel out of curiosity. Nigel keeps a cattle prod handy in case they get too close.
- Ridiculously Cute Critter: By sea reptile standards.
- Scary Teeth: Long like needles and sharp like knives, used to catch slippery fish.
- Weaksauce Weakness: Like crocodiles, they have strong muscles to close their mouth but the muscles opening it are weak. So he can disarm one just by grabbing its head from behind.
A long necked sea reptile.
- Artistic License Paleontology: Possibly the restoration in the Walking with... series that is most hated by paleontologists, down to The Scrappy levels. The shedding tail is a pure invention of the show, both gratuite and nonsensical (How would an aquatic reptile propel itself in the water without a tail? Why have a tail at all if it was so unnecessary that the animal could shed it entirely and suffer no ill effects? How long would it take for an animal that size to grow it back?); and worse, it was an assumption based itself on a fringe theory about Tanystropheus being related to lizards (who don't all shed their tail), that almost no taxonomists defended even back then. To add insult to injury, the show restored Tanystropheus's face much thinner than its skull, making it look goofy.
- Gentle Giant: Nigel identifies it as not dangerous right away. It only eats small fish.
- Life-or-Limb Decision: The speculative tail shedding.
- Long Neck: So long, in fact, that it barely has a body!
- Mix-and-Match Critters: Half snake, half iguana.
- Noodle People: A noodle reptile.
- Science Marches On: According to the latest revision, it was not adapted to swim in any shape or form so it would have lived on the shore or in shallow waters only, and its posterior region was much heavier than the front despite what its long neck might suggest. Ironically, this is a return to the consensus theory (i.e. Tanystropheus was a seashore egret) that had been abandoned before the show came out.
A small, primitive pterosaur.
- Anachronism Stew: Shown around 10 million years too early. The longer-snouted Preondactylus was a closer match.
- The Cameo: It is the same species seen in the first episode of Walking with Dinosaurs, and it only appears at the beginning of the segment.
- Misplaced Wildlife: Inverted. It was misplaced in "New Blood", which was set in Arizona, but it is at home here, surrounded by European animals.
- No Name Given: Only called "pterosaur".
Unnamed theropod dinosaur
A small, primitive dinosaur seen briefly at the beach.
- Anachronism Stew: Obviously, there is always room for new discoveries, but there are no known theropods from this time in Europe (not identified as the location, but home to Peteinosaurus, Cymbospondylus, Nothosaurus and Tanystropheus). The closest thing is the small dinosauriform Saltopus.
- The Cameo: Only shown at the beginning of the segment.
- From Nobody to Nightmare: Shown here to say that dinosaurs have just appeared in this time. According to Nigel, they are all still small and non threatening like this one.
- Historical Villain Downgrade: Ironically, the first known theropod from Europe is Liliensternus a couple of million years later, which despite being a relative of Coelophysis was a respectable 5-meters-long beast; the smaller coelophysoids like Procompsognathus and Coelophysis itself only arrived some dozen million years later. Maybe Nigel should have worried about walking on land.
- No Name Given: Only identified as "coelurosaur" in accompanying material, probably following the old tendency to call all small theropods coelurosaurs regardless of actual philogeny. As per current definition, coelurosaurs don't appear until the Middle Jurassic.
- Suspiciously Similar Substitute: To "New Blood"'s Coelophysis. They look close enough to have been modified from the same model, but they are still different and the coat is also different. This is most likely to avoid Misplaced Wildlife as Coelophysis is a North American genus.
A huge, armoured predatory fish relative from 360 million years ago.
- Bigger Is Better: Nigel won't set up for Stethacanthus. He wants to meet a Dunkleosteus, and a big Dunkleosteus at that.
- Cliffhanger: The first episode ends with Nigel in a shark cage, as a Dunkleosteus charges onto it.
- The Dreaded: The Ancient Mariner's crew is both fearful and looking forward to meet it.
