"Helicoprion," the Buzzsaw Shark!
This guy sounds like he's straight out of a horror movie! "Helicoprion," often known as the "buzzsaw shark," was a type of shark-like fish with a spiral jaw that resembled the edge of a buzzsaw. These grim-looking creatures were also built for speed thanks to their aquadynamic shape. They lived in Earth's waters from the Devonian period, 419.2 million to 358.9 million years ago, until the Triassic period.
According to fossil records, these fish grew to be roughly 25 feet long. So they were 5 feet longer than the largest known great white shark.
“Plesiosaurs,” a Real Sea Monster!
These incredible beasts were about as close to the Loch Ness monster as possible. "Plesiosaurs," a type of aquatic reptile, had four flippers and a body like a boat. There were Plesiosaurs with long necks and those with short necks, and they existed from the Triassic period 201.4 million years ago through the end of the Cretaceous period 66 million years ago, when they perished along with the other non-avian dinosaurs. They had a widespread oceanic existence.
These animals were not just unusual compared to what is now living, but they were also widely scattered and extremely diversified. A real sea monster!
“Tanystropheus Hydroides,” All Neck and Not Much Brain!
During the Triassic period, some 242 million years ago, "Tanystropheus hydroides" existed in the Tethys Sea off the former supercontinent Pangaea. (That was when all of the continents were joined together.) Researchers were able to identify these extinct marine reptiles because of strange fossils discovered on the present-day border between Switzerland and Italy. They possessed strange, broomstick-like necks that extended to a length of ten feet, which was three times longer than their torsos.
Tanystropheids, like long-necked plesiosaurs, have small heads on the front and these odd-looking little bodies well behind their enormous necks. They were clumsy and uncoordinated.
“Habelia Optata,” a Miniature Sea Monster!
When we think of sea monsters, we usually picture them as huge creatures that could tear you apart with little effort. But it turns out that sea monsters can also come in tiny packages. The full-grown "Habelia optata" could only grow to a maximum of 1.6 inches in length. They were armored arthropods with tails as long as the rest of their bodies. For collecting and devouring their prey, these small marine predators featured helmet-shaped heads and creepy mouth appendages.
Fossils of "Habelia optata" have been discovered in British Columbia, Canada, and they date back to the Cambrian period, which was 538.8 million to 485.4 million years ago.
“Lyrarapax Unguispinus” Showed No Mercy!
When it comes to the most deadly creatures to rule the seas, this claw-faced sea monster had completely different characteristics from anything swimming in our waters now. And it ruled during the Cambrian era as well. Even for its time, “Lyrarapax unguispinus” was an odd arthropod species among many that thrived during the Cambrian period. As one of the first extreme predators on the planet, this deadly arthropod took no prisoners.
It possessed a claw-like attachment on the front of its skull that it used to catch prey and could grow up to 3.2 feet in length.
“Mosasaurus Hoffmanni” Fed on Other Mosasaurs!
Even though they aren't the most bizarre creatures here, nonetheless, "mosasaurs" deserve the title of "sea monsters." These marine reptiles, which preyed on other mosasaurs as well as other moving objects, roamed the waters of the planet until meeting the same end as the nonavian dinosaurs. According to research, “Mosasaurus hoffmanni” could reach lengths of up to 56 feet. Following the asteroid impact, the diverse marine ecosystems that mosasaurs lived in collapsed.
All mosasaurs died out as a result of this collapse, as they were dependent on the marine ecosystems for food. They were never to be seen again.
“Placodonta,” Not Your Average Reptile!
These guys had buck teeth so bad they could have picked apples through a picket fence! A group of turtle-like Triassic sea reptiles known as the "Placodonta" existed in what is now China, the Middle East, and Europe. Placodonts had buck teeth in the front used to scrape shells and mollusks from reefs and the ocean floor. But they also possessed flat crushing plates at the rear of their jaws for chewing.
The average length of a Placodont was between 3.3 and 6.6 feet; the longest ones reached 9.8 ft. The earliest known fossils were discovered in 1830.
“Eurypterids” Were Sea Scorpions the Size of Humans!
A group of ocean-dwelling arthropods known as "sea scorpions," or "eurypterids" resembled modern-day scorpions. What made them odd was that they were rather large in comparison to those that are alive now. One eurypterid fossil, for instance, was discovered in New York and is thought to have originated from a sea scorpion bigger than an average person. Certain members of this group could even grow to be longer than 8 feet.
Until they went extinct at the end of the Permian period from 298.9 million to 251.9 million years ago, sea scorpions terrorized the seas for more than 200 million years.
“Saccorhytus Coronarius” Had No Anus!
