Alien Biospheres: Part 11 - Islands

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Lets GOOOO!!!! It's giant nightmare spider time BAYBEE!!

👍︎︎ 13 👤︎︎ u/TigerDragon747 📅︎︎ Jul 15 2021 🗫︎ replies

I hate how every time you think the lophostomes are getting a chance, the osteopods screw every thing up

👍︎︎ 26 👤︎︎ u/not_ur_uncle 📅︎︎ Jul 14 2021 🗫︎ replies

FINALLY!!!

👍︎︎ 5 👤︎︎ u/Excellent_Crow2702 📅︎︎ Jul 15 2021 🗫︎ replies

NEW VIDEO
YAY

👍︎︎ 3 👤︎︎ u/invertabrate-lover42 📅︎︎ Jul 15 2021 🗫︎ replies

It's so fucked up how none of the dwarf elephants are still around.

👍︎︎ 3 👤︎︎ u/123420tale 📅︎︎ Jul 16 2021 🗫︎ replies

Hey, did anyone notice that at 17:59, a symbol flashes in the bottom right corner? It's purple and has a white crop circle type pattern in it.

👍︎︎ 2 👤︎︎ u/HypnagogianQueen 📅︎︎ Jul 16 2021 🗫︎ replies
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This video is brought to you by Campfire Technology. Campfire Blaze is a browser-based application packed with tools to help you exhaustively catalogue all your worldbuilding and storytelling in one place. The interface is both very easy to use and incredibly comprehensive, with built-in sections for maps, timelines, cultures, species, languages, and narrative elements like characters, relationships, and story arcs, but you can also add additional pages, folders, articles, and panels to flesh out your project in as much detail as you want. You also have the ability to customize each of your pages with their own themes and templates and to link different pages together to keep all of your information cross-referenced, and you can even join different projects together as part of a shared universe. Blaze’s free version already comes with the basic functions of all of these features, but if you want to add even more options, Blaze has extremely flexible pricing, letting you individually buy whichever modules you’re interested in either as a subscription or a one-time purchase, or just unlock everything for only a few dollars a month. To sign up for Blaze or to learn more, check out the link in the description. In the last episode, we saw how the eastern and western clades began to diverge from each other as a result of the separation of the two continents. But as well as these continents, there are numerous other landmasses across the planet, each one representing a separate instance of allopatry, isolated from and unaffected by evolutionary developments that take place elsewhere in the world. Of particular relevance are islands, which differ from continents in several key aspects that have significant implications for the species that inhabit them. The defining characteristics of islands are their size and their isolation, both of which will affect the potential species richness the island can support: the larger the island is, the greater the number of species it can accommodate, and the closer it is to the mainland, the easier it will be for new species to migrate to it. But these same factors also exert unique pressures on the island’s inhabitants, often resulting in highly unusual species and ecosystems in comparison to the mainland. For our alien planet, there’s no way we could realistically delineate the ecosystems of every single one of the thousands of islands across the ocean, but we can focus on a select few of them that best exemplify the effects of ecological isolation on the native species. Much of the time, islands will have once been part of the mainland before becoming separated by continental drift or rising sea levels. On our alien planet, many such islands are likely to form when the eastward and westward movement of the continents eventually grinds to a halt, at which point, the coastal mountain ranges, no longer being sustained by tectonic activity, will diminish as they’re eroded by wind and rain, and as both continents begin to drift south, the regions of northern tundra will be moved out of the arctic circle. Both of these factors will decrease the area available for the formation of glaciers, which may ultimately bring the ice age to an end, returning the world to a greenhouse state. This will have many effects on the flora and fauna of the mainland, which we’ll follow up on in future episodes, but as this happens, the melting ice caps will cause a considerable rise in sea levels, trapping many species on the islands that form as the low-lying areas become submerged. Let’s take a closer look at just one of these islands, a small landmass about 50 kilometres across just off the coast of the eastern continent that we’ll call Isla Proxima. On islands like this, the native species will initially be more or less identical to those found on the nearby mainland, which in this case will include clades such as the titanopods, cryptodonts, and camptopods that live along the northern coast, but soon after they become stranded, these clades may undergo some rapid developments in response to their newfound isolation. The smaller a landmass is, the less food and space it will offer, and on an island as small as Isla Proxima, animals that require large amounts of resources may struggle. In particular, large predators often do poorly on islands, since they require extensive hunting grounds and sizable prey populations, which small islands are rarely able to support. On top of this, species that find themselves on islands habitats have to contend with the founder effect, the reduction in genetic variation that arises from a new population being established by a small number of individuals, which results in a high degree of inbreeding and increases the risk of extinction. Predators typically live at much lower population densities than their prey, and the very few members of a given species that become stranded on newly formed islands may not be sufficient to form to a stable breeding population. All of these factors mean that large predators are especially vulnerable to dying out in isolated habitats and so are frequently absent on small islands, although there are some notable exceptions we’ll touch on