- Eats Babies/I Am A Humanitarian: The larger adult eats a smaller one attracted by the remains of its last meal, zero fucks given.
- Irony: It has no teeth. Those scary teeth-like things are bony plates that are actually part of its head's skeleton.
- Scary Teeth: Though they're not actually teeth.
- Vomit Indiscretion Shot: It vomits its prey's bony plates and the shark mail Nigel put on them almost as soon as it eats.
A small armoured fish. Although distantly related to Dunkleosteus, it is completely inoffensive.
- All There in the Manual: Not named onscreen.
- Artistic License Paleontology: Bothriolepis was a bottom feeder that lived mostly in freshwater (although it could venture into the sea close to the shore) and ate rotten vegetarian matter. Those muscled pectoral fins were to push itself along the ground, and it could only see upwards. Here, it is shown swimming near the sea surface and catching Nigel's bait.
- The Bait: Takes the bait and is used in turn to bait the Dunkleosteus.
- Black Bead Eyes: It has two small, button-like black eyes on the top of its head.
- Monster Munch: Appears only so it can be eaten by the Dunkleosteus.
- Posthumous Character: It is killed right in its introduction and its role mostly happens when it is dead.
- What Measure Is a Non-Badass?: So it is okay for a TV crew to kill an innocent fish just for a chance to attract a larger one?
A bizarre-looking early shark.
- Always Someone Better: Nigel takes notice of it because of how weird it is, but he can't wait for it to go and a Dunkleosteus to arrive. Ironically, he's in a shark cage and Stethacanthus is closer to what he would be using the cage for in real life.
- Animals Not to Scale: It appears to be average for a shark, when in reality was rather small (c. 70 cm long)
- Artistic License Paleontology: It was also a bottom feeder, and thus unlikely to be attracted to Nigel's cage.
- Black Bead Eyes: Well, it is a shark.
- Cow Tools: Besides its long fin whips and claspers, it has a bizarre, anvil-like structure where its dorsal fin should be, and there are teeth growing out of it. Nigel speculates that it could have a role in display for mating or territoriality.
- Everything's Even Worse with Sharks: Just when they were waiting for Dunkleosteus, this guy appears.
- Prehistoric Monster: Take a shark, and make it as bizarre as you can. Stethacanthus is weirder.
- Prop Recycling: Nonetheless, it is still the same ol' shark model used for Hybodus and Physogaleus, but with the whips and anvil added.
- Suspiciously Similar Substitute: Yet another shark that comes first and is irrelevant next to the prehistoric Sea Monster of choice.
- Threatening Shark: Subverted. The cage protects Nigel, and the Dunkleosteus he is hoping for is far worse.
A large Egyptian horned pachyderm from 36 million years ago.
- Accidental Pun: Lampshaded by Nigel, who says that it has a "funny name".note
- All Animals Are Domesticated: Averted. It turns down Nigel's offer of food and charges at him.
- And Now For Something Completely Different: This is a large terrestrial quadruped, not a seagoing animal. Nigel handwaves that it qualifies as a Sea Monster because it swims brackish waters to visit different islands in the mangroves.
- Author's Saving Throw: Included here after its notable absence from Walking with Beasts's "Whale Killer", which is also about Basilosaurus and set in the same location.
- Awesome, but Impractical: Its giant horns are useful for fighting, but because of the way they're positioned, they obscure its vision.
- Graceful in Their Element: Averted. It is equally awkward on land and in water.
- Mix-and-Match Critters: One third elephant, one third rhinoceros, one third hippopotamus.
- Prehistoric Monster: One of the best Truth in Television examples. This is a rhinoceros-like animal with the horn numbers doubled, even though it's maladaptative and limits its senses.
- Rhino Rampage: Although it's more closely related to elephants.
- Rule of Cool/Sequel Escalation: Sure, they could have just reused Moeritherium, but who would have wanted that? Moeritherium would never go on Rhino Rampage against Nigel.
