Chapter 3: The Ordovician Radiation
Hello everyone before we start on this chapter, I want to address an inaccuracy that slipped by me in the last chapter. I depicted Anomalocaris exoskeleton as tough and armored when in reality it was actually quite soft and squishy. This notably makes the fight between the Anomalocaris pair quite inaccurate and I do apologize for this and I will attempt to avoid any other major inaccuracies slipping through the cracks in the future (Outside of science marches on coming into effect of course, I can't really help that) with all that said, let us dive right into the next chapter in this series.
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Earth 450 million years ago, it is now the Late Ordovician period. At this point in time the global sea levels have continued to rise and this has left much of the Earth's landmasses partially submerged, forming great shallow seas. This, combined with a warm climate, has allowed life to continue thriving. The creatures that call Earth home, however, are quite different from what lived during the Cambrian. Notably most of the Cambrian fauna have not survived the transition into the Ordovician, however, the survivors were if nothing else quick to take advantage of the empty niches.
Notably an event known as the Ordovician Radiation, occurred at the beginning of the period and it has seen the rise of many new families of animals, who have quickly diversified into many forms in response. These creatures have now become the dominant families of the Ordovician and many still have relatives alive today. Notably in the seas of what is the northern continent of Laurentia, which is situated around the equator, life thrives.
For the first time in Earth's history great coral reefs have formed, while corals have been around since the Cambrian it is only now they have begun to diversify and form reefs. These reefs are the richest places for life on Earth, with all kinds of strange creatures calling them home. Sponges and Brachiopods are among these creatures. Trilobites have also survived the End Cambrian Extinction and have become more diverse than ever. Take Isotelus rex, at 2 feet in length, it is one of the largest of the Trilobites.
Also in the reefs are small chordates, like Astraspis. Astraspis is notably descended from creatures like Haikouichthys and Pikaia, however, at around 7.9 inches in length it is quite a bit bigger than its earlier relatives. Notably Astraspis is covered in thick armor for protection against predators and this is very much a necessity, as there are plenty of powerful predators that call this reef home. Astraspis notably are still at the bottom of the food chain and due to still lacking jaws they are forced to suck up small organisms. The Astraspis, however, are unaware that they are being watched.
Suddenly one of the Astraspis is grabbed by a predator, as the rest of the group flees heading to the rocks to hide. The attacker is a monstrous looking creature known as Megalograptus ohioensis. The predator quickly swims off looking for a secluded place to hide and eat its meal in peace. With the threat gone, the Astraspis quickly calm down and head back to their normal activities.
Elsewhere, the Megalograptus begins to feed. The long arms of the Megalograptus are covered in sharp spines that it uses to impale its prey. From there the Megalograptus uses its smaller appendages to cut up the food and pull pieces into its mouth for consumption. Megalograptus is notably part of the Eurypterid order. Eurypterids are notably an order of Arthropods, that arose during the middle of the Ordovician and they have been successful ever since.
Eurypterids are notably also known by some as sea scorpions, however, despite their nickname they are only distantly related to modern scorpions, which have yet to even evolve at this time. Megalograptus is notably one of the most successful of the Eurypterids, with the largest species often getting to lengths of up to 2.7 feet, a truly impressive size. After finishing its meal the Megalograptus begins to rest allowing the food in its stomach to digest.
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The reefs are not the only places that harbor life, notably the open ocean has plenty of impressive creatures in its own right. These seas are notably teeming with unimaginable numbers of small creatures known as plankton. These plankton are the backbone of marine ecosystems, with many creatures feeding on them. There are other larger creatures out here too. Cephalopods are notably one of the most successful groups.
Cephalopods are a notable Class of Mollusk that evolved at the end of the Cambrian. They notably rose to prominence during the Ordovican and they have been successful ever since. Notably, many orders have since appeared to take up many different ecological niches. Tarphycerids, like these Trocholites are notable for their coiled shells, they hang out on the sea bottom, looking for whatever food they can find. Some Cephalopods, meanwhile, have straight shells and they have also become absolutely enormous.
