Athyrmagaia, Earth's Lost Brother

Our first destination in our exploration of life throughout Doppleganger (and our titular main focus throughout this project) will be the most spectacular and beautiful world of all; Athyrmagaia. Even back in the 29th century, when this planet was first discovered, finding planets with life on them was no longer that much of a surprise. Though they are indeed quite rare, our invention of the Alcubierre drive has made them much easier to find, reducing what could be thousands of years of space travel to just mere minutes or hours. This, paired with the comprehensive galactic mapping provided by the Fraternity, also aided in the process. Indeed, thanks to this technology, we now know of over 200 different worlds with life within the Milky way.

What makes Athyrmagaia truly special, however, is that it is one of the most Earth-like planets ever discovered, to the point that our researchers have even referred to it as "Earth's Lost Brother". This shouldn't be that much of a surprise, considering that the rest of the Doppleganger system appears like a crude replica of our own Sol, but it is nonetheless a very remarkable discovery. Not only does it have the same atmospheric composition (nitrogen, oxygen, argon and carbon dioxide), but it also has roughly the same mass, diameter, density and gravitational pull. It also has a carbon-based DNA/RNA biosphere, with microbes,  fantastical-looking "plants", "animals", and a variety of transitional life forms. By finding this planet, we have also found new friends and allies in it's native people, the Astutocentaurus, further adding to our list of interstellar comrades in the Fraternity.

The planet isn't without it's alien "quirks", however. The name we gave this planet is of Greek origin, and when translated to English, it means "Toyland". Indeed, many of the forms of life that live here look like they'd be at home in a child's toy chest. Others, however, might look like they came from your spouse's drawer. The "spiders" look like dolls, the "snails" look like toy trains and cars, and a seemingly endless amount of other life forms look like something best left unsaid. The native "plants" have cuticles made of a glossy bioplastic, and have clonal stems akin to stacked LEGOs. The dominant endoskeletal organisms are actually modular descendants of arthropod-like organisms, and they are capable of disassembling and reassembling their bodies at will. The Astutocentaurus can do this as well, and boy oh boy do they make the friggin' most of it. The organisms that could be considered "vertebrates" are evolved from radially symmetrical ancestors and some of the forms that live down under look like something out of Harald Stumpke's nightmares. 

Today it is the 40th century, and the entire sum of knowledge regarding this remarkable planet is the culmination of over 200 years of research. Even today, we are still learning more about this planet's biosphere, it's past, the origins of life, and the cultures of the many different native peoples that call it home. With the help of friends both on and off world, our knowledge of this world will continue to grow.

The Streaked Cavyhawk

 

While they have been around much longer and are still highly successful, the Pachyalatan Heteropods are not the only flight capable extant "bird" analogues on Athyrmagaia. Having denser bones than actual birds, Pachyalatans have higher body weight averages compared to Terran birds of similar dimensions, and are even more limited in terms of maximum size, the largest known non-flightless species only being capable of flight in short bursts. This proves to be disadvantageous, as it limits the altitude at which they can fly. It may have served them well over the past couple hundred million years, but it was only a matter of time until a more well-adapted competitor would colonize the skies.

Tracing their origins to an arboreal, predatory weasel-like Euathyrmatherian that lived in the canopies of a primordial Borean rainforest 73 MYA, the Polypterans ("many wings") initially started out as nocturnal gliders that hunted in forested areas. About 23 MYA, however, when the ancient forests started to recede and give way for great deserts, savannahs and grasslands, selective pressures eventually gave way to powered flight, and the Polypterans started to expand to a larger array of predatory niches, outcompeting Pachyalatan "birds of prey" and becoming aerial apex predators reminiscent of hawks and eagles. The complex modular, zooid-based biology of Athyrmatherians seems like it would be unfavorable and needlessly costly for a flying animal, but nonetheless the Polypterans have managed to modify this body plan to such an extent that they have become extremely effective fliers in their own right, managing to re-evolve powered flight independently from non-Athyrmatherian Arthropulmonians. This success is made possible by their possession of hollow bones and a unidirectional air sac system, which allows them to fly greater distances and achieve much larger sizes than their Pachyalatan competitors. At the moment, the Polypterans have left the other "bird" niches untouched, allowing for the continued existence of their apparently "inferior" Pachyalatan counterparts. If the right selective pressures take place, however, the Polypterans have the potential to replace the Pachyalatans entirely within the next hundred million years.

One family of Polypterans, the Rocida, has managed to give rise to some of the largest and most fearsome predators that ever took to the air. Named after the enormous elephant-eating birds of middle eastern folklore, the Rocids are a very diverse group of northern hemisphere predators, ranging from smaller eagle-like hunters of small monotherians and pachyalatans, to enormous, teratorn-sized predators that are large enough to kill livestock. The largest of these beasts tend to live in the mountains, where the absence of the more earthbound Polycarnivorans has given them to fill the role of apex predator in their stead. If their reputation as ferocious, almost mythological predators wasn't enough, Rocids also have a gruesome, if not downright disgusting mode of reproduction. Much like the flesh flies, the Rocids use the carcasses of their fallen prey as both a nest and a food source for their larvae, which are born moist-skinned and boneless before eventually emerging their hosts as composite neonates. Such a manner of reproduction would normally be unprecedented for animals of their size, but being Athyrmatherians, their multi-stage life cycles make this grotesque method of propagation a necessity.

