Temnodontosaurus, which lived about 200 million years ago, had eyes of a unique size. Their diameter was 26 centimeters with an almost two-meter skull size of this lizard.
Thanks to the discoveries of recent years, the study of sea dinosaurs of the Mesozoic, which for a long time remained in the shadow of their distant terrestrial relatives - dinosaurs, is experiencing a real renaissance. Now we can quite confidently reconstruct the appearance and habits of giant aquatic reptiles - ichthyosaurs, pliosaurs, mosasaurs and plesiosaurs.
The skeletons of aquatic reptiles became known to science among the first, having played an important role in the development of the theory of biological evolution. The massive jaws of a mosasaurus, found in 1764 in a quarry near the Dutch city of Maastricht, clearly confirmed the fact of the extinction of animals, which was a radically new idea at that time. And at the beginning of the 19th century, discoveries of skeletons of ichthyosaurs and plesiosaurs made by Mary Anning in southwestern England provided rich material for research in the field of the still emerging science of extinct animals - paleontology. In our time, marine species of reptiles - saltwater crocodiles, sea snakes and turtles, as well as Galapagos iguana lizards, make up only a small proportion of the reptiles living on the planet. But in the Mesozoic era (251–65 million years ago), their number was incomparably greater. This, apparently, was favored by the warm climate, which allowed animals incapable of maintaining a constant body temperature to feel great in water, an environment with a high heat capacity. In those days, sea lizards roamed the seas from pole to pole, occupying the ecological niches of modern whales, dolphins, seals and sharks. For more than 190 million years, they formed a “caste” of top predators, hunting not only fish and cephalopods, but also each other.
Kronosaurus was a terror of the seas of the Early Cretaceous era (125–99 million years ago) and one of the largest marine reptiles of all time. His name was given in honor of Kronos, one of the ancient Greek titans.
Back in the water
Like aquatic mammals - whales, dolphins and pinnipeds, sea lizards descended from air-breathing land-based ancestors: 300 million years ago, it was reptiles that conquered land, managing, thanks to the appearance of eggs protected by a leathery shell (unlike frogs and fish), to move from reproduction to water to reproduce outside the aquatic environment. Nevertheless, for one reason or another, one or another group of reptiles at different periods again “tried their luck” in the water. It is not yet possible to accurately indicate these reasons, but, as a rule, the development of a new niche by a species is explained by its unoccupied position, the availability of food resources and the absence of predators.
The real invasion of lizards into the ocean began after the largest Permian-Triassic extinction event in the history of our planet (250 million years ago). Experts are still arguing about the causes of this disaster. Various versions have been put forward: the fall of a large meteorite, intense volcanic activity, a massive release of methane hydrate and carbon dioxide. One thing is clear: over a period of time that is extremely short by geological standards, out of all the diversity of species of living organisms, only one in twenty managed to avoid becoming a victim of an environmental disaster. The deserted warm seas provided great opportunities for the “colonizers,” and this is probably why several groups of marine reptiles arose in the Mesozoic era. Four of them were truly unparalleled in number, diversity and distribution. Each group - ichthyosaurs, plesiosaurs, their relatives the pliosaurs, and mosasaurs - consisted of predators that occupied the top of the food pyramids. And each of the groups gave birth to colossi of truly monstrous proportions.
The most important factor that determined the successful development of the aquatic environment by Mesozoic reptiles was the transition to viviparity. Instead of laying eggs, females gave birth to fully formed and fairly large young, thereby increasing their chances of survival. Thus, the life cycle of the reptiles discussed here now took place entirely in the water, and the last thread connecting the sea lizards with the land was broken. Subsequently, apparently, it was this evolutionary acquisition that allowed them to leave shallow waters and conquer the open sea. Not having to go ashore removed size restrictions, and some marine reptiles took advantage of gigantism. Growing up big isn't easy, but once you've grown up, try to beat him. He will offend anyone himself.
Shonisaurus is the largest marine reptile in the history of evolution, dating back more than 200 million years. Such a hulk weighed up to 40 tons. It probably fed on small schooling fish and squid.
Ichthyosaurs - bigger, deeper, faster
The ancestors of fish-lizard ichthyosaurs, who mastered the aquatic environment about 245 million years ago, were small inhabitants of shallow waters. Their body was not barrel-shaped, like those of their descendants, but elongated, and its bending played an important role in movement. However, over the course of 40 million years, the appearance of ichthyosaurs changed significantly. The initially elongated body became more compact and ideally streamlined, and the caudal fin with a large lower blade and a small upper one in most species was transformed into almost symmetrical.
Paleontologists can only guess about the family relationships of ichthyosaurs. It is believed that this group separated very early from the evolutionary trunk, which later gave rise to such branches of reptiles as lizards and snakes, as well as crocodiles, dinosaurs and birds. One of the main problems still remains the lack of a transitional link between the terrestrial ancestors of ichthyosaurs and primitive marine forms. The first fish lizards known to science are already completely aquatic organisms. It is difficult to say what their ancestor was.
The neck length of elasmosaurs that lived 100 million years ago often exceeded the total length of their body and tail. The neck was their main tool for hunting fish and cephalopods.
The length of most ichthyosaurs did not exceed 2–4 meters. However, among them there were also giants, reaching 21 meters. Such giants included, for example, Shonisaurs, who lived at the end of the Triassic period, about 210 million years ago. These are some of the largest marine animals that have ever lived in the oceans of our planet. In addition to their enormous size, these ichthyosaurs were distinguished by a very long skull with narrow jaws. To imagine a shonisaurus, as one American paleontologist joked, you need to inflate a huge rubber dolphin and greatly stretch its face and fins. The most interesting thing is that only the young had teeth, while the gums of the adult reptiles were toothless. You may ask: how did such colossi eat? To this we can answer: if Shonisaurs were smaller, then one could assume that they chased prey and swallowed it whole, as do swordfish and its relatives - marlin and sailfish. However, twenty-meter giants could not be fast. Perhaps they fed themselves with small schooling fish or squid. There is also an assumption that adult shonisaurs used a filtration apparatus like a whalebone, which allowed them to strain plankton from the water. By the beginning of the Jurassic period (200 million years ago), species of ichthyosaurs appeared in the seas, relying on speed. They deftly pursued fish and swift belemnites - extinct relatives of squids and cuttlefish. According to modern calculations, the three- to four-meter ichthyosaur stenopterygius developed a cruising speed no less than one of the fastest fish, tuna (dolphins swim twice as slow) - almost 80 km/h or 20 m/s! In water! The main propellant of such record holders was a powerful tail with vertical blades, like those of fish.
