20 Amazing Sea Monsters from the Past

For anyone interested in paleontology and marine life, I give you the top 20 most ferocious sea creatures to have ever existed.

20. Anamalocaris saron

20 Amazing Sea Monsters from the Past

Anamalocaris was the world's first super predator appearing in the Cambrian seas 525 million years ago. It grew up to about a meter in length and preyed primarily on trilobites and other small animals. It belonged to a group of animals called dinocarids which were closley related to the Arthropods. The Dinocarids (meaning terrible shrimp) were thought to have gone extinct at the end of the Cambrian. However, a recent find in Germany suggested that they indeed hung on until the early Devonian about 400 million years ago. The first two parts of anamolcaris were its mouth appendages which resembled a shrimp and its mouthpiece which were thought to be a jellyfish. The mouthparts were given the name "anamalocaris" which means "odd shrimp". It wasn't until many years later that a whole body was found and the paleontologists realized that the two parts belonged to the same animal.

19. Cameroceras trentonense

Cameroceras was a prehistoric species of orthocone (straight shelled) nautiloid that ruled the seas in the late Ordovician period about 455 million years ago. The Nautiloids are a primitive group of cephalopods that have chaecteristic chambered shells to control buyancy and simple pinhole camera eyes. The only species left today is the chambered nautilus, but they were much more abundant in the Ordovician and had a variety of shell types such as the coiled, straight, curled, blunted and flattened shell types. By some estimates, the shell of Cameroceras could measure up to 30 feet long and during the ordovician, it was both the largest animal on earth and the largest animal yet to exist. It fed on a variety of prey including trilobites, sea scorpions and jawless fish.

18. Pterygotus anglicus

Pterygotus was one of the largest sea scorpions (eurypterids) and arthropods to ever live and the largest marine species. It measured up to 3 meters long and could weigh in excess of 150 kgs. It's favorite prey was likley primitive fish (our distant ancestors). The eurypterids where closley related to living spiders and scorpions, but where as modern scorpions have pincers that are modified front legs, the pincers of pterygotus were modified mouth parts (chelicerae). Pterygotus lived in the late Silurian around 420 million years ago and in terms of size it was only trumped by two other species of eurypterids: jaekelopterus and hibbertopterus, but these didn't make the list because they were both freshwater species and hibbertopterus was a scavenger. hibbertopterus, pterygotus and jaekelopterus were the three largest arthropods to ever have existed.

17. Parapuzosia seppenradensis

Parapuzosia was the largest species of ammonite to have ever lived. The ammonites were a group of cephalopod molluscs that first appeared 400 million years ago in the Devonian, thrived during the Mesozoic and died out with the non-avian dinosaurs at the end of the Cretaceous period. Contrary to populart belief, despite having a shell they were not closley relatied to the nautiloids; their closest living relatives are squid and octopus. Parapuzosia lived during the late Cretaceous and is estimated to have had a shell that could reach 3.5m in diameter and a total mass of 705 kg.

16. Archelon ischyros

Archelon was a prehistoric sea turtle that lived around 80 million years ago. It measured 4 meters long, had a 4.9 meter flipper span and weighed in at 2200 kg, making it the largest sea turtle that ever lived and the second largest turtle behind Stupendemys. Unlike most living turtles, it didn't have a solid shell but instead had a bony framework that supported a leathery carapce for protection.

15. Tusotuethis longa

Tusotuethis longa was a prehistoric species of squid that lived in the late cretaceous period around 80 million years ago. It was about the same size as the modern giant squid with a hood length of 1.8 meters and a total length with the tentacles outstretched of up to 11 meters long. It's closest living relative is the mysterious vampire squid but unlink either the vampire squid and giant squid, tusotuethis lived in the surface waters of the ancient oceans.

14. Elasmosaurus platyurus

Elasmosaurus was the largest of the elasmosaurs, arguably the most iconic group of marine reptiles charecterized by their long necks and small heads. Elasmosaurus lived about 80 million years ago and grew up to 14 meters long and weighed up to 2000 kg with a neck up to 8 meters long. It primarily fed on fish and ssquid and the long neck allowed it to sneak up on them. It used its four flippers to fly throguh the water much like penguins do today. While they could widley move their head side-to-side, they had a very limited capacity to move it laterally so they could not stick their heads out of the water in the swan-shaped manner that is often seen in depictions

13. Leedsicthys problematicus

Leedsicthys was a giant Pachycormid fish that lived during the late Jurassic period roughyl 150 million years ago. Its closest living relative is the bowfin but unlike the bowfin which is a voracious predator, Leedsicthys was a gentle filter feeder using enormous gill rakers to sive out tiny plankton from the water. The remains found thus far are highly fragmentary and size range estimates haver ranged from 13.5 meters in length to 27.5 meters in length, quite possibly making it the largest fish that ever lived. However recent estimates have narrowed down the length to roughly 16.5 meters in length, still making it as big as large whales today.

