History Main / PerilousPrehistoricSeas

** ''Series/WalkingWithDinosaurs'': The third episode, ''Cruel Sea'' is entirely set on the shores of Late Jurassic England, showcasing just how much of a danger the seas could be. Best shown when a ([[ArtisticLicensePaleontology massively oversized]]) ''Liopleurodon'' suddenly rises up to scoop a fishing ''Eustreptospondylus'' and drag it underwater to devour it. That said, the episode focuses on an ichthyosaur known as an ''Ophthalmosaurus'' where several young are trying to make an effort to survive and the hardships that come with it, including having to deal with underwater predators like adults of its own kind and the aforementioned ''Liopleurodon''.

* ''VideoGame/{{Roblox}}'': The ''Dinosaur Simulator'' playthrough allows players to access the seas and even play as aquatic animals such as ''Mosasaurus'', ''Ichthyosaurus'', ''Elasmosaurus'', ''Pliosaurus'', and even megalodon. Given the nature of the game, players are expected to hunt for other aquatic creatures in order to survive as well as avoid being hunted down by other predators.

* ''WesternAnimation/TheLandBeforeTime'': While aquatic creatures, such as Elsie the ''Elasmosaurus'' in ''[[WesternAnimation/TheLandBeforeTimeVTheMysteriousIsland The Mysterious Island]]'' have made brief appearances, the ninth film, ''[[WesternAnimation/TheLandBeforeTimeIXJourneyToBigWater Journey to Big Water]]'' places them on central focus, namely an ''Ophthalmosaurus'' named Mo, who befriends Littlefoot as a BloodBrothers, and an antagonistic ''Liopleurodon''. The titular "Big Water" is really the sea, which Mo wants to return to as his family is really there, and while the ''Liopleurodon'' is a massive threat, it only attacks Mo and The Gang of Five because they're nearby food, is starving to a lack of preferred prey, and is stranded in a lake.

* ''Series/PrehistoricPlanet'': The episode ''Coasts'' places significant emphasis on the oceanic residents of the Cretaceous Period, with each of them displaying their lifestyle and struggles.

** ''Series/WalkingWithDinosaurs'': The third episode, ''Cruel Sea'' is entirely set on the shores of Late Jurassic England, showcasing just how much of a danger the seas could be. Best shown when a ''Liopleurodon'' suddenly rises up to scoop a fishing ''Eustreptospondylus'' and drag it underwater to devour it. That said, the episode focuses on an ichthyosaur known as an ''Ophthalmosaurus'' where several young are trying to make an effort to survive and the hardships that come with it, including having to deal with underwater predators like adults of its own kind and the aforementioned ''Liopleurodon''.

** ''Series/SeaMonsters'' naturally is about these, from giant sea scorpions and cephalopods in the Ordovician period to mosasaurs of the Niobrara Sea (more commonly known as the Western Interior Seaway) in what's dubbed the Deadliest Seas of all time. Many of the creatures that Nigel encounters are actually quite docile, or at least uninterested in attacking him, and are more concerned with their own needs. While there are genuine threats like the megalodon, ''Liopleurodon'', and the ''Tylosaurus'', this only ends up being the case whenever Nigel gets too close to them, otherwise, they are only hunting for their preferred prey and react in a way any other animal would. That said, in the end, a ''Tylosaurus'' family [[spoiler:does cross into PrehistoricMonster territory by approaching and attacking Nigel's ship]].

** In season one episode ''Devils of the Deep'', the rescue team travels to the Gogo Reef in the days of the Devonian period. During this mission, an ''Onychodus'' almost bites an arm off of Leon, a ''Titanichthys]] comes rather ominously close to colliding with Leon and Jack while they're distracted with an argument, and a foursome of ''Dunkleosteus'' come scarily close to maiming or killing team leader Drew.

** ''Series/SeaMonsters'' naturally is about these, from giant sea scorpions and cephalopods in the Ordovician period to mosasaurs of the Niobrara Sea (more commonly known as the Western Interior Seaway) in what's dubbed the Deadliest Seas of all time. Many of the creatures that Nigel encounters are actually quite docile, or at least uninterested in attacking him, and are more concerned with their own needs. While there are genuine threats like the ''Megalodon'', ''Liopleurodon'', and the ''Tylosaurus'', this only ends up being the case whenever Nigel gets too close to them, otherwise, they are only hunting for their preferred prey and react in a way any other animal would. That said, in the end, a ''Tylosaurus'' family [[spoiler:does cross into PrehistoricMonster territory by approaching and attacking Nigel's ship]].

