If you are reading this, then congratulations! You are currently ahead in a brutal billion year old race for survival. You are currently able to read this because the genes of your ancestors, with a few lucky mutations, have gifted unto you the traits that make it possible to survive, perhaps even flourish in your ecosystem. With a little luck, you may survive to pass on this winning genetic formula on to your spawn (if you haven't done so already), where it will hopefully serve them just as well as it has served you. Those are the rules of a little game we call the Survival of the Fittest, and you are winning. Congratulations. You're a credit to your species. However, before we give you the impression that this article is about you, we'd like to remind you that we at Cracked are dedicating this article to the many unfortunate species that died without passing on their genes to new generations, and have thus disappeared from us forever. Wherever you are, we miss you.
Well, some of you anyway.
When we're talking about prehistoric life, there are three main periods that we can talk about, all of which have big names. You have the ancient Paleozoic, where the first creatures worthy of the title begin to evolve in the sea, conquer the land, and diversify into many different groups. Then you have the Mesozoic, dominated by a certain famous family of large reptiles, and finally, the period in which you and I live, the Cenozoic era, dominated by mammals.
The chart of life on Earth
However, we at Cracked have never been good with them fancy big words, so we typically refer to these three ages as the Age of Scary Shit, the Age of Big Scaly Shit, and the Age of Furry Shit. (Do a Google image search for that, we dare you.)
We at Cracked refer to the Paleozoic as the Age of Scary shit for rather obvious reasons. Pretty much everything that evolved during this time went out of its way to be as strange or utterly terrifying as it possibly could be. We start off with the Cambrian era. This was the age when the first complex creatures began to evolve. Mother Nature, immediately betraying her dark, psychotic tendencies, immediately went out of her way to make them all as horrific as possible.
Creatures like Anomalocaris here were considered normal back in the Cambrian.
Most of the creatures around at this time were invertebrates (a creature without a skeleton), and a lot of the invertebrates that were around were arthropods (creatures with jointed limbs, such as insects, crustaceans and arachnids.) All of them were incredibly strange. The dominant predator at the time was called Anomalocaris. While only a metre long, he might not seem impressive. However, compared to his tiny prey, he was truly monstrous, gliding over the Cambrian realm like the alien spaceships from Independence Day. In fact, most of the Cambrian sea must have looked like an alien planet, with most creatures having too many eyes or legs or other unidentifiable squishy parts. However, at the same time, some of the first primitive fish were evolving, with the newest in must-have evolutionary gear, the first primitive backbone. Eventually, bizarre animals like Anomolacaris gave way to these intrepid creatures - men with real backbone. This format became so successful that you are probably one of their great to the power of several billion grandchildren, and so are most of all the other mouse-size-and-bigger creatures on the planet.
Moving on another seventy-odd million years, we get to the Ordovician and Silurian ages. Creatures generally started looking a bit more like things that a normal human being could call an animal, but nature still had plenty of Freaky Juice left in the tank. The invertabrates were still the dominant order of animals around, with the horrors going from bad (one-metre long marine scorpions), to worse (swimming relatives of scorpions called eurypterids, growing up to three metres in length), to utterly horrific (enormous nine-metre shelled squidlike animals, called orthocones.) Some intrepid arthropods even invaded the land at last, stamping their presence on to the early landscape together with the earliest land plants, in a landmark breakthrough for life on Earth.
Above, a Cameroceras, a type of giant Orodovician Orthocone, laughs at the inferiority of a time-travelling diver. Below, Brontoscorpio attacks Pterygotus, a large eurypterid, in an underdog story some 400 million years before the evolution of dogs.
During this time, our own fish ancestors had somehow survived the gauntlet of creepy-crawlies they had to face, and while they had yet to evolve all of the features animals have today, such as a proper jaw, they were still evolving slowly yet surely to compete with the vicious arthropods they shared their seas with. In fact, as the Silurian ended and the Devonian began, fish evolution began to accelerate in different directions. Some fish began to evolve jaws. Others had evolved bony armour to protect themselves from attack. Eventually, the invertebrates were left in the evolutionary dust, as fish went on to dominate the Devonian oceans.