The streaked cavyhawk (Deinopteryx agrestis) is an eagle-sized "solitary" Rocid endemic to the open grasslands of Borea. Though a comparatively small creature compared to other Rocids, it is still rather large by the standards of our own birds of prey, growing about as large as bald eagle at adulthood. It feeds on a large variety of smaller prey animals, with its main prey of choice being the prairie hopcavy (Batrachocavia gramineus). Despite its rather shrimpy size, it retains many of the same features as its bigger cousins. It has four wings, the primary upper abdominal pair being larger and used to create lift, and the secondary lower abdominal pair being smaller and used for steering like the tail fan of a bird. Both wing pairs are somewhat bat-like, and are comprised of collagen fiber and muscle reinforced patagium stretched out by elongated digits and a styliform bone in the elbow. Similar to pterosaurs, the upper wing pair contains air sacs that run down the length of the limb bones. When on the ground, the animal walks bipedally using the first wing pair as legs, bearing its weight on its thumbs and the knuckle of its second digit (first wing finger). Liftoff is achieved by vaulting with its wings. Uniquely among Athyrmatherians, the cranial zooid is directly fused to the thoracic zooid, and is unable to detach from the shoulders. The upper and lower "neck" tagmata are extremely lengthened, bearing a highly mobile elbow-like joint, and the auripods are located on the thoracic zooid rather than the neck. As an aerial predator, the streaked cavyhawk is well-armed for catching, killing and eating its prey. The labrum and gnathopods form a hooked, three-part beak with tooth-like serrations, with especially powerful "jaw" muscles that give the creature a powerful bite for tearing meat from the carcasses of freshly killed prey. The dewlegs of the thoracic and upper abdominal zooids terminate in powerful, recurved pincer-like claws used for grasping and seizing prey. These claws can exert enough force to break the bones of whatever unfortunate animal gets caught in its clutch. The smaller thoracic pincers house a pair of spinnerets, which secrete a fibrous silk used for nesting.

A "solitary" animal, the streaked cavyhawk lives most of its life on its own, and is highly territorial even towards towards other members of its species. They don't mate for life either, and as soon as the male finishes copulating, he leaves just as quickly as he arrives. The mother, on the other hand, is a dedicated parent, and looks after her offspring to ensure the continuation of her lineage. Like all Rocids, the streaked cavyhawk uses the carcasses of prey animals, specifically the prarie hopcavy, as edible nests for hundreds of maggot-like larvae that she births live. These maggots immediately burrow into the flesh of the carcass, and the mother suspends the carcass on a tree branch by wrapping it in silk, regularly marking the cadaver with a pheromone that serves as a deterrent for predators and scavengers. After about a week of feeding on the carcass, usually only a couple dozen of maggots of the original hundred survive, and twelve of them latch together in three groups of four, secreting mucus from their skin to form three composite cocoons. These cocoons, after twenty days of metamorphosis, hatch into three composite neonates that resemble snow white infant versions of their mother. From here on out, the mother cares for her three babies much like a bird would, feeding them pieces of meat from her kills. After about ten months, these babies grow into juveniles, and as soon as they learn how to fly they set off to live entirely on their own, reaching full maturity at five years old.

Pachyalatans of the Borean Steppe

 

Powered flight is a very ambitious capability for any animal clade to evolve towards. In order to fly, an animal not only has to be aerodynamic and capable of catching the wind, but also has to fight against the forces of gravity in order to stay aloft as long and efficiently as possible. Despite this, powered flight has evolved independently at least four times on Earth, so it seems like flight is almost a guarantee if the conditions are correct. With roughly 99% of Earth's gravity and an atmosphere of nearly identical density and composition, Athyrmagaia has also managed to develop its own menagerie of independently evolved flight-capable animals.

A very notable clade of volant creatures are the Pachyalatans ("thick fliers"), a class of flight-capable, warm-blooded Heteropods that are found on all parts of the planet. The Pachyalatans are the planet's closest analogues to birds, and have evolved to occupy a similar range of ecological niches in a world that is otherwise dominated by Athyrmatherians. They even resemble their Earthen counterparts in many ways, making them very far removed from the marine radially symmetrical lineage their earliest pisciphysan ancestors evolved from. Like all Heteropods, they possess four lungs, four vertebral columns, and an inverted upper jaw that opens upward, with the nostrils located on the sides of an immobile lower jaw and a specialized pair of front nostrils called a nasorium at the chin. Additionally, both male and female Pachyalatans possess a "genital tail", a specialized secondary tail used for reproduction as either a penis or an ovipositor. Their bodies are covered in fur and feather-like integumentary structures called pectinofibers, which are used for thermoregulation as well as aerodynamics. Their jaws, while inverted, are often beaked with an outer sheathe made of keratin. Their wings are composed of membranes of muscular, reinforced skin, which are supported by a thick, bony wingtip of heavily fused digits (hence the clade's systematic name). When on the ground, they walk quadrupedally by bearing their weight on their splayed-out hind limbs and the thumbs of their wings. For efficient and maintained flight, their four lungs contain unique channels and pockets that allow for a unidirectional air flow while breathing. Unlike either pterosaurs or birds, however, their bones are relatively dense and lack hollow spaces, which limits their maximum size and flight altitude. Despite this, their additional body weight does prove to be beneficial in flight, using inertia to make sharp turns and quick aerial maneuvers. 