later. Therefore, Isla Proxima may not be able to accommodate the cryptodonts and other large onychodonts, so these species may go extinct on this island soon after the rising sea levels sever its connection to the mainland. While other large animals on Isla Proxima will likely face similar pressures, things will generally be easier for megafaunal herbivores like the titanopods, especially with the disappearance of the big predators, letting them browse on the island’s vegetation without fear of attack. However, in comparison to the endless stretches of bountiful steppe and forests on the mainland, the tiny island offers a very limited supply of food, which the titanopods will have to adapt for if they’re to survive. One of the most common evolutionary trends for island-dwelling animals is described by Foster’s rule, which posits that species may undergo a change in body size to best suit the availability of resources in their environment. While this can theoretically apply to any habitat, the most obvious and dramatic examples of this phenomenon usually occur in isolated environments like islands, so much so that Foster’s rule is sometimes simply called “the island rule”. Since smaller animals need less food to survive, large animals that end up on islands very often exhibit a significant reduction in body size in comparison to their mainland counterparts. This manifestation of Foster’s rule is called insular dwarfism, and can be seen in bovids like the anoa, or dwarf buffalo, in the dozens of unrelated species of dwarf elephants, and is even known to have happened among dinosaurs like Europasaurus and Magyarosaurus. Generally, the smaller the island is, the fewer resources will be available, and therefore the more extreme the effects of insular dwarfism will be, so on an island as small as Isla Proxima, the local titanopods may end up shrinking down to less than a quarter of the size of their relatives on the eastern continent. Since such a small island will only be able to maintain a very limited level of biodiversity, this clade will contain only a single species, which, to contrast them with their larger cousins, we’ll call Nanopus proximensis. But while large animals like these may respond to their isolation on Isla Proxima by getting smaller, somewhat paradoxically, Foster’s rule may also result in other animals evolving in the opposite direction; living on a small, secluded island means there won’t be much competition, which, along with the lack of large predators, will relieve a lot of evolutionary pressure for the inhabitants, particularly for animals that would otherwise need to remain small to help them hide or escape danger. This means that for small animals, islands may actually offer greater access to resources than the mainland, and therefore, in accordance with Foster’s rule, they may undergo a change in body size, in this case resulting in insular gigantism, growing much larger than their continental relatives. On earth, this is seen in numerous species like the Tenerife giant rat, the giant parrots of New Zealand like the kakapo, and the New Caledonian giant gecko, the largest living gecko species. On our alien planet, some of the most common and adaptable osteopods are the eurycheirids, which by this point have become a very successful and widespread group, with their endothermy letting them survive in a variety of climates, and their generalist diets helping them take advantage of every available food source, giving rise to clades like the lystrocheirids in the deserts and the related trypanocheirids in the temperate steppes and woodlands, and being so prolific, its more than likely that at least a few species will end up on Isla Proxima. The mainland varieties can vary in size from only about 20 centimetres to almost a meter, and are primarily small scavengers and generalist omnivores, but on Isla Proxima, once the onychodonts die out, not only will they be free to grow bigger, but also to move into the vacant predatory niches. Although their maximum size will be constrained by the limited food and space on the island, they may still grow into some of the largest of all eurycheirids, going from generalist scavengers to dedicated predators. They may evolve to use their broad digging claws and strong forelimbs to grab large prey and wrestle it to the ground, while their serrated pedipalps, once used for stripping meat from inside carcasses, may adapt into sharp saw-like appendages to pierce the prey’s hide and tear off chunks of flesh. Once again, due to the limited species richness the island can support, this clade will only include a handful of species, all of which will be united in a single genus that we’ll call Teratocheirus. But these won’t be the only creatures to take advantage of the demise of the onychodonts. Ever since the onychodonts first evolved, they’ve dominated the niches of terrestrial hypercarnivores thanks to adaptations like their thermoregulation, centaurism, and cursoriality. Meanwhile, the other dromaeopods that lack these specializations have been on the decline for the last few tens of millions of years, and have been largely outcompeted in most open habitats, but a few of these more basal forms will still survive as small mesocarnivores in tropical latitudes. However, if any of these species end up on Isla Proxima, then once the onychodonts disappear, they’ll experience a huge decrease in competitive pressures, and will now be free to exploit the macropredatory niches that they’ve been precluded from on the mainland, which may once again result in an instance of insular gigantism. This will likely bring them into competition with the teratocheirids, so the two clades may need to undergo some form of niche partitioning, which may involve specializing for different styles of hunting. Like most other basal dromaeopods, these forms may use their powerful back legs and great speed to chase down prey over short distances, making them much more able to tackle fast-running prey, while the eurycheirids don’t have the same adaptations for