In the seas, the Devonian fishes went on to reign supreme. Mother Nature abhors a vaccuum, and she realised that with the eurypterids and orthocones gone, there wasn't a lot left that could qualify as truly terrifying. So, she went to work on the fish she had at her disposal, and made something truly horrific with them.
Twelve-times winner of the Miss Devonian beauty queen competition, Dunkleosteus was the indisputed ruler of the oceans at this time.
The crowning horrific glory for Nature at this time was Dunkleosteus, who can be best described as "Jaws, only moreso." Nine metres long and weighing in at up to four tons, with armour plating, bony plates that grew downwards into the mouth into tooth-like shears, and the third most powerful bite of all time, up to 8000 pounds per square inch, it can safely be thought of as one of the most horrific animals ever to evolve. In the environment that had given rise to this monster, survival was hard. Even other armoured fish were crunchy snacks to Dunkleosteus, and even the earliest sharks which were starting to evolve had a hard time. Dunkleosteus even turned upon itself from time to time, with juvenile Dunkleosteus fossils found within the ribcages of larger Dunkleosteus. In this kind of environment, it would have been little surprise to discover that some fish were starting to leave the water altogether. The first amphibians had started to evolve from primitive lungfish, creating arms and legs from their fins, and primitive lungs from their gills. They weren't ready to fully leave the water yet, and when they did so they had some vicious predators, like the powerful freshwater fish Hyneria. However, the land offered early amphibians a safe haven from the predators of the water. They only shared the land with the forests that had sprung up, along with the small arthropods that had colonised the land ahead of them.
Early amphibian Hynerpeton flees a predatory Hyneria fish.
However, nature had other ideas in mind for our intrepid ancestors, and as life entered the Carboniferous era, the blanket of plants that had grown unchecked pumped masses of oxygen into the atmosphere. This was a big deal for the landgoing arthropods, who had no proper lungs, and thus could not take up a great deal of the good stuff. However, they could now use the oxygen boost in order to get an evolutionary supercharge. Oh, and did they use it.
Super-arthropod Arthropleura takes on fighting amphibian Anthracosaurus.
Insects, arachnids, and a whole slew of other kinds of creepy-crawlies all evolved to become super-sized in this O2 rich environment. The largest was Arthropleura, a three-metre long millipede, who, while a vegetarian, would nonetheless would have been an imposing sight as it crawled looking for forage in the Carboniferous forests. There were also giant spiders the size of house cats, huge dragonflies with wingspans to rival an eagle's, and more besides. Amphibians had also evolved to become more powerful predators in the newly hostile environment, yet more significantly, some had ditched their soft, porous skin and instead evolved tough, scaly skin, and started laying hard-shelled eggs that wouldn't shrivel up on land. And thus they become the very first reptiles, and the next important stage in evolution. Reptiles would evolve to become the dominant form of life for a very, very long time to come, as the oxygen boom died down, and the arthropods gradually shrank back down to their regular teeny-tiny size again.
The Permian era saw the first large reptiles evolve to dominate the landscape. They weren't related to the dinosaurs who were yet to evolve, nor were they related to any reptile that survives today. Many of them were Synapsids, better known as mammal-like reptiles. The more famous of the early Permian synapsids were characterised by a large sail that the large reptiles sported on their backs.
Two Dimetrodon, the most iconic Permian predator, face off.
One thing that was unique about mammal-like reptiles was their, well, likeness to mammals. Though creatures like Dimetrodon, the top sail-backed predator, didn't look like mammals, they had some mammal-like traits. For instance, Dimetrodon had a set of teeth that varied greatly in size and shape. Some were used for slicing, some piercing, some shearing. This is a trait that only modern-day mammals typically have, and is not shared by reptiles or amphibians. Later Permian synapsids took these traits even further.
Gorgonops was the dominant Late Permian predator, and in some ways more mammal than reptile.