Okay, it's time to introduce you to one of the strangest sea monsters on our list. And by all accounts, it may look cute, but looks can be deceiving! "Saccorhytus coronarius" was a wrinkled sac that lacked an anus. Yes, you heard me right! They most lightly used their huge mouths to excrete. Microfossils unearthed in China provide evidence that these oddballs existed during the Cambrian period, some 500 million years ago.
These minion-like creatures are little understood, but it is speculated that they spend their days hunting for food in the mud of the ocean floor. They may be linked to mud dragons and penis worms.
“Ichthyosaur,” Like a Dolphin on Steroids!
Ichthyosaur's look may be described as a reptilian version of a dolphin on steroids! These predators all share a common trait: they all have long snouts that point forward. The first ichthyosaurs appeared about 250 million years ago and became extinct about 90 million years ago. In the late Triassic period, several enormous ichthyosaurs coexisted with species as small as 1 foot in length, even though they were enormous creatures themselves.
A fossilized jawbone discovered in the United Kingdom in 2018 was attributed to a marine reptile more than 85 feet in length, making it around the size of a blue whale.
“Tullimonstrum Gregarium” Was About As Weird as It Gets!
These sea beasts look like they are straight out of a children's animated movie like "Monsters, Inc." "Tullimonstrum gregarium," or Tully monsters," as they're known, were a flexible species that had stalked eyes and long, thin appendages that acted as a claw-like feature. Like a long arm with teeth at the end. Because of the peculiar nature of these species, modern scientists can't agree on where they belong in the evolutionary tree.
Whatever they were, these beasts only exist as fossils from Illinois, and they hunted in maritime coastal conditions 300 million years ago. What a weird creature!
“Odontochelys Semitestacea,” Not Your Average Turtle!
These guys remind me of the mutant Ninja Turtles! In the Triassic period, 220 million years ago, "Odontochelys semitestacea" swam in the coastal waters of what is now China. This turtle was an early fossil find, but didn't resemble any living turtles. Like modern turtles, these most ancient turtles have the chest piece, or "plastron," but lack the protective shell known as a carapace. So, here we have toothed, carapace-less, early versions of turtles.
Odontochelys possessed a long, pointed snout that was lined with teeth, in contrast to the mouths of modern turtles, which are beaked and contain no teeth.
“Typhloesus Wellsi,” the Alien Goldfish!
"Typhloesus wellsi" has been given the nickname "alien goldfish" because of their peculiar appearance. It looks like they may have been dropped on Earth during the Carboniferous period, 358.9 million to 298.9 million years ago, by a visiting alien species that had grown weary of keeping them as pets and decided to dump them here. We're joking, of course, but when something is so bizarre, it's hard to believe it's from this world.
It is possible that this species was an early form of gastropod since it used to shoot a toothy "tongue" out of its gut in order to grab food.
“Basilosaurus” Resembles a Huge Sea Serpent
Between 37.8 million and 33.9 million years ago, "Basilosaurus," with a thin body that could extend up to 59 feet, traveled over the water like a huge sea snake. Because the researchers who gave it the name thought the enormous life form was a marine reptile like a mosasaur or ichthyosaur, they gave it the name Basilosaurus, which means "king lizard." This sea serpent is actually closer to a species that we all know.
The animal was a mammal and a cousin of current whales; it was neither a snake nor a lizard. They were mistaken when they originally named it.
“Fanjingshania Renovata,” the Earliest Version of “Jaws”
When this shark-like fish was first described in 2022, it was hailed as being unlike any vertebrate ever found. "Fanjingshania renovata" is a type of fish that falls midway between a bony fish and a shark on the fish family tree. It is covered in spiny fins, has teeth-like scales, and bone armor. It existed during the Silurian age 443.8 million to 419.2 million years ago in what is now southern China.
And while this predator was only six inches long, it packed a serious punch. "Fanjingshania renovata" is the earliest known ancestor that had jaws.
“Opabinia Regalis,” Ate Like an Elephant!
"Opabinia regalis," a little middle Cambrian creature from British Columbia, has five eyes and claws on its long, flexible nose to grasp food. Around 505 million years ago, the species navigated the ancient oceans with the help of lateral lobes and a tail fan. Opabinia is one of the most bizarre animals ever discovered. When it was recreated in 1972, it was so shocking because it resembled an extraterrestrial creature from a science fiction film.
Opabinia had no teeth but a lengthy trunk for picking up food. It could only eat soft food since it was toothless. It ate similarly to elephants.
“Archelon Ischyros,” Just a Huge Turtle!
The sea turtles we see now aren't very unusual, but what if they were substantially larger? That seems a little out of the ordinary. If you go back in time 65 million years, you'll find that the ocean was home to "Archelon ischyros," giant turtles that were 15 feet in length. They would have been enormous compared to modern turtles, such as the leatherback, which can grow to a maximum length of about 5.9 feet.
It seems that one of the most common characteristics of these prehistoric creatures is their sheer size. So many of them were enormous, or even monstrous, perhaps!