pursuit-hunting, but will still be able to employ ambush tactics to hunt smaller or slower prey, and are adaptable enough to subsist on carrion and mixed vegetation if need be. Along with nanopus and teratocheirus, these dromaeopods, which we’ll place in the genus Rhomaleopus, will be some of the many clades on Isla Proxima whose evolution will be shaped by Foster’s rule, resulting in substantially different ecosystems from those on the mainland in only a few million years following its separation. However, the longer an island remains isolated, the more divergent its ecosystems will become. On earth, Madagascar has been separated from Africa for over 88 million years, and as a result, about 90% of all Madagascan plant and animal species are found nowhere else in the world. Our alien planet offers some even more extreme examples, with some landmasses, like many of the islands dotting the southern ocean, having been isolated since the invasion of land over 150 million years ago, and with such a long period of isolation, they’ll be totally unlike any other environment on the planet. A key factor relating to this is that, unlike Isla Proxima, none of the mainland clades will have ever had any presence on these landmasses, since they only evolved after these islands became separated, so everything that comes to live there will have had to disperse there from elsewhere. In the case of plants, most chemophytes reproduce by releasing their diaspores into the wind, so while the early chemophytes were spreading across the mainland, some of these diaspores may have been swept up by the winds of the massive storm systems that were common during this time, and, by sheer luck, may have been blown across the sea to some of these islands. Dispersing across such huge distances by accident will obviously be an extremely rare event, so these islands will initially be home to only a handful of plant species, but some chemophytes may be more likely to make the journey than others. Once the xylophytes evolve, most of them will still make use of wind dispersal like other plants, but in the swamps along the coasts of the old supercontinent, some plants may have evolved to take advantage of the plentiful rivers and floodwaters for dispersal. Once fertilized, their female gametangia may grow into bulbous pods that detach from the parent plant and drop into the water below, floating downstream and eventually settling on a new stretch of riverbank. This same strategy is used by plants on earth like coconut palms, knickernuts, and the looking glass tree, which produce buoyant structures called drift seeds, or drift fruit, that are adapted for being dispersed by water currents. Although these xylophytes will have initially evolved in the coastal swamps, these drift fruit may serve as a preadaptation for colonizing islands, since they’ll be able to cross stretches of water that would be virtually impossible to bridge using wind dispersal, with some drift seeds on earth known ride the ocean currents for thousands of kilometres, and to remain adrift for months at a time. If some of these xylophytes evolve similar specializations for oceanic dispersal, they may become some of the most common and successful plants in coastal and island habitats. On account of their buoyant drift fruit, we’ll call these plants coelophytes. And fortunately for these coelophytes, the islands that they arrive on will not only be devoid of competition from other plant clades, but also of any of the mainland herbivores, and so act as a safe haven for them to diversify and flourish, but it will only be a matter of time before other colonists find their way here. Before the evolution of flight and semiaquatic lifestyles, most animals will be confined to the supercontinent, but eventually, a very small minority of species might happen upon another form of oceanic dispersal: rafting events occur when organisms are carried from one landmass to another by floating mats of vegetation and other debris. As improbable as this may seem, this has been directly, albeit very rarely, observed on earth, such as how green iguanas have been recorded rafting over 100 kilometres between islands in the Caribbean, and the biogeography of some clades suggests that rafting events like these can even take place over distances of thousands of kilometres, which is thought to be how lemurs originally arrived on Madagascar and how the ancestors of new world monkeys and caviomorph rodents travelled from Africa to South America. Even though these events are extremely rare, over timespans of millions of years, they’re bound to happen at some point, and even a single breeding pair reaching a new landmass may be enough to establish a population. The most likely animals to undergo rafting events are species that are small enough to have their weight supported by floating mats of plant matter, and are hardy enough to survive a journey that might take anywhere from several days to a few weeks. This being the case, the malacoforms seem like prime candidates for rafting, since they’re tiny enough to stay afloat on even the smallest piece of debris, including, for instance, the drift fruit of the coelophytes. Any malacoforms that infest the tissues of these fruit may be carried with them once they detach from the parent plant, serving as a perfect vessel to ferry them between islands and letting them spread relatively quickly among all the landmasses that the coelophytes reach. On the other hand, rafting events involving larger animals will happen much less frequently, since they’ll require much sturdier rafts such as mats of fallen branches, logs, and other driftwood, which aren’t likely to form very often. Relating to what we mentioned at the beginning of this episode, the rate at which new species will raft to a given island will be contingent on its size and its distance to the mainland, so landmasses like those off the southwest coast of the supercontinent, which are relatively large and only a few hundred kilometres away, are likely to experience a relatively high rate