The Mesozoic World

The Mesozoic world

By Joseph Porta

Before the Mesozoic

The Mesozoic world was unlike anything seen before or after, neither in the Palaeozoic, nor in the Cenozoic would life grow to the size it held in the Mesozoic era. The Mesozoic ended like it began, with a huge cataclysmic extinction event that wiped out a vast amount of the then dominant group, it seems almost poetic that the very thing that set the stage for the age of the Dinosaurs, would also end their dominance, and kill off all the non-avian members of the group. Unlike the Palaeozoic where life grew to enormous lengths in the oceans of the earth, and the dominant group on land shifted between amphibians and then reptiles, the Mesozoic was thoroughly dominated by one extraordinary group of diapsid reptiles, the Dinosaurs. While the Dinosaurs "only" ruled on land, some of them grew to epic proportions, eventually becoming the largest animals ever to live on the planet, easily overshadowing even the largest of the Ordovician Orthocones, or the biggest Oliogene fish. To Tell the story of the Dinosaurs, and indeed all other life of the Mesozoic, one would first have to dissect the Palaeozoic age, since its early lifeforms would start the evolutionary race between prey and predator, that would eventually give rise to the great reptiles of the Mesozoic.
In the Precambrian Supereon, which covered the Hadean, Archean, and Proterozoic eons, a good 4 billion years, life on earth was at its best very primitive. Then, around 541 million years ago, a brief yet important event known as the Cambrian explosion would set the stage for all life to follow. When the Cambrian began, with an evolutionary bang, life would go from rather primitive lifeforms, and evolve into a sea of different lifeforms, the ever present and very successful Trilobites appeared during the Cambrian, the very first vertebrates would evolve, the first known fish Haikouichtys of the Agnatha Superclass, would set the stage for, first and foremost the evolution of fish, and later down the line the reptiles, and the mammals. Just as the Cambrian began with a literal explosion of marine life, it would end with an extinction, although not as serious as the one that would occur a good 40 million years later. After the mass extinction in the Cambrian, the Relatively short Ordovician would follow, lasting a mere 41.2 million years, in this short time however, Orthocones like Cameroceras, which were by far the largest living animal the world had seen up to that point, and arthropods would flourish. While the Arthropods themselves were very successful in the Cambrian, they would fill in the niches of other animals, giant scorpions like Brontoscorpio, Megalograptus and Pterygotus would be the apex predators of the Ordovician, and later the Silurian. The transition from the Ordovician to the Silurian would be marked by yet another extinction event, this would be the second largest mass extinction second only to "the great dying" that would end the Permian. The extinction between the Ordovician and the Silurian is thought to have been brought on by mass cooling of the world, and a global drop in the sea level, this would severely devastate the fish population, as they can't regulate their own body temperature, they would need to search for warmer waters, where their main food would be scarce. When the Silurian began, around 443,8 million years ago, the surface world would still be a barren wasteland, with carbon dioxide levels too high for any animals to survive. Then around 433 million years ago, the very first vascular plant Cooksonia would evolve, even though the surface of earth was a barren wasteland, this primitive plant could live outside the water, and start the production of Oxygen through photosynthesis, turning the Carbon dioxide into breathable air, though not that fast. The first animals to venture unto land in the Silurian, and in the Ordovician were the arthropods. Euryptids like Brontoscorpio and Megalograptus would take to the land to lay eggs, and then buy their time and wait for the young ones to hatch, since all arthropods breathes by absorbing the oxygen into their blood, the animals could breathe in the mostly oxygen deprived wasteland. During the Silurian the Sharks would evolve, this new order, the Elasmobrachii would go on to become one of the most successful animal