** In season one episode ''Devils of the Deep'', the rescue team travel to the Gogo Reef in the days of the Devonian period. During this mission, an onychodus almost bites an arm off of Leon, a titanichthys comes rather ominously close to colliding with Leon and Jack while their distracted with an argument, and a foursome of [[FiendishFish dunkleosteus]] come scarily close to maiming or killing team leader Drew.
** In season two episode ''Sea Serpents'', the rescue team rescue Eocene wildlife from both the terrestrial and marine side of the environment. And over the course of their adventures out on the ocean, the rescue team manage to encounter several dangerous sealife, with the climactic final rescue of the episode involving the rescue team protecting a pod of zygorhiza that are in the midst of birthing from getting hunted and eaten by a combined group of [[MonsterWhale basilosaurus]], [[ThreateningShark otodus angustidens]], and a newly discovered giant species of [[ReptilesAreAbhorrent choristodere]] called dracosuchus.

* ''Literature/TheNewDinosaursAnAlternativeEvolution'': Taking place after the Mesozoic Era, but the asteroid not hitting the Earth, marine reptiles continued to evolve alongside the dinosaurs. Ammonites have become more predatory with the appearance of the ''Kraken'' which attacks with poisonous barks. Plesiosaurs and Pliosaurs remained dominant predators in the oceans like the ''Birdsnatcher'', Pelorus, and Pterosaurs like the ''Soar'' also prey upon Ammonites like the ''Kraken'' to make the latter's role more challenging. That said, ''Soars'' also falls prey to ''Birdsnatchers''.

* ''VideoGame/ARKSurvivalEvolved'': [[DownplayedTrope The setting of the game seems more contemporary, yet primordial]], filled with what appears to be modern iterations of prehistoric animals like dinosaurs. Most of the ones that dwell under the seas include ''Basilosaurus'', ''Coelacanth'', ''Ichthyosaurus'', ''Liopleurodon'', ''Megalodon'', ''Mosasaurus'', and ''Plesiosaurus''. While all of them can be tamed, their behavior in the wild varies; some like Coelacanth are docile, while others like ''Basilosaurus'', ''Plesiosaurus'', and even ''Liopleurodon'' are more curious in nature unless provoked. Still, there are those that act aggressively upon notice like ''Mosasaurus'' and ''Megalodon'' and are likely to make traversing through the waters difficult unless you're well-prepared and leveled.

* ''VideoGame/{{Roblox}}'': The ''Dinosaur Simulator'' playthrough allows players to access the seas and even play as aquatic animals such as ''Mosasaurus'', ''Ichthyosaurus'', ''Elasmosaurus'', ''Pliosaurus'', and even ''Megalodon''. Given the nature of the game, players are expected to hunt for other aquatic creatures in order to survive as well as avoid being hunted down by other predators.

* ''WesternAnimation/Primal2019'': The Season 2 premiere, ''[[Recap/Primal2019E11SeaOfDespair Sea of Despair]]'' has Spear and Fang having to build a raft set off to the seas in their quest to save Mira. Along the ride, Spear and Fang have to hunt for food, which comes under the form of the turtle ''Archelon''. While hunting the turtle isn't too hard, given that Spear and Fang are experienced hunters by that point, they are soon forced to contend against threats that they're not comfortable going up against, such as a ''Liopleurodon'', a flock of ''Tropeognathus'', and a ''Megalodon''.

Our general understanding of prehistoric life in seas and oceans is just as unclear and speculative as it is of the dinosaurs and the Ice Age, with the additional fact that we are not as well-versed about underwater life as we are about terrestrial life. Based on fossil evidence, much of what has been uncovered and studied have been known to look ferocious and most likely predatory in nature, such as the mosasaurs of the Mesozoic and the legendary shark ''Megalodon'' of the Cenozoic. While not as common as stories about dinosaurs, there have been a number of works that have placed focus on these animals, usually being depicted as deadly beasts who reigned the seas as apex predators. On other occasions, less frightening sea creatures of prehistoric times have also been depicted, being seen struggling to adapt and survive in a hostile environment filled with predators on all sides.

* ''WesternAnimation/SeaMonstersAPrehistoricAdventure'': This documentary is set in the Western Interior Seaway 82 million years ago and focuses on a young female ''Dolichorhynchops'', chronicling her life from her birth to her death. Dolly is threatened by the various predators of the inland sea, including ''Xiphactinus'', ''Cretoxyrhina'', and ''Tylosaurus''.

