Chapter 4: Claws and Jaws

Earth 423 Million Years Ago, it is now a time known as the Siluiran. It has been 20 million years since the Ordovician Extinction and life has begun to slowly but surely bounce back from the extinction. The Silurian, however, has not been a peaceful time for life to recover, while no extinction events to rival the Ordovician Extinction have occurred, fluctuations in ocean temperatures and the amount of Oxygen in the water have caused drastic swings to the Earth's climate. Multiple minor extinctions have occurred over the last 20 millions years, fueled by the ever changing landscape of the Earth. The Earth's surface, meanwhile, has also not remained dormant either during this time.

Gondwana has continued to drift south, the great ice sheets that formed during the Ordovician remain, however, they have significantly decreased in size. To the north fragments of what will one day become North America, and Europe sit around the Equator giving them a warm climate. Tectonic activity has caused the continents to move and drift; they are now on a collision course with one another and soon they will collide to form yet another supercontinent. The Northern Hemisphere meanwhile is dominated by a great ocean that covers much of the planet. Meanwhile around the Earth's many continents, the shallow seas have once again filled with life, with many survivors of the Ordovician Extinction having multiplied once again.

The constant extinction events of the Silurian have kept life on edge, despite this many new creatures have evolved some of which are unlike anything the Earth has yet seen.

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This can be seen no better than in what is now modern day China. The warm sunlit waters are teeming with life, great coral reefs have once again formed and they are teeming with life. Brachiopods sit stationary sifting through the waves, snatching up microscopic organisms as they do. Trilobites have also survived the extinction, however, their diversity has significantly fallen, yet they still struggle on with new forms having evolved. Take Phacops, a common global genus, they don't look very special compared to the average Trilobite, however, they and other Trilobites have begun to adopt a new defense mechanism.

They can notably curl into little balls shielding their vulnerable undersides completely from danger, similar behavior will be adopted in later unrelated animals like pill bugs and armadillos. Another resident that lives alongside the Trilobites is a jawless fish known as Dunyu. Fish notably fared far better during the Ordovician Extinction than other families and they have even begun to diversify in response to the open niches. Dunyu itself isn't very different from the earlier Astraspis, however, its armor has become even more extensive for even better protection from predators.

Not all fish have remained bottom dwellers, however, notably some have taken a massive leap forward in their evolution. Take Entelognathus, a type of fish with a new feature jaws. Jaws are a relatively recent evolution in fish having first appeared just a few million years before and yet already many types of fish have adopted jaws. Jaws notably allow fish to feed on a wider variety of food than before, allowing them to take up higher roles on the food chain. Notably Entelognathus uses its jaws to crack open hard shelled prey.

Brachiopods are a personal favorite meal. The Entelognathus slowly swims up to its prey and grabs a Brachiopod in its jaws. Afterwards, using its powerful jaw muscles it is able to crack open the hard shell of its victim. The Entelognathus then begins to feed on the soft innards of its victim. Entelognathus itself is part of a class of fish known as Placoderms.

Placoderms were notable for being the very first jawed fish and from them many other groups have evolved and diversified even now in the Silurian there are a multitude of different types of jawed fish already, many of whom take up many different ecological roles.

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Elsewhere we find one of these other types of fish, meet Guiyu oneiros, another type of jawed fish. Guiyu is not a Placoderm, instead it is a Sarcopterygian, or lobe finned fish. Lobe finned fish stand out for their fins which are distinct from Actinopterygians, or ray finned fish. The fins of lobe finned fish are notably better at supporting weight than the fins of ray finned fish, a feature that in time will become important in our own evolution. For now, however, Guiyu is not focused on such matters, rather its survival in day to day life is a more pressing matter.

At around a foot long Guiyu isn't an especially large animal and while it can hunt smaller creatures there are far larger predators it must watch out for, after all fish still do not yet rule the ocean. Watching in the shadows of some rocks is a large predator, a member of another lineage that survived the Ordovician Extinction and has diversified. The predator bursts out from hiding with impressive speed. The Guiyus' fast reflexes allow it to avoid the attack and maneuver around the predator. The Guiyu quickly swims away escaping a possible death.