In the Jurassic period, which became the golden age of ichthyosaurs, these lizards were the most numerous marine reptiles. Some species of ichthyosaurs could dive to depths of up to half a kilometer or more in search of prey. These reptiles could distinguish moving objects at such a depth due to the size of their eyes. So, the diameter of the eye of Temnodontosaurus was 26 centimeters! Only the giant squid has more (up to 30 centimeters). The eyes of ichthyosaurs were protected from deformation during rapid movement or at great depth by a unique eye skeleton - supporting rings consisting of more than a dozen bone plates developing in the eye shell - the sclera.
The elongated muzzle, narrow jaws and shape of the teeth of fish lizards indicate that they ate, as already mentioned, relatively small animals: fish and cephalopods. Some species of ichthyosaurs had sharp, conical teeth that were good for grabbing nimble, slippery prey. In contrast, other ichthyosaurs had broad teeth with blunt or rounded tips to crush the shells of cephalopods such as ammonites and nautilids. However, not so long ago, the skeleton of a pregnant female ichthyosaur was discovered, inside which, in addition to fish bones, they found the bones of young sea turtles and, most surprisingly, the bone of an ancient seabird. There is also a report of the discovery of remains of a pterosaur (flying lizard) in the belly of a fish lizard. This means that the diet of ichthyosaurs was much more diverse than previously thought. Moreover, one of the species of early fish lizards discovered this year, which lived in the Triassic (about 240 million years ago), had serrated edges of the rhombic cross-section of its teeth, which indicates its ability to tear off pieces from prey. Such a monster, which reached a length of 15 meters, had practically no dangerous enemies. However, for unclear reasons, this branch of evolution stopped in the second half of the Cretaceous period, about 90 million years ago.
Traces of necrosis were found in the bones of tylosaurs that lived 90–65 million years ago. As a rule, such pathologies are characteristic of animals that dive to great depths.
Plesiosaurs and pliosaurs are dissimilar relatives
In the shallow seas of the Triassic period (240–210 million years ago), another group of reptiles flourished - the nothosaurs. In their lifestyle, they most closely resembled modern seals, spending part of their time on the shore. Nothosaurs were characterized by an elongated neck, and they swam with the help of a tail and webbed feet. Gradually, some of them replaced their paws with fins, which were used as oars, and the more powerful they were, the more the role of the tail weakened.
Nothosaurs are considered the ancestors of plesiosaurs, which the reader knows well from the legend of the monster from Loch Ness. The first plesiosaurs appeared in the mid-Triassic (240–230 million years ago), but their heyday began at the beginning of the Jurassic period, that is, about 200 million years ago.
At the same time, pliosaurs appeared. These marine reptiles were closely related, but they looked different. Representatives of both groups - a unique case among aquatic animals - moved with the help of two pairs of large paddle-shaped fins, and their movements were probably not unidirectional, but multidirectional: when the front fins moved down, the rear fins moved up. It can also be assumed that only the front fin blades were used more often - this saved more energy. The hind ones were put to work only during attacks on prey or rescue from larger predators.
Plesiosaurs are easily recognized by their very long necks. For example, in Elasmosaurus it consisted of 72 vertebrae! Scientists even know skeletons whose necks are longer than the body and tail combined. And, apparently, it was the neck that was their advantage. Although plesiosaurs were not the fastest swimmers, they were the most maneuverable. By the way, with their disappearance, long-necked animals no longer appeared in the sea. And one more interesting fact: the skeletons of some plesiosaurs were found not in marine, but in estuarine (where rivers flowed into the seas) and even freshwater sedimentary rocks. Thus, it is clear that this group did not live exclusively in the seas. For a long time, it was believed that plesiosaurs fed mainly on fish and cephalopods (belemnites and ammonites). The lizard slowly and imperceptibly swam up to the flock from below and, thanks to its extremely long neck, snatched the prey, clearly visible against the background of the light sky, before the flock rushed to its heels. But today it is obvious that the diet of these reptiles was richer. The found skeletons of plesiosaurs often contain smooth stones, probably specially swallowed by the lizard. Experts suggest that it was not ballast, as previously thought, but real millstones. The muscular section of the animal’s stomach, contracting, moved these stones, and they crushed the strong shells of mollusks and crustacean shells that had fallen into the womb of the plesiosaur. Skeletons of plesiosaurs with remains of benthic invertebrates indicate that in addition to species that specialized in hunting in the water column, there were also those that preferred to swim near the surface and collect prey from the bottom. It is also possible that some plesiosaurs could switch from one type of food to another depending on its availability, because the long neck is an excellent “fishing rod” with which it was possible to “catch” a wide variety of prey. It is worth adding that the neck of these predators was a rather rigid structure, and they could not sharply bend or lift it out of the water. This, by the way, casts doubt on many stories about the Loch Ness monster, when eyewitnesses report that they saw exactly a long neck sticking out of the water. The largest of the plesiosaurs is the New Zealand Mauisaurus, which reached 20 meters in length, almost half of which was a giant neck.
The first pliosaurs, which lived in the late Triassic and early Jurassic periods (about 205 million years ago), closely resembled their plesiosaur relatives, initially misleading paleontologists. Their heads were relatively small, and their necks were quite long. Nevertheless, by the middle of the Jurassic period, the differences became very significant: the main trend in their evolution was an increase in the size of the head and the power of the jaws. The neck, accordingly, became short. And if plesiosaurs hunted mainly for fish and cephalopods, then adult pliosaurs chased other marine reptiles, including plesiosaurs. By the way, they didn’t disdain carrion either.
The largest of the first pliosaurs was the seven-meter Romaleosaurus, but its size, including the size of its meter-long jaws, pales in comparison with the monsters that appeared later. The oceans of the second half of the Jurassic period (160 million years ago) were ruled by Liopleurodons - monsters that may have reached 12 meters in length. Later, in the Cretaceous period (100–90 million years ago), colossi of similar sizes lived - Kronosaurus and Brachauchenius. However, the largest pliosaurs were the Late Jurassic period.