12. Dakosaurus maximus

Dakosaurus belonged to a kind of prehistoric crocodiles knows as the "thalattosuchians" which flourished during the late Jurassic. Unllike modern crocodiles, they had no armor plating and theil limbs were modified into flippers. Most had pointed, conical teeth that were used for catching fish but Dakosaurus had curved serrated teeth indicating that it was going after much larger prey than its relatives. Dakosaurus itself could grow up to 4.5 meters in length.

11. Thalattoarchon saurophagis

Thalattoarchon was a primitive Ichthyosaur that lived during the early Triassic period roughly 244 million years ago. While many other ichthyosaurs had teeth ideally adapted for snatching up fish, Thalattoarchon had much thicker teeth suited for grabbing larger prey such as other marine reptiles (saurophagis means "lizard-eating"). It was the first apex predator identified in the Mesozoic seas appearing only four million years after the first Ichthyosaurs appeared roughly 248 million years ago. Interestingly enough, the oldest known icthyosaurs were already fully aquatic with no amphibious transitional forms having yet been identified. That notwisthstanding that they only appeared 3 million years after the greatest mass extinction ever (the end-Permian extinction which wiped out 95% of all marine life) indicates that their transition from land to the sea took place very rapidly.

10. Xiphactinus audax

Xiphactinus were a voracious species of predatory fish that lived during the mid to late cretacious roguhly 100 to 65 million years ago. They likley consumed anything that they could fit in their mouths and their diet likley included other fish, small marine reptiles and sea birds. Their name means "sword-ray" which is based off of their sword-like teeth which gave them such a menacing appearence.

9. Shastasaurus sikanensis

Shastasaurus sikanensis was the largest ichthyosaur, the largest marine reptile and the largest predator of the Mesozoic. It could grow up to 24 meters long and weigh in at 75 tonnes, making it around the same size as the modern sperm whale. It lived during the late triassic roughly 210 million years ago and was probbably the largest animal yet to evolve at the time. Compared to other ichthyosaurs it had a ver short snout that was less than 10% of its total length and it completley lacked teeth. Based on this, it has been suggested that shastasaurus was a suction feeder that preyed mainly on squid. It alsa had a ventrally flattened body. The Triassic was the heyday of the Ichthyosaurs where in which they dominated the seas. They continued to thrive in the Jurrasic but went into decline in the Cretacious

8. Pontolis magnus

Pontolis was a prehistoric species of walrus that inhabited North America from 7 to 9 million years ago. It was roughly the size of a modren elephant seal (33% larger than the largest modern walrusses) and a 60 cm long skull. Its large robust canines indicate that it was well suited for takling large prey items such as smaller marine mammals, sea turtles and large fish.

7. Parahelicoprion clerci

Parahelicoprion was a bizzare species of shark that ruled the seas of the late Carboniferous period to the early Permian. It belonged to a group of sharks known as Eugeneodontids that where charecterized by an extension of their lower jaw that grew into a whirl with the teeth creating a saw shaped formation. It could move this whirl back and fourth against the teeth in its upper jaw to creating a slicing action to butcher soft-bodied prey. Helicoprion itself could grow up to 11 meters long.

6. Basilosaurus cetoides

Basilosaurus was an animal that served the role as apex predator in the worlds' oceans 40-35 million years ago. Despite its name, it was not a marine reptile but a primitive whale. When its remains were first found, it was thought to be a mosasaur (a kind of marine lizard) and was given the name basilosaurus which means "king lizard" but it was later identified as a mammal, however, the name stuck. Basilosaurus grew up to 20 meters making it the first "great whale" and was also among the first fully aquatic species of whale. However, unlike living whales, it had a very long body and some more primitive traits such as various kinds of teeth, unfused neck vertebrate and elbows, small hindlimbs and a distinct tail.