of rafting events, and so share many clades in common with the mainland, while more remote landmasses may see only see one or two rafting events throughout their existence, which will have some crucial implications for their biogeography. Long before the first osteopods, the lophostomes were already a well-established group, even including various megafaunal clades among their ranks. Along with the ubiquitous malacoforms, a few of these larger species might have also been rafted across the sea during this early period. Perhaps in one chance event, a few members of a small, adaptable species of the ancestral desmostracans were sent on a voyage of over 2000 kilometres to make landfall on the island off the supercontinent’s southeastern coast, a landmass which we’ll hereafter call Crescentia. If enough of them survive to overcome the founder effect and form a stable breeding population, then they’ll find themselves in an ideal sanctuary, lacking any other animals beside the malacoforms they feed on. This will be especially fortunate for them considering that a few million years after this rafting event occurs, competition from the newly evolved osteopod clades will drive most of the older lophostome species to extinction, with the only lineage of desmostracans that survive on the mainland descending from a clade of small malacovores. But on Crescentia, they’ll be safely secluded from the developments taking place on the supercontinent, and thus they’ll survive as the only representatives of an ancient branch of lophostomes that won’t exist anywhere else in the world. These surviving species will represent what’s known as a relict, the remnant of a population or clade that was once widespread, but now retains only a fraction of its former range and diversity. An area or habitat that supports a relict is called a refugium, which islands frequently serve as, such how the thylacine survived on the island of Tasmania up until the last century despite having died off on the Australian mainland thousands of years earlier, and how New Zealand is home to the tuatara, which, although it closely resembles a lizard, is actually the only surviving species of rhynchocephalian, an entirely separate clade of reptile that once had a global distribution before being largely wiped out along with the non-avian dinosaurs. Likewise, Crescentia will serve as a refugium for these relict desmostracans, which will continue to thrive on the island even as the megafaunal lophostomes are replaced by the osteopods elsewhere in the world. We’ll call their unique lineage the notoforms. Once they’ve fully colonized the island, the lack of competition will have several immediate effects: first of all, although their lack of an internal skeleton and the diminishing levels of atmospheric oxygen will still restrict them to only a dozen or so kilograms at the most, the abundance of food and the absence of any osteopods to compete will once again result in insular gigantism, with many species growing much larger than the vast majority of the mainland lophostomes, much like how the lack of mammals in New Zealand has allowed the giant wētā to evolve into one of the largest insects on earth. Another common occurrence among animals that migrate to isolated or uncolonized habitats is for them to undergo an adaptive radiation, rapidly diversifying into a multitude of different forms to fill all the unoccupied niches. An especially famous example of this is Darwin’s finches, which all descend from a recent common ancestor that arrived on the Galapagos islands within the last 2-3 million years that then promptly evolved into over a dozen different species. This effect will be particularly extreme on an island like Crescentia, since all the niches for animals larger than the malacoforms will be completely vacant when the notoforms first arrive, leaving almost the entire food web up for grabs. The original notoform species that first rafted to the island was a small, generalist omnivore, a lifestyle that many subsequent notoforms species may retain. But soon after they arrive, one branch may specialize for feeding on vegetation, evolving a large, powerful gut supported by bulky, weight-bearing legs and strong, compact mouthparts to masticate plant matter. Being indiscriminate herbivores, they won’t need the antennae-like sensory tentacles of the early notoforms to sift through the leaf-litter for food, so these appendages may shrink to not interfere with feeding, and their banded shell may acquire a distinct saddle shape to let them angle their heads upward to reach for food. We’ll call these herbivores thyreostracans. Meanwhile, another group may specialize for carnivory, evolving into the island’s first large predators. Like most lophostomes, the notoforms won’t be very nimble animals, with their stubby, boneless limbs only letting them manage an awkward waddling gait. However, the desmostracans are more manoeuvrable than most lophostomes thanks to their flexible banded shell, and reducing the shell even further will allow the muscles along their flank to contribute to locomotion, increasing their stride length by bending the body into an alternating S-shape. This will make them some of the fastest of all land-dwelling lophotomes, which in addition to other adaptations such as camouflage patterns to conceal them amid the undergrowth and sharp toothy mouthparts to latch onto prey, will let them fill the majority of the carnivorous niches on Crescentia, from small worm-like mesocarnivores to meter-long macropredators. Both the thyreostracans and these predators, which we’ll call campylospondyls, will continue to proliferate over tens of millions of years to exploit all the niches Crescentia has to offer, resulting in ecosystems completely unlike anything on the mainland. However, over the 50 million years following their arrival on the island, the conditions may eventually come into place for another rafting event to occur. Perhaps this time, a handful of small, arboreal platydonts will be cast out to sea within a tangle of