groups. The Silurian lived to see three mass extinctions, none of them as serious as the one before, or the ones that would follow. When the Silurian ended, the Devonian began, the Devonian is perhaps best known for the Placoderms, the armour plated bony fish that would dominate the seas such as Donkleosteus, but during this time the sharks would diversify, giving birth to the rather strange Stethacanthus with its "Iron board" fin and Xenacanthus with its Eel like body, that looks nothing like modern day sharks. During the Devonian, the Arthropods would go from hunting the fish, to be hunted by their descendants, the tetrapods. The tetrapods is a superclass encompassing all land going vertebrates, some of the fish would before and during the Devonian evolve into Amphibians. Now the amphibians would dominate the world until the Reptiles would emerge in the Carboniferous, and grow to take the place of the Amphibians following the Carboniferous rainforest collapse around 305 million years ago. The Devonian ended with one of the most destructive extinction events, killing off 19% of all families, and around 50% of all genera. When the dust cleared, The Carboniferous began, classified by large and extensive coal forests, these in turn made the Oxygen level on land increase exponentially, to around 150% of what it is today. This in turn made the Insects grow into enormous sizes, with dragonflies like Meganeura with a wingspan of around 60 cm. Or Arthropleura, the two to three-meter-long centipede. This means that the Scorpions would once again grow to relatively huge proportions like the 70-cm long Pulmonoscorpius. The Carboniferous ended with a huge ecological collapse, causing the once abundant rainforests to be reduced to nothing but a few isolated "islands"
When rainforests disappeared, the once green and tropical Pangea was terraformed into an almost barren wasteland that would dominate the continent until the Jurassic. When the Permian began, the world was, like in the Carboniferous, consisting of one single great landmass called Pangea. With the former lush and fertile supercontinent would turn into a largely desert filled wasteland. This however would be the time for the reptiles to dominate on land. Synapsid reptiles like Edaphosaurus and Dimetrodon would dominate land, these reptiles are perhaps most famous for having a sail on their back, with many people mistaking them for Dinosaurs, who evolved from a different group of reptiles. The Synapsid reptiles like Dimetrodon would evolve into the dicynodonts of the late Permian and early Triassic. During the late Permian, the Synapsids had evolved into large predators like the Gorgonipsids, and large herbivores like Lystrosaurus. In the end of the Permian, a good 250 million years ago, the Permian ended with a great dying, the single largest extinction event in the entire history of the earth. It is still widely debated how the extinction came about, some suggest that it may have been caused by the impact of a gargantuan Meteor, or perhaps due to the Siberian traps, the Permian death would end up killing a good 96% of all marine life, and 70% of all land vertebrates, a good 53% of all insect families and 83% of all insect genera would die out, this is the only known mass extinction of insects. When the now relatively empty world would start to lick its wounds, life was almost non-existing. The reptiles would help repopulate the oceans, and the Archosaurs would find gargantuan success on land. When the Triassic began, the world was still healing, the dicynodonts were few in number, and were reduced to the rather large species Placerias, but the most important result of the Triassic, was a rather small bipedal archosaur, called Eoraptor. Eoraptor was revolutionary in many ways, its descendants would go on to dominate land for the next 165 million years, the Dinosaurs. The Dinosaurs were not the only successful Archosaurs however, the Pterosaurs already began conquering the skies and hunting its former masters, the insects, and the Rauisuchian Postosuchus. In the oceans, the Nothosaurs and the Ichthyosaurs ruled the open oceans and the shallow seas, with the Placoderms living near to the coast to hunt shellfish. The stage was set for the Dinosaurs to evolve into the giant Sauropodomorphs, the Swift Dromaeosaurids, the ferocious Carnosaurids and the powerful Tyrannosaurids.