5. Dunklesosteus terrelli

Even if it wasn't the most powerful sea predator that ever lived it was certainly the most intimidating. Dunkleosteus was a species of placoderm; a group of extinct fish that were charecterized by armor plating on their head and shoulders. Dunkleosteus lived 380 to 360 million years ago when the placoderms thrived and it would have been the top predator of the time. When it went in for a kill, it could open its mouth in .1 seconds, creating a suction action that would suck their prey into their jaws which would then clamp shut. Dunkleosteus didn't have teeth but rather dermal plates that acted like teeth and when the jaw sliced shut it would have acted like a meat cleaver.

4. Mosasaurus hoffmannii

At 18 meters in length Mosasaurus was the larget of a group of marine lizards closley related to today's monitor lizards known as mosasaurs. It was also the largest lizard ever to live. Mosasuarus was the top predator of the seas in the late creacious and would eat virtually anything that swam. Apart from the two visisble rows of teeth they had an additional one in their upper jaw that would hold their prey in place while they attempted to swallow it. As the Ichthyosaurs went into decline in the cretacious, they were gradually replaced by the mosasaurs.

3. Pliosaurus funkei

At 13,5 meters in length and weighing up to 45 tonnes, Pliosaurus funkei, also known as predator X was the largest of the plesiosaurs (a group of marine reptiles that included both the small-headed long necked elasmosaurs and the big-headed short necked pliosaurs). Predator X was first discovered on the island of Svalbard in Norway and is estimated to have had a bite force four times as powerfule as Tyreannosaurus Rexs'. Even though it wasn't the largest, it was unquestionably the most powerful marine reptile that ever lived and the most fearsome predator of the mesozoic. Before you ask about Liopluerodon, BBC botched that in their Walking with Dinosaurs' series where they stated it grew up to 25 meters long when in reality there isn't any evidence it grows past 9 meters in length. Predator X lived in the late Jurassic period about 150 million years ago.

2. Livyatan melvillei

Livyatan (also known as "Leviathan") was an extince species of raptorial sperm whale that lived 12 to 9 million years ago. It was given the name "Livyatan" because Livyatan is the hebrew word for Leviathan and in the novel "Moby Dick" the whale was often reffered to as "Leviathan" and it was given the species name "melvillei" after the author, Herman Melville. At 13.5-18 meters in length and weight 45-60 tonnes, Livyatan was slightly smaller than the modern sperm whales but was a far more voracious predator and could easily tear it to pieces in a confrontation. Its skull was 3 meters long and 2 meters wide and it had teeth that grew up 35 cm long, making them the largest functional teeth of any known animal. Unlike modern sperm whales which suck their prey (usually giant squid) into their mouth, Livyatan would have used its chompers to prey on other marine mammals such as the cetotheres (small baleen whales) as well as large fish. Like the modern sperm whale, the shape of livyatans' skull suggests that it had a large spermaceti organ that could generate powerful clicks (at 230 decibels, sperm whales are the loudest animals on earth) to stun prey.

1. Carcharocles megalodon

Perhaps the most famous sea monster of all time of all time, at 15 to 18 meters long and weighing in at 50-60 tonnes, Megalodon was quite possibly the most powerful predator that ever lived. It lived 25-2.5 million years ago and ate virtually everything else that swam, but given that it's teeth have been found embedded in the bones of prehistoric whales, it seems they were it's preffered prey. With its row of 18cm teeth and 20 tonnes of bite force, it could turn them into mincemeat. Contrary to popular beleif, there is little evidence to suggest that the Great white is the closest living realtive to megalodon. It was originally placed in the same genus as the great white shark (Carachodon) but this seems to have been a knee-jerk reaction because the great white is the largest living non finter-feeding shark species. Unfortunatley, all that is left of megalodon is its teeth and a few scattered vertbrate, but even those were enought to show us what a monster megalodon was like when alive. FYI, there is no evidence that megalodon is still alive and the discovery channel documentary was fake.

As a side note, whether or not Megalodon or Leviathan should have gotten the top spot was a tough call to make because they're pretty evenly matched. I ended up going with Megalodon because even though their maximum size estimates are the same, the minimum size estimates for Livyatan are lower. But what's interesting is that these two lived at the same time so they would have crossed paths from time to time and we can only speculate who would've won in a direct confrontation. As another side note thoguh, large predators seldom fight and most often avoid each other because if their territory can provide them with enough prey, all engaging the other predator would do is put them at an unecessary risk of injury.


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  • Well I learned something + enjoyed reading this... make more <3

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