fallen branches, brought by the currents to the shores of Crescentia. Even though by this point, the island will have been thoroughly colonized and its ecosystems filled, the arrival of these platydonts will pose a significant threat for the notoforms. Because islands generally have lower levels of competition and predation than the mainland, newly introduced species can quickly become invasive and cause considerable ecological disruption, as seen in species like the brown tree snake in Guam, the common brushtail possum in New Zealand, and the water hyacinth in Madagascar. In this case, these platydonts will present a new source of competition that the notoforms will have no way of preparing for, and will have a huge competitive advantage due to their internal skeletons and active respiration, which will let them exploit niches that are inaccessible to the notoforms and allow them to undergo an adaptive radiation of their own, giving rise to a new lineage that we’ll call the xenodonts. Since they’re already predominantly arboreal, the xenodonts may quickly come to monopolise the niches in the tree tops, feeding on leaves that the bulky thyreostracans on the ground can’t reach, and within the relative safety of the canopy, they can proliferate and evolve into larger forms. And following the changes in climate and atmospheric composition taking place during this period, the megafaunal notoforms will gradually begin losing ground, giving the xenodonts the opportunity to take their place as the Crescentia’s dominant fauna. One of the xenodonts’ most distinct advantages will be their speed, as their skeleton and limb configuration will give them more efficient locomotion than even the campylospondyls, which one clade may take advantage of to become fast, nimble predators. These forms may retain some arboreal behaviours, but may also exploit the relative lack of competition on the forest floor and spend time hunting at ground-level as well, with the hooked claws that originally evolved to help them climb trees now letting them to latch onto and disembowel their prey. However, such large claws will be at risk of being worn down from abrasion against the ground, so they’ll need to evolve some way of keeping them sharp. One solution is to keep the claw raised off the ground, like the foot claws of dromaeosaurids, or the retractable claws seen in most varieties of cats, the Madagascan fossa, and the grey fox, all of which rely on their claws to climb trees and catch prey, and so keep them retracted when not in use to prevent unnecessary wear and tear. Alternatively, another option is knuckle-walking, a fairly rare condition wherein the animal supports its weight on its knuckles, keeping the tips of the digits off the ground so they can be used for other purposes. Knuckle-walking can be seen in semi-arboreal animals like chimpanzees and gorillas, which use their dextrous fingers for handling food and climbing, but it’s also seen in animals that need to maintain long, sharp claws to help them feed, such as the giant anteater, which uses its huge claws to break open insect mounds, while the extinct chalicotheres, which used their claws to reach for and pull down tree branches, even saw the parallel evolution of both knuckle-walking and retractable claws. While the anatomy of the osteopod foot isn’t exactly equivalent to that of vertebrates, these xenodonts will have inherited flexible ankle joints from their arboreal ancestors to wrap around and grip tree branches, so when they come down to the ground, they may walk on their wrists with their feet bent backwards, keeping the points of their claws facing upward and away from the ground, a trait for which we’ll call them streptotarsans. Meanwhile, the relative lack of competition and bounty of vegetation may encourage some of the other xenodonts to independently evolve a ground-dwelling lifestyle and adapt into dedicated herbivores. No longer needing to remain light enough to be supported by the tree branches, these herbivores can now afford to grow much larger, evolving into a clade of heavy-set browsers that fill similar niches to the megalobrachids on the mainland, and convergently evolving strong, robust mandibles with flattened teeth to crush and grind down plant material, and a large, multi-chambered foregut to maximize digestive efficiency. Unlike the megalobrachids though, their front walking legs, used by their arboreal ancestors to reach out for and hook onto branches, may retain their large-sickle shaped claws to assist the pedipalps in reaching upward and pulling down foliage towards the mouth. Once again, these claws will need to be kept long for them to be effective in feeding, so these animals will also need to a way of preventing them from becoming worn down. But unlike the streptotarsans, which need to keep all of their claws sharp so they can be used for climbing trees, these exclusively ground-dwelling herbivores will only need to keep their feeding claws long, which provides an additional option beyond retractable claws or knuckle-walking. In other episodes, we’ve seen centaurism evolve in both the onychodonts and the allobrachids, in both instances evolving as a means to allow the animal to run faster and more efficiently, but in this clade, centaurism may occur as a natural consequence of evolving a ground-dwelling lifestyle, as only the hind three pairs of legs evolve to bear the animals weight, with the claws on these limbs becoming blunt and hoof-like, while the front limbs may become specialized for feeding by being held off the ground to stop their claws from scraping against the soil. This will make them vaguely analogous to animals like therizinosaurus, which, thanks to its centaurism, could afford evolve enormous rake-like feeding claws to reach for vegetation. Due to this distinctive feeding arrangement, we’ll call these xenodonts brachiocephalians. The brachiocephalians and streptotarsans will represent only a fraction of the diversity that the xenodonts will achieve over the tens of millions of years that they