The Triassic

The Triassic started with a mass extinction, the great dying emptied the world and set the stage for the age of the Dinosaurs. 230 million years ago the first Dinosaur Eoraptor appeared, and soon after, a mere 10 million years later the Dinosaurs had evolved into a myriad of different species groups and genera. Around 220 million years ago the Coelurosaurs, most notably Coelophysis, were very successful, and the Prosauropods had already grown to gigantic size. In the air, the Reptiles began to dominate, the Pterosaurs, like Peteinosaurus was taking over the ecological niche that the insects used to fill, and began preying on the insects, who themselves used to be the top predators of the skies. In the Oceans, the Nothosaurs were very successful, and the Ichthyosaurs were from very small sizes like Mixosaurus, to the gargantuan size of Shastasaurus, and the Placoderms lived in the shallow coast areas, feeding on shellfish. When the Oceans died off, the reptiles began colonizing them, filling in the ecological niche that that some of the larger fish used to fill, some of them growing to a staggering 22 meters, and adapting to the life in the sea, with the Nothosaurs being named the "seals of the Triassic", adapting to a mostly aquatic lifestyle, only venturing onto land when not hunting, and the Ichthyosaurs adopting a complete aquatic lifestyle, losing their limbs, and having them replaced by fin like flippers, and even some of them developing a dorsal fin, and later a dolphin like body. The Archosaurian success story is not only limited to the Dinosaurs and the Pterosaurs, the Rauisuchians like Postosuchus grew to relatively large sizes, and would be the biggest predators in their vicinity, only having to fear another larger Postosuchus. As the Triassic began with a great dying, it similarly ended with a mass extinction. In the last 10 million years of the Triassic, the last of the Rauisuchians and the dicynodonts all died out, leaving the world to the Archosaurs, and the Thrixadonts, and later the Mammalian descendants of the Thrixadonts. When the end of the Triassic approached, the Plesiosaurs appeared, and the Placoderms disappeared, together with the Nothosaurs, who evolved into the plesiosaurs. The ichthyosaurs had gotten their largely dolphin like appearance, and the first real Sauropods would have evolved from the Prosauropods. The supercontinent Pangea would begin to crack, and the new waterways that would come to be would change the coastlines of Pangea, killing of the Placoderms when the open sea became bigger and the shallow coast areas would become fewer in number, this in turn changed the monsoonal parts of the continent, and the great deserts of the continent would steadily shrink, and be replaced by fertile lush forests and jungles. During the Triassic only two oceans existed, the Early Tethys sea, the sea that would split Pangea, and further expand the distance between the two future continents. The other ocean was the Panthalassa sea, a good three times as large as the Pacific Ocean

The Jurassic

The Jurassic began in the dust of the Triassic, a good 201,3 million years ago, and was marked by two extinction events, one 183 million years ago, and one at the end of the Jurassic 145 million years ago, a mere 56,3 million years after it began. The Jurassic was marked by the breakup of Pangea, and in the end the start of the breakup of Laurasia and Gondwanaland, the two following Supercontinents. The animal and plant life in the Jurassic varied between the early and the late Jurassic. In the early Jurassic, the Prosauropods were still abundant, and the Sauropods had not yet achieved the immense size they are known for, and the Therapods like Coelophysis and Herrerasaurus had disappeared, and in their place more advanced carnivores such as Dilophosaurus had emerged. The Dinosaurs was not the only group to change however, the Nothosaurs had disappeared completely, they had evolved into the Plesiosaurs, such as the at this point extinct Plesiosaurus, the Ichthyosaurs had adapted to a completely specialized aquatic lifestyle, looking more like a fish, or a Cetean than a reptile like it did in the Triassic. A new player in the Jurassic seas were the Pliosaurs, the short-necked Plesiosaurs that would sire the well-known Liopleurodon and Kronosaurus later in the Jurassic and the Cretaceous respectively. The Pterosaurs would also evolve, the Ramphorynchoid group still the only of the Pterosaurs, characterised by their long tail, short wingspan, and a mixture between a piscivorous and insectivorous lifestyle, the Ramphorynchoids would later die out, and leave the world to the Pteodactyloidea, characterised by their short tail, huge wingspan, and their predominantly piscivorous lifestyle. The thrixadonts disappeared, and were replaced by mammals. When the late Jurassic began, Pangea had almost split completely up, but the Sauropods of the northern hemisphere could still wander all the way down to Antarctica in search for food. The therapods had by this time spawned giant predatory dinosaurs, in particular the Carnosaurs like Allosaurus and its relatives such as Sauropghnahax who were specialised Sauropod hunters. Smaller almost bird like therapods had also evolved, the only two-meter-long Ornitholestes specialised in eating insects, but would not miss the opportunity to kill and eat a newly hatched Sauropod. Perhaps most important in the Jurassic, was the appearance of the first birds, the oldest known bird Archaeopteryx evolved around 152 million years ago. As life on the ground changed, so did life in the earth's oceans. The giant marine reptiles had further evolved, and adapted, and the crocodiles had even begun to live in the water, species such as Metrorynchus had completely lost its legs, and had them replaced by flippers, furthermore, its scales were soft, and not built for fighting, but rather for speed and agility. The reptiles had to share the oceans with its ancient tenant, the fish. In the Jurassic, the sharks would be hunted by the marine reptiles, and in turn some of the smaller marine reptiles would be hunted by the sharks, one of the more successful sharks of the Jurassic was the shark Hybodus, which had hunted in the oceans ever since the Permian, surviving a staggering 3 extinction events, including the great dying. The giant Sauropods had at this time become the biggest living creatures on the earth so far, with giants like the 13-meter-tall Brachiosaurus, or the 35-meter-long Diplodocus, and the ever so famous Apatosaurus. The Saurischians were not the only dinosaurs however, the Ornithischian Dinosaurs were also rather successful, the Stegosaurs like Stegosaurus and Kentrosaurus were very successful, and their relatives the Ankylosaurs would also begin to appear during this time, and would completely take over the niche of the Stegosaurs in the Cretaceous. The Sauropods were formally thought to have died out on the northern Hemisphere when sea level rose during the late Jurassic - early Cretaceous.