[[folder:Fanfiction]]

* Having had a prolific history as a paleoartist, Luis V. Rey is no stranger to prehistoric marine life. [[https://luisvrey.files.wordpress.com/2012/11/mosasaurb1.jpg?w=584 One of them]] shows a ''Tylosaurus'' pair trying to attack a ''Quetzalcoatlus''. This particular artwork has been used as the book cover for a book called ''Prehistoric Monsters''.

* ''WesternAnimation/SeaMonstersAPrehistoricAdventure'': This documentary is set in the Western Interior Seaway 82 million years ago and focuses on a ''Dolichorhynchops'' named Dolly, chronicling her life from her birth to her death. Dolly is threatened by the various predators of the inland sea, including ''Xiphactinus'', ''Cretoxyrhina'', and ''Tylosaurus'' though they don't really serve as antagonists and while a ''Cretoxyrhina'' and a ''Tylosaurus'' do kill Dolly's mother and brother respectively, they do so out of natural predation than malice.

* Another documentary ''WesternAnimation/SeaMonstersAPrehistoricAdventure'' (this one released by Magazine/NationalGeographic and is formally known as ''Sea Monsters: A Prehistoric Adventure'') is set in the Niobrara Sea 82 million years ago and focuses on a ''Dolichorhynchops'' named Dolly, chronicling her life from birth till death. Unlike most apex predators, Dolly is portrayed sympathetically, trying to survive in the harsh seas of the Late Cretaceous. There are predators, including ''Xiphactinus'', ''Certoxyrhina'', and especially ''Tylosaurus'' though they don't really serve as antagonists and while a ''Ceroxyrhina'' and a ''Tylosaurus'' do kill Dolly's mother and brother respectively, it's more out of natural predation than malice.

* Another documentary [[SimilarlyNamedWorks also titled]] ''Sea Monsters'' (this one released by Magazine/NationalGeographic and is formally known as ''Sea Monsters: A Prehistoric Adventure'') is set in the Niobrara Sea 82 million years ago and focuses on a ''Dolichorhynchops'' named Dolly, chronicling her life from birth till death. Unlike most apex predators, Dolly is portrayed sympathetically, trying to survive in the harsh seas of the Late Cretaceous. There are predators, including ''Xiphactinus'', ''Certoxyrhina'', and especially ''Tylosaurus'' though they don't really serve as antagonists and while a ''Ceroxyrhina'' and a ''Tylosaurus'' do kill Dolly's mother and brother respectively, it's more out of natural predation than malice.

** ''Series/SeaMonsters'' naturally is about these, from giant sea scorpions and cephalopods in the Ordovician period to mosasaurs of the Niobrara Sea (more commonly known as the Western Interior Seaway) in what's dubbed the Deadliest Seas of all time. Many of the creatures that Nigel encounters are actually quite docile, or at least uninterested in attacking him, and are more concerned with their own needs. While there are genuine threats like the ''{{Megalodon}}'', ''Liopleurodon'', and the ''Tylosaurus'', this only ends up being the case whenever Nigel gets too close to them, otherwise, they are only hunting for their preferred prey and react in a way any other animal would. That said, in the end, a ''Tylosaurus'' family [[spoiler:does cross into PrehistoricMonster territory by approaching and attacking Nigel's ship]].

Our general understanding of prehistoric life in seas and oceans is just as unclear and speculative as it is of the dinosaurs and the Ice Age, with the additional fact that we are not as well-versed about underwater life as we are about terrestrial life. Based on fossil evidence, much of what has been uncovered and studied have been known to look ferocious and most likely predatory in nature, such as the mosasaurs of the Mesozoic and the legendary shark ''{{Megalodon}}'' of the Cenozoic. While not as common as stories about dinosaurs, there have been a number of works that have placed focus on these animals, usually being depicted as deadly beasts who reigned the seas as apex predators. On other occasions, less frightening sea creatures of prehistoric times have also been depicted, being seen struggling to adapt and survive in a hostile environment filled with predators on all sides.

* ''WesternAnimation/Primal2019'': The Season 2 premiere, ''[[Recap/Primal2019E11SeaOfDespair Sea of Despair]]'' has Spear and Fang having to build a raft set off to the seas in their quest to save Mira. Along the ride, Spear and Fang have to hunt for food, which comes under the form of the turtle ''Archelon''. While hunting the turtle isn't too hard, given that Spear and Fang are experienced hunters by that point, they are soon forced to contend against threats that they're not comfortable going up against, such as a ''Liopleurodon'', a flock of ''Tropeognathus'', and a ''{{Megalodon}}''.