hold dominion over the Crescentian ecosystems, but even these creatures won’t be able to maintain their supremacy in the face of a rapidly changing climate. With the onset of the ice age, the landscape of Crescentia will change drastically, with most of the lush jungles giving way to seasonal forests and tundra. This will be a huge challenge for the native species, as most animals on Crescentia won’t have any form of thermoregulation, making them very sensitive to cold temperatures, and with the scarcity of food brought on by the retreat of the tropical forests, only a small minority of Crescentia’s former diversity will manage to survive. But on top of this, during the glacial periods, the stretch of sea between Crescentia and the eastern continent will shrink as the sea levels drop, and if the sea freezes over, it may be possible for animals to travel from one landmass to the other. Crossing a several hundred-kilometer stretch of sea ice will be a hazardous and impractical journey for most animals, but a small number of migratory or wide-ranging species from the mainland might be able to trek across the ice and find their way to Crescentia. The most likely animals to make a journey like this are small, adaptable species that are able to withstand the cold, which on earth include animals like the arctic fox and the Falkland Islands wolf, both of which were able to cross the frozen seaways that formed during the last ice age to arrive on Iceland and the Falkland islands respectively, and are both the only land mammals other than humans to ever inhabit their home islands. In this case, the allodonts living on the southern coast of the eastern continent are generalist enough to feed on whatever food they can find on the icy plains, and their endothermy will help them resist the cold once the ice age arrives, an advantage they may strengthen by evolving a shaggy coat of fur from the tiny setae that cover their bodies, a near-identical development to what occurred in the closely related thecopods, making the two clades appear very similar despite existing on opposite sides of the planet. For these cold-adapted allodonts, which we’ll call eriotheres, migrating south would present an escape from the fierce competition of the mainland, prompting at least one species to cross the frozen seaway to Crescentia. By the time they arrive, almost all the large xenodonts will have died out, so they’ll face very little competition as they move into the island’s megafaunal niches. And once the ice age ends, they’ll become stranded on Crescentia as the sea ice melts, leaving them to thrive in allopatric isolation just as the notoforms and xenodonts did before them, undergoing their own radiation over the coming tens of millions of years as Crescentia continues to slowly drift south. But Crescentia will be only one of thousands of islands scattered across the ocean, many of which will be too small and remote to be reached by crossing sea ice or land bridges, and for which rafting events will be vanishingly rare. By far the most likely animals to make it to islands like these will be the flying and semiaquatic clades, especially migratory species that are adapted for travelling over long distances. The first clade of animals to develop flight were the opisthopterans, and once long-ranging species like the magnopterans evolve, it won’t be long before some of them adapt for a sea-going lifestyle, soaring over the ocean and snatching acanthopods out of the water, much like seabirds and fishing bats on earth. For animals like these, remote islands will serve as ideal mating grounds, where they can carry out their courtship and lay their eggs without needing to worry about predators. This degree of safety may even encourage some animals to spend their entire lives here, which may go hand in hand with another development. Flight provides a number of distinct advantages, especially when it comes to dispersal and escaping predators, but it comes at a steep metabolic cost, hugely increasing the amount of food the animal needs to consume and requiring a number of anatomical specializations to be efficient. This means that if a flying animal finds itself in an isolated environment with few predators, then flight may no longer be useful enough to justify its energetic demands, and the species may end up losing its ability to fly altogether. As such, flightlessness is an extremely common evolutionary trend on islands, seen in groups like the elephant birds of Madagascar, kiwis and moa in New Zealand, dodos on Mauritius, and many many others. Becoming flightless may also allow species to expand into new niches with which flight would be incompatible. Since the majority of seabirds feed on fish, they obviously need to enter the water in order to find and catch their prey, but swimming and flying are very different forms of locomotion, mainly due to the drastic difference in density between water and air, and specializing for moving through one medium will unavoidably decrease the animal’s efficiency of moving through the other. This is exemplified by seabirds like the pelagic cormorant, whose short, broad wings help them steer while underwater, but also give them the lowest flying efficiency of any bird species. This tradeoff has also shaped the evolution of specialized feeding behaviours: some flying piscivores, like skimmers and greater bulldog bats, never enter the water but instead fly overhead and snatch up fish that swim near the surface, while others, like gannets and brown pelicans, dive into the water to pursue their prey. For species that specialize for piscivory, the pressure to evolve effective swimming may outweigh the benefits provided by flight, so becoming flightless will allow them to adapt more completely for aquatic life, and has consequently occurred in many seabirds, like penguins, great auks, and some varieties of waterfowl. Likewise, many of the island-dwelling magnopterans will no longer need to worry about evading predators or dispersing to new areas, so they can afford to give up flight