The Cretaceous

The Cretaceous began 145 million years ago after yet another mass extinction at the end of the Jurassic. By the time of the Early Cretaceous the fractured Islands of Europe were starting to come together, and North America were being pushed away from the rest of Laurasia, by the young Atlantic ocean, which at the same time was tearing through South America and Africa, dividing the once giant Gondwanaland, this did not happen overnight though, it took many million years before the continents would go on to assume the shapes that are reminiscent of today, and India itself would not join Asia before the very late Cretaceous. In the early Cretaceous the Dromaeosaurs evolved, with their bird like features the Dromaeosaurs would look like a big bird of prey. The single most successful group of Dinosaurs would come to prosperity in the early Cretaceous; The Iguanodonts, who at the height of their success could be found on every continent, including Antarctica. With the Iguanodonts at every continent, there would naturally be predators to hunt them. In America and Africa relatives of Allosaurus, the Charcarodontosaurids would hunt Iguanodonts, in South America Giganotosaurus and Tyrannotitan would hunt Iguanodonts and Sauropods, in North America Acrocanthosaurus would hunt Iguanodonts and other Ornithopods while in Africa Charcarodontosaurus would hunt Iguanodonts like Ouranosaurus. The Carnosaurs, were however not the only ones to hunt Iguanodonts. In North America and Asia, the Dromaeosaurs like Utahraptor, Deinonychus and Velociraptor would hunt Iguanodonts, and the Tyrannosaurids would likewise hunt Iguanodonts, especially the Hadrosaurs, like Parasaurolophus, Edmontosaurus, and Saurolophus. Another Success story from the Cretaceous are the Ceratopsians like Torosaurus and Triceratops, while starting as small critters in the Jurassic, by the cretaceous they would have diversified, there would be the small Protoceratops in Mongolia, and the large and well known Triceratops in North America. In Asia, the Protoceratops would have become prey to the Velociraptors and the Tyrannosaurids like Tarbosaurus Bataar, referred to by some scientists as Tyrannosaurus Bataar, due to the striking similarity to its North American relative Tyrannosaurus Rex. In North America, the Tyrannosaurs would reign supreme, being the largest terrestrial predators on the continent, only being countered by giant Crocodiles such as Deinosuchus. Giant members of the group like Tyrannosaurus would have few enemies by the times they would have reached adulthood, probably only another large Tyrannosaur or an adult Ankylosaur. The Ankylosaurs, a very successful member of the Thyreophora family, had by this time overtaken the niche of the Stegosaurs, and had diversified as well, all the way from the miniscule Minmi, to the pointy Polacanthus, to the Armoured Ankylosaurus with its Bony tail club. While life had prospered on land, the Oceans would feel empty in the mid cretaceous compared to that of the Jurassic, while Pliosaurs like Kronosaurus and Plesiopleurodon were highly successful, they would together with the Ichthyosaurs and many of the Plesiosaurs die out in the mid Cretaceous due to a fall of oxygen level in the oceans, killing off massive amounts of fish, and thus also depriving many predators of food. One success story from the Cretaceous oceans however, comes in the form of the Mosasaurs. The earliest known member of Mosasauria, Dallassaurus was alive during the emptying of the Oceans, being only about 85 centimetres long, it would have survived far better than the larger sea reptiles, since it would need less food, so by the time the Oceans had recovered from the extinction, the stage would have been set for the Mosasaurs to conquer the deep. By the Maastrichtian of the Cretaceous the Mosasaurs would have diversified into a myriad of different Species and Genera, and they would occupy many different niches. Mosasaurs like Tylosaurus and Mosasaurus would have been the Apex predators