Emerging out of the depths and spooking the Trocholites group is a massive Endoceras giganteum. At up to 20 feet in length, Endoceras is one of the biggest creatures to have evolved so far in Earth's history, a truly marvelous sight. Endoceras is notably part of its namesake order, the Endocerids notable for their straight shells. Endoceras is notable for being the apex predator of the Ordovician, once they reach full size nothing can threaten them. Endoceras itself is notably a poor horizontal swimmer, causing it to swim vertically.
They will even use their arms to walk along the sea bottom as they search for prey. In this case this Endoceras has spotted an Isotelus. The Islotelus attempts to scurry away, however, the Endoceras begins to crawl after it. The Isotelus is suddenly grabbed by one of the Endoceras 10 arms. The Endoceras then pulls the Isotelus towards its main weapon, a massive parrot-like beak.
A sickening crunch rings through the water, the beak of the Endoceras is notably perfectly designed to crack even the hardest shells, a perfect tool for hunting Arthropods. The Endoceras quickly finishes its meal. Afterwards the Endoceras ascends back into the water. The water notably carries the weight of the Endoceras effortlessly. Endoceras and other cephalopods have a rather unorthodox mode of locomotion in the water.
Rather than paddles, or fins like most aquatic creatures Cephalopods utilize jet propulsion to swim. Jet propulsion notably involves sucking in water through an appendage, the water is then pushed out helping the Endoceras move in a backwards motion. The Endoceras begins to swim off content to calmly survey its territory. The Isotelus will keep the massive cephalopod fed for the time being at least.
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Elsewhere, we find a different drama unfolding with the Trocholites. It is breeding season for the Trocholites and as a result many are gathered to reproduce. Males notably outnumber females and as a result there is quite a lot of competition for mates. These competitions are not a violent affair, however, instead the males rely on their shells. The males with the brightest shells are more attractive to the females.
These males are more likely to attract suitable mates than males with dull colored shells. After finding suitable mates the female Trocholites will begin to pair up and mate with the males fertilizing the eggs inside of the females. Afterwards they break off and leave each other. The females will notably head to the reefs afterwards to lay their eggs. The reefs notably serve as a safe haven for the young while they grow and mature, after all survival in the open ocean wouldn't be an easy affair.
Trocholites notably have quite long lifespans, with many individuals living up to 20 years, however, they are only sexually mature for a few of these years, and in the meantime the young will lead very different lives to the adults. Young Trcholites notably live higher up in the water column, being more maneuverable they can swim far more easily in the more chaotic waters.
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Back in the reef meanwhile we find the Megalograptus once again on the prowl. Megalograptus are notably sexually dimorphic with the females outsizing the males. They also aren't afraid to cannibalize each other. Being a rather large individual this female rules the reef without much competition. She suddenly spots a male also on the prowl.
This male is only half the size of the big female, meaning he should be an easy meal. The female uses her paddle-like tail to get a quick burst of speed. She snags her prey with her spiny lie arms, the male thrashes around but it is no use. She quickly tears her prey apart, the male never stood a chance. As she begins to feed, the commotion attracts another Megalograptus, this time a 2 foot long female.
She begins to grab the other end of the carcass, however, the big female is having none of it. She swipes at her rival displaying her spines, this is enough to drive her rival off. She then resumes her meal. Competition over food can be quite violent with Megalograptus after all no one likes to share. What's left of this carcass will likely be food for the Trilobites.
Elsewhere, the smaller female is trying her hand out in hunting. She targets a group of Isotelus hoping to snag one. She quickly swims towards her prey grabbing one, however, the Isotelus is stronger than it looks. The Isotelus' large size notably makes it hard for the Megalograptus to get a good grip and the big Trilobite is even able to drag the Megalograptus along the seafloor as it fights. Finally the Isotelus is able to break free, once again the Megalograptus has been foiled out of a meal.
The Megalograptus swims off, luckily, for her there is plenty of prey here in the reef and she will likely find something soon.
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Back in the open ocean we find the Endoceras from earlier on patrol. The cephalopod has notably sensed the presence of another Endoceras. Endoceras are mostly solitary animals and as a result meetings can often be quite violent affairs, cannibalism is notably quite common. Our Endoceras swims towards the other Endoceras and it isn't long until they are face to face. This other Endoceras, is quite a bit smaller than the resident Endoceras.