Meet Pterygotus a worldwide genus containing multiple species and at up to 6.6 feet in length with its claws fully extended, this is one of the larger species one can find. Eurypterids notably survived the Ordovician Extinction and they have quickly diversified and snagged the position of apex predator without the Endocerids to hunt them anymore. Pterygotus itself is one of the larger Eurypterids and they have become perfectly adapted for hunting prey like fish. The massive claws have notably replaced the spines present on earlier Eurypterids like Megalograptus and they notably allow Pterygotus to grab its prey far more efficiently, the claws are also perfect for crushing through armor. The tail meanwhile allows Pterygotus to swim quite quickly in spite of its large size.

Pterygotus itself is an ambush predator and while it can swim quite quickly it can only sustain the speed for a short period of time, as a result it must make sure it is in range before attempting an attack. For now the massive arthropod will be forced to wait and see if anything else stops by.

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Not all fish are complete pushovers in these waters, for there is one type that has become a formidable predator in its own right, meet Megamastax. At up to 3 feet long, Megamastax is enormous for a vertebrate of this time and it comes equipped with the perfect tools for killing. Inside of Megamastax mouth are multiple teeth perfectly built to crush through tough armor and bone. On top of this Megamastax is quick and agile allowing it to chase down many of the animals that share these waters with it. This one has spotted a group of Dunyu.

The Megamastax quickly swims towards the fish. The Dunyu immediately head for the cover of the nearby rocks, however, they are not fast enough to outswim a Megamastax. The Megamastax grabs one of the Dunyu and using its powerful jaws crushes the unfortunate animal. The Megamastax then proceeds to rip apart its prey. The Dunyu will satisfy the ferocious predator for the time being at least, however, it won't be long before the Megamastax grows hungry again.

...

Elsewhere we find ourselves in a very different frontier, dry land. Dry land has notably been relatively sparse for much of Earth's history; it was only during the Ordovician that certain plants began to move onto the land in the form of mosses and liverworts. These plants were notably restricted to the coastlines as well as rivers and lakes of the Earth's continents. This has notably remained true into the Silurian for the center of the Earth's many continents are dry and barren wastelands. Massive sandstorms are a frequent occurrence ripping across the landscape at high speeds.

Around water sources, however, it is a very different story. Mosses and liverworts remain, however, they have now been joined by more complex organisms. Meet Cooksonia, a missing link between Vascular and Nonvascular plants. While they lack the roots of modern plants they have Vascular tissue, a first in plant evolution. Cooksonia are notable for their success throughout the Silurian; they notably stand out as a worldwide genus with a mass of mini forests of them carpeting the ground. They are not the only organisms that make up these forests, however, in fact they aren't even the largest ones.

Towering above the Cooksonia is not a plant but a massive type of fungi, meet Prototaxites. At up to 26 feet in height Prototaxtites is a titan in its time, dwarfing the multitude of plants that share the shorelines with it. Hiding below the layers of Cooksonia meanwhile is another kingdom of living things, for the first time in Earth's History animals have made the leap and become terrestrial. Small millipedes are among the first of these creatures; they notably crawl through the undergrowth on multiple pairs of legs searching for food. Living on land has a notable set of challenges that living in the water doesn't, notably the force of the Earth's gravity is far stronger on dry land than in the water.

On top of this for a long time the oxygen levels in the air were far lower than they are in the water causing animals to remain aquatic for the most part, only some types of animals like Eurypterids would make the occasional journey onto shorelines to lay their eggs. In the last few million years, however, oxygen levels have gradually risen thanks to plants like Cooksonia pumping it out into the air. The Cooksonia also provide shade and food for animals like the Millipedes. All of this combined with the fact that the land has less competition than the seas has caused many animals to become pioneers and colonize the land. Unfortunately for the Millipedes that live in these mini forests, some of the animals that have come onto land are far less friendly.

True Scorpions have made their first appearance in the Silurian and while they started out as aquatic animals, they have quickly colonized the land becoming the apex predators thanks to a lack of larger animals to compete with them. This scorpion has spotted a millipede. Quickly the scorpion grabs the millipede with its claws before using its stinging tail to finish the job. The tail's stinger is notably filled with venom, a deadly liquid that helps to kill and break down the prey. The scorpion quickly begins to feed.