* ''Franchise/WalkingWithDinosaurs'':

** ''Series/WalkingWithBeasts'': The second episode, ''Whale Killer'' takes place in Late Eocene, Pakistan. The central animal, ''Basilosaurus'' is the Tethys Sea's apex predator, inspiring fear towards all other aquatic life, though infants and juveniles are still in danger of being preyed upon. The focus of the episode is on a mother ''Basilosaurus'' soon to give birth and its struggle in trying to catch prey before giving birth, showcasing that the prehistoric seas are a hard life, even for apex predators.

** ''Dino Crisis 2'' is set in a world where a portion of the Cretaceous Period is displaced into the future due to tampering and overestimated research on 3rd Energy. As a result, an underwater facility became the swarming spot of packs of ''Mosasaurus'' and ''Plesiosaurus'' who proceed to kill off any divers and researchers they come across. Dylan and Regina also end up battling against a pack of ''Plesiosaurs'' and ''[[PteroSoarer Pteranodon]]'' on their way to the facility via their boat. Regina herself discovers that the underwater section of the facility has been taken over by ''Mosasaurs'' who have killed all of the facility's workers there as well as a ''Plesiosaurus'' who thrives in the 3rd Energy Reactor as its territory. As usual in the franchise, both creatures act akin to {{Prehistoric Monster}}s.

* A popular early paleoart trope in the 19th century was nightmarish scenes of [[https://commons.wikimedia.org/wiki/File:Great_Sea-Dragons.jpg prehistoric sea creatures battling each other]] in a dark, tumultuous ocean.

* ''WesternAnimation/TheLandBeforeTime'': While aquatic creatures, such as Elsie the ''Elasmosaurus'' in ''The Mysterious Island'' have made brief appearances, the ninth film, ''Journey to Big Water'' places them on central focus, namely an ''Ophthalmosaurus'' named Mo, who befriends Littlefoot as a BloodBrothers, and an antagonistic ''Liopleurodon''. The titular "Big Water" is really the sea, which Mo wants to return to as his family is really there, and while the ''Liopleurodon'' is a massive threat, it only attacks Mo and The Gang of Five because they're nearby food, is starving to a lack of preferred prey, and is stranded in a lake.

* ''Series/PlanetDinosaur'': The episode ''Fight for Life'' has segments dedicated to life in the seas of the Jurassic period, revolving around the marine reptile ''Kimmerosaurus'' and its struggle for survival against the much larger plesiosaur ''Pliosaurus'' [[note]]at the time, it was known provisionally as "Predator X"[[/note]]. The former can take refuge in shallow water, but must venture into the deeper ocean for feeding, where it is vulnerable for predation by ''Pliosaurus'', which uses its greater size and power along with its marginally higher speed to overwhelm its prey. The episode closes off with the narration noting that the odds were always in the predators' favor in the struggle for survival, and that ''Pliosaurus'' ""ruled the oceans for more than 100 million years."

* ''Series/PlanetDinosaur'': The episode ''Fight for Life'' has segments dedicated to life in the seas of the Jurassic period, revolving around the marine reptile ''Kimmerosaurus'' and its struggle for survival against the much larger plesiosaur ''Pliosaurus'' [[note]]at the time, it was known provisionally as "Predator X"[[/note]]. The former can take refuge in shallow water, but must venture into the deeper ocean for feeding, where it is vulnerable for predation by ''Pliosaurus'', which uses its greater size and power along with its marginally higher speed to overwhelm its prey.

* ''Series/PrehistoricPlanet'': The Episode, ''Coasts'' places significant emphasis on the oceanic residents of the Cretaceous Period, with each of them displaying their lifestyle and struggles.

** ''Series/SeaMonsters'' naturally is about these, from giant sea scorpions and cephalopods in the Ordovician period to mosasaurs of the Niobrara Sea (more commonly known as the Western Interior Seaway) in what's dubbed the Deadliest Seas of all time. Many of the creatures that Nigel encounters are actually quite docile, or at least uninterested in attacking him and are more concerned with their own needs. While there are genuine threats like the ''{{Megalodon}}'', ''Liopleurodon'', and the ''Tylosaurus'', this only ends up being the case whenever Nigel gets too close to them, otherwise, they are only hunting for their preferred prey and react in a way any other animal would. That said, in the end, a ''Tylosaurus'' family [[spoiler:does cross into PrehistoricMonster territory by approaching and attacking Nigel's ship]].