That is because this Endoceras is a male and he has come to the court the resident Endoceras, who is a female. The male notably shows off his colorful shell to the big female, who seems quite receptive to it. The courting behavior of the male is quite similar to that of the related Trocholites, however, it is on a much bigger scale. The moment itself is a tense one for the male, if the female is not receptive to him she might try to eat him instead. After a few moments the tension begins to subside, the female seems receptive to the male's advances.
The pair soon begin to embrace each other with their tentacles as they start mating. The male quickly fertilizes the eggs of the female Endoceras. As the embrace ends the male swims off, this pair is notably unlikely to ever meet again, however, the male has done his job and ensured the survival of his species. The female Endoceras will notably carry the eggs for a time and once it is time to lay them she will head to the reef.
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A few days later, we find ourselves on the beach that sits near the reef. Notably carcesses wash up frequently on the shore line; the lack of scavengers means that they will sit and rot in the sun. The center of the continent of what will one day become North America is mostly barren; however along the rivers and streams there is something peculiar, that something is greenery. Sitting on rocks are groves of primitive terrestrial plants, the first of their kind to colonize the land. These plants are notably not very impressive by today's standards, however, they are very important, without these early colonizers it is unlikely that animal life would've ever colonized the land meaning these plants are true pioneers.
The plants themselves mainly consist of mosses and liverworts, being non vascular plants they notably lack the roots and the multitude of tubes that make up Vascular plants. They notably sit quietly on rocks and other surfaces, a sign of things to come in the future.
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Back on the beach, meanwhile, something is happening. Emerging from the surf is a peculiar sight, a Megalgraptus. The Megalograptus itself is not alone, following behind it are a multitude of other members of its kind. Megalograptus and other Eurypterids notably stand out for their ability to come ashore. They accomplish this thanks to their legs and also thanks to their lungs.
The lungs of Megalograptus are quite primitive, however, they give them a massive edge in allowing them to come ashore. Megalograptus notably engage in this behavior so they can reproduce. Soon hundreds of Megalograptus begin to crowd onto the shoreline all here for the same purpose. This phenomenon notably happens all over the globe this time of year, with millions of Megalograptus coming together for the same purpose. Soon males begin to fight over females to mate with.
The beaches themselves often become a cacophony of violence during these competitions. Once this is settled many Megalograptus begin to mate and lay their eggs. The big female is one of these Megalograptus; she notably digs out holes in the sand as she lays her eggs. After this is done the big female begins to cover the nest with sand. Finally the Megalograptus begin to head back out to sea.
Soon the beach is empty once again. Beneath the surface of the sand thousands of eggs are buried ready to hatch once the time comes, for now, however, the eggs will sit quietly beneath the sand till the time comes.
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About a week later, we find ourselves back in the reef. Life has continued on as normal for the creatures of the reef, however, something big is about to happen. Coming in from the open ocean is a multitude of Troholites, they have come to lay their eggs. The Trocholites quickly spread out as they begin laying their eggs on rocks and other surfaces throughout the reef. The warm waters of the reef will notably help the eggs incubate.
This event will notably last about a week with many Trocholites moving in day by day. The Trocholites are not the only ones here to lay their eggs, however. Emerging from the water are dozens of female Endoceras. The giant cephalopods notably are here for the same reason as their smaller relatives. The creatures of the reef begin to scatter and hide as they move in, even, the mighty Megalograptus knows better than to be caught out in the open.
Our big female is among these individuals. She quickly finds a secluded place to lay her eggs. The eggs themselves are around an inch in length and in these eggs the young will incubate. The young will take anywhere from 8 months to a year to hatch in the meantime they will sit here. After she is finished laying her eggs the big female begins to swim off leaving the eggs.
Afterwards hunger begins to take over. The female Endoceras quickly begins to comb the area for prey. Hiding in a rock crevice is the big female Megalograptus lying motionless. Unfortunately for the arthropod the Endoceras spots her. The Endoceras quickly attempts to grab the Megalograptus, reaching into the rocks with her tentacles.
The Megalograptus, strikes at the arms of the Endoceras, with her spines. The Megalograptus then sees an opening and bolts with the Endoceras in hot pursuit. The Endoceras crawls after her prey, navigating the rocks and corals with ease. The Endoceras then finally catches up to its prey. The Endoceras promptly grabs the tail of the Megalograptus.
