Time travelers should stay out of the water! For this list, we’re diving into the most fascinating and remarkable sea creatures from prehistoric times. These ancient giants and fearsome predators ruled the oceans long before humans roamed the Earth.
Our countdown includes:
- **Mesosaurus**: A small, ancient reptile that lived in the Permian period, known for its aquatic lifestyle and evidence of having lived in freshwater environments.
- **Kronosaurus**: A massive marine reptile from the Cretaceous period, it had a crocodile-like snout and was a formidable predator with powerful jaws.
- **Helicoprion**: Famous for its spiral-shaped teeth that resemble a buzzsaw, this prehistoric shark was a unique and enigmatic predator from the Permian period.
- **Megalodon**: One of the most famous prehistoric sea monsters, the Megalodon was a colossal shark with jaws that could crush almost anything in its path, making it one of the largest and most powerful predators ever to have lived.
- **Livyatan Melvillei**: A gigantic prehistoric whale that was a top predator in its time, Livyatan had massive teeth and a powerful bite, making it a fearsome competitor in the ancient seas.
What’s YOUR favorite prehistoric sea monster? Let us know in the comments!
Our countdown includes:
- **Mesosaurus**: A small, ancient reptile that lived in the Permian period, known for its aquatic lifestyle and evidence of having lived in freshwater environments.
- **Kronosaurus**: A massive marine reptile from the Cretaceous period, it had a crocodile-like snout and was a formidable predator with powerful jaws.
- **Helicoprion**: Famous for its spiral-shaped teeth that resemble a buzzsaw, this prehistoric shark was a unique and enigmatic predator from the Permian period.
- **Megalodon**: One of the most famous prehistoric sea monsters, the Megalodon was a colossal shark with jaws that could crush almost anything in its path, making it one of the largest and most powerful predators ever to have lived.
- **Livyatan Melvillei**: A gigantic prehistoric whale that was a top predator in its time, Livyatan had massive teeth and a powerful bite, making it a fearsome competitor in the ancient seas.
What’s YOUR favorite prehistoric sea monster? Let us know in the comments!
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Short filmTranscript
00:00Time travelers should stay out of the water.
00:03Welcome to WatchMojo, and today we're counting down our picks for the Top 20 Incredible Prehistoric
00:09Sea Monsters.
00:10For this list, we're looking at the most fascinating and remarkable sea creatures from
00:13prehistoric times.
00:1620.
00:17Eucalyptus
00:18Eurypterids are a type of extinct aquatic arthropods, informally referred to as sea
00:22scorpions.
00:23And Eucalyptus was the king of them all.
00:26Walking in at around 7.5 to 8.5 feet, Eucalyptus is currently the largest arthropod that scientists
00:31have discovered.
00:32It was described from a claw found in Germany in 2007 that's nearly a half-meter long.
00:38Living during the Devonian period, Eucalyptus was believed to have been an apex predator
00:42of its day.
00:43And with its impressive size and formidable claws, we can see how it would be a tough
00:47opponent to fight off.
00:48We're also incredibly thankful that bugs don't get this big today.
00:5219.
00:53Elasmosaurus
00:54This sea monster hails from a family of plesiosaurs, marine reptiles that were known for their
00:59wide bodies and long, extended necks.
01:01The Elasmosaurus was an extremely large variation of a plesiosaur that lived primarily during
01:07the late Cretaceous period of evolution.
01:09So long was the neck on this variation that an Elasmosaurus was rarely able to raise its
01:14head above water for any extended period of time.
01:18Instead, this slow-swimming sea monster preferred to stalk its prey from below, often springing
01:23upon schools of fish, while concealed beneath the deep and dark ocean waves.
01:3018.
01:32Dacosaurus
01:34If you're looking for a clue as to what the temperament of the Dacosaurus was like
01:42when this extinct carnivore roamed the Jurassic and Cretaceous oceans, then just look at what
01:47its name means in English – biter lizard.
01:50The Dacosaurus possessed rows of sharp and serrated teeth that made good upon this title,
01:55giving this beast a jaw structure similar to that of a killer whale.