Creatures like Gorgonops, the most powerful land predator to evolve before the dinosaurs, had prominant canines, in contrast to other creatures like crocodiles. It was even believed to have scent glands like a dog, although attempting to pet it wouldn't have been a smart move. Mammal-like reptiles were at their prime, dominating the surface of the planet. Lystrosaurus, a squat, tusked Synapsid herbivore, was probably one of the most numerous creatures to ever exist. However, these traits were not enough to save them from the cataclysms that soon followed the era. During the late Permian and Early Triassic eras, an enormous mass extinction occured, with almost 90% of all ocean-going life disappearing, and 70% of land life going with it. Most of the large mammal-like reptiles disappeared forever, with only their smaller relatives surviving.
Even Lystrosaurus, an early Triassic herbivore and one of the most successful and abundant creatures of all time, did not survive the extinction.
As with the extinction of the dinosaurs that was to follow, there are many theories concerning the Permian Extinction's cause, but no-one really knows why it happened. Some say it was an asteroid impact, others say it was due to rising volcanicity.
However, the vaccuum that was left by the dominant mammal-like reptiles did not stay empty for long. Alongside the mammal-like reptiles, a different type of reptile had been evolving. It was a type of Archosaur, a recently-evolved reptile group that includes crodiles and alligators. This one didn't appear to be an evolutionary winner. It could stand upright with its legs underneath it, while most mammal-like reptiles had legs that stuck out to the sides. It was a small and quick predator, and must have been fairly insignificant next to bulky creatures like Lystrosaurus. However, these small creatures survived the mass extinction, and were quick to fill the gap.
Creatures like Euparkeria might not have looked like much, but they would stamp their mark on prehistory.
While the last of the large mammal-like reptiles plodded slowly towards extinction, these small Archosaurs were thriving, and evolving. The small, swift creatures pushed their evolutionary traits ever further, and became one of the most numerous land-going lifeforms around. These were the first primitive dinosaurs, and would dominate the coming Mesozoic era.
We at Cracked refer to the Mesozoic as the Age of Big Scaly Shit because, well, for obvious reasons again. During this age, pretty much everything important had scales and grew pretty big. Who are we kidding, you really could just get away with calling this the Age of the Dinosaurs. However, the earliest dinosaurs living in the Triassic weren't what you might call impressive by the standards of what was to come. However, this era was still an important stage in dinosaur evolution. At around the time of the Triassic, there was only one, very large continent, called Pangaea. It was dominated by wet and dry seasons. For part of the year, there would be rain and abundant water. In the other part there came mass drought. This was the climate the dinosaurs evolved into.
Coelophysis was a typical early dinosaur, a small predator that got a mouthful of a name by some bearded paleontologist.
Most of the early dinosaurs around would have looked like Coelophysis here. (pronounced Seel-O-Fie-Sis. A lot of dinosaurs didn't get lucky in the names department, and a lot are difficult to pronounce. Check out Cracked's own article on The Ten Lamest Dinosaur Names to see the really unlucky ones.) This basic design of a long, stiff tail for balance, lithe, muscular legs, and s-shaped neck would last throughout the dinosaur's reign in the form of many of the small predatory dinosaurs. It would also serve as the template for some of the much larger predators that would evolve later. For the time being though, predatory dinosaurs weren't the top predators. At this stage, the big kids on the Triassic block were other large reptiles, like Postosuchus, a close relative, but not a dinosaur.
Predatory Pretender Postosuchus Pesters Peaceful Placerias, one of the few surviving large mammal-like reptiles, in a display of alliteratory aggression.
Despite the fact that dinosaurs like Coelophysis had yet to reach the top of the food chain, they were still abundant. Indeed, not all dinosaurs were small predators either. From the same ancestors as Coelophysis, another kind of dinosaur had evolved to fill the "large herbivore" niche that had been left. Called "Prosauropods", they were the ancestors of the huge, famous, long-necked sauropods that would dominate the landscape in the Jurassic era, but must have been impressive in their own right, and the first indicator that the dinosaurs were on their way to the top. The most famous was Plateosaurus, who grew up to nine metres long and weighed over a ton. Even Postosuchus was too small to be a threat to it.
Plateosaurus, a prosauropod. As in, it was the ancestor of sauropods, and not a political advocate of them.
