The mid-equatorcene: 25 million years post-establishment

Now, 25 million years post establishment, the planet of chiroptosphere is starting to change. The supercontinent chiroptos is starting to split into two smaller continents, although it is still joined enough that species can freely move from one continent to the other. More of the land is becoming situated further away from the equator, making the land cooler. Much more of the forests are now temperate, and the planet has its first cold desert and boreal forest.

The chirolopes

The chirolopes are Chiroptosphere’s first clade of flightless herbivore. Descended from the pterosaur-like chirotaurs, they have now lost their wing membrane, but retained two of their wing digits, first only vestigially, but now they are being put to use again. Their teeth have changed to fit a herbivorous lifestyle, and their stomachs are currently being adapted into vegetation digestion machines. They are able to sense potential predators before they see them with the excellent sense of smell they inherited from their fruit-eating ancestors. A mutation that produced a single, bony, horn-like spike on their heads is quickly becoming adapted for interesting purposes.

The steppe chirolopes are very deer-like in appearance. They are adapted for fast running, turning both pairs of feet into hoof-like structures. On their front feet, two of their toes have evolved into a cloven hoof, while the other has stayed vestigial. Their hind feet more resemble the hooves of edmontosaurus, with one central hoof-like toe, the rest becoming vestigial. They use their odd, hollow horn to increase the intensity of their chirps, and can call with them to other herd members that are kilometres away.

The forest chirolopes are smaller, with more primitive feet. The front pair have two large supporting toes and one that looks vestigial until they stand bipedally- they then use one front paw to support themselves on a tree, and the other to grip high-up branches and bring them toward their mouth. Their back feet retain all five toes, but they are not yet suited for bearing the entire weight of the animal alone. Their horns are not used in intraspecific combat, but in display- those with a larger horn are more likely to get a mate. Unlike in most horned mammals, the horn is present in males and females, and the mate selection is done mutually.

For a few million years, chirolopes are abundant, but the introduction of any large herbivore to an ecosystem means a large carnivore will inevitably evolve to hunt them.

The dromeolocators

The dromeolocators are Chiroptosphere’s first clade of large ground predators. They are at a disadvantage to their prey, having inherited the strange, inverted hind limbs of their chiroschian ancestors, but they are finding innovative ways around this. They have also inherited their foggy eyesight and excellent echolocation abilities - a dromeolocator would not be able to see whether the object in front of them was a tree or a prey item, but with their echolocation they can discern a completely immobile prey item from the rock it is sitting on. Because of their prey’s astute sense of smell, they have learned to stalk their prey downwind.

The ambush dromeolocators, though big, are very good at hiding. Tigers can get away with being orange, for their prey is colourblind, while dromeolocators have to house algae in their fur to appear green. They lie in wait for hours, fooling all but other dromeolocators, until a chirolope walks by, and then they use their powerfully muscled legs to leap up to 13 metres toward their prey.

The pursuit dromeolocators, meanwhile, do not ambush their prey, but are still incapable of running because of their awkward limb configuration. The solution? They engage in chases where they hop toward their prey. Though this may look funny at a distance, the dromeolocators are incredibly powerful jumpers, and, for all their running prowess, the chirolopes often fall prey to them.

An unusual arms race

Since the chirolopes and the dromeolocators first evolved, an unusual arms race has been set in motion. The dromeolocators, descendants of microbats, locate their prey using echolocation- making sounds and then measuring how long it takes the sounds to echo back to them to decipher the shapes that surround them. At first, they used sounds that were out of the chirolopes’ hearing range. But it wasn’t long before a group of chirolopes appeared that could hear the sounds they made. This forced the dromeolocators to adapt a new sound frequency, which forced the chirolopes to evolve to be able to hear it. This arms race has been going on since the beginning of the two clades’ existence, and it will likely continue for millions more years to come.

The arms race has had two main effects on the two groups. First, their numbers are hugely variable over time; as the chirolopes and dromeolocators constantly gain advantage over the other, there are huge population booms and collapses. Second, even the individuals in each species have hugely variable frequencies of sounds and hearing ranges. This ensures the safety of at least a few individuals in a species should the other group gain the advantage, but it effectively prevents co-operation between more than a few individuals at a time, because many individuals’ sounds will be of a different frequency and they will therefore not be able to hear each other. Because of this, carnivores live alone or with their young, and herbivores live in small family groups of up to 15 individuals.

The chirosaurians

The chirosaurians are a clade of reptile-like chiroschians. Most of them are insectivores, but some eat small plants and seeds. They have retained the awkward limb configuration of their ancestors, albeit with some small changes to their hind feet that make walking easier, but they don’t really need anything more effective- their strategy is simply to run under the nearest bush when they hear something coming. The five toes on their hind feet have fused into one, bulky foot.

Notably, they are not warm-blooded- instead, they are mesotherms. They can raise their body temperature by just a few degrees on cold nights, but with their slow, lazy lifestyle, it would be a waste of energy to constantly expend effort to remain at the same temperature. Instead, they control their body temperature using two main strategies; they spend time in the sun or the shade when they want to be warmer or cooler, and to help this, they pump blood in or out of the remnants of their wings to warm or cool it, using them like the sails of some lizards. They have quickly colonised every available habitat, even the deserts, except the strip of boreal forest at the very north of the continent- it seems this clade has a bright future ahead of them.