While the terrestrial creatures of this time don't exactly seem very special they are undoubtedly important, for without these early pioneers who took the leap, it is very likely that many of the great terrestrial creatures that call our planet home would've never evolved if not for early terrestrial invertebrates.

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Around a week later we once again find ourselves back in the reef. On the sea bottom looking for food is the group of Phacops. Despite having fallen slightly in diversity in the aftermath of the Ordovician Mass Extinction, Trilobites are still quite successful animals, notably pretty much every marine ecosystem still contains them in quite significant numbers, this is in spite of many other creatures that now compete with them in the waters. Suddenly the Phacops curl up into little balls for they have spotted danger. Swimming towards them is the Megamastax from earlier and it seems that Phacops are on the menu today.

The Megamastax probes the Phacops looking for an opening. The Megamastax grabs one of the Phacops and attempts to bite into it. Unfortunately for the Megamastax it seems that the Phacops armored exoskeleton is holding up. Frustrated, Megamastax drops the Phacops to the floor. It seems that today the Phacops has survived its brush with death.

The Megamastax meanwhile swims off, it will have to search elsewhere for food. As it patrols it spots a potential prey item. The Guiyu from earlier is swimming around, likely looking for food itself, however, in nature it isn't uncommon for the hunter to become the hunted. The Megamastax swims towards the Guiyu hoping to snag a meal. The Guiyu notices the Megamastax and takes off attempting to evade its attacker.

The Guiyu's best chance is to get to the rocks where it can find somewhere to hide. The Megamastax swims as quickly as it can hoping to catch up to its potential prey. The Guiyu finally reaches the rocks, but it isn't out of the woods yet. While the Megamastax larger size makes moving through the rocks difficult it can still manage to, albeit somewhat clumsily. The Guiyu finally reaches a set of rocks to hide in.

The Megamastax peers in, however, it is no use the Guiyu has escaped this time. The Megamastax swims off while the Guiyu waits for the predator to leave before popping out. The Guiyu then swims off.

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Elsewhere the Megamastax is taking a moment to rest, the chase has made it quite tired causing it to take a moment to recover lost energy. Unfortunately for the Megamastax, being tired can have deadly consequences in the Silurian seas. Suddenly the Megamastax is grabbed in the claws of the hungry Pterygotus. Normally the Megamastax speed would've saved it, but that is not the case this time. The hungry Pterygotus quickly despatches the Megamastax as it then begins to feed.

The Pterygotus uses its claws to rip off chunks of flesh to pull unto its mouth. The Megamastax will feed the Pterygotus for a few days at least. After finishing its meal the Pterygotus leaves the rest of the carcass to the scavengers. The hungry Entelognathus is quick to take advantage of an easy meal. What's left of the carcass belongs to him.

While the Silurian has seen an increase in the diversity of fish they still do not yet rule the Earth, even monsters like Megamastax remain subservient to the mighty Eurypterids like Pterygotus and this status quo will continue into the start of the next period despite this, however, fish will continue to grow in size and diversity as more and more types continue to evolve.

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Earth 408 million years ago. It is now a time known as the Devonian period. The Silurian came to an end without any real major events or mass extinctions occurring, in spite of this the Devonian has seen some changes and as the period continues on, the status quo will continue to change more and more. Here in what is now Germany we find a massive reef ecosystem teeming with life. The reef itself has an absolutely massive amount of biodiversity.

Some creatures are very familiar like the trilobite Chotecops, a close relative of Phacops. Chotecops itself is the most common animal that inhabits the reef. Another common arthropod in the region is a creature from a bygone era, meet Mimetaster, a close relative of the earlier Marella and one of the last of their family. Mimetaster is not the only animal in the reef that is the last of an ancient lineage swimming above is one of the last of the Radiodonts, meet Schinderhannes. Radiodonts notably saw a decline in diversity in the aftermath of the Cambrian Extinction Event in spite of this, however they were able to recover and even found success in the Ordovician.