“Otodus Megalodon,” Not Something You Should Think About While Swimming!
Another recent animal that was oversized was the “Otodus megalodon.” Megalodon, the largest shark ever recorded, is believed to have dominated ocean ecosystems between 23 million and 2.6 million years ago. Based on fossilized teeth, it was at least three times longer than a current great white shark. In scientific circles, there is disagreement over the actual dimensions of the beast, which may have measured up to or even 80 feet in length.
This shark was so large that it could have easily consumed an Orcinus orca in a few bites. Thanks to Hollywood movies, Megalodons are really quite famous.
“Titanokorys Gainesi”—No Ordinary Vacuum Cleaner!
"Titanokorys gainesi" was one of the biggest predators during the Cambrian period, despite only being 2 feet long. The primitive arthropod moved around the ocean floor while capturing prey with its toothy, circular mouth and vacuuming it up like a Roomba. Fossils discovered in British Columbia that are half a billion years old show that the creature's helmeted head was unusually massive, accounting for around two-thirds of its whole body length.
When it comes to being a predator, having a built-in vacuum cleaner-like method for catching prey must have come in very handy. Just suck it in as you go. Brilliant!
“Websteroprion Armstrongi,” the Heavy Metal Worm!
How scary would it be to meet this guy? A powerful worm from the Devonian era and an extinct relative of modern marine worms were called "Websteroprion armstrongi." The carnivore dwarfed its fellow prehistoric worms, measuring up to 6.6 feet in length. It was so big, in fact, that as soon as Canadian specimens were used to define the species in 2017, it surpassed all previous records for the size of a marine jawed worm.
The researchers named the huge worm's genus Websteroprion after death metal musician Alex Webster of the band “Cannibal Corpse,” as if a big worm wasn't already metal enough.
“Dunkleosteus Terrelli” Was a Chunky Predator
A bus-sized armored fish known as "Dunkleosteus terrelli"—more often referred to as "Dunk"—inhabited the Devonian era. Researchers thought the Dunk was 30 feet long when they first started finding Dunk skulls in Cleveland 150 years ago. However, a 2023 study found that the creatures were actually 13 feet long, but extremely chunky. The superpredator "Dunkleosteus terrelli" had jaws like blades and could slice through any animal that got in its way.
The most likely reason for their demise is due to modifications in ocean conditions during the so-called "Hangenberg Event," which resulted in a sharp decline in marine oxygen levels.
“Nothosaurus Zhangi,” the Stuff of Nightmares
A nothosaur species, "Nothosaurus zhangi," was identified in a 2014 research that appeared in the journal Scientific Reports. It had a lower jaw that was 26 inches long and an estimated total body length of up to 23 feet. These predators used their forelimbs as propellers through the water, snatching prey with fang-like teeth. They were really built for speed. "Nothosaurus zhangi" inhabited what is now southern China around 245 million years ago.
By all accounts, most of these sea creatures are scary, but this guy is the stuff of nightmares. It's hard to believe that creatures existed on this planet.
“Dolichosaurus”—Snakes With Legs!
"Dolichosaurus" were tiny, thin lizards that slithered through the water in pursuit of food. They were discovered in English fossils in the middle of the 19th century and existed throughout the Cretaceous era. The biggest dolichosaurs, were only around 2 feet long, but they had necks that were longer than those of contemporary lizards and included many cervical vertebrae. They possessed an unusually long neck for lizards but were closely related all the same.
These creatures were basically snakes with legs. So if you are the type of person with a fear of snakes, these creatures would really creep you out!
“Diplocaulus Magnicornis,” We Hope You Never Come Back!
Even among the most bizarre aquatic animals from prehistoric times, "Diplocaulus magnicornis" sets itself apart thanks to its boomerang-shaped head. Although scientists don't know why this amphibian developed such an odd head, it probably had something to do with how the species swam. During the Permian era, the American Museum of Natural History estimates that Diplocaulus magnicornis existed around 275 million years ago. Modern-day Texas is where this species' fossils were left behind.
When it comes to monsters of the sea, many times it's their shape that freaks people out the most. Because they are so unusual, they give us that nightmarish feeling.
“Penis Worms”—Yes, You Heard Me Correctly!
The vicious "penis worms" of the Cambrian era are the last group. Don't be fooled by their humorous appearance; 500 million years ago, these marine worms were fierce predators with mouths lined with fangs that preyed on many other sea creatures. Penis worms were armored to avoid becoming prey in the hostile Cambrian waters. These creatures lived in cone-shaped shells, just like hermit crabs. It's a pity they were given such an unfortunate name!
The priapulida group comprises the fossils of the shell-dwelling penis worms. The well-endowed Greek god "Priapus" is honored by the group's name. I'm sure he'd be delighted!