* ''Literature/JourneyToTheCenterOfTheEarth'': There is a strange, modern example depicted in the book known as the Lidenbrock Sea, which is located deep underneath the Earth. It is teeming with ravenous prehistoric creatures of the cretaceous like ichthyosaurs and plesiosaurs and the main trio is forced to travel across the seas in their efforts to further explore the center of the Earth whilst having to bear all sorts of threats as well as the sight of a plesiosaur and an ichthyosaur fighting against one another.

* ''VideoGame/EccoTheDolphin'' and its sequel have prehistoric levels. There are Dunkleosteus, trilobites, and prehistoric jellyfish enemies as well as alien enemies,but the ''Pteranodon'' in ''VideoGame/EccoTheTidesOfTime'' helps Ecco by carrying him over obstacles too high to jump over.

* ''Website/SpecWorld'': In a hypothetical world where dinosaurs and other extinct animals lived, mosasaurs continued to evolve and compete against one another with species like the ''Gigantoserpens'' and the "Nile Mosasaur" (''Apep aegyptianus''). It is said that the seas underwent several changes, which caused ocean-dwellers to undergo an "overdrive" regarding their evolution. Mosasaurs would eventually evolve into "Lizardwhales" and while larger, their diet changed to smaller creatures like giant cephalopods and small fishes. Hesperornithoforms like the many forms of Seaguin inhabit and swim across the Arctic Ocean, catching fish, though their small size make them susceptible to being prey to other animals and rely on their agility to escape and fend for themselves.

The world of prehistoric life is a fascinating one, teeming with all sorts of bizarre, unique, and otherwordly creatures that have not existed for a million years. This, coupled with the fact that many are heavily sized, meant that they are a vivid source of imagination for many and various interpretations can be made out from them.

While the dinosaurs are undoubtedly the most famous (and most favored) examples of these, that is not to say that life in the seas was no less mysterious than its terrestrial counterpart. If anything, the underwater realms of the prehistoric world are arguably more mystique and otherwordly than the dinosaurs, its predecessors in the Paleozoic, and the Age of Mammals of the Cenozoic; this may have something to do with our perception and knowledge towards the oceans and it's fauna.

Our general understanding of prehistoric life in seas and oceans is just as dubious and speculative as we can say about dinosaurs and the Ice Age, with the additional fact that we are not as well-versed about underwater life as we are about terrestrial life. Based on fossil evidence, much of what has been uncovered and studied have been known to look ferocious and most likely predatory in nature, such as the ''mosasaurs'' of the Mesozoic and the legendary shark, {{Megalodon}} of the Cenozoic. While not as common, there have been a number of works that have placed focus on these animals, usually being depicted as deadly animals who reigned the seas as apex predators. On other occasions, less frightening sea animals of prehistoric times have also been depicted, being seen as creatures who struggle to adapt and survive in a hostile environment filled with predators on all sides, as displayed with the prehistoric oceans.

This trope can fall under ArtisticLicensePaleontology, seeing, as mentioned above, our knowledge of prehistoric life is based on evidence collected and studied by paleontologists as well as speculative thoughts and depictions in real life. On another note, because sea life is generally harder to describe and understand than terrestrial life, moments of ShownTheirWork are a lot harder to be seen here.

As detailed above, this trope has a lot of overlaps with PrehistoricMonster, SeaMonster, and HazardousWater although there are more sympathetic perspectives added to the trope, provided the narrative's main focus is on a creature whose habitat is the sea and is trying to find a way to survive. Also compare DeathWorld if certain depictions of the seas are unrelentingly brutal in comparison to other examples. Given that most of the creatures of Prehistoric Seas were either carnivores or piscivores, AlwaysABiggerFish is a common occurrence and also potentially serves as a demonstration of how little land animals stand a chance against something that is out of their element. Can also overlap with OceanOfAdventure on a number of occasions, especially if the main focus is on a marine animal.

* [[https://upload.wikimedia.org/wikipedia/commons/f/f7/Knight_Tylosaurus.jpg One artwork]] by famed paleoartist Creator/CharlesRKnight was a ''Tylosaurus'' pursuing a duo of fishes in what appears to be during a high tide. The art does a good job of establishing ''Tylosaurus'' as a predator, with its design in the artwork being very evocative of it being a prehistoric {{Sea Serpent|s}}.