- Science Marches On: The year after the show, it was published that it also lived in rainforests inland and actually survived there for longer. So it lived in mangroves, but it wasn't a mangrove specialist as implied in the show.
DorudonA small primitive whale. For tropes, see entry in Walking with Beasts.
BasilosaurusThe first filter whale-sized cetacean, but it is an active hunter instead of a filter feeder. For other tropes, see Walking with Beasts.
- Stock Footage Failure: Like in WWB, a shot of a modern whale raising its tail over the surface is used in one scene. Unlike in WWB, you can see not just the fluke but also the dorsal fin of the modern whale, revealing that it has a much shorter tail than Basilosaurus.
The largest shark ever, an active hunter instead of a filter-feeder like the whale shark. It swam the world's oceans as recently as 4 million years ago.
- All There in the Manual: The Megalodon name comes from the species name, C. megalodon. The genus is either Carcharodon or Carcharocles.
- Apocalypse How: Will be killed by the Ice Age and thus miss modern humans by a geological hair breath.
- Bigger Is Better: Nigel finds a juvenile in the coast relatively early, but he is not content until they find an adult out at sea.
- Black Bead Eyes: Like any other shark.
- Cliffhanger: The second episode ends with the Megalodon seemingly eating Nigel alive. This isn't the case, of course.
- The Dreaded: The plan to deal with an adult Megalodon causes an argument among the Ancient Mariner's crew.
- Expy: Since only the teeth are known, its aspect and behavior is taken from the modern great white shark (which actually coexisted with it and is not its descendant).
- One-Hit Kill: Specialized in rushing from the deep and killing whales with one bite to the belly.
- Shark Fin of Doom: Shown thrice. One when the segment begins; another when the Ancient Mariner attracts an adult Megalodon for the first time; and the third one when it sails next to the boat and Nigel manages to stick the "shark cam" on the fin dorsal itself.
- Prehistoric Monster: What happens when you apply Animals Not to Scale to a great white shark. Sure, the show's called Sea Monsters, but Nigel does call this one a "monster" to its face.
- Suspiciously Similar Substitute: To Dunkleosteus. Both are giant fish top predators, both make fearsome sharks look pathetic in comparison, both try to get Nigel through the shark cage, and both are used for the episode's Cliffhanger.
- Threatening Shark: It makes the shark from Jaws look like a minnow.
- They Wasted a Perfectly Good Plot/What Could Have Been:
- Megalodon was distributed worldwide and existed for 20 million years, which means any giant Miocene marine predator could have been featured alongside it. Candidates include killer whale-sized dolphin Macrodelphinus, true killer whale Orcinus citoniensis, four-tusked walruses Pontolis and Gomphotaria, largest crocodile ever Purussaurus, seagoing gharial Piscogavialis, and Giant Flyer Toothy Bird Pelagornis. Monster sperm whale Livyatan only gets left out because it wasn't discovered until 2010.
- The first location being a South American Pacific kelp forest and their mention in the book almost confirms that the seagoing ground sloth Thalassocnus was going to be featured but was cut. Alternatively, a setting in the northern Pacific during the Miocene (which also had kelp forests) could have included desmostylians like Paleoparadoxia, a.k.a. the lovechildren of manatees and hippopotamuses.
A small whale with long tusks.
- Anachronism Stew: Actually from the Late Miocene rather than the Pliocene.
- Black Bead Eyes: Unusually for a mammal.
- Meaningful Name: Odobenocetops means "Whale-faced Walrus".
- Mix-and-Match Critters: Looks like a mix between a narwhal, a walrus and a manatee.
- Monster Munch: Only featured as a potential prey source for Megalodon, although it does escape the segment unharmed. The team invokes this when they disguise a camera as an Odobenocetops.
- Ridiculously Cute Critter: Seriously, why aren't there stuffed toys of this thing?
- What Measure Is a Non-Cute?: Probably why it is allowed to live.
Unnamed whaleA medium-sized filter-feeding whale hunted by the adult Megalodon.