These surviving Radiodonts notably grew to massive sizes and became filter feeders swimming peacefully through the waves of the open ocean and feeding on small creatures like Plankton. Unfortunately for the Radiodonts, the Ordovician Mass Extinction proved to be another massive blow to their numbers and the Radiodonts did not recover the same diversity as before this time. The Radiodonts have now been in decline since the start of the Silurian and now Schinderhannes is the only one that's left once it's gone the once great Radiodont order will forever be gone never to return. Schinderhannes itself spends its time feeding on small animals on the seafloor and evading the larger predators of the reef.

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Elsewhere in the reef we can find some of the other creatures of this reef. Take Taxocrinus, part of a class of animals known as Crinoids. Crinoids are part of the Echinoderm phylum and they have been around since the Ordovician. There are many different types, who take up many different ecological roles. Taxocrinus itself spends its days attached to rocks and other structures as they use their featherlike structures on top to sift through the waves and pick out small microscopic organisms like plankton.

Not all Echinoderms are so friendly, however meet Urasterella, a type of starfish. Starfish have also been around since the Ordovician, but unlike the Crioids they have become fearsome predators. Today the Urasterella has a taste for brachiopods. The predator slowly but surely moves towards its prey. The hungry Urasterella then wraps its arms around its prey as it begins to feed.

After finishing its meal the Urasterella begins to move on. Starfish like Urasterella are a very successful type of animal and they are one that can still be found in abundance in our oceans today, an undeniable evolutionary success story.

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Back with the group of Chotecops, we find another type of animal has now joined them. These are Drepanaspis, a type of jawless fish, it seems that even in the Devonian jawless fish remain a common component of the environment. The small group of Drepanaspis patrol the sea bed looking for food. As they swim they pass another type of fish, this one, however, is of the jawed variety. Meet Dipnorynchus, a type of lobe finned fish, however, Dipnorynchus isn't just a normal type of lobe finned fish, for it is an early type of lungfish.

Lungfish are a new type of lobe finned fish, that are destined to become more common as the Devonian drags on, they also come equipped with a variety of advantages over regular fish. As their name implies they are some of the first vertebrates to have lungs as well as gills, this allows them to have a second source of oxygen should the waters they are living in become anoxic. They also have powerful fins that allow them to walk on the sea bottom. Dipnorhynchus themselves are omnivores, giving them a varied diet allowing them to consistently find food be it small animals, or even plant matter should all else fail. Notably as fish like these become more common they will continue to develop adaptations that will eventually lead them to a new frontier, dry land.

For now, however, these creatures are still restricted to the waters.

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A little ways away from the reef, we find ourselves in open water. The microscopic organisms that make up the ocean's food web have long since recovered since the Ordovician Mass Extinction. Plankton survive once again in great abundance in the open water. In response to this burst of life some animals have evolved to feed on this new bounty of food. Swimming peacefully through the water is Tityosteus, a type of placoderm.

Placoderms have continued to diversify leading into the Devonian while all types of fish have seen an increase in their numbers, Placoderms have seemingly become the most successful type of fish. At up to 8.2 feet long Tityosteus, is one of the largest vertebrates to have evolved at this time. Despite their massive size and fearsome appearance these creatures are gentle giants and only microscopic plankton have anything to fear from them. Large sizes like this will only become more common and in fact in the future some animals will grow to dwarf Tityosteus. It seems that filter feeding is an excellent recipe for getting bigger after all, food is very plentiful and being larger means you have less to fear from predators.

Eventually the shale begins to swim off, moving away from the reef as they continue the search for food.

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Back in the reef we find ourselves back with the Drepanaspis from earlier, still feeding alongside the Chotecops. As they feed, however, they are unaware that they are being watched by the apex predator of this reef. Lurking in the coral nearby, is a massive Jaekelopterus rhenaniae, a close relative of Pterygotus. Jaekelopterus is similar to Pterygotus in appearance, but at up to 9.8 feet in length it dwarfs even its already massive relative. Jaekelopterus notably stands out for being not just the largest Eurypterid, but it is also the largest arthropod of all time.

The massive predator sits patiently, waiting for its prey to get too close. One of the unfortunate Choteocops makes the fatal mistake of getting too close. The Jaekelopterus suddenly bursts out from hiding and grabs the hapless Trilobite in its claws. Normally Chotecops ability to curl into a ball would grant it protection, but unfortunately for the Trilobite it has no time to react. The Jaekelopterus crushes its prey as it begins to rip it apart for consumption.