Liopleurodons, which inhabited the depths of the sea 160 million years ago, could move quickly with the help of large flippers, which they flapped like wings.
Even more?!
Recently, paleontologists have been incredibly lucky with sensational finds. Thus, two years ago, a Norwegian expedition led by Dr. Jorn Hurum extracted fragments of the skeleton of a giant pliosaur from the permafrost on the island of Spitsbergen. Its length was calculated from one of the skull bones. It turned out - 15 meters! And last year, in the Jurassic sediments of Dorset County in England, scientists had another success. On one of the beaches of Weymouth Bay, local fossil collector Kevin Sheehan dug up an almost completely preserved huge skull measuring 2 meters 40 centimeters! The length of this “sea dragon” could be as much as 16 meters! Almost the same length was the juvenile pliosaur found in 2002 in Mexico and named the Monster of Aramberri.
But that's not all. The Natural History Museum at Oxford University houses a gigantic lower jaw of a macromerus pliosaur measuring 2 meters 87 centimeters! The bone is damaged, and it is believed that its total length was no less than three meters. Thus, its owner could reach 18 meters. Truly imperial sizes.
But pliosaurs were not just huge, they were real monsters. If anyone posed a threat to them, it was themselves. Yes, the huge, whale-like Shonisaurus ichthyosaur and the long-necked Mauisaurus plesiosaur were longer. But the colossal pliosaur predators were ideal “killing machines” and had no equal. Three-meter fins quickly carried the monster towards the target. Powerful jaws with a palisade of huge teeth the size of bananas crushed bones and tore the flesh of victims, regardless of their size. They were truly invincible, and if anyone can be compared with them in power, it was the fossil megalodon shark. Tyrannosaurus rex next to giant pliosaurs looks like a pony in front of a Dutch draft horse. Taking a modern crocodile for comparison, paleontologists calculated the pressure that the huge pliosaur’s jaws developed at the time of the bite: it turned out to be about 15 tons. Scientists got an idea of the power and appetite of the eleven-meter Kronosaurus, who lived 100 million years ago, by “looking” into its belly. There they found the bones of a plesiosaur.
Throughout the Jurassic and much of the Cretaceous period, plesiosaurs and pliosaurs were the dominant ocean predators, although it should not be forgotten that there were always sharks nearby. One way or another, large pliosaurs went extinct about 90 million years ago for unclear reasons. However, as you know, a holy place is never empty. They were replaced in the seas of the late Cretaceous by giants that could compete with the most powerful of the pliosaurs. We are talking about mosasaurs.
Mosasaurus to mosasaurus - lunch
The group of mosasaurs, which replaced and perhaps supplanted the pliosaurs and plesiosaurs, arose from an evolutionary branch close to monitor lizards and snakes. In mosasaurs that completely switched to life in water and became viviparous, their paws were replaced by fins, but the main mover was a long, flattened tail, and in some species it ended in a fin like a shark’s. It can be noted that, judging by the pathological changes found in the fossilized bones, some mosasaurs were able to dive deeply and, like all extreme divers, suffered from the consequences of such dives. Some species of mosasaurs fed on benthic organisms, crushing mollusk shells with short, wide teeth with rounded tops. However, the conical and slightly bent back terrible teeth of most species leave no doubt about the eating habits of their owners. They hunted fish, including sharks, and cephalopods, crushed turtle shells, swallowed seabirds and even flying lizards, and tore apart other marine reptiles and each other. Thus, half-digested plesiosaur bones were found inside a nine-meter-long tylosaur.
The design of the skull of mosasaurs allowed them to swallow even very large prey whole: like snakes, their lower jaw was equipped with additional joints, and some bones of the skull were articulated movably. As a result, the open mouth was truly monstrous in size. Moreover, two additional rows of teeth grew on the roof of the mouth, making it possible to hold prey more firmly. However, we should not forget that mosasaurs were also hunted. The five-meter-long Tylosaurus found by paleontologists had a crushed skull. The only one who could do this was another, larger mosasaurus.
Over 20 million years, mosasaurs rapidly evolved, giving rise to giants comparable in mass and size to monsters from other groups of marine reptiles. Towards the end of the Cretaceous period, during the next great extinction, giant sea lizards disappeared along with dinosaurs and pterosaurs. Possible causes of a new environmental disaster could be the impact of a huge meteorite and (or) increased volcanic activity.
The first to disappear, even before the Cretaceous extinction, were the pliosaurs, and somewhat later the plesiosaurs and mosasaurs. It is believed that this happened due to a disruption in the food chain. The domino principle worked: the extinction of some massive groups of unicellular algae led to the disappearance of those who fed on them - crustaceans, and, as a consequence, fish and cephalopods. Marine reptiles were at the top of this pyramid. The extinction of mosasaurs, for example, could be a consequence of the extinction of ammonites, which formed the basis of their diet. However, there is no final clarity on this issue. For example, two other groups of predators, sharks and teleosts, which also fed on ammonites, survived the Late Cretaceous extinction event with relatively few losses.
Be that as it may, the era of sea monsters is over. And only after 10 million years sea giants will appear again, but not lizards, but mammals - the descendants of the wolf-like Pakicetus, which was the first to master the coastal shallow waters. Modern whales trace their ancestry from him.
Incredible facts
The modern ocean is home to many incredible creatures, many of which we have no idea about. You never know what lies there - in the dark, cold depths. However, none of them compares with the ancient monsters that dominated the world's oceans millions of years ago.
In this article we will tell you about lizards, carnivorous fish and predatory whales that terrorized marine life in prehistoric times.
Prehistoric world
Megalodon
Megalodon may be the most famous creature on this list, but it's hard to imagine that the school-bus-sized shark ever actually existed. Nowadays, there are many different scientific films and programs about these amazing monsters.
Contrary to popular belief, megalodons did not live at the same time as dinosaurs. They dominated the seas from 25 to 1.5 million years ago, which means they missed the last dinosaur by 40 million years. In addition, this means that the first people found these sea monsters alive.
The megalodon's home was the warm ocean that existed until the last ice age in the early Pleistocene, and it is believed that it was this that deprived these huge sharks of food and the ability to reproduce. Perhaps in this way nature protected modern humanity from terrible predators.
Liopleurodon
If there was a water scene in the Jurassic Park movie that included some of the sea monsters of the time, Liopleurodon would definitely appear in it. Although scientists argue about the actual length of this animal (some say it was up to 15 meters), most agree that it was about 6 meters, with a fifth of the length being the pointed head of Liopleurodon.
