The dinosaurs of the sea.

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Since the life has started on the Blue Planet, many of the prehistoric ocean creatures have either evolved into some modern species or gone extinct. However, by studying their fossils, scientist can put together mysteries from the deep past and allow researchers to better understand marine life. To these days, the vast ocean still holds some of the largest most-feared predator on Earth. Yet, no matter what we find in the depths, none of them seem to come close to the giant terrors that roamed the seas in Earth’s past. These enormous predators made pre-historic oceans a truly treacherous, dangerous place to venture in. Here, we will look at seven of the fiercest sea monsters that once roamed the world’s oceans.

1. Megalodon

Reaching lengths of up to 60-70 feet (18-21 meters) and an estimated maximum weight of over 60 tons, Megalodon is the largest known predator in Earth’s history. As opposed to a genus, Megalodon is a single species that stands out more than any other prehistoric aquatic predator. Its bite force has been estimated to have been at least 10 tonnes. It also has rammed prey from below, to stun them, as the fossilized bones of whales occasionally show signs of serious impact wounds. Ruler of the seas for roughly 25 million years during the Early Miocene to the end of the Pliocene period (some 3.6 million years ago), Megalodon have gone extinct during the time when Earth underwent significant climate changes which would have but significant pressures on the Megalodon. The Oceans cooled and sea levels dropped, and many large marine mammals which the Megalodon relied on for food disappeared during this approximate time.

The raw 3D model of Helicoprion made by “Idaho Virtualization Laboratory” based on the newest research

2. Helicoprion

Most known for its extremely bizarre “tooth whorl,” the Helicoprion seems like a cross between a shark and a chainsaw. Unfortunately, while named in 1899, very little of them has been preserved to give palaeontologists a clear picture of the structure of this unique-looking shark. Being a cartilaginous fish, Helicoprion lived 290 million years ago around North America, Eastern Europe, Asia, and Australia. The entire fish was around 33 feet (10 meters) in length, but other finds suggest that it could have been as long as 39 feet (12 meters). The “tooth whorl” −contains all the teeth of the lower jaw− was discovered in Idaho and measured 18 inches (45 cm) in length. It is generally accepted that when this amazing beast caught and consumed prey, the jaw closed and, unbelievably, the teeth rotated backwards in a sawing motion.

3. Basilosaurus

Initially thought to be a reptile, hence the name means“king lizard,” Basilosaurus was the first prehistoric whale known to science with the first fossils discovered on the Gulf Coast. Measuring at least 56 feet (17 meters) in length, this huge predator is believed to have been common in the Tethys Sea in the late Eocene (around 41 to 33 million years ago). The skull of Basilosaurus is superficially crocodilian in shape, exhibits large jaw muscle attachment areas, and a fearsome set of teeth with canine-shaped incisors in front, and flattened, serrated triangular ‘molars’ in back. The Basilosaurus is at the top of the food chain in its habitat, fed on prey (i.e., smaller whales, sharks, or other large fish) that was considered too big by other predators of the age, which goes to show just how big this creature really was. That said, studies have revealed that Basilosaurus was quite restricted in the way it moved. Basilosaurus had relatively weak muscles and could not dive or swim for extended periods. Unlike today’s whales, it also lacked the ability to do a thing called echolocate, which is when animals send out calls to the environment and listen to the echoes of returning calls from objects near them.

4. Kronosaurus

The genus name Kronosaurus, meaning ‘Kronos lizard,’ was named after the Greek mythology titan Kronos. It belongs to an extinct group of marine reptiles known as the Plesiosauria, commonly referred to as Plesiosaurs (distinguished by proportionally shorter necks and more robust bodies). This apex predator lived in shallow seas across the Pacific Ocean during the early Cretaceous period and had been known to have fed on smaller Plesiosaurs. The size of Kronosaurus is susceptible to exaggeration, given errors in reconstruction, confusion between various genera, and sometimes the inability to distinguish between juvenile and full-grown specimens. Current estimates put Kronosaurus at around 30 to 33 feet (9 to 10 meters) in length. As huge as Kronosaurus was, its teeth were not very impressive. Sure, they were each a few inches long, but they lacked the lethal cutting edges of more advanced marine reptiles (not to mention prehistoric sharks). Presumably, Kronosaurus compensated for its blunt teeth with a lethally powerful bite and an ability to chase prey at high speed: Once Kronosaurus got a firm grip on a plesiosaur or marine turtle, it could shake its prey and then crush its skull as easily as an undersea grape. Although Kronosaurus fossils have only been identified in Australia and Colombia, the extreme distance between these two countries points to the possibility of worldwide distribution.

5. Dunkleosteus

The marine animals of the Devonian period, over 100 million years before the first dinosaurs, tended to be small and meek, but Dunkleosteus was the exception that proved the rule. Dunkleosteus is known by about 10 species, which have been excavated in North America, Western Europe, and northern Africa. An analysis of Dunkleosteus jawbones has demonstrated that this vertebrate could bite with a force of about 8,000 pounds per square inch, putting it in a league with both the much later Tyrannosaurus Rex and the much later giant shark Megalodon. Dunkleosteus was a genus of Placoderm, an entire class of fish that has been extinct around 360 million years ago. The most likely explanation of its extinction is that it succumbed to changes in ocean conditions during the so-called “Hangenberg Event,” which caused marine oxygen levels to plunge–an event that would not have favoured multi-ton fish like Dunkleosteus. Secondarily, Dunkleosteus may have been outcompeted by smaller, sleeker bony fish and sharks, which went on to dominate the world’s oceans for tens of millions of years thereafter.

DBPLivyatan and Megalodon comparison

6. Livyatan

This Ancestor of the Modern Sperm Whale used to be named Leviathan until recently in 2010, it is learned that it had already been used for a genus of mastodon erected a full century before. The genus name, Livyatan melvillei, was inspired by the biblical sea monster and the species name by Herman Melville, the author of the famous novel Moby-Dick. Leviathan possessed the longest teeth (excluding tusks) of any known animal has ever used for eating, about 14 inches long, which were used to tear into the flesh of its unfortunate prey. Amazingly, Leviathan even had bigger teeth than its undersea archenemy megalodon, though the slightly smaller teeth of this giant shark were sharper. Some palaeontologists believe Livyatan was the behaviourally dominant of the two. Current estimates suggest large Livyatan could reach 18 meters in length.

7. Anomalocaris

model of Anomalocaris

The oldest genus on this list, Anomalocaris lived over half a billion years ago in the Cambrian period which is the oldest of the Paleozoic periods. Anomalocaris, from the Greek meaning “unusual shrimp,” was a major predator of those ancient seas, possibly one of the first apex predators. A computer modelling of the Anomalocaris mouthparts suggests they were in fact better suited to sucking on smaller, soft-bodied organisms. Anomalocaris had a disk-like mouth that resembled a slice of pineapple. Two large ‘arms’ with barb-like spikes were positioned in front of the mouth; used to grab prey and bring it to its mouth. For the time in which it lived, Anomalocaris was a truly gigantic creature, reaching lengths from 2 feet (60 centimetres) to a staggering 6 feet (2 meters). Anomalocaris also has some of the largest extremely sophisticated eyes that stuck out from its head on stalk, up to 4 cm in diameter. Its large lenses suggest that it could see in very dim light at depth, like amphipod crustaceans, a type of prawn-like creature that exists today. Fossils from the Cambrian in the Burgess Shale in Canada, and formations in China, Greenland, Australia, and Utah show that this large, ancient shrimp was widespread during the Cambrian Explosion, filled with creatures alien to us today.

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