- Fanon: It is never identified in the franchise, but fans have basically agreed that it is Cetotherium.
- Impending Doom P.O.V.: Seen from the "shark cam" attached to the adult Megalodon.
- Monster Munch: Appears only as, and when the Megalodon makes it its prey.
- No Name Given: In fairness, it's most likely not meant to be a particular whale.
The largest bony fish ever, a whale-like filter feeder from 155 million years ago.
- Animals Not to Scale: Like Liopleurodon, it is much larger than the real animal actually was (about 16 meters long).
- Awesome, but Impractical: For all the awe of its size, there doesn't seem to be a real advantage to it.
- Blood Is Squicker in Water: Happens everytime a critter gets a bite out of the sick one.
- Death by a Thousand Cuts/Eaten Alive: Hungry carnivores (sharks, crocodiles, and eventually pliosaurs) hang onto a sick one and begin to eat as it continues swimming. The fish could take losing a lot of pounds, but the problem is that predators just keep coming one after another.
- Gentle Giant: Extremely large, but totally harmless.
- Giant Equals Invincible: Subverted. Predators don't bother usually with hunting it due to its size, but it has no way to outrun them or fight back. Once they start eating it alive, there is no stop. Its only defense is to travel in groups and hope someone else gets eaten, much like any given fish in the Ocean.
- Mighty Glacier: They are as ridiculously slow as ridiculously gigantic.
- Mix-and-Match Critters: Your average fish + a filter feeding whale.
A speedy marine crocodile.
- Fragile Speedster: Very fast, but lacks the armor plating of other crocodiles. As Nigel puts it, it has "sacrificed defense for speed".
- Mix-and-Match Critters: Clearly a crocodile, but with the soft skin and fins of a shark.
- Never Smile at a Crocodile: It eats chunks out of a wounded Leedsichthys, and it must be dissuaded from biting Nigel, unlike the Hybodus.
- Those Two Bad Guys: Feeds on the sick Leedsichthys along with Hybodus, and it is just as ridiculously small compared to Liopleurodon.
Your average Jurassic shark, returned. For more tropes, visit Walking with Dinosaurs.
- Cow Tools: The head horns. Sure, they had them in Walking with Dinosaurs already, but this time their bizarre nature is explicitly addressed.
- Informed Attribute: Nigel calls them the weirdest sharks because of the horns. This is harsh considering he met anvil-finned Stethacanthus not long ago.
- Those Two Bad Guys: Now with a reptilian friend, Metriorhynchus.
The reputed largest carnivorous reptile of all time. See Walking with Dinosaurs for other tropes.
- Adaptational Wimp: It is still touted as the largest predator of all time and the crew is afraid of it, plus it gets the second place to the Jurassic all by itself. However, its omnicidal power is far removed from what it was in Walking with Dinosaurs. It only appears scavenging in this segment, first of squids used to bait juveniles and then feeding on the dead Leedsichthys.
- The Nose Knows: They can feed both at night and day, because they live in "a world of smell" and are not reliant on sight according to Nigel.
- Scary Teeth: Also noted. They cut through the Leedsichthys hide like butter, while in WWD they mostly ate prey whole.
- Strong Family Resemblance: The teeth and the long face makes it instantly recognizable as a relative of Nothosaurus and Elasmosaurus, despite each being almost 100 million years apart in opposite directions.
- Weaksauce Weakness: They can be turned away by a stench that is bad enough.
A human-sized, flightless seabird from 75 million years ago.
- Action Survivor: How does a bird even dare live in this sea? Nevermind a flightless bird that must actually look for its food underwater. And the land is inhabited by tyrannosaurs so they should also look the other way when on the shore.
- Feathered Fiend: Subverted. They're ugly and aggressive, but also harmless.
- Graceful in Their Element: They can't fly or even walk on land, but are graceful swimmers.
- Mix-and-Match Critters: Like a cross between a penguin and a sea lion, but somehow bigger and uglier.
- Noisy Nature: On land, at their nesting grounds.