Many people think that 6 meters is not so much, but the smallest representative of these monsters is capable of swallowing an adult. Scientists have recreated a model of Liopleurodon's fins and tested them.
During the research, they found that these prehistoric animals were not so fast, but they were not lacking in agility. They were also capable of making short, quick and sharp attacks similar to those made by modern crocodiles, which makes them even more terrifying.
Sea monsters
Basilosaurus
Despite the name and appearance, they are not reptiles, as it might seem at first glance. In fact, these are real whales (and not the most frightening ones in this world!). Basilosaurs were the predatory ancestors of modern whales and measured between 15 and 25 meters in length. It is described as a whale, somewhat resembling a snake due to its length and ability to wriggle.
It’s hard to imagine that, while swimming in the ocean, one could stumble upon a huge creature that looked like a snake, a whale and a crocodile at the same time, 20 meters long. The fear of the ocean would stick with you for a long time.
Physical evidence suggests that basilosaurs did not have the same cognitive abilities as modern whales. In addition, they did not have echolocation capabilities and could only move in two dimensions (this means that they could not actively dive or dive to great depths). Thus, this terrible predator was as stupid as a bag of prehistoric tools and would not be able to pursue you if you dived or came onto land.
Cancerscorpios
It's not surprising that the words "sea scorpion" only evoke negative emotions, but this representative of the list was the creepiest of them all. Jaekelopterus rhenaniae is a special species of crustacean scorpion that was the largest and most fearsome arthropod of its time: 2.5 meters of pure clawed terror under its shell.
Many of us are terrified of small ants or large spiders, but imagine the full spectrum of fear experienced by a person who would be unlucky enough to encounter this sea monster.
On the other hand, these creepy creatures went extinct even before the event that killed all the dinosaurs and 90% of life on Earth. Only a few species of crabs survived, which are not so scary. There is no evidence that ancient sea scorpions were poisonous, but the structure of their tails suggests that they may have been.
Read also: A huge sea monster washed up on the coast of Indonesia
Prehistoric animals
Mauisaurus
Mauisaurus was named after the ancient Maori god Maui, who, according to legend, pulled the New Zealand carcass from the ocean floor with a hook, so just from the name you can understand that this animal was huge. The Mauisaurus's neck was about 15 meters long, which is quite a lot compared to its total length of 20 meters.
His incredible neck had many vertebrae, which gave it special flexibility. Imagine a turtle without a shell with a surprisingly long neck - that’s what this creepy creature looked like.
He lived during the Cretaceous period, which meant that unfortunate creatures jumping into the water to escape velociraptors and tyrannosaurs were forced to come face to face with these sea monsters. Mauisaurs' habitats were limited to the waters of New Zealand, indicating that all inhabitants were in danger.
Dunkleosteus
Dunkleosteus was a ten-meter predatory monster. Huge sharks lived much longer than Dunkleosteus, but this did not mean that they were the best predators. Instead of teeth, dunkleosteus had bony growths, like some species of modern turtles. Scientists have calculated that their bite force was 1,500 kilograms per square centimeter, which put them on par with crocodiles and tyrannosaurs and made them one of the creatures with the strongest bite.
Based on facts about their jaw muscles, scientists concluded that Dunkleosteus could open its mouth in one fiftieth of a second, swallowing everything in its path. As the fish grew older, the single bony dental plate was replaced by a segmented one, which made it easier to obtain food and bite through the thick shells of other fish. In the arms race called the prehistoric ocean, Dunkleosteus was a real well-armored, heavy tank.
Sea monsters and monsters of the deep
Kronosaurus
Kronosaurus is another short-necked lizard, similar in appearance to Liopleurosaurus. What is noteworthy is that its true length is also known only approximately. It is believed that it reached up to 10 meters, and its teeth reached up to 30 cm in length. That is why it was named after Kronos, the king of the ancient Greek titans.
Now guess where this monster lived. If your assumption was related to Australia, then you are absolutely right. Kronosaurus's head was about 3 meters long and it was capable of swallowing an entire adult human. In addition, after this there was room inside the animal for another half.
Also, due to the fact that the flippers of kronosaurs were similar in structure to the flippers of turtles, scientists concluded that they were very distantly related and assumed that kronosaurs also went to land to lay eggs. In any case, we can be sure that no one dared to destroy the nests of these sea monsters.
Helicoprion
This shark, 4.5 meters long, had a lower jaw that was a kind of curl, strewn with teeth. She looked like a hybrid of a shark and a buzz saw, and we all know that when dangerous power tools become part of a predator at the top of the food chain, the whole world trembles.
Helicoprion's teeth were serrated, which clearly indicates the carnivory of this sea monster, but scientists still do not know for certain whether the jaw was pushed forward as in the photo, or moved slightly deeper into the mouth.
These creatures survived the Triassic mass extinction, which could indicate their high intelligence, but the reason could also be their living in the deep sea.
Prehistoric sea monsters
Melville's Leviathan
Earlier in this article we already talked about predatory whales. Melville's Leviathan is the most terrifying of them all. Imagine a huge hybrid of an orca and a sperm whale. This monster was not just a carnivore - it killed and ate other whales. It had the largest teeth of any animal known to us.
Their length sometimes reached 37 centimeters! They lived in the same oceans at the same time and ate the same food as megalodons, thus competing with the largest predatory shark of the time.
Their huge heads were equipped with the same echo-sounding devices as modern whales, making them more successful at hunting in murky waters. In case it wasn't clear to anyone from the start, this animal was named after Leviathan, the giant sea monster from the Bible and Herman Melville, who wrote the famous Moby Dick. If Moby Dick had been one of the Leviathans, he would certainly have eaten the Pequod and its entire crew.
Marine reptiles
When studying life in the Mesozoic, perhaps the most striking thing is that almost half of all known species of reptiles lived not on land, but in water, in rivers, estuaries and even in the sea. We have already noted that in the Mesozoic, shallow seas became widespread on the continents, so there was no shortage of living space for aquatic animals.