The chirats

It was not long before one herbivorous clade started exploiting the wonderful ability of picking leaves off bushes with trunks. Descended from the basal plains chirolopes, the trunked chirolopes could reach higher than their cousins- however, their success was short-lived, as a group of long-necked chirolopes that we will discuss later quickly outcompeted them. Trunked chirolopes did not completely disappear, though- one group quickly adapted to become the omnivorous hyadonts.

The hyadonts are a unique clade of trunked animals in that they are not strictly herbivorous. Their diet consists of mostly fungus, roots, tubers, and bulbs, sometimes leaves, and the occasional carcass. They use their powerful dog-like nose, inherited from their fruit bat ancestors, to sniff out nutritious fungus and tubers. They then use their shovel-like trunk to dig them up. Sensory hairs on their trunk aid in this task. Although they lack the robust gut of their leaf-eating ancestors, their digestive system can still digest some kinds of rarer leaves, which they will again find with their powerful sense of smell. They will also use their noses to find carcasses left behind by predators, and some of them are becoming more and more specialised for this task. Like their ancestors, the plains chirolopes, their horns are hollow, used as a resonating chamber to amplify sounds. They call to other members of their small family groups to communicate the presence of predators or large amounts of food.

The hyadonts

It was not long before one herbivorous clade started exploiting the wonderful ability of picking leaves off bushes with trunks. Descended from the basal plains chirolopes, the trunked chirolopes could reach higher than their cousins- however, their success was short-lived, as a group of long-necked chirolopes that we will discuss later quickly outcompeted them. Trunked chirolopes did not completely disappear, though- one group quickly adapted to become the omnivorous hyadonts.

The hyadonts are a unique clade of trunked animals in that they are not strictly herbivorous. Their diet consists of mostly fungus, roots, tubers, and bulbs, sometimes leaves, and the occasional carcass. They use their powerful dog-like nose, inherited from their fruit bat ancestors, to sniff out nutritious fungus and tubers. They then use their shovel-like trunk to dig them up. Sensory hairs on their trunk aid in this task. Although they lack the robust gut of their leaf-eating ancestors, their digestive system can still digest some kinds of rarer leaves, which they will again find with their powerful sense of smell. They will also use their noses to find carcasses left behind by predators, and some of them are becoming more and more specialised for this task. Like their ancestors, the plains chirolopes, their horns are hollow, used as a resonating chamber to amplify sounds. They call to other members of their small family groups to communicate the presence of predators or large amounts of food.

The slobats

The slobats are Chiroptosphere’s first clade of animals specialised for climbing. They are descended not from any ground animal, but from a group of flying chirotaurs that would hang upside-down from branches with all four of their limbs. The slobats spend all of their time in trees, hanging beneath the branches like sloths. They have long, curved claws that they use to grip branches. They have only one of these claws on their forelimbs, a result of four of their digits having been used in their wing. On their hindlimbs, two of their five toes have been absorbed into their foot, and the other three have grown curved claws. Their young is not fully developed at birth, and so for a few months they cradle the pups on their stomach.

The basal slobats, also known as the upside-down slobats, are odd gliders. They have retained some of the petagium of their bat ancestors, as well as one of their wing digits, which is fused to their foot. They are active frugivores, and often glide from tree to tree in search of more food. What makes them unique is that, because they spend all their time hanging upside down, instead of pulling themselves upright before gliding, they actually just propel themselves off the branch and then glide upside down. To do this, they have undergone minor physical changes, including their eyes moving to the middle of their heads so that they can see both above and below them. They have spread through the rainforests of chiroptosphere.

The sloth slobats, a more specialised clade, originated from a group of herbivorous gliding slobats. Like sloths and koalas on earth, they get so little nutrition from their diet of leaves that they have to spend all of their time eating and move very slowly. They have lost their petagium, as their unenergetic lifestyle can no longer support gliding. Their mouth and teeth have changed greatly to accommodate plant matter, as they now have cheeks, and soft, blunt teeth. They inhabit both tropical and temperate forests.

Diversification of savannah herbivores

The earliest dedicated herbivore group on the planet were the chirolopes, which immediately diverged into the plains chirolopes and the forest chirolopes. Now, some time later, the plains chirolopes have further diversified into two more groups. The ancestral plains chirolope was a basic, antelope-like animal, with two-toed hooves on its front feet and one-toed hooves on its back feet. It had a hollow horn which it used to resonate sound, calling to other members of its family group from far away. This ancestral form has given rise to two successful new clades, the more basal gazirolopes and the very derived giralopes, both of which live on the open plains and savannahs of chiroptosphere.

The grazing gazirolopes are very similar to their ancestors. The main difference is that now, instead of having a keratinous sheath on the front of their toe, it is now on the bottom of their toe, which means their skin no longer takes the brunt of their galloping. Their resonating horn has also grown much thicker, forming no longer a horn, but a bump on their head.