- Monster Munch: They exist to show how badass all the other animals are by getting eaten.
- Prehistoric Monster: Proof that nature can do this to anything. It is a seabird, but with teeth, flightless, and the size of a human.
- Toothy Bird: It retains the teeth of primitive birds, and puts them to good use when catching fish (modern seabirds would probably be toothed today if all Mesozoic seabirds had not died out in the K/Pg mass extinction).
One of many large sharks in the American interior seaway.
- All There in the Manual: Not identified onscreen.
- Always Someone Better: Given how much else lives in this sea, it only merits a cameo, but would be a fearsome top predator almost anywhere else. In fact, the show recycles the Megalodon model for it.
- Blood Is Squicker in Water: Shown inspecting a pool of blood, although it isn't the cause of it.
- The Cameo: Only appears in this brief shot. However, it is duly noted.
- Prop Recycling: It reuses the Megalodon model.
- Threatening Shark: Downplayed considering this sea is filled with even more dangerous beasts.
A large predatory bony fish with a flattened face.
- Always Someone Better: Like Squalicorax, it probably would have been a top predator if it lived in a different sea.
- Animals Not to Scale: The one attacking a Pteranodon is oversized to the point of easy confusion with Squalicorax or even Tylosaurus.
- Big Eater: Eating a two meter long bird in one gulp!
- Blood Is Squicker in Water: The actual perpetrator, as a result of hunting a Hesperornis.
- Early-Bird Cameo: Shown in the prologue of the series as the reason why taking a dip in Prehistory would be a bad idea. Ironically, it turns out to be one of the less threatening predators in its environment.
- Irony: A fish that eats fish-eating birds and almost eats a fish-eating pterosaur at one point.
- Nightmare Face: A perpetual one, due to its compresion.
- Red Baron: Called "the bulldog fish" due to its short face and protruding teeth.
- The Worf Effect: Eating a man-sized Hesperornis in one gulp.
A small coastal mosasaur.
- Always Someone Better: Would qualify as a top predator if it didn't have a giant cousin.
- Lesser of Two Evils: A smaller relative of the giant Tylosaurus.
- Mix-and-Match Critters: Although related to snakes, they look more like monitor lizards, crocodiles or other sea reptiles. The snake connection is implied more in this case by having it swimming in a reef near the shore, much like a modern sea serpent.
- Prop Recycling: Modified from the same model as Tylosaurus, although it is stockier and with a shorter tail, rather than a transplant.
- The Worf Effect: It lives among the shore rocks, in part, because it is scared of the large oceanic going Tylosaurus. That's what the Mariner is actually after.
- Anachronism Stew: Despite being confirmed by Word of God, it didn't evolve until 68 million years ago. The fans have basically agreed that the tyrannosaur seen in this episode is actually the time period accurate Daspletosaurus.
- The Cameo: It only appears once in the segment.
- Noisy Nature: It roars at the beach for no seeming reason. Is it trying to scare the Ancient Mariner?
- Rule of Cool: Why is it on a rock right on the sea surface? How did it even got there? Why is it roaring? Why is it there 7 million years before its time? Rule of Cool, that's why.
- Stock Dinosaurs: So stock, it is used to establish the Cretaceous setting in both the timeline and the actual segment. And it roars in both.
The famous flying reptile. For tropes related to "Chased by Dinosaurs", see Walking with Dinosaurs.
- All Animals Are Domesticated: Despite never seeing a human before, one becomes a pet to Nigel in exchange for fish. Which in turns makes this an example of Domesticated Dinosaurs.
- Anachronism Stew/Misplaced Wildlife: Inverted. Shown correctly in the North American interior seaway after "Chased by Dinosaurs" misplaced it millions of years earlier and in South America.
- Animal Reaction Shot: The one tamed by Nigel screeches in panic when Nigel's boat is capsized.
- Giant Flyer: Not giant giant, but still big enough to qualify.