Giants like these all but displaced the last sluggish mammal-like herbivores. However, it wasn't all bad news for the synapsids. Living in burrows across the Pangaean landscape, you might have found a type of mammal-like reptile so mammal-like you might have mistaken it for your typical household dog. It still had scales, as well as the curious sprawling gait of other mammal-like reptiles, and laid eggs, but otherwise it was almost entirely mammalian. Creatures like these cynodonts were the ancestors of all modern day mammals living today. Fortunately, their ancestors would survive and outlive the dinosaurs, and go on to dutifully evolve into you, as well us here at Cracked. If it weren't for them, you wouldn't be sat here reading this right now. Who knew? Maybe evolution isn't such a bitch after all.
A mother cynodont, ancestor to modern-day Cracked contributors, with her young in a burrow. Cynodonts were already the leading species in the esteemed field of dick jokes, even in the Triassic. 
Meanwhile, as the dinosaurs dominated the land, other strange reptiles arose to conquer the skies and seas. An order of reptiles closely related to the dinosaurs, called Pterosaurs, evolved bat-like wings and took to the air. Other types of reptile took to the sea. Some kept lizardlike shapes, but others took on radically different forms. For instance, one type of sea-going reptile, the Icthyosaurs, must have had ancient personality issues, as they didn't look much like other reptiles at all, instead taking on a sleek, fishlike shape. (If you want to look like a smartass in front of your friends, this process, where two unrelated types of creature evolve the same type of adaptations to deal with the same type of problems is called "convergent evolution.")
Icthyosaurs on parade. The largest Icthyosaur ever, Shonisaurus, is flanked by smaller Californosaurus.
By the end of the Triassic, dinosaurs and their reptilian relatives dominated the land, the sea, and the air, and they were ready to move on to bigger things. In the Jurassic, bigger was definitely better as far as life was concerned. The period was named after the Jura mountains in France, but despite being named after something French, it produced some of the most awe-inspiring creatures ever to roam the Earth. One feature of the Triassic was the fact that there was one Supercontinent, Pangaea. This changed in the Jurassic, as the continent broke up to create two continents, with the frankly superb names of Laurasia and Gondwanaland. This resulted in a big rise in sea levels, opening up new avenues for enormous sea creatures to evolve. On the land, the dinosaurs would also evolve to become huge. As early as the final stages of the Triassic, some of the first giant herbivores were evolving, and predators were stepping up their game to compete. Whereas the earliest dinosaur predators like Coelophysis weren't serious hunters, some of the new ones were, as was made apparent by the new early Jurassic species, such as Dilophosaurus, one of the most misrepresented creatures of all time.
Dilophosaurus was an early Jurassic hunter that is one of the only creatures to be more badass in real life than in film. Above, the Jurassic Park version. Below, how it would appear in real life.
While the real Dilophosaurus didn't spit poison and eat fat people as portrayed in the 1993 classic Jurassic Park, the true creature was a lot more frightening. It was six metres in length, as opposed to Spielberg's midget, and weighed half a ton. It had powerful jaws and sharp claws, and would have been capable of killing and eating creatures substantially larger than the lizards and insects Coelophysis would have hunted. Predatory dinosaurs would only get bigger and more dangerous from hereon in. Which was good for the predators, because their prey would reach colossal sizes.
Jurassic sauropods dominated the landscape, and grew to enormous lengths and heights. The name of Seismosaurus here translates to "Earthquake lizard."
The sauropods, the famous long-necked, four-legged giants, were in every sense of the phrase a Force of Nature. There was nothing to rival their sheer size on land back then, and it remains that way today. There were some key advantages to being a huge sauropod - firstly, having a bigger body means having a bigger gut, meaning that the enormous sauropods had a huge cauldron of an intestinal system that let them get the most out of their leafy vegetarian diet. Plants contain cellulose, a tough fibrous substance that is hard to break down without the correct enzymes, which very few animals have even today. The huge stomachs of a giant sauropod would have helped immensely, and some would have even swallowed stones to help grind up the vegetation. Another big advantage was the fact with their long necks, they would have been capable of browsing on choice meals that other unfortunate herbivores couldn't have gotten near to. While most sauropods were long, some, such as Brachiosaurus or Sauroposeidon, grew incredibly tall, and would have been able to reach leaves that even smaller sauropods couldn't. Another huge advantage was that when full-grown and healthy, a big sauropod would have been all but immune to attacks by predators. Which was good news, because the age of the huge two-legged meat eaters was dawning.