The Pachyalatans have enjoyed a quite lengthy and prosperous existence, having first evolved roughly 315 MYA back when megafaunal Heteropods still dominated Borea and Comedia. Even after the Borea-Comedian mass extinction 230 MYA, the Pachyalatans have managed to reclaim their former niches, though it is uncertain if the modern Borea-Comedian Pachyalatan clade is descended from extinction event survivors or colonists from Austrus. Though they continue to be quite prevalent in the Borea-Comedian skies, they, like their terrestrial Saurophysan cousins, are facing a degree of competition from Athyrmatherian copycats. About 70 MYA, the Polypterans, a class of flight capable Euathyrmatherians, had entered the evolutionary scene, and at some point in more recent prehistory they managed to outcompete the Pachyalatans in the "bird of prey" niche thanks to their lighter bone structures allowing for larger body sizes. Considering the extremely malleable nature of the Athyrmatherian anatomy, it's entirely possible that one day these creatures may eventually replace the Pachyalatans as the dominant aerial fauna. For the time being however, the Polypterans have been unable to expand beyond the niches of aerial hypercarnivores, so the Pachyalatans have managed to endure the trials of natural selection. A very good sample of the diversity of Pachyalatans can be glimpsed in the grasslands and steppes of Borea, the largest continent on the planet.

    Yellow-chested seeder (Passermimus crocogastrus) - The yellow-chested seeder is a small, roughly pigeon-sized diurnal Passermimid ("passerine mimic"). Passermimids belong to a larger order of Pachyalatans called the Passercnemiformes ("passerine legs"), which are the planet's rough equivalent to perching birds. Named after the bold, yellow coloration of its chest, neck and abdomen, the yellow-chested seeder almost resembles a songbird when in flight, but once it lands on the ground it exhibits a quadrupedal, bat-like gait. The way it "perches" on branches is oddly bat-like as well, as it hangs upside-down with its reversed hind feet. Though it belongs to a clade of mostly tree-dwelling fliers, the yellow-chested seeder has adapted to its vast, open grassland environment by becoming a generalist ground forager, its diet being comprised largely of the dropped seeds of star grasses as well as small ground invertebrates such as Stegospondyls.

The yellow-chested seeder is represented by three genetically isolated regional subspecies. The eastern yellow-chested seeder lives in the steppes of Borea's far east, which intersect both the eastern and western hemispheres of Athyrmagaia. The two other subspecies, the greater and lesser yellow-chested seeders, lives in the two larger steppes at Borea's west, the fomer having a larger yellow chest marking than the latter.

     While largely solitary, the yellow-chested seeder mates for life in monogamous pairs, and have strong parental instincts. It is also migratory, traveling to the dry shrublands of southern Comedia during the winter seasons. It breeds during mid spring, and females lay a total of four to five eggs. Like a majority of Passermimids, it prefers to nest above ground in the branches of tree-like Olekirkophytes, and its young, which are initially blind and naked, grow to maturity at a fast rate. As adolescents, they typically learn how to fly by the time summer ends.

    Rainbow wangrouse (Galliphallus chromacalvus) - The rainbow wangrouse is a large, diurnal Phalliphasianid ("penis pheasant"), a family of medium to large-sized Pachyalatans that occupy a game fowl-like niche in the western steppes. The Phalliphasianids are representative of a much more basal group of modern Borea-Comedian Pachyalatans, and are presumed to be the closest living relatives of the prehistoric Pachyalatans that outlived the Borea-Comedia Mass Extinction Event. Though it is still capable of flight, the rainbow wangrouse is primarily a ground-dwelling creature that both forages and nests on solid ground. As a direct result of a more terrestrial existence, it is also a comparatively poor flier, and usually only flies in short, low-altitude bursts in order to evade predators. Most Phalliphasianids tend to be omnivores that feed on a combination of fruit, small herpetofauna and invertebrates. In the absence of fruit bearing plants in its native range, however, the rainbow wangrouse has become a generalist mesocarnivore, with its preferred prey being cold-blooded herpetofauna such as small Saurophysans and ophidimorph Tagmatasaurians. If available, it will also feed on fresh carrion. It is especially well-adapted for feeding on ophidimorphs, as they have evolved a high tolerance to their stinging, electrically charged bites. Bodies of water are relatively sparse in its range, so it gains a large bulk of its hydration from the food it eats.