The rest of the group of animals scatter like cockroaches from a flame, for they have no intention to stick around. After finishing its meal the massive Jaekelopterus begins to swim off as it starts to patrol its territory. Jaekelopterus itself is a very successful genus of animal and they are perfectly adapted for a variety of environments while this one lives in a reef many other its kind rule the estuaries that dot the coasts of the northern continents. Unfortunately for this Jaekelopteus he is not alone. Emerging from a nearby clump of coral is another Jaekelopterus.

Jaekelopterus are solitary creatures by nature and they only tolerate other members of their kind during the breeding season. The conflict quickly escalates as the two size each other up. Oftentimes one individual will be larger than the other and physical conflict can be avoided, but this time the two individuals are evenly matched. Soon the pair turn to violence as the resident male strikes first ramming his rival. The rival male is only briefly winded by the blow and he quickly seeks to retaliate.

The rival male quickly swims towards his rival and grabs his front leg with one of his claws. The resident male quickly pulls his leg loose, before striking the rival male across the face with his own claws. The pair then begin to wrestle with each other, seeking to get in good strikes with their claws as they struggle. The resident male begins to overpower his rival pushing him to the seabed. Sand is kicked up as the pair battle on the ocean bottom.

The rival male is able to make some space as he pushes the resident male off and attempts to flee. The resident male is having none of it, however, and he grabs his rival by the tail. The rival male then strikes the resident male hard across the face with his tail briefly winding him. The rival male then goes for another attack of his own, however, the resident male quickly recovers from the blow, as he now seeks to pay his rival back. He quickly reengages his opponent as he grabs a hold of his rival with one of his claws.

He then pulls a chunk of his rival's armor off. The rival male seems to finally get the point as he flees the area as quickly as possible, the resident male pursuing him for a bit before finally relenting.

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Sometime later we find the resident male resting after his battle. For now at least he has retained control of his territory, however, there will likely be other competitors in the future after all his turf is a prime hunting ground. For now at least he can rest knowing he has won for today, another small victory in the game of life.

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The age of Giant Eurypterids is a notable one in Earth's long history, however, it wouldn't last forever and in fact by the Devonian these massive beasts reign as the apex predators of the Earth was already on borrowed time. As the Devonian continues on Eurypterids will begin to decline in numbers and as this happens fish will quickly multiply, while the Eurypterids as a whole will survive for another 156 million years they will no longer be the top predators of our planet, for the future rulers are the fish that are already diversifying in number around them and some of these fish like the relatives of creatures like Dipnorynchus are destined to colonize the next frontier of Earth dry land.

Trivia

This episode is primarily based on the Kuanti Formation for the first segment and the Hunsruck Shale for the second.

Before anyone says Pterygotus and Jaekelopterus are oversized I include the claws in my lengths I gave to them as they give a better idea of how big they actually are. Most estimates do not, that is why they are given higher estimates than what Wikipedia says for example.

Phacops and Pterygotus are not actually known from the Kuanti Formation, however, they are both worldwide genera and on top of that the Kuanti despite having an impressive amount of fish seems to lack much in the way of other types of fauna hence their inclusion, this way the Silurian's fauna is better represented.

The Pterygotus species here was originally intended to be P angilicus, however, since that particular species is only known from the Early Devonian I changed it to be an unnamed species that is admittedly heavily based off of P angilicus.

I originally intended to give both Pterygotus and Jaekelopterus larger roles before I downsized their roles, to make way for some of the other creatures featured.

Hunsruck Sea Spiders were considered before being cut, as was a Hunsruck Ammonite of some kind. These were cut to keep the roster from getting too bloated (Tbh it already kind of is).

The climax of the 2nd segment was originally going to be the Jaekelopterus attacking and being driven off by the shale of Tityosteus, but I felt that this scene played too much into the vertebrate vs. arthropods trope present in way too many pieces of Paleozoic media (Cough Walking with Monsters cough) so I changed it to be a fight between 2 Jaekelopterus, this climax is likely more exciting anyways.

That's all for this chapter see y'all in the next one.