In the Mesozoic layers there are a large number of fossil reptiles adapted for life in water. This fact can only mean that some reptiles returned back to the sea, to their homeland, where the ancestors of dinosaurs - fish - appeared long ago. This fact requires some explanation, since at first glance there was a regression here. But we cannot consider the return of reptiles to the sea to be a step backward from an evolutionary point of view simply on the grounds that Devonian fish came out of the sea onto land and developed into reptiles after passing through the amphibian stage. On the contrary, this position illustrates the principle according to which each actively developing group of organisms strives to occupy all varieties of the environment in which it can exist. In fact, the movement of reptiles into the sea is not very different from the colonization of rivers and lakes by amphibians in the Late Carboniferous (photo 38). There was food in the water and the competition was not too fierce, so first amphibians and then reptiles moved into the water. Already before the end of the Paleozoic, some reptiles became aquatic inhabitants and began to adapt to a new way of life. This adaptation went mainly along the path of improving the method of movement in the aquatic environment. Of course, reptiles continued to breathe air in the same way that a modern whale, a mammal, although similar in body shape to a fish, breathes air. Moreover, Mesozoic marine reptiles did not evolve from any one land reptile that decided to move back into the water. Fossil skeletons provide undeniable evidence that they had different ancestors and appeared at different times. Thus, fossil remains show how diverse the response of organisms was to changing environmental conditions, as a result of which a vast space was created, abundant in food and suitable for settlement.
Extensive information has been obtained from the study of fossil remains contained in marine mudstones and chalk limestones; These fine clastic rocks preserve not only bones, but also imprints of skin and scales. With the exception of the smallest and most primitive species, most marine reptiles were predators and belonged to three main groups: thyosaurs, plesiosaurs and mosasaurs. Briefly characterizing them, we must first note that ichthyosaurs acquired an elongated shape similar to fish (Fig. 50) and were excellently adapted to fast swimming in pursuit of fish or cephalopods. These animals, reaching 9 meters in length, had bare skin, a dorsal fin and a tail like a fish, and their four limbs turned into a kind of seal flippers and were used to control the movement of the body when swimming. All the fingers in these flippers were closely connected, and there were additional bones in them to increase strength. The large eyes of ichthyosaurs were adapted to see well in water. They even had one very significant improvement in the reproduction process. Being air-breathing animals that lived in seawater, they could not lay eggs. Therefore, ichthyosaurs developed a method of reproduction in which the embryo developed inside the mother’s body and, upon reaching maturity, was born alive. They became viviparous. This fact is established by the discovery of perfectly preserved remains of female ichthyosaurs with fully formed young inside their bodies, the number of young reaches seven.
Rice. 50. Four groups of animals that acquired a streamlined body shape as a result of adaptation to life in water: A. reptile, B. fish, C. bird, D. mammal. Initially they had different appearances, but in the course of evolution they acquired external similarities
The second group includes plesiosaurs, which, unlike the fish-like ichthyosaurs, retained the original body shape of reptiles, reaching 7.5-12 meters in length. If not for the tail, the plesiosaur would have looked like a giant swan. Of course, the ancestor of the plesiosaur was not at all the same land reptile that gave rise to the ichthyosaurs. The legs of plesiosaurs turned into long fins, and the head, set on a long neck, was equipped with sharp teeth that closed and reliably held the most slippery fish. Such teeth prevented chewing; The plesiosaur swallowed its prey whole and then crushed it in its stomach using pebbles. The diet of plesiosaurs can be judged from the stomach contents of one of them, which apparently died before the stones in its stomach had time to properly crush the food it swallowed. It was found that the bones and fragments of shells contained in the stomach belonged to fish, flying reptiles and cephalopods, which were swallowed whole, along with the shell.
The third group of marine reptiles is called mosasaurs because they were first discovered near the Moselle River in northeastern France. They could be called “belated” because they appeared only in the Late Cretaceous, when ichthyosaurs had been populating the seas for almost 150 million years. The ancestors of mosasaurs were lizards rather than dinosaurs. Their length reached 9 meters, they had scaly skin, and their jaws were designed in such a way that they could open their mouths wide, like snakes.
A streamlined body as an adaptation to living conditions in an aquatic environment is found not only in ichthyosaurs and mosasaurs. The same can be seen in a number of animals that lived before and after the Mesozoic, and in the Mesozoic (Fig. 50).
Thanks to the discoveries of recent years, the study of sea lizards of the Mesozoic, which for a long time remained in the shadow of their distant terrestrial relatives - dinosaurs, is experiencing a real renaissance. Now we can quite confidently reconstruct the appearance and habits of giant aquatic reptiles - ichthyosaurs, pliosaurs, mosasaurs and plesiosaurs.
The skeletons of aquatic reptiles became known to science among the first, playing an important role in the development of the theory of biological evolution. The massive jaws of a mosasaurus, found in 1764 in a quarry near the Dutch city of Maastricht, clearly confirmed the fact of the extinction of animals, which was a radically new idea at that time. And at the beginning of the 19th century, discoveries of skeletons of ichthyosaurs and plesiosaurs made by Mary Anning in southwestern England provided rich material for research in the field of the still emerging science of extinct animals - paleontology.
Nowadays, marine reptile species - saltwater crocodiles, sea snakes and turtles, and Galapagos iguana lizards - make up only a small proportion of the reptiles living on the planet. But in the Mesozoic era (251-65 million years ago) their number was incomparably greater. This, apparently, was favored by the warm climate, which allowed animals incapable of maintaining a constant body temperature to feel great in water, an environment with a high heat capacity. In those days, sea lizards roamed the seas from pole to pole, occupying the ecological niches of modern whales, dolphins, seals and sharks. For more than 190 million years, they formed a “caste” of top predators, hunting not only fish and cephalopods, but also each other.
Back in the water
Like aquatic mammals - whales, dolphins and pinnipeds, sea lizards descended from air-breathing land-based ancestors: 300 million years ago, it was reptiles that conquered land, managing, thanks to the appearance of eggs protected by a leathery shell (unlike frogs and fish), to move from reproduction to water to reproduce outside the aquatic environment. Nevertheless, for one reason or another, one or another group of reptiles at different periods again “tried their luck” in the water. It is not yet possible to accurately indicate these reasons, but, as a rule, the development of a new niche by a species is explained by its unoccupied position, the availability of food resources and the absence of predators.