    The rainbow wangrouse is a very sexually dimorphic animal, and males are significantly larger and more colorful than females. Aside from his bald, brightly colored face with garish wattles and combs, the most distinctive feature of the male rainbow wangrouse is his hypertrophied genital tail, which is tipped with a brightly colored, star-shaped fringe of retractable hydrostatic soft tissue that enlarges when pumped full of blood. Male wangrouses are typically solitary and highly territorial creatures, but during the breeding season of early spring, they will gather in large groups called leks to attract mates, displaying to females by wobbling their facial growths and waving their engorged genital fringes. Males with the largest and most colorful wattles and genital fringes are favored most by females, as the brighter and larger display features are apparently indicative of a healthier and more worthy mate. Unlike the yellow-chested seeder, the rainbow wangrouse does not mate for life, and males prefer to mate with as many females as possible rather than invest in a lifelong commitment to a single mate. Despite this, female rainbow wangrouses are dedicated and loving parents, and though their offspring are born with fully developed eyes and learn to walk within mere minutes, the mother diligently protects and raises her young until they are ready to live entirely on their own.

    With underdeveloped flight capabilities limiting their ability to travel, rainbow wangrouses do not fly south during the winter. To make things more difficult, the herpetofauna that the wangrouse preys on sleep off the winter by going into torpor underground, which means it is unable to hunt as soon as the cold sets in. To survive the winter, the rainbow wangrouse experiences a radical shift in diet, preying on endothermic Monotherians that remain active even during the midst of the cold season. It even has a winter season coat, which is greyer in color, and its skin changes from brightly colored hues to a purplish black, with the wattles receding in size. Their genital tail, which is prone to frostbite, is held flush against the chest and abdomen, kept warm by the animal's own body heat.

    Oxfeeding skeet (Culicirhynchus orlok) - The oxfeeding skeet is a small, nocturnal Proboscirhynid ("proboscis nose") that lives in the western Borean steppes. It is a member of a superfamily of Passercnemiformes that are highly specialized for a diet comprised of liquids. Proboscirhynids have evolved to feed by using a modified nasorium as a proboscis, to the point that it has basically become a secondarily evolved mouth that has entirely replaced the function of the true mouth. As a result of this, their actual mouths are almost entirely vestigial save for a small claw-like upper jaw, leaving the nasorium as the sole inlet for the buccal cavity. They retain both of their tongues, which are elongated and capable of darting in and out of the nasorium. Most Proboscirhynids are nectarivores or frugivores that live in forests and jungles, drinking nectar or injecting digestive enzymes into fruit to drink the liquid soup. Others, however, are predators, using their proboscis to skewer prey and inject them with a corrosive venom.

    The oxfeeding skeet is a unique outlier among it's needle-nosed brethren. It possesses the same straw-like proboscis as its cousins, but it is far too large in size for the rather small flowers of the plants that live in its native steppe, and none of them bear edible fruit either. As a result of this apparent scarcity of palatable plant-based food, it has developed a very literal taste for blood. Much like the vampire bats of Latin America, members of the genus Culicirhynchus ("mosquito beak") are ectoparasitic hematophages, and feed exlusively on the blood of large, sleeping endotherms. True to its name, the oxfeeding skeet's preferred source of blood are large-bodies Fauxungulates such as the mock ox. The creature feeds at night while its target is asleep, and using specialized heat receptors at the base of its upper mandible, seeks parts of it's target's body where the blood vessels are closest to the surface such as the zooid connection surfaces. It then uses its blade-like tongues to bore into the soft tissues. Its saliva contains a numbing agent, so as it drinks up its fill of blood, its sleeping prey doesn't even notice. As soon as its done feeding, the skeet rests and allows itself to digest its meal before flying back home. During the day, the oxfeeding skeet nests underground, digging burrows using the thick claws of their hind legs. Like many Passercnemiforms, it is a K-strategist that cares for its eggs and young.

    Though the skeet's feedings do not usually have long term adverse effects on their victims, this isn't always the case. When an oxfeeding skeet drinks the blood of large herbivores, it may also contract bloodborne pathogens in the prey animal's blood, which results in the skeet becoming an asymptomatic carrier that unwittingly spreads the disease to its other victims via its saliva. Additionally, at least 10% oxfeeders carry Vermibovis hematolateus ("blood-lurking cow-worm") a genetically chimeric endoparasitic Tumeofauna that has evolved to utilize the oxfeeding skeet as a means of spreading. This vicious parasite targets adult individuals of the mock ox species (of which it shares some of its DNA with), and spends its oocyte stage in the salivary glands of the oxfeeding skeet. When the skeet feeds, the Vermibovis oocyte germinates within the blood stream, and starts to steal mitochondrial DNA from neighboring tissues. By combining its own DNA with that of the host through meiosis, it then starts to self-replicate and spread mitochondrial hybrid offspring, which fuse with the host's tissues in the form of malignant tumors that spread through the blood stream, eventually killing the host by invading vital organs. The parasite remains alive for about 30 hours after the host's death, extending fruiting bodies through the tumors on the outside, and by giving off large amounts of heat with muscular vibrations, it coaxes the oxfeeding skeet to drink the infected blood of its fruiting bodies. If the oocyte manages to survive its journey from the stomach to the salivary glands, the reproductive cycle will continue anew.