The Megalograptus attempts to break free, however, it is no use. Soon the Endoceras grabs the center of the Megalograptus body as she begins to control her prey. The Megalograptus fights and struggles, however, her fate is already sealed. The Endoceras pulls the Megalograptus into its massive beak as a sickening crunch rings out. With her prey dead the Endoceras can finally begin to feed.
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A few days later the Endoceras and the Trocholites begin to leave the reef, their work being done. The young embryos will incubate slowly but surely inside their eggs once they hatch they will have to survive on their own. Some individuals won't even get that far. While the eggs were laid in secluded locations, some of them get unlucky and are found by predators. Megalograptus notably won't turn down free meals and the eggs make a tasty snack.
Most of the eggs will survive, however, and these individuals will be the driving force of the next generation.
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Meanwhile back on the beach, that borders the reef night has fallen. As the waves calmly lap the empty shore something begins to stir in the sand. Young Megalograptus begin to emerge from the sand. These young look like miniature versions of their parents and they are already ferocious predators in their own right. As the young hatch, they take off towards the sea.
They quickly swim off, heading for deeper waters. They then begin to search for places to hide. A multitude of rocks and corals will serve as nice hiding spots. Young Megalograptus notably feed on small animals, often the juveniles of other species. They will notably take a few years to grow before eventually reaching their adult size.
In the meantime they must be mindful of the other larger predators that call these waters home.
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Another year passes and we find ourselves back in the reef. For months now cephalopod eggs have sat and slowly developed, now it is time for them to hatch. Out of their eggs multiple young cephalopods begin to emerge. Young Trocholites quickly begin to leave the rock crevices they were born in as they start exploring. Soon multitudes of young Trocholites fill the reef.
Trocholites aren't the only ones who are being born. Endoceras young also begin to hatch. In time these young will grow to enormous sizes, however, for now at least they are nothing if not small. Megalograptus are quick to take advantage of the bounty of cephalopods. They quickly swim in snatching up young animals.
This notably weeds out the weaker individuals, an important part of the species survival as a whole. One young Endoceras finds a nice hole in the rocks to rest in. She takes a moment to catch her breath, having just survived her first great hurdle. If she is lucky she could grow up to be just as massive as her mother is, however, survival is anything but easy, she will have to make it to her adult size first. For now at least, however, she can focus on resting peacefully in the reef currently safe from danger.
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The Ordovician is a truly remarkable period in Earth's History being arguably just as important as the Cambrian. This period of life, however, would see a catastrophic end. Throughout Earth's History there have been many species that have come and gone so far and sometimes like with the end of the Ediacaran and Cambrian periods multiple species die out in a relatively short time. These events are known as extinction events, however, normally more species survive overall and persevere than die out during these events. This has not always been the case, however.
Throughout the Phanerozoic Eon there will be 5 events known as mass extinction events, or the big 5 as they have been dubbed, during these catastrophes up to 70% or more of all living organisms will die out in the geologic blink of an eye. The first of these events would notably happen at the end of the Ordovician.
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Notably in a twist of fate, one of the main causes of this extinction would be the land plants. As the plants sit on rocks, they would begin to break the rocks down releasing a substance known as phosphorus. Soon massive amounts of phosphorus would be swept up by rainstorms and released into the ocean. As this phosphorus was swept into the seas underwater plants like algae would soon begin to use this substance. Soon, algal blooms would begin to occur.
Soon these blooms would begin to decrease the amount of Oxygen in the water, in a cruel twist of fate, plants, would be a cause of the First Mass Extinction of the Phanerozoic Eon, as animals would soon begin to suffocate in the oxygen depleted waters.
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This wouldn't be the only cause, however. Notably the supercontinent of Gondwana would continue to drift south eventually reaching the South Pole. Elsewhere tectonic activity would begin to push up massive volcanoes and mountain ranges. All of this would contribute to a swift drop in temperature as an ice age would grip our planet. Massive ice sheets would begin to spring up and spread all across Gondwana.