01:59As a result, many marine biologists believe the Dacosaurus to be one of the apex predators
02:03of its day, ripping and tearing chunks out of just about anything that was unfortunate
02:08enough to be caught within its jaws.
02:1117.
02:12Sarcosuchus
02:13While not technically a sea monster, as it primarily inhabited freshwater bodies, Sarcosuchus
02:18was nevertheless an aquatic creature.
02:20A massive crocodile-like Sarcosuchus inhabited what are now South America and Africa during
02:25the Cretaceous period.
02:29Sarcosuchus was an opportunistic predator that fed on pretty much anything that came
02:39near it.
02:40This huge croc could reach more than 30 feet long and often weighed over 4 tons.
03:00Given its enormous size, girth, and distinctive nub on its snout, we doubt anyone would mistake
03:05this beast for a log floating down a river.
03:0916.
03:10Mesosaurus
03:11Generally regarded as one of the earliest marine reptiles, Mesosaurus was an aquatic
03:14predator native to the early Permian period.
03:17In more recent years, we've learned more about their habitats, like the fact that they likely
03:21existed in a hypersaline water body.
03:24Shaped roughly like a crocodile, albeit with a long neck and tail and webbed feet, Mesosaurus
03:29is believed to have hunted fish and crustaceans, and may have spent some of its time on land
03:34as its remains have primarily been found in what would have been coastal regions.
03:38Mesosaurus also helped provide some strong evidence of continental drift, since its fossils
03:42have been discovered in South America and Africa.
03:4515.
03:46Thalassomodon
03:47A relative of the Elasmosaurus, Thalassomodon was another plesiosaur.
03:52Clocking in at around the same length as its cousin, it was among the biggest of these
03:56marine reptiles.
03:57At around 35 feet long, 19 of which consisted of its neck, Thalassomodon lived up to its
04:02name, which translates to Sea Lord.
04:05This plesiosaur ruled the sea that divided what is now North America during the late
04:09Cretaceous.
04:11Like long-necked dinosaurs, Thalassomodon also ate stones to aid in digestion, or possibly
04:16ballast.
04:17You can see specimens displayed at museums around the United States.
04:2114.
04:22Stethacanthus
04:23Sharks have been around for eons, and while their basic design has not changed because
04:28of how efficient they are as predators, there have been a few strange variations on body
04:33type over the epics.
04:34One of the most bizarre appeared on the Stethacanthus.
04:37This shark, which lived from the late Devonian to the late Carboniferous periods, may have
04:41been only a few feet long, but they had a strange anvil-shaped dorsal fin, referred
04:47to as a spine-brush complex.
04:50There are various theories about the purpose of this odd protrusion, including to attract
04:54mates, a way to latch on to larger sea creatures, or else to ward off those same threats.
05:0013.
05:01Cretoxyrhina
05:02Look out Mako sharks and back off hammerheads!
05:05For this prehistoric shark was one of the biggest and baddest beasts during the Cretaceous
05:10period.
05:11Fossils of Cretoxyrhina were first discovered during the mid-1800s, and provide images of
05:24a fearsome and frightening species of shark that earned its nickname of Ginsu shark, thanks
05:30to its mouth full of razor-sharp teeth.
05:33Cretoxyrhina was one of, if not the largest predatory shark of its time, with very few
05:38natural predators to its name.
05:40Indeed, giant marine reptiles and other sea creatures of all kinds fell victim to this
05:45efficient killing machine, essentially placing Cretoxyrhina at the very top of the food chain
05:51during its time on Earth.
05:5312.
05:54Shastasaurus
05:55Have you ever wondered which species of marine reptile was the biggest of the big?
05:59Well, then look no further than the Shastasaurus, which exists today as the largest discovered
06:04marine reptile on record.
06:07The Shastasaurus hails from the family of reptiles known as ichthyosaurs, and were toothless
06:12beasts who rarely delved into extremely deep water, preferring instead to feed closer to
06:17the surface.