    Unlike a lot of other northern hemisphere Passercnemiformes, the oxfeeding skeet does not have a set breeding season, mating whenever it is ready to do so and if current circumstances allow. It also does not migrate; to survive winter, it goes into a state of torpor within its burrow, surviving off of fat reserves it has accumulated from its feedings. If a female is pregnant while in torpor, she is able to essentially halt the development of the eggs entirely, with the egg formation process resuming as soon as she wakes up in early spring.

    Black wormtweezer (Vermivenator melanopterus) - The black wormtweezer is a crepuscular species of ground-foraging Locustarhynchid ("lobster beak") that is slightly smaller than the yellow-chested seeder. Apparently closely related to Proboscirhynchids, the black wormtweezer is part of a comparatively small family that exhibits a cranial anatomy intermediate between that of standard Passercnemiforms and more derived Proboscirhyncids. It is a proficient ground forager that lives in the northernmost areas of the steppes that border Borea's vast temperate forests, hunting invertebrates that dwell in the moister alluvials of this particular area. Its beak is long, thin and pincer-like, with a reduced yet still fully functional mouth at the very back of its jaws. Its tongues, which are elongated and tipped with dense taste receptors, are housed within the passages of the nasorium rather than the mouth proper. The black wormtweezer hunts its wormlike prey by inserting its beak into the ground, using it to detect vibrations while darting the tips of its muscular tongues in and out of its nasorium to find any edible organisms. As soon as it detects the taste or movement of an edible morsel, it quickly displaces the dirt with it's upper mandible to expose the organisms, quickly downing its food with quick snaps of its jaws. To ensure greater success in finding prey, it is most active during the mornings and afternoons, when the lower amounts of sunlight the moist, vulnerable "worms" to dwell closer to the surface.

    The black wormtweezer is mainly a solitary animal, breeding during early spring. Males do not form leks, instead establishing individual courting grounds in which they will encourage a female to approach by emitting a coarse, rasping groan. The male will then try to win the female over with a courtship dance involving wing movements and delicate, metronome-like twitches of his upper mandible. The male is not in any way involved in the rearing of young, and will instead aim to copulate with as many females as he can. The female, however, remains a dedicated parent, and will look after her young until they are fully independant. Unlike many other Passercnemiforms, newborn wormtweezers are born with already opened eyes and a full coat of downy pectinofibers. Being dependant on their mother's however, they will cling onto her back and belly until they are large enough to keep up to pace with their mother on foot. During the winter, the black wormtweezer flies to the tropical rainforests of Borea's deep south, where food is plentiful year-round.

The Prairie Hopcavy

 Though one of the defining characteristics of the Athyrmatherians is their modular, zooid-based physiology, this trait is not as ubiquitous as it may seem. Some lineages, such as the Polycarnivorans, are diontogenetic, with a growth series that diverges into two separate adult morphs. The secondary adult morph is a singular animal that never becomes a zooid, retaining the relatively unmodified bauplan of its larval stage via neoteny. In most cases, these "paedomorphs" are nothing more than an alternate growth stage. However, there is a very notable exception. In the shadows of much larger modular creatures, Athyrmagaia's rodent and insectivore niches are filled by the diminutive Monotherians, a diverse superorder of Euathyrmatherians that have completely forgone the modular adult growth stage in favor of being fully functional, independent animals. Seemingly evolving from the same branch as the Polycarnivorans, it is not entirely understood how the Monotherians evolved or when. One of the most commonly accepted theories is that these animals evolved as a result of the paedomorphic and composite adult stages of an ancestral species becoming reproductively isolated from one another, a phenomenon that occasionally happens among extant Polycarnivorans today. The earliest known Monotherians in the fossil record were subterranean, mole-like animals similar to the paedomorphs of modern Polycarnivorans, but over millions of years of evolutionary time. the order has achieved a staggering level of biodiversity. They are currently one of the most speciose groups of Euathyrmatherians alive today.