This would contribute to a swift drop in sea levels as all around the globe the great inland seas would retreat, destroying once great reef habitats. Soon many of the creatures of these reefs had nowhere to go and with their habitats destroyed and with ocean temperatures dropping rapidly they would quickly fade into extinction. Some less specialized species would adapt, however, to the new lower temperatures and for a time it looked as if life may recover unabated once again, however, the extinction event was far from over. Soon the temperature would shift again as the Earth warmed up once more. As the temperature rose the environments would be changed once again, this would spell doom for many of the creatures, who had just adapted to life in the cold waters.
Finally around 443 million years ago, after 2 million years of drastic global change the Earth would stabilize. In total 85% of every living species on Earth had been wiped out. Many families would see drastic drops in diversity. Many types of Coral would notably vanish into extinction never to return. Trilobites as a whole would survive, but many species have been wiped out, never again will they be as diverse as they had been during the Cambrian and the Ordovician. The great Endocerids, like Endoceras itself, once the apex predators of the Ordovician, were also gone.
As horrible as this event was, however, it would also breed opportunity. While many individual species had died out unlike many other extinction events throughout Earth's history most families as a whole would pull through and now with the door open they could begin to seize many roles now left open by the extinction event. As the Silurian would begin many species would begin to diversify into new forms and many of these creatures would become instrumental in our own evolution, as creatures unlike anything the Earth had seen up to this point would begin to appear, the stage is set for new creatures to take up the mantle.
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Trivia
This episode is not actually based on any real formations as there are no real good Ordovician formations to my knowledge that actually have all of the types of animals I wanted to include in this chapter as a result this episode is more or less a hodgepodge of North American Ordovician animals that all more, or less lived at the time same time.
I originally intended to split this episode into segments with the first one focusing on the Fezouata Formation in Morocco. This formation is dated to the Early Ordovician about 480 MYA and it is most notable for the presence of Aegirocassis, a filter feeding Radiodont. This would've notably allowed for the gap in time between this episode and the last one to be shorter and I felt at the time that it would be a good segway into the Late Ordovician segment featured here. This idea was ultimately scrapped, however, as I couldn't come up with a good story for a Fezouata Formation segment and I also couldn't find an interesting cast outside of Aegirocassis and the Conodonts to feature as a result of these factors I chose to cut the segment instead and focus purely on the Late Ordovician segment and the extinction event for this chapter. I am ultimately saddened by the cutting of this segment, however, I ultimately think it was necessary for the story.
Originally Endoceras was going to be the central creature of this chapter and it would've followed the journey of one to adulthood. Ultimately I am happy I chose not to go through with this idea, as I feel like this would've led to Endoceras getting too much page time and it would've led to the other creatures getting shafted (This was a notable problem in WWB as it oftentimes had too much focus on the focus animal in episodes like Next of Kin and Sabertooth, notably my favorite episodes New Dawn and Whale Killer lack a true focus animal and have multiple species have the spotlight and I ultimately think this will be the approach I take in most chapters of this series). Ultimately I am happy with my decision to focus on multiple species in their day to day survival, as it allows all of the creatures to get shown off more.
The Megalograptus beach scene is based on fossils of such events happening with Eurypterids. I also took heavy inspiration from horseshoe crabs, for a lot of the behaviors showcased in the beach scene, for lack of a better substitute.
Originally I was going to give Astraspis a larger role but I felt like this played into the overdone narrative of "Vertebrate Superiority", as well as the villainization of Arthropods done in documentaries like WWM hence why I gave it a much smaller role (It doesn't help that Astraspis is kind of a boring animal when you get right down to it).
I was originally going to use Aphetoceras as the token Tarphycerid, however, I quickly found out Aphetoceras is only known from the Early Ordovican causing me to change plans and use Trocholites instead.
I originally planned for a scene with Endoceras hunting a group of Trocholites, however, this got cut as I felt like it gave this chapter too many scenes of predation, I also feel like it made the Endoceras feel too monstrous, which, is not what I was going for. The Trocholites mating scene was notably thrown in as a replacement scene and I am ultimately happy with how it turned out as it gave Trocholites a lot more spotlight in the story.
I based a lot of the reproductive behaviors of Trocholites and Endoceras on modern day Nautilus if only because of the lack of a better reference.
Well that's all for this chapter, next time we will dive right into the Silurian…