Allosaurus examines its latest kill. Dubbed "the lions of the Jurassic", Allosaurs were the top predators.
Growing up to twelve metres long, the major hunters of the Jurassic were the Allosaurs. Armed with a mouthful of razor-sharp jaws, hook-like talons, and weighing over two tons, it was the largest land predator yet to evolve. It would have been the only creature capable of taking down a large sauropod, and then only working in groups to target a sick or young individual.
Taking on a herd of sauropods was a risky proposition. Famous Allosaurus Big Al and his friends show you how it's done right.
Of course, Allosaurus wouldn't have exclusively attacked sauropods. There were plenty of new, different types of dinosaurs evolving, all with their own methods of survival. Some such as small, two-legged Dryosaurus would have ran in flocks like modern-day gazelles, whereas some grew defensive weapons like large spines and plates, like the famous Stegosaurus.
Fun fact: Stegosaurus' name means "roof lizard." The plates on its back were probably a kind of solar heating system.
It wasn't just the dinosaurs that were evolving either. You might have had to look hard in the treetops or burrows, but you might have found some of the earliest true mammals. They were small and mouselike, still at the begininng of their evolutionary journey, and would have probably spent most of their time trying not to take a much shorter journey down the throat of a carnivorous dinosaur. But they were there, surviving. And they weren't the only new kids on the block either. Some of the tiniest dinosaurs must have decided that they were sick of being stuck to the ground, and so they too to the trees and evolved feathers, and became some of the very first birds.
Archaeopteryx: The earliest known bird. Solid ground is sooooo last week.
In some ways, the first birds, such as Archaeopteryx (Ark-Ay-Op-Ter-Ix) were still more dinosaur than bird. Instead of a beak, they had a lizardlike mouth with teeth. They still had hands with claws on their wings. And most of all, it still had a nigh-unpronouncable name. It still wasn't ready to rule the skies - the Pterosaurs still had a monopoly on that market, and it probably couldn't fly properly by flapping its wings, instead gliding under the jungle canopy looking for food. But still, it was the Orville and Wright of the avian world, which makes it an evolutionary breakthrough.
The going down of shit wasn't restricted to the land, however. Everything that made the Jurassic the most bad-assed era yet applied to the oceans too. The Jurassic was the time of some of the greatest ocean life ever to exist, from giant predatory Loch-Ness-esque reptiles, to the most enormous fish ever to evolve. Leedsichthys, for instance, was the largest fish of all time, the size of good-sized whale, but it found its match in large predatory marine reptiles like Liopleurodon.
Leedsicthys, the largest fish of all time, is shadowed by ravenous reptile Liopleurodon. While Liopleurodon didn't have magical powers, it was a powerful predator all the same.
Marine reptiles ruled over the oceans with an iron flipper, although marine turtles are all that remain of their legacy today. Pliosaurs like Liopleurodon were the dominant predators, with icthyosaurs and long-necked plesiosaurs hunting smaller prey alongside them. There were even types of crocodile that lived their whole lives at sea.
Two Plesiosaurus hunt fish, while an Opthalmosaurus icthyosaur swims overhead. Metriorhynchus, a marine crocodile, chills out on the sea bed.
By the end of the Jurassic, everything was just going so well for the reptiles. They were the top dogs everywhere, and that was millions of years before there even were any dogs. Still, while their time wasn't up yet, the times were a-changin, and so were the reptiles themselves. During the Cretaceous period, a myriad of new and different forms arose to adapt to changing conditions. The temperature was cooling down, and the continents had further split up. Cretaceous Earth wouldn't have been so very different from modern day Earth, aside from all the gigantic killer lizards roaming all over the place.
On land, one of the biggest missing faces was that of the sauropods. They were in decline after their glory days of the Jurassic, and while they were still around, they didn't dominate the landscape as much as they used to in most places. Instead, new types of large herbivores arose to fill the gap.
Iguanadon, one of the most numerous dinosaurs ever.