One order, the Eumonotherians, looks remarkably similar to mammalian rodents at a passing glance. They walk on four limbs, have bodies covered in insulating fur, and have a set of what resemble "incisors" in the front of their mouth. Also, unlike many other Athyrmatherians, Monotherians have managed to evolve true viviparity, and give live birth rather than lay eggs. Their surface level resemblance to our rodents, however, is merely a form of convergent evolution. Upon closer inspection of their external and internal anatomy, their Euathyrmatherian affinities become crystal clear. Though they possess an internal hydroxyapatite skeleton, they are not vertebrates, and actually belong to Athyrmagaia's "arthropod" phylum, the Stegospondyla. Rather than a proper spinal column, their backbone is comprised of two stiffened girdles formed from fused, internalized tergites, which are connected at the middle of the body by a ball-and-socket joint. This backbone is much more rigid than a proper vertebrate spine, a consequence of their ancestors having heavily compressed bodies that relied on their modularity for body flexibility. Due to this, their bodies are poorly optimized for mammalian style cursoriality, so rather than running, Monotherians have adopted a frog-like saltatory (hopping) gait, possessing long frog-like hind legs with elongated toes. Their ears also lack pinnae, appearing as a pair of similarly frog-like tympanum (external eardrums) behind their eyes. These ears have evolved independently of the limb-derived auripods of their modular ancestors. What appear to be their "incisors" are actually insect-like mouthparts, consisting of an upper labrum and two lower mandibles capable of independent movement. Unlike other Euathyrmatherians, however, the horny parts of the jaws do not contain a bony core, and instead grow from sockets at the tips of the jaws. These pseudo-teeth are constantly growing and self-sharpen with use. Forever freed from the developmental constraints of modular zooid specialization, the forelimb digits (which are fused into singular claw-like bones in most other Euathyrmatherians) have secondarily re-evolved articulated joints via a process analogous to hyperphalangy. Unlike diontogenetic paedomorphs, which have an extremely simplified through-gut, Monotherians have re-evolved a more organized and specialized digestive system, complete with a stomach and intestines. As a consequence of their ancestors being mole-like fossorial creatures, Monotherians have relatively poor color vision compared to their relatives, and ground-dwelling predators that specialize in preying on them do not need to use biliverdin for camouflage.

In the great Western Weave of Borea, one of the most common animals is the prairie hopcavy (Batrachocavia gramineus), an herbivorous, cavy sized Eumonotherian that resembles a hybrid of a toad and a hamster. Hopcavies are crepuscular, being most active during sunrise and sunset. In between these periods of activity, they sleep in underground burrows to conserve energy and avoid the mid-day predators. Their main source of food and water are the leaves and seed-bearing florets of star grass, and they play a part in dispersing their seeds by defecating. These animals are mostly solitary, but in the cases where they meet one another willingly, they mate for life. Prairie hopcavies are a potential food source for a multitude of predators, being one of the main prey items of choice for a species of large predatory flier that patrols these open landscapes. Fortunately, hopcavies are more than capable of evading danger and defending themselves. Their powerful hind legs allow them to jump great distances, and their chisel-like mandibles (which are specially adapted for chewing through tough PLA-based vegetation) are sharp and powerful enough to leave painful, bloody bite wounds on a would-be predator.

Ruminantiforme Skull Morphology

 

Ruminantiforme Euathyrmatherians are superbly well-adapted for herbivory, and no other part of their skeletal anatomy reflects this better than their skulls. From the outside, the head of an animal such as Xenobos almost resembles that of an Earth tetrapod, with the horny beak calling to mind herbivorous ornithopod dinosaurs in particular. However, upon inspection of the bones, the skull morphology is unmistakably that of an Athyrmatherian. What appears to be the animal's jaw is actually a specialized pair of forelimbs called "gnathopods", and the maxilla is actually a hinge-jointed upper mandible called a "labrum". Though Ruminantiformes have mastered the ability to slice and chew the tough leaves of Olekirkophytes, they don't have any true teeth in the traditional sense.  In place of incisors, they possess a broad, external horny beak at the tips of their jaws, formed from the rhampotheca of the labrum and the "nails" of the gnathopods. In place of actual molars, they possess an alternative processing system formed from the actual lower mandibles and flat, molar-like papillae on their palates. Both the papilla and the mandibles form four grinding plates sheathed in iron oxide-reinforced keratin. Much like the teeth of rodents, the papillae and the sheathes of the lower mandibles are constantly growing, so Ruminantiformes keep this growth in check by bruxing. To ensure their food doesn't fall out of their mouths, Ruminantiformes have evolved a "cheek".

Due to their very alien oral anatomy, the method by which Ruminantiformes chew their food is hard to compare to any Earth analogues. The general chewing style of the internalized lower mandibles closest resembles an inverted version of that of a hadrosaur, with the inside surface of the mandibles sliding and grinding against the outside surface of the papilla. Unlike hadrosaurs, however, the mandibles move in an elliptical cyclic motion, moving forward and grinding against the papillae as they move backwards. This allows Ruminantiformes to chew and swallow their food at the same time, and they repeatedly regurgitate the partially digested cud to repeat the process until the food is ready for further stages of digestion.

Fenrir Skeletal Anatomy

 

Like most Athyrmatherians, an individual fenrir (Cynorhynchus lycanthropus) is not one, but multiple separate animals (or zooids) that attach in a single file line to form specialized tagmata, with the attachment being facilitated by a combination of specialized jaw and tail-derived couplers, tessellation, and an industrial strength airtight seal composed of a fibrous mucus. While this anatomy is extremely bizarre by the conventions of animals from Earth, it is par for course for these unique beasts, and is so well-developed that it would be nearly impossible to identify them as modular without any prior knowledge of their biology. What sets the fenrir and its relatives apart from other Euathyrmatherians, however, is their adaptations for pursuit predation. True to their genus name (Cynorhynchus = "dog beak"), fenrir have developed adaptations that largely mirror those of our own canids. Their thoracic and abdominal locomotor legs have extremely mobile shoulder bones that attach to the axial skeleton solely by muscle, and have lower limb bones that are slightly longer than the upper limb bones. They are also digitigrade, supporting a majority of their body weight on their phalanges without the actual foot bones making contact with the ground. The pelvic locomotor limbs emulate those of canids as well, even though what appear to be their thighs are actually modified "shoulders", and their "ankles" are actually elbows. The anterior and posterior tagmata of each zooid have a high range of up and down motion and a moderate range of side-to-side motion, allowing for the animal to gallop very efficiently. Their jaws, while weaker than those of the contemporary, more cat-like Cephalovenatorids, are nonetheless well-reinforced in order to withstand the stresses and forces of struggling prey, with a firmly anchored labrum (upper jaw) and stiffened joints in the gnathopods. The telson, which is usually made of a stiff rod of bone in other groups, is instead composed of more flexible cartilage in fenrir, and is used for both stability during pursuit and communication between pack members.