The real invasion of lizards into the ocean began after the largest Permian-Triassic extinction event in the history of our planet (250 million years ago). Experts are still arguing about the causes of this disaster. Various versions have been put forward: the fall of a large meteorite, intense volcanic activity, a massive release of methane hydrate and carbon dioxide. One thing is clear: over a period of time that is extremely short by geological standards, out of all the diversity of species of living organisms, only one in twenty managed to avoid becoming a victim of an environmental disaster. The deserted warm seas provided great opportunities for the “colonizers,” and this is probably why several groups of marine reptiles arose in the Mesozoic era. Four of them were truly unparalleled in number, diversity and distribution. Each group - ichthyosaurs, plesiosaurs, their relatives the pliosaurs, and mosasaurs - consisted of predators that occupied the top of the food pyramids. And each of the groups gave birth to colossi of truly monstrous proportions.
The most important factor that determined the successful development of the aquatic environment by Mesozoic reptiles was the transition to viviparity. Instead of laying eggs, females gave birth to fully formed and fairly large young, thereby increasing their chances of survival. Thus, the life cycle of the reptiles discussed here now took place entirely in the water, and the last thread connecting the sea lizards with the land was broken. Subsequently, apparently, it was this evolutionary acquisition that allowed them to leave shallow waters and conquer the open sea. Not having to go ashore removed size restrictions, and some marine reptiles took advantage of gigantism. Growing up big isn't easy, but once you've grown up, try to beat him. He will offend anyone himself.
Ichthyosaurs - bigger, deeper, faster
The ancestors of fish-lizard ichthyosaurs, who mastered the aquatic environment about 245 million years ago, were small inhabitants of shallow waters. Their body was not barrel-shaped, like those of their descendants, but elongated, and its bending played an important role in movement. However, over the course of 40 million years, the appearance of ichthyosaurs changed significantly. The initially elongated body became more compact and ideally streamlined, and the caudal fin with a large lower blade and a small upper one in most species was transformed into almost symmetrical.
Paleontologists can only guess about the family relationships of ichthyosaurs. It is believed that this group separated very early from the evolutionary trunk, which later gave rise to such branches of reptiles as lizards and snakes, as well as crocodiles, dinosaurs and birds. One of the main problems still remains the lack of a transitional link between the terrestrial ancestors of ichthyosaurs and primitive marine forms. The first fish lizards known to science are already completely aquatic organisms. It is difficult to say what their ancestor was.
The length of most ichthyosaurs did not exceed 2–4 meters. However, among them there were also giants, reaching 21 meters. Such giants included, for example, Shonisaurs, who lived at the end of the Triassic period, about 210 million years ago. These are some of the largest marine animals that have ever lived in the oceans of our planet. In addition to their enormous size, these ichthyosaurs were distinguished by a very long skull with narrow jaws. To imagine a shonisaurus, as one American paleontologist joked, you need to inflate a huge rubber dolphin and greatly stretch its face and fins. The most interesting thing is that only the young had teeth, while the gums of the adult reptiles were toothless. You may ask: how did such colossi eat? To this we can answer: if Shonisaurs were smaller, then one could assume that they chased prey and swallowed it whole, as do swordfish and its relatives - marlin and sailfish. However, twenty-meter giants could not be fast. Perhaps they fed themselves with small schooling fish or squid. There is also an assumption that adult shonisaurs used a filtration apparatus like a whalebone, which allowed them to strain plankton from the water. By the beginning of the Jurassic period (200 million years ago), species of ichthyosaurs appeared in the seas, relying on speed. They deftly pursued fish and swift belemnites - extinct relatives of squids and cuttlefish. According to modern calculations, the three- to four-meter ichthyosaur stenopterygius developed a cruising speed no less than one of the fastest fish, tuna (dolphins swim twice as slow) - almost 80 km/h or 20 m/s! In water! The main propellant of such record holders was a powerful tail with vertical blades, like those of fish.
In the Jurassic period, which became the golden age of ichthyosaurs, these lizards were the most numerous marine reptiles. Some species of ichthyosaurs could dive to depths of up to half a kilometer or more in search of prey. These reptiles could distinguish moving objects at such a depth due to the size of their eyes. So, the diameter of the eye of Temnodontosaurus was 26 centimeters! Only the giant squid has more (up to 30 centimeters). The eyes of ichthyosaurs were protected from deformation during rapid movement or at great depth by a unique eye skeleton - supporting rings consisting of more than a dozen bone plates developing in the eye shell - the sclera.
The elongated muzzle, narrow jaws and shape of the teeth of fish lizards indicate that they ate, as already mentioned, relatively small animals: fish and cephalopods. Some species of ichthyosaurs had sharp, conical teeth that were good for grabbing nimble, slippery prey. In contrast, other ichthyosaurs had broad teeth with blunt or rounded tips to crush the shells of cephalopods such as ammonites and nautilids. However, not so long ago, the skeleton of a pregnant female ichthyosaur was discovered, inside which, in addition to fish bones, they found the bones of young sea turtles and, most surprisingly, the bone of an ancient seabird. There is also a report of the discovery of remains of a pterosaur (flying lizard) in the belly of a fish lizard. This means that the diet of ichthyosaurs was much more diverse than previously thought. Moreover, one of the species of early fish lizards discovered this year, which lived in the Triassic (about 240 million years ago), had serrated edges of the rhombic cross-section of its teeth, which indicates its ability to tear off pieces from prey. Such a monster, which reached a length of 15 meters, had practically no dangerous enemies. However, for unclear reasons, this branch of evolution stopped in the second half of the Cretaceous period, about 90 million years ago.
In the shallow seas of the Triassic period (240–210 million years ago), another group of reptiles flourished - the nothosaurs. In their lifestyle, they most closely resembled modern seals, spending part of their time on the shore. Nothosaurs were characterized by an elongated neck, and they swam with the help of a tail and webbed feet. Gradually, some of them replaced their paws with fins, which were used as oars, and the more powerful they were, the more the role of the tail weakened.
Nothosaurs are considered the ancestors of plesiosaurs, which the reader knows well from the legend of the monster from Loch Ness. The first plesiosaurs appeared in the mid-Triassic (240–230 million years ago), but their heyday began at the beginning of the Jurassic period, that is, about 200 million years ago.
At the same time, pliosaurs appeared. These marine reptiles were closely related, but they looked different. Representatives of both groups - a unique case among aquatic animals - moved with the help of two pairs of large paddle-shaped fins, and their movements were probably not unidirectional, but multidirectional: when the front fins moved down, the rear fins moved up. It can also be assumed that only the front fin blades were used more often - this saved more energy. The hind ones were put to work only during attacks on prey or rescue from larger predators.