- Irony: Eats fish, almost gets eaten by a fish (Xiphactinus).
- Ptero Soarer: Though to BBC's credit, this is the most accurate (for its time) pterosaur depicted in the series.
- Team Pet: One becomes this for Nigel's boat crew. Nigel feeds it fish and it sits on the boat with them. It seems to take a liking to the crew, seeing as it appears to be genuinely frightened when a mosasaur capsizes Nigel's boat.
The largest sea turtle ever.
- Gentle Giant: So harmless, Nigel ignores all precautions to swim on the back of one.
- Half the Man He Used to Be: The first one encountered by the crew has been severed in half by a mosasaur attack.
- Prop Recycling: It is clear the "dead half turtle" and the "other living turtle" are played by the same half turtle prop.
- Turtle Island: Downplayed. The half turtle is found floating on the sea surface, and it is still large enough to make the boat stop. A living one can easily transport a person (or a few) on its shell. But neither would ever be mistaken for an actual island.
- Turtle Power: A massive sea turtle. Means little in Hell's Aquarium.
- The Worf Effect: Just imagine what mosasaurs can do, if they can chow through the half of this and be so confident in themselves to leave the other half.
The largest plesiosaur ever.
- Camera Abuse: One hits the underwater camera with the snout while inspecting it.
- Gentle Giant: It feeds on small fish so it is harmless to humans. They ignore the Mariner when they pass it during their migration.
- Long Neck: Its most evident feature.
- Mix-and-Match Critters: Sometimes compared to a snake rammed through a sea turtle.
- Stock Ness Monster: Pretty much how Nessie is imagined to look.
- Strong Family Resemblance: Easy to recognize as a relative of Nothosaurus and Liopleurodon due to its triangular head and fish-trap type teeth, despite being separated from either by hundreds of millions of years.
The largest mosasaur ever and actual top predator of the episode.
- Always a Bigger Fish: The Tylosaurus pack attacks the lifeboat sent to rescue Nigel from an earlier Xiphactinus attack. And they are natural predators to everything else seen in this episode.
- Big Bad: Poses the biggest threat of the sea monsters.
- Camera Abuse: During the final credits, one bites at the camera.
- Cliffhanger: Zigzagged. They attack the rescue lifeboat near the episode's end, but the occupants make it to the larger ship (this would probably be left for the next episode in an actual cliffhanger). Then, The Stinger has them attack the ship in even greater numbers, while the crew is sleeping, and this would be the actual cliffhanger of the episode if it wasn't the end of the series already.
- Covers Always Lie: No, they never get near the shark cage.
- The Dreaded: This thing manages to scare Nigel's Pteranodon.
- Expy: Attacking the lifeboat after confusing it with a turtle seems taken from great white sharks, and the family bounds and concerted attacks, from killer whales.
- The Family That Slays Together: To quote the narrator: "The only thing worse than swimming with a 60-foot-long killer marine reptile... is swimming with its family."
- Hero Killer: Like the Megalodon, it comes close. But The Stinger implies that it succeeds.
- I Am A Humanitarian: They eat everything, including other mosasaurs. The narrator doesn't clarify if the same species of mosasaur.
- Lightning Bruiser: And they were even faster in Real Life.
- Monster Is a Mommy: They travel in family groups and take care of their young. One of them can be seen swimming next to its mother when the lifeboat is attacked.
- Rule of Cool: If modern snakes and lizards are any indication, it's unlikely that mosasaurs were social animals or took care of their offspring, but it is cooler to see them do so.
- Sea Monster: The straightest example of them all. Why is the Cretaceous the deadliest sea of all? Because it is filled to the brim with giant predators. What are all those predators afraid of? This guy.
- Science Marches On: It is now known that it had a vertical shark-like tail fin instead of a flat paddle-like one. This, combined with the fact that it was warm-blooded, would have made it an even faster, more active hunter and give it access to polar regions.
- Zerg Rush: It travels in groups, and they attack all at once. And then they surround the boat...