The Steppe Fenrir

 

Where there are herbivores, there are undoubtedly predators that hunt them. On Athyrmagaia's two largest continents, Borea and Comedia, the niches of warm-blooded macropredators are occupied by the Polycarnivorans, an order of Euathyrmatherians that are almost ubiquitous across both of the neighboring continents. The Polycarnivorans are divided into two major suborders that have representatives on both continents, the roughly canid-like Cynorhynchiformia and the bear or cat-like Cephalovenatiformia. A very fragmentary fossil record indicates that both of these suborders evolved as a result of geological isolation between two populations of a shared common ancestor, with the rising sea levels that followed the end of an ice age submerging an ancient land bridge that connects the two continents. The isolation resulting from the flooding of this land bridge caused the evolution of the Cynorhynchiformia on Borea, and the Cephalovenatiformia on Comedia. Eventually a second, albeit shorter ice age exposed the trans-continental land bridge once more, and the biotic interchange that immediately followed allowed the two lineages to immigrate between the land masses, with niche partitioning allowing some of these species to coexist. Despite a number of differences, there are a number of traits that unify the Polycarnivorans as a single order: most of them are Diontogenetic, possessing a bifurcating growth series where the runts of the litter never become zooids, instead setting off on their own to carve out a separate niche. Polycarnivorans also exhibit either a heavily reduced posterior sclerite or lack one entirely.

On Borea, the durable, hard-to-kill modular physiology of Athyrmatherian prey has provided selective pressures that favor cooperative or semi-cooperative hunting strategies. As a result, the most prevalent family of endothermic predators are the pack hunting Cynorhynchidae. The apex predators of many of Borea's habitats are the fenrir (Cynorhynchus lycanthropus), large, highly adaptable Cynorhynchid pursuit predators that rival our own grey wolves (Canis lupus) in overall size. There are several subspecies of fenrir that have adapted to various environments. One subspecies, the steppe fenrir (Cynorhynchus lycanthropus steppe) has adapted to hunt in the vast steppes and savannahs that comprise the middle of the continent, with their primary prey of choice being the mock ox (Xenobos borealis). Fenrir are exceptional predators, with both deadly weaponry and very keen senses at their disposal that allow them to track and apprehend prey. Their sense of smell is very powerful, and their olfactory turbinates so extensive that they partially wrap around their brain. Like many of our own predators, fenrirs possess binocular vision, with their eyes facing forward to allow for depth perception. Their auripods, ears derived from an internalized pair of limbs, are pointed and highly mobile, and are used to triangulate the origins of sounds. Their three-part beaks are attached to powerful muscles, with serrated tooth-like projections on both their gnathopods and labrum for slicing and ripping flesh. Sharp, blade-like internal mandibles and palatine papillae function a lot like carnassials, and are used to shear meat. The locomotor legs of the thoracic and upper abdominal zooids bear a hypertrophied, semi-retractable sickle claw on the outside of each foot, which is kept raised off the ground in order to prevent unneeded wear. The sickle-like claws are similar in function to those of our extinct dromaeosaurs, as the fenrir use them for prey restraint, hooking deeply into the hides of their prey with a deadly grip. Last but not least, the dewlegs of the thoracic zooid have evolved into raptorial limbs tipped with sharp, dagger-like claws. These claws serve as puncturing instruments for breaking the airtight mucus seals between their prey's zooids. Since a majority of Euathyrmatherian herbivores possess full color vision, dull and drab colors are not sufficient enough for effective camouflage. To combat this, many species of Fenrir (and a lot of other Polycarnivorans as well) use biliverdin as a pigment for their skin and hair, giving them a green color that allows them to more easily blend in with surrounding foliage. Steppe fenrirs in particular possess a vertically striped coat that breaks up their silhouette amongst the leaves of star grasses, which can range from green to a yellowish color. They also have seasonal coats; during the summer, their fur turns from green striping to white and brown striping to match the seasonal pigment changes of the grass.