Plesiosaurs are easily recognized by their very long necks. For example, in Elasmosaurus it consisted of 72 vertebrae! Scientists even know skeletons whose necks are longer than the body and tail combined. And, apparently, it was the neck that was their advantage. Although plesiosaurs were not the fastest swimmers, they were the most maneuverable. By the way, with their disappearance, long-necked animals no longer appeared in the sea. And one more interesting fact: the skeletons of some plesiosaurs were found not in marine, but in estuarine (where rivers flowed into the seas) and even freshwater sedimentary rocks. Thus, it is clear that this group did not live exclusively in the seas. For a long time, it was believed that plesiosaurs fed mainly on fish and cephalopods (belemnites and ammonites). The lizard slowly and imperceptibly swam up to the flock from below and, thanks to its extremely long neck, snatched the prey, clearly visible against the background of the light sky, before the flock rushed to its heels. But today it is obvious that the diet of these reptiles was richer. The found skeletons of plesiosaurs often contain smooth stones, probably specially swallowed by the lizard. Experts suggest that it was not ballast, as previously thought, but real millstones. The muscular section of the animal’s stomach, contracting, moved these stones, and they crushed the strong shells of mollusks and crustacean shells that had fallen into the womb of the plesiosaur. Skeletons of plesiosaurs with remains of benthic invertebrates indicate that in addition to species that specialized in hunting in the water column, there were also those that preferred to swim near the surface and collect prey from the bottom. It is also possible that some plesiosaurs could switch from one type of food to another depending on its availability, because the long neck is an excellent “fishing rod” with which it was possible to “catch” a wide variety of prey. It is worth adding that the neck of these predators was a rather rigid structure, and they could not sharply bend or lift it out of the water. This, by the way, casts doubt on many stories about the Loch Ness monster, when eyewitnesses report that they saw exactly a long neck sticking out of the water. The largest of the plesiosaurs is the New Zealand Mauisaurus, which reached 20 meters in length, almost half of which was a giant neck.
The first pliosaurs, which lived in the late Triassic and early Jurassic periods (about 205 million years ago), closely resembled their plesiosaur relatives, initially misleading paleontologists. Their heads were relatively small, and their necks were quite long. Nevertheless, by the middle of the Jurassic period, the differences became very significant: the main trend in their evolution was an increase in the size of the head and the power of the jaws. The neck, accordingly, became short. And if plesiosaurs hunted mainly for fish and cephalopods, then adult pliosaurs chased other marine reptiles, including plesiosaurs. By the way, they didn’t disdain carrion either.
The largest of the first pliosaurs was the seven-meter Romaleosaurus, but its size, including the size of its meter-long jaws, pales in comparison with the monsters that appeared later. The oceans of the second half of the Jurassic period (160 million years ago) were ruled by Liopleurodons - monsters that may have reached 12 meters in length. Later, in the Cretaceous period (100–90 million years ago), colossi of similar sizes lived - Kronosaurus and Brachauchenius. However, the largest pliosaurs were the Late Jurassic period.
Liopleurodons, which inhabited the depths of the sea 160 million years ago, could move quickly with the help of large flippers, which they flapped like wings.
Even more?!
Recently, paleontologists have been incredibly lucky with sensational finds. Thus, two years ago, a Norwegian expedition led by Dr. Jorn Hurum extracted fragments of the skeleton of a giant pliosaur from the permafrost on the island of Spitsbergen. Its length was calculated from one of the skull bones. It turned out - 15 meters! And last year, in the Jurassic sediments of Dorset County in England, scientists had another success. On one of the beaches of Weymouth Bay, local fossil collector Kevin Sheehan dug up an almost completely preserved huge skull measuring 2 meters 40 centimeters! The length of this “sea dragon” could be as much as 16 meters! Almost the same length was the juvenile pliosaur found in 2002 in Mexico and named the Monster of Aramberri.
But that's not all. The Natural History Museum at Oxford University houses a gigantic lower jaw of a macromerus pliosaur measuring 2 meters 87 centimeters! The bone is damaged, and it is believed that its total length was no less than three meters. Thus, its owner could reach 18 meters. Truly imperial sizes.
But pliosaurs were not just huge, they were real monsters. If anyone posed a threat to them, it was themselves. Yes, the huge, whale-like Shonisaurus ichthyosaur and the long-necked Mauisaurus plesiosaur were longer. But the colossal pliosaur predators were ideal “killing machines” and had no equal. Three-meter fins quickly carried the monster towards the target. Powerful jaws with a palisade of huge teeth the size of bananas crushed bones and tore the flesh of victims, regardless of their size. They were truly invincible, and if anyone can be compared with them in power, it was the fossil megalodon shark. Tyrannosaurus rex next to giant pliosaurs looks like a pony in front of a Dutch draft horse. Taking a modern crocodile for comparison, paleontologists calculated the pressure that the huge pliosaur’s jaws developed at the time of the bite: it turned out to be about 15 tons. Scientists got an idea of the power and appetite of the eleven-meter Kronosaurus, who lived 100 million years ago, by “looking” into its belly. There they found the bones of a plesiosaur.
Throughout the Jurassic and much of the Cretaceous period, plesiosaurs and pliosaurs were the dominant ocean predators, although it should not be forgotten that there were always sharks nearby. One way or another, large pliosaurs went extinct about 90 million years ago for unclear reasons. However, as you know, a holy place is never empty. They were replaced in the seas of the late Cretaceous by giants that could compete with the most powerful of the pliosaurs. We are talking about mosasaurs.
Mosasaurus to mosasaurus - lunch
The group of mosasaurs, which replaced and perhaps supplanted the pliosaurs and plesiosaurs, arose from an evolutionary branch close to monitor lizards and snakes. In mosasaurs that completely switched to life in water and became viviparous, their paws were replaced by fins, but the main mover was a long, flattened tail, and in some species it ended in a fin like a shark’s. It can be noted that, judging by the pathological changes found in the fossilized bones, some mosasaurs were able to dive deeply and, like all extreme divers, suffered from the consequences of such dives. Some species of mosasaurs fed on benthic organisms, crushing mollusk shells with short, wide teeth with rounded tops. However, the conical and slightly bent back terrible teeth of most species leave no doubt about the eating habits of their owners. They hunted fish, including sharks, and cephalopods, crushed turtle shells, swallowed seabirds and even flying lizards, and tore apart other marine reptiles and each other. Thus, half-digested plesiosaur bones were found inside a nine-meter-long tylosaur.