Creatures like Iguanodon would set the standard for the upcoming dinosaur species. Aside from being the star of a Disney movie, it also has the distinction of being the first dinosaur to be discovered, when its teeth were found in rocks out of a uarry in Sussex, England by scientist Gideon Mantell in 1822. (Fun fact: the term "Dinosaur wouldn't be coined for another twenty years, when Sir Richard Owen gave them the famous name.) He thought that the teeth looked like they belonged on a giant Iguana, hence the dinosaur being given the name "Iguanadon," meaning Iguana tooth. Unfortunately, the scientist of the time thought that Iguanadon even looked like an Iguana, with unfortunate results.
Models of what Iguanadon was thought to look like. Imagine making a Disney movie with one of these as the hero.
It was the same teeth that Mantell found that gave Iguanadon a big advantage in the early Cretaceous. Whereas sauropods simply swallowed their food whole, Iguanadon would have chewed its food properly, letting them better extract all of the nutritious goodness from its meals. It also happened to be pretty large at nine metres long, and would have travelled in enormous herds for safety, plus, deciding that evolutionary leaps like opposable thumbs were for sissies, it also had a vicious spike instead of a thumb, making it a kind of proto-Ash-from-Evil-Dead. Which was a good thing, really. there were some vicious new predators around. However, some of the new predators were something new and somewhat terrifying. Meet Utahraptor.
You don't need to be a paleontologist to know that raptors (Dromaeosaurs in smartassspeak) were fucking terrifying. Their speed, agility, and frightening array of claws and teeth made them incredible hunters, even usurping larger predators like Allosaurus for a while. However, Utahraptor, one of the earliest raptors to evolve, was especially scary for one specific reason when compared with its contemparies. Remember the raptors in Jurassic park? In the film they made them too big. The real-life Velociraptor was only the size of a large dog or a wolf, although another raptor called Deinonychus would have been a pretty good fit for the film version at around 3.4 metres long.
Utahraptor was around twice as big as that.
Utahraptor is a pretty solid contender for the most lethal land predator of all time. It would have been every bit as fast and agile as its smaller cousins, and would have probably hunted in packs in a similar fashion. This, combined with its size and strength, would have allowed it to attack even big herds of Iguanadon.
A raptor hunt probably looked a fair bit like this.
With predators like these, it was little surprise that different types of dinosaurs evolved new, extreme means of defending themselves. For instance, Iguanadon probably employed a "strength in numbers" strategy. travelling in colossal herds with over a thousand members. The Ceratopian order of dinosaurs, the order including horned dinosaurs like Triceratops, began to evolve, with small, sheep-sized Protoceratops facing off against Velociraptor in what is now the Gobi desert in Mongolia. Protoceratops was hardcore. While it didn't have any horns, and was quite small compared to Triceratops, it did have the same bony frill and bad attitude its larger cousin would inherit. Paleontologists unearthed a Protoceratops entangled with a Velociraptor in death, both animals perfectly fossilised. The raptor had stuck its claw in the Protoceratops' jugular, but the stricken animal still managed to crush the raptor's arm in its beak and smash its skull with its forelimb before it finally realised it was dead.
On the left, the famous fossil. On the right, what the fight might have looked like. Also, Batman was there.
Other creatures went even further. For instance, another new type of dinosaur, known as Ankylosaurs, evolved armour that covered their entire bodies. Some even had armour on their eyelids.
An early ankylosaur, Polacanthus, fends off a predator.
Early Ankylosaurs, like early Ceratopians, still weren't fully evolved, and didn't have all of the features that their ancestors would have, but were still pretty hardcore in their own right. A lot, like Polacanthus or Gastonia, in addition to the armour plating embedded into the skin, had rows of blade-like spikes sticking out of the sides of their bodies and tails. When they swung their tails, the blades would cross over the top of each other, like a giant set of scissors. It was like a prehistoric chainsaw.
The result of a google image search for "prehistoric chainsaw"
However, different dinosaurs in different places had different ways of dealing with their predator issues. Whereas in Northern territories strength in numbers and big sharp pointy bits were in fashion, in Southern territories old habits were dying hard. In Southern America, the sauropods were still in charge, and that meant that the order of the day was being really big. Like, really big.
Argentinasaurus was big.