entirely to let them more efficiently hunt aquatic prey. This flightlessnness may be accompanied by an increase in body size, not only due to insular gigantism, but also because larger sizes increase diving efficiency. This will be complemented by their efficient respiratory system and the internal support provided by their gladius, letting them grow into some of the largest lophostomes on the planet. To support a heavier body, their wings and canards, having a much greater degree of musculature than the boneless walking legs, may take over the role of locomotion on land as well, letting them awkwardly haul themselves along the ground, unlike most other opisthopterans, which fold their wings backwards when they land. These wings may shorten into a pair of powerful flippers to provide effective underwater propulsion, while the canards will help them steer and maintain stability, making their style of swimming less like that of wing-propelled divers like penguins and auks and more similar to foot-propelled divers like loons and the extinct Hesperornis. Along with a more streamlined body, they may evolve valves within their spiracles to let them hold their breath while underwater, and the regional endothermy that lets their wing muscles function optimally will also allow them to maintain a stable body temperature in cold water, which will be of great benefit once the ice age arrives, and will give them an advantage in competing with other semiaquatic clades like the aktatheres. These creatures, which we’ll call dyptopterids, will be just one of many opisthopteran clades that independently become flightless in response to their secluded island habitats, and once they’re sufficiently adapted for a semiaquatic lifestyle, they’ll be able to swim across the sea and reach other islands or even the coasts of the mainland, coming ashore to breed and to lay their eggs. However, the evolution of the dyptopterids will be shortly followed by the appearance of the pleuropterans, which, having also evolved flight, will share the same long-distance capabilities as the opisthopterans, and so will likewise be poised to spread across the planet and find their way to habitats that are unreachable for other clades. Since the opisthopterans evolved over 60 million years before the pleuropterans, they’ll have had a head-start in colonizing most islands, but a perfect opportunity for the pleuropterans may arise with one particular geological development. Over millions of years, underwater volcanic activity fuelled by hot spots on the planet’s mantle can produce plumes of rock large enough to emerge above the ocean’s surface, effectively creating brand a new island or even chain of islands as the crust slowly drifts over the top of the hotspot. On earth, islands like Iceland and Hawaii were formed through this process, and on our alien planet one such hotspot may occur in a remote region of the ocean, resulting in the formation of an archipelago that we’ll call Pyronesia. When they first form, these islands will be nothing but barren outcrops of solid rock, completely devoid of any native species, but even habitats as desolate as this will still attract species to colonize them. However, as this archipelago will be over 4000 kilometers away from the nearest coast, it will be almost impossible to reach by passive dispersal mechanisms like rafting, so flying animals will once again be the most likely organisms to find their way here, including not only the opisthopterans but also the newly evolved pleuropterans. Like the ancestors of the dyptopterids, the flying species that arrive on Pyronesia will likely be migratory acanthovores that come to the islands to feed and lay their eggs away from the perils of the mainland. As they migrate to the archipelago, they may unwittingly bring other clades with them, such as phoretic malacoforms clinging to their skin and the diaspores of plants adapted for animal-assisted dispersal like the chromatophytes. The populations that these species establish will slowly transform the archipelago into a stable habitat through a process called ecological succession, the progressive change in the structure and composition of an ecosystem over time. Succession can be subdivided into primary succession, in which an ecosystem forms in a brand new habitat with no pre-existing species, and secondary succession, when the ecosystem recovers after an ecological disturbance. Pyronesia will be a perfect example of the former, as the landscape will initially consist of nothing but newly exposed rock. The first stage of succession is initiated by pioneer species, usually small plants, lichens and fungi that are hardy enough to grow on bare rock, which, assisted by erosion from the wind, waves, and rain, will start to break down the rock into mineral-rich soil. In the case of Pyronesia, the pioneer species may include some of the chromatophytes, which, being epiphytes, are already adapted for growing in the absence of soil, and without any towering altiphytes around them to block out sunlight, they’ll have a much easier time growing on these islands than in the rainforest, forming a carpet of multicolored filaments along the ground. These pioneer species will pave the way for intermediate species like some of the other brachyphyte clades and various caulophytes, which will further contribute to soil formation until it ultimately becomes suitable for trees to take root. In most ecosystems across this planet, the niches of trees are filled by the xylophytes, but with the exception of the coelophytes, these plants aren’t well-suited for long-distance dispersal, as their diaspores are much smaller and more prone to desiccation than plants like the chromatophytes, making them comparatively unlikely to survive a trip all the way across the ocean. This means the xylophytes may not have much of a presence on Pyronesia, providing an opportunity for other plants on the archipelago to move into their niches. The xylophytes’ signature adaptation is their layer of rigid tissues that gives them the structural