The design of the skull of mosasaurs allowed them to swallow even very large prey whole: like snakes, their lower jaw was equipped with additional joints, and some bones of the skull were articulated movably. As a result, the open mouth was truly monstrous in size. Moreover, two additional rows of teeth grew on the roof of the mouth, making it possible to hold prey more firmly. However, we should not forget that mosasaurs were also hunted. The five-meter-long Tylosaurus found by paleontologists had a crushed skull. The only one who could do this was another, larger mosasaurus.
Over 20 million years, mosasaurs rapidly evolved, giving rise to giants comparable in mass and size to monsters from other groups of marine reptiles. Towards the end of the Cretaceous period, during the next great extinction, giant sea lizards disappeared along with dinosaurs and pterosaurs. Possible causes of a new environmental disaster could be the impact of a huge meteorite and (or) increased volcanic activity.
The first to disappear, even before the Cretaceous extinction, were the pliosaurs, and somewhat later the plesiosaurs and mosasaurs. It is believed that this happened due to a disruption in the food chain. The domino principle worked: the extinction of some massive groups of unicellular algae led to the disappearance of those who fed on them - crustaceans, and, as a consequence, fish and cephalopods. Marine reptiles were at the top of this pyramid. The extinction of mosasaurs, for example, could be a consequence of the extinction of ammonites, which formed the basis of their diet. However, there is no final clarity on this issue. For example, two other groups of predators, sharks and teleosts, which also fed on ammonites, survived the Late Cretaceous extinction event with relatively few losses.
Be that as it may, the era of sea monsters is over. And only after 10 million years sea giants will appear again, but not lizards, but mammals - the descendants of the wolf-like Pakicetus, which was the first to master the coastal shallow waters. Modern whales trace their ancestry from him. However, that's another story. Our magazine talked about this in the first issue of 2010.
Some of the largest creatures that have ever inhabited this world lived millions of years ago. Below are ten of the biggest, baddest sea monsters that once roamed the oceans:
10. Shastasaurus
Ichthyosaurs were marine predators that looked like modern dolphins and could reach enormous sizes and lived during the Triassic period about 200 million years ago.
Shastasaurus, the largest species of marine reptile ever found, was an ichthyosaur that could grow to more than 20 meters. It was much longer than most other predators. But one of the largest creatures to ever swim the sea was not exactly a fearsome predator; Shastasaurus fed by suction, and ate mainly fish.
9. Dakosaurus
Dacosaurus was first discovered in Germany, and with its strangely reptilian yet fish-like body, it was one of the main predators in the sea during the Jurassic period.
His fossil remains were found over a very wide area - they were found everywhere, from England to Russia to Argentina. Although it is usually compared to modern crocodiles, Dakosaurus could reach 5 meters in length. Its unique teeth led scientists to believe it was a top predator during its terrible reign.
8. Thalassomedon
Thalassomedon belonged to the Pliosaur group, and its name is translated from Greek as “Lord of the Sea” - and for good reason. Thalassomedons were huge predators, reaching up to 12 meters in length.
It had nearly 2 meter long flippers, allowing it to swim in the depths with deadly efficiency. Its reign as a predator lasted until the late Cretaceous period, until it finally came to an end when new, larger predators such as Mosasaurs appeared in the sea.
7. Nothosaurus
Nothosaurs, reaching a length of only 4 meters, were aggressive predators. They were armed with a mouthful of sharp, externally directed teeth, indicating that their diet consisted of squid and fish. It is believed that Nothosaurus were primarily ambush predators. They used their sleek, reptilian physique to sneak up on their prey and surprise it when attacking.
It is believed that Nothosaurus were relatives of pliosaurs, another type of deep sea predator. Evidence obtained from fossil remains suggests that they lived during the Triassic period about 200 million years ago.
6. Tylosaurus
Tylosaurus belonged to the Mosasaurus species. It was huge in size, reaching more than 15 meters in length.
Tylosaurus was a meat eater with a very varied diet. Traces of fish, sharks, smaller mosasaurs, plesiosaurs, and even some flightless birds have been found in their stomachs. They lived at the end of the Cretaceous period in a sea that spanned what is now North America, where they sat tightly at the top of the marine food chain for several million years.
5. Thalattoarchon Saurophagis
Only recently discovered, Thalattoarchon was the size of a school bus, reaching almost 9 meters in length. This is an early species of ichthyosaur that lived during the Triassic period, 244 million years ago. Because they appeared so soon after the Permian extinction (the largest mass extinction on Earth, when scientists believe 95% of marine life was wiped out), its discovery gives scientists new insights into the rapid recovery of ecosystems.
4. Tanystropheus
Although Tanystropheus was not strictly a marine animal, its diet consisted mainly of fish, and scientists believe that it spent most of its time in the water. Tanystropheus was a reptile that could reach 6 meters in length and is believed to have lived during the Triassic period about 215 million years ago.
3. Liopleurodon
Liopleurodon was a marine reptile that reached more than 6 meters in length. It primarily lived in the seas that covered Europe during the Jurassic period, and was one of the top predators of its time. Its jaws alone are believed to have reached more than 3 meters - this is approximately equal to the distance from floor to ceiling.
With such huge teeth, it is not difficult to understand why Liopleurodon dominated the food chain.
2. Mosasaurus
If Liopleurodon was huge, then Mosasaurus was colossal.
Evidence obtained from fossil remains suggests that Mosasaurus could reach up to 15 meters in length, making it one of the largest marine predators of the Cretaceous period. The Mosasaurus's head was similar to that of a crocodile, and was armed with hundreds of razor-sharp teeth that could kill even the most heavily armored opponents.
1. Megalodon
One of the largest predators in marine history and one of the largest sharks ever recorded, Megalodons were incredibly fearsome creatures.
Megalodons prowled the depths of the oceans during the Cenozoic era, 28 to 1.5 million years ago, and were a much larger version of the great white shark, the most feared and powerful predator in the oceans today. But while the maximum length that modern great white sharks can reach is 6 meters, Megalodons could grow up to 20 meters in length, which means they were larger than a school bus!
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