of their respective locations, while Mosasaurs like Prognathodon and Globidens would be highly specialized, focusing on armoured prey, and then small Mosasaurs like Hailisaurus would have hunted smaller fish and sea going birds. Now the Cretaceous seas would not belong to the reptiles entirely, giant turtles like Archelon would surf gently through the deep, filtering food, while being preyed upon by Mosasaurs. The fish of the Cretaceous, both bony fish and sharks would be food for the Mosasaurs, and even hunt the Smaller Mosasaurs, fish like Xiaphactinus, would swallow their prey, such as birds, small Pterosaurs, and even other smaller Xiaphactinus. The sharks of the Cretaceous would in many ways resemble those in the Oceans today, sharks like Cretoxyrhina, thought to be an ancestor of the Charcarodon family, bears a striking resemblance to the Great White Shark, would hunt fish and reptiles alike. While Cretoxyrhina would most likely act like a great white shark, another Cretaceous shark would specialize in entirely different field. Ptychodus would crush shells, possibly Ammonites. Another shark in the ocean, is the ever present Hybodus, the highly successful shark mentioned in the Jurassic part, this however, would be the final age where Hybodus would be found in the Ocean, surviving the Permian, Triassic, and the 3 Jurassic extinctions it would disappear after the KT extinction event that killed off the Dinosaurs 65 million years ago. A highly unusual shark, Scaparnorynchus, would essentially be a prehistoric goblin shark, is thought to have lived from the Aptian of the Cretaceous to the Paleogene, but there is no evidence for this. As mentioned before, many of the Plesiosaurs died out in the Mid Cretaceous extinction, the Elasmosaurids would go on and be relatively successful, with members like Elasmosaurus, characterized by its abnormally long neck, originally thought to be its tail, these would hunt by propelling into a school of fish, and catch as many as possible between their sharp teeth. Having dominated the Earth for 165 million years, and adapting to all climates, and living though 4 mass extinctions, the Dinosaurs would by the end of the Cretaceous stand before a chain of destructive events that would eventually bring around their downfall. In North America, extensive volcanism would have devastated forests and changing the fertile and lush plains into lava steppes, this would devastate the Hadrosaur population, who was more in tune with the lush swamps, the decline of the Hadrosaurs would impact the Tyrannosaurs, who relied upon the Hadrosaurs for food. In the east, India had collided with Asia, creating the Deccan traps, extensive volcanism would follow, further impacting the environment, this combined with the volcanism in North America would throw extensive amounts of dust particles into the air. Now had this been the "only" case of environmental disasters, the Dinosaurs might simply have adapted further, but one disaster seldom travels alone. A huge distance from the Dinosaurs, their demise was approaching earth, smashing through the atmosphere a Huge Meteorite at with a diameter of 10000 meters would bring about the final demise of the Dinosaurs. Off the Coast of the Yucatan peninsula the Meteorite would impact with the power of 10 billion nuclear bombings of Hiroshima, everything within a range of 1000 kilometres would die instantly, huge tsunamis would smash the coasts, shockwaves would tear through flesh and bone, and a thick layer of dust would cloud out the sun, killing off huge amounts of plants, this would kill off a huge amount of Herbivores, removing the Carnivores only food source, in the end 65% of all life on earth would be lost, and it would take the earth millions of years to recover, and when it had, the great Dinosaurs were gone, never to return.

















References:
http://www.prehistoric-wildlife.com/index.html
Walking with Dinosaurs by the BBC
Walking with Dinosaurs Companion book by Tim Haines
Walking with Monsters by the BBC