support to grow enormously tall trunks to reach upward for light, but although this has allowed them to become the dominant form of tree across the planet, it’s unlikely to be a unique adaptation. Even on earth, plant’s that we would recognize as trees have evolved independently across many clades, like for example, how palm trees are actually more closely related to grasses than to conifer trees. Similarly, on our alien planet, even though the xylophytes are the most widespread group of tree-like plants, there are likely to be many other plants that have convergently evolved tough, inflexible stems for greater support, and on Pyronesia, with very few xylophyte species to compete with, one such clade may now be able to grow into the archipelago’s dominant large flora, a clade of plants that we’ll call nothodendrons. And throughout the process of succession, new niches will also be opened for animals as well, which may incentivize the migratory opisthopterans and pleuropterans to take up permanent residence here and to integrate with the local ecology, and with no other diplostomes or osteopods on the islands, the conditions will be ideal for both clades to undergo an adaptive radiation to spread into every niche the islands have to offer. Unlike the ancestors of the dyptopterids, the opisthopterans on these islands will still need to contend with a considerable amount of competition and predation from the pleuropterans, and so they may still retain their flight to help them escape danger. Due to their limited size and lack of a true skeleton, they won’t be able to effectively compete for the niches of apex predators and megafaunal herbivores, and so will be relegated to the niches of malacovores, scavengers, and even frugivores and nectarivores, convergently evolving to fill similar niches to the picopterans and latopterans on the mainland. On the other hand, the pleuropterans will be at the top of the food chain, so once they begin adapting for ground-level niches, their flight may be more of a hindrance than an asset, with their wings restricting their movement through the dense groves of nothodendrons. But if they become flightless, the middle two pairs of legs and the wing membrane they support can shrink so as to not get in the way of the forelimbs and hindlimbs, which will be the only legs involved in locomotion, making these forms the only quadrupedal osteopods to evolve thus far, and thus giving them some of the most efficient locomotion of any land animal. In reference to the vestiges of the wing membrane connecting their legs, let’s call these animals chlamypterans. No longer constrained by the demands of flight, these chlamypterans will now be free to expand into new niches they would otherwise be precluded from. As mentioned in part 9, leaves are difficult to digest and don’t offer enough nutrition for folivores to maintain a very active lifestyle, making them a poor food source for flying animals, but once these theropterans become flightless, they won’t need to maintain such a high-energy diet and will now be better able to exploit the niches of large herbivores, similar to how the majority of ratite species took up herbivory after they gave up flight. To cope with a constant input of tough, nutrient-poor foliage, these theropterans may evolve an expanded, complex foregut like many of the megafaunal herbivores on the mainland, and an elongated cephalothorax to browse on the leaves of the nothodendrons. In compliance with foster’s rule, their body size will be contingent on the availability of food on their home island, which, while not enough to let them grow to sizes comparable to mainland megafauna like the titanopods, will still let these animals, which we’ll call hypsirhynchids, evolve into some of the largest animals on Pyronesia. And with clades like these filling the herbivorous niches, other varieties of chlamypterans may subsequently adapt to prey on them. Having evolved from the same flying ancestors as the hypsirhynchids, they’ll inherit the same long-legged gait, chasing down their prey in a sort of bounding gallop. Their pedipalps, used by their ancestors to snatch acanthopods out of the water, may evolve scythe-like claws to kill and dismember their prey, recalling large island-dwelling predators like the giant marabou stork and the enormous pterosaur hatzegopteryx. With the evolution of these predators, which we’ll call temnorhynchids, all the major niches of the Pyronesian ecosystems will be filled, and the process of succession will reach a point of equilibrium, culminating in what’s sometimes called a “climax” or “steady state” community. Processes like these will occur on each and every one of the innumerable islands on this planet, each one independently cultivating its own unique assemblage of species and ecosystems, with the few we’ve described here serving to illustrate a small selection of noteworthy island-dwelling clades to evolve throughout the planet’s history up to about 20 million years or so after the ice age comes to an end. But away from isolated habitats like these, there are other innovations quietly taking place across the planet at large that deserve special attention. In the next episode, we’ll return to the mainland to take a closer look at the evolution of sociality and cooperative behaviours. Thanks to all the artists over on discord who contributed artwork for this episode, who save me an enormous amount of time and effort when making these videos while simultaneously making them look a hell of a lot better in the process. Links to the main server and the alien biospheres fan server in the description. And once again, a massive thanks to all the patrons, whose continued support makes videos like this possible. Thanks for watching, and I’ll see you in the next video.
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Channel: Biblaridion
Views: 361,086
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Length: 46min 31sec (2791 seconds)
Published: Wed Jul 14 2021
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