The giralopes, on the other hand, are browsers. Their flexible necks have grown very tall to be able to reach higher-up leaves, the largest species sometimes reaching eight metres in height when they hold their necks up- the biggest animals chiroptosphere has seen so far. Their body has changed drastically to accommodate their long neck, with stumpy legs and a back that points downward. Their hooves have widened and flattened to bear the extra weight. Their resonating horn has become much smaller to lessen the weight the neck has to bear. At ten tons, they are too large to have fur without overheating, so they don’t. They also keep cool with the help of a loose flap of skin hanging off their neck, which doubles as a display structure, emblazoned with different colours and patterns depending on species, sex, and age.

Diversification of forest herbivores

The earliest dedicated herbivore group on the planet were the chirolopes, which immediately diverged into the plains chirolopes and the forest chirolopes. Now, millions of years later, the forest chirolopes have further diversified into two main groups. The ancestral forest chirolopes were quadrupedal deer-like animals that could temporarily lean on trees on their hind legs to reach for leaves. Neither their front or back feet had hooves, instead having five digits on their back feet and three gripping digits on their front. They also had a single horn on their head that was used in sexual selection, present in both sexes. This ancestral form has given rise to two new clades, the quadrupedal unilopes and the bipedal chirozinos, both of which are the dominant herbivores in the forests and rainforests of chiroptosphere.

The unilopes, named so for their single horn, are quadrupedal grazers. They don’t feed as much on grass as they do on bushes, as the forest floor isn’t as lush with grass as plains are. Their feet have convergently evolved into hooves, but unlike the gazirolopes and the giralopes, their back hooves are three-toed. They are experts at quickly bounding through the trees at the sight of something that might be a predator.

The chirozinos are bipedal browsers. Their ancestors, once needing a tree to lean against, got more and more comfortable standing on their hind legs, until they could walk, run, and lived their whole life on them. This radical change of posture has necessitated huge physical changes. For example, their feet have become plantigrade, their gluteus muscles have enlarged into buttocks, and their young, unable to balance bipedally at birth, have to ride on their mother’s back for their first few months of life. Large claws on their hands help them sort through leaves and defend themselves against predators. Their single horn has developed a sort of membrane, which is a variety of different shapes and colours depending on the species.

The suchosaurians

The crocodilian niche has been filled many times on earth, so perhaps it was inevitable that a crocodile-like animal would evolve on Chiroptosphere, too. The chirosaurians were perfect for this niche, as their mesothermy allowed them to spend most of their time resting in the sun and only occasionally eating. So, eventually one species gradually made the switch from insectivory to full carnivory.

The suchosaurians are crocodilians in every sense of the word. They hide in the shallows, their thick hide resembling floating branches and their long ears, used in echolocation, resembling floating leaves. When a large herbivore comes near the water, they strike, pulling the animal’s limbs off or pulling it into the water with a vigorous deathroll. Because of their mesothermy- they only regulate their temperature when they would otherwise freeze to death- they are able to go months without a big meal. They have lost their fur, as it would otherwise trap water on them when they crawl out onto land to warm themselves up, and instead they have thick skin to defend themselves from injury. They have forgone the specialised teeth of other mammals for the ability to lose as many as they need in hunting prey and then regrow them.

The herosaurians are fish-eaters that evolved from basal suchosaurians. They have a wildly different lifestyle, standing in shallow water and waiting for fish to assume safety from fish-eating bats in their shadow, and then snapping them up when they come too close. Unlike the rest of the chirosaurians, they are not sprawl-legged, which both allows them to stand with their bodies above the water and to grow to much larger sizes. The combination of their leg configuration, their easy diet, and their lack of need to spend energy on a constant body temperature has allowed them to grow to huge sizes, the largest species being 6 metres (20 feet) long. This giant size has allowed them to become gigantotherms, animals that are so large they can keep a constant body temperature without expending any energy toward it.

The rockodonts

For about twenty million years now, there has existed a clade known as the hyadonts, omnivorous animals that would use their short trunk to dig up tubers and roots. Some species supplemented their diet with the plentiful carrion, and recently one group has abandoned their previous diet and used their excellent sense of smell to become the planet’s first dedicated group of scavengers- the rockodonts.

Rockodonts have a range of different lifestyles depending on the species, but they all share some basic characteristics. Unlike their hyadont ancestors, their limbs are long and their bodies are not close to the ground. They all have trunks in some form, even if they don’t all use them for the same purpose. They all have an exceptionally good sense of smell that they use to find dead animals from far away.

Some rockodonts will actively attempt to chase the predatory dromeolocators away from their kills. They grind their front hooves on rock to sharpen them, and their trunks are shorter as not to get in the way of their teeth, though their trunks are still an important part of handling their food. They travel in family groups so their odds at chasing away a dromeolocator without injury are better. Other rockodonts will try to find carrion that has been abandoned. Though most of the meat will usually have been eaten already, the long-trunked species have a secret weapon- they use their trunks to grip rocks and use them to break the bones open, revealing nutritious bone marrow, a resource that only they can get at. They will collect rocks that are particularly good at breaking open these bones, and often pass them down to their children.

The next step: the early Expansocene