06:19One can only imagine what it was like to behold the sight of this creature in the flesh, as
06:23The Shastasaurus ranged from 25 to 69 feet long, depending on the species.
06:30In other words, watch out.
06:3211.
06:33Bacillosaurus
06:34Although the suffix to this next creature implies that the Bacillosaurus was a reptile,
06:39further research has actually proven it to be a prehistoric species of whale.
06:43Nevertheless, the name stuck, and probably for the best, as Bacillosaurus possesses a
06:49frightening look far different than many of its modern cousins.
06:52Maybe it's the creature's long snout full of sharp teeth, or the slithering eel-esque
06:57quality to its physique.
06:59Or maybe it's the fact that Bacillosaurus was fond of chomping down upon the skulls
07:02of its prey with amazingly impressive force, crushing bone and chewing up flesh with the
07:08greatest of ease.
07:09Whichever reason you choose, Bacillosaurus wins almost every time.
07:1410.
07:15Tylosaurus
07:16During the twilight years of the Cretaceous period, a marine reptile species known as
07:21the Mosasaur took hold as one of the most common hunters of the era.
07:25Tylosaurus serves as one of the most frightening examples of these Mosasaurs, thanks to its
07:30incredible size and fiercely aggressive nature.
07:39The creature's long, rounded snout was often used as a battering ram of sorts during battle,
07:44with the Tylosaurus serving as the sort of equal-opportunity predator which fed upon
07:48birds, fish, and sharks alike.
07:51They typically hunted in shallow waters, and were not beyond leaping above the waves to
07:56catch a low-flying or flightless bird or two, with the Tylosaurus's toothy grin likely
08:01serving as the prey's last frightful sight before death.
08:069.
08:07Cronosaurus
08:08Cronosaurus is a member of the Pliosaur clade, a subgroup of Plesiosaurs with short necks
08:12and tails, but with large heads and mouths full of teeth that make them look like flippered
08:17crocodilians.
08:18Roaming the seas during the early Cretaceous period, Cronosaurus grew to around 30 to 36
08:23feet long.
08:24Despite its size, however, it was believed to have been an active and speedy swimmer,
08:28using its four flippers to swiftly turn about in the water to pursue its prey.
08:32Although, given that its bite force was around twice that of modern-day saltwater crocodiles,
08:37anything that entered those jaws was unlikely to live long.
08:418.
08:42Pliosaurus Fungi
08:43Also known as Predator X, discovered in 2006, this marine reptile was nicknamed Predator
09:01X.
09:02The remains unearthed placed Predator X in the family of Pliosaurs, extremely large predatory
09:07reptiles that thrived in European and South American waters during the late Jurassic period.
09:13Given the taxonomic name Pliosaurus Fungi in 2012, it was one of the largest Pliosaurs
09:18on record, with artist renderings painting a frightening portrait of a large-headed,
09:23razor-toothed monster that likely prowled the icy waters off the coasts of Scandinavia.
09:28Although the remains of Predator X are partial,
09:29in 2008, in an island in the high Arctic, a fossil was dug out of the frozen earth.
09:36Its skull alone was nearly twice that of T-Rex.
09:40Although the remains of Predator X are partial, and don't create a complete portrait of
09:44what this monster looked like, the images of this muscular sea-killer remain a scary
09:49sight indeed.
09:517.
09:52Mauisaurus
09:53Plenty of Pliosaurs swam the prehistoric oceans, but the claim to fame of Mauisaurus
09:58is that it had one of the longest necks, in terms of vertebrae number, out of any of them.
10:02Although scientists believe the Mauisaurus was much larger, recent reassessments have
10:06put it shorter than initial estimates, with its body's total length still being a respectable
10:1126 feet.
10:12Named for the Maori demigod Maui, Mauisaurus lived in the seas around present-day New Zealand
10:17approximately 77 million years ago.
10:20What can we say except, it's awesome!
10:236.
10:24Helicoprion
10:25As we've already established, sharks have come in many odd varieties over the years,
10:30and easily the weirdest is Helicoprion.
10:33When scientists first discovered the strange spiral of teeth, they weren't quite sure
10:37how they fit in with its mouth, due to the lack of a complete skeleton.
10:39While a few different positions were postulated, the real position is believed to have been
10:44on the lower jaw as a kind of buzzsaw of teeth that grew inward as new teeth replaced old
10:49ones.
11:05Despite this strange feature, Helicoprion was quite the successful predator, living
11:08through the extinction event between the Permian and Triassic periods.
11:135.
11:14Liopleurodon
11:15The next sea monster on our list may possess a name that translates to smooth-sided teeth,
11:28but there's nothing easy or relaxed about the Liopleurodon.
11:32Indeed, there was little that could stand up against this apex predator that prowled
11:36European waters during the Jurassic period, thanks to Liopleurodon's no-nonsense capacity
11:41for killing.
11:43The Liopleurodon was a strong, propulsive swimmer, and likely pounced upon its prey with
11:48an ambush-type approach, probably striking before any form of prey knew what hit them.
11:536.
11:54Liopleurodon
11:55One specific species of Liopleurodon, known as L. pharaox, has even been measured at over
12:09twenty feet, making this sea monster the stuff of which all bad dreams are made.
12:224.
12:24Mosasaurus
12:25We've already mentioned the Tylosaurus as one of the scariest examples from the prehistoric
12:35Mosasaur family, but what about its even bigger and badder cousin, the Mosasaurus?
12:40This beast could reach an estimated length of almost sixty feet, definitely a good deal
12:45smaller than the one shown in Jurassic World, but still a massive predator with nightmarish
12:49teeth.
12:51The Mosasaurus didn't possess incredible eyesight, however, and didn't often delve
12:55too deep when looking for food.
12:57Instead, these creatures took to shallow waters for their prey, attacking smaller fish, turtles,
13:02and mollusks with ruthless and relentless precision.
13:103.
13:14Dunkleosteus
13:16Many fearsome fish have swum the world's oceans, but few were as formidable as Dunkleosteus.
13:21Living during the Devonian period, Dunkleosteus was a type of armored fish that could reach
13:25up to nearly twenty-nine feet long, easily dwarfing many modern-day aquatic predators.
13:36While they lacked teeth, Dunkleosteus had powerful jaws, with bone-like beaks that it
13:41used to crush and chomp its prey.
13:50It was basically the fish equivalent of a tank in terms of size and durability, if not
13:55attack strength.
13:56We certainly would not want to run into faces like that in a battle, or anywhere else for
14:00that matter.
14:012.
14:02Megalodon
14:03Its name means big tooth, and with good reason.
14:06The prehistoric sea monster known as the Megalodon was one of the most frightening species of
14:11shark to ever roam the oceans.
14:14Scientists estimate that it reached lengths of up to fifty-nine feet.
14:20We're just lucky it went extinct about 3.6 million years ago, at least to our knowledge.
14:25So strong and impactful was Megalodon upon its local aquatic communities that entire
14:30ecosystems could be affected by how this apex predator chose to hunt its food.
14:34The Megalodon was the OG of prehistoric shark badasses.
14:46Before we get to our top pick, here are some honorable mentions.
14:49Odobenocetops.
14:50How about those tusks?
14:55Hallucigenia.
14:58A worm with legs.
15:04Anomalocaris.
15:05Is this an alien squid?
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15:311.
15:32Livyatan Melvillei
15:33A contemporary and competitor of Megalodon during the Miocene Epoch, Livyatan Melvillei
15:39is an extinct genus of sperm whale.
15:41Named for the Hebrew name of the biblical Leviathan, as well as Herman Melville who
15:45wrote Moby Dick, this whale would have been an even more terrifying foe for Captain Ahab.
15:54Ranging between 44 and 57 feet long, Livyatan was not only one of the biggest predators
15:59to ever live, it also had some of the largest sharp teeth of any animal.
16:05This Leviathan was so enormous, it even ate other whales.
16:09Whale song is beautiful, but we have a feeling Livyatan's songs sounded like death metal.
16:14Do you agree with our picks?
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