When taking down large herbivores, fenrir utilize a highly coordinated strategy to ensure that every single zooid of their prey's body is incapacitated before they eat. Four fenrir attack from the sides, charging at the flanks before grappling with their sickle-clawed thoracic legs. Once they have a hold, they puncture the mucous seals between the body zooids with their raptorial arms, proceeding to rip out large pieces of flesh and pressure supporting adipose tissue from the edges of the connection surfaces with their jaws. As this happens, another pack member attacks the cranial zooid, biting the throat to rupture the hearts inside the neck. Eventually, the fenrir attacking the sides gouge out so much soft tissue from around the connection surfaces that the prey's coupling joints break due to the lack of support, causing the zooids separate and fall apart. From there, the pack members will start to feed on the still barely living zooids, plunging their serrated beaks into the delicate distribution membranes to more easily access the nutritious viscera.

Much like our own wolves, fenrir are highly social pack hunters that live in altruistic packs. The size of a pack may be variable between regional populations and subspecies, but usually a pack can range in size between 2 to even 12 members, with 4 to 7 members being the average. The pack structure is different from that of wolves however, with a much looser hierarchy where the members of the pack are more or less equals. Most species live, sleep and breed in simple underground dens, which are often dug near rocky outcroppings. As is the case for most Polycarnivorans, fenrir are diontogenetic, possessing both a zooid-based composite adult form and a smaller, non-modular paedomorphic adult form. Rather than setting off on their own to live a separate niche, however, paedomorphic fenrir remain as a part of the pack, and have a mutually beneficial relationship with their modular brethren. This mutualism is so tightly knit that they are able to recognize each other as the same species. Paedomorphic fenrir are called "denkeepers" and their role in the pack is to maintain and guard the pack's den as well as look after the developing offspring while the bigger and stronger fenrir are gone. As a reward for its contributions, the denkeeper is brought back its own share of a kill following a hunt. This social dynamic is completely unique to the Cynorhynchus genus. Pack members, fenrir and denkeeper alike, consolidate bonds by grooming one another.

Fenrir are oviparous, and females produce 25 miniscule, marble-sized eggs that spend half of their incubation period within their mother's body. The mother then lays her clutch in the den to spend the remainder of their incubation period under the denkeeper's watchful care. Eventually, the eggs hatch into separate unspecialized larvae that are born sexless. If all these eggs survive, 24 of these larvae link together in groups of 4 and then pupate, emerging as 6 composite fenrir "pups", becoming either male or female as they develop a composite body plan. The remaining 25th larvae, however, will remain independent, and grow into a denkeeper instead. Mothers feed their pups by regurgitating partially digested meat stored in their crop.

The Mock Ox

 

Of all the Euathyrmatherian Fauxungulate herbivores that inhabit Athyrmagaia, among the most successful clades of all would have to be Borea's Ruminantiformes. True to their name, the Ruminantiformes have the most well-developed foregut fermentation system of any herbivore on the planet, utilizing both symbiotic, proteinase K-secreting gut microbes and a specially evolved, multi-chambered crop in their thoracic zooids to break down the tough PLA-based tissues of Olekirkophyte foliage back into lactic acid and lactide. Superbly adapted for herbivory, the cranial zooids of many Ruminantiformes almost resemble the heads of ornithopod dinosaurs at a passing glance, with a short, broad three-part beak at the tips of the upper mandible and gnathopods, evolved for cutting or cropping vegetation. They have also evolved the ability to chew, and the internalized lower mandibles and palatine papillae have been modified into mineralized grinding plates. One of the chief clades nested in this highly prolific lineage of herbivores are the quite fittingly named Xenobovidae, a family consisting of both large-bodied heavyweight grazers and lithe, antelope-like sprinters. A trait that sets this particular family apart from other related Ruminantiformes is their possession of ceratopods, a pair of modified limbs at the front of the thoracic zooid that are each tipped with a single enlarged claw. The ceratopods are essentially mobile horns, and are often used for either combat, display, or even both.

 

The second largest and arguably most iconic member of the Xenobovidae family is the diurnal, grassland-dwelling Xenobos borealis, a large-bodied ox-like herbivore roughly equal in height and weight to a domestic dairy cow (Bos taurus) but exceeding it in length. Xenobos borealis, or the "mock ox" as it is more commonly referred to as, is a very common sight in Borea's grasslands, particularly the Western Weave and Central Savannah, as its diet is mostly comprised of various species of Astrogramineae (star grasses). Like most Ruminantiformes, Xenobos walks in an unguligrade fashion, supporting its weight on four-clawed hooves. Aside from its large size, one of the most distinguishing features of Xenobos borealis is its greyish brown body hair, with a black stripe running down from the tip of its upper mandible to the nape of its neck, and an additional white stripe over its eyes and a red stripe on the cheek for males. The posterior sclerites (the keratin plates on the top of the lower abdominal zooid) are ossified and covered in an array of sharp keratinous spines. This appears to have evolved as a defense against predators, as the spiny backside of the animal often discourages carnivores from attacking directly from behind. The ossified core of this armor plating also plays a role in calcium storage, and gravid females recycle this extra calcium to help form the bones of their developing calves. Both sexes possess thick, inward-curving ceratopods that are held forward at a neutral stance. Males (or bulls) have longer and more curved ceratopods than the females (cows), and in both sexes they can be used as effective weapons for self-defense. In the case of bulls, the ceratopods can be used to fight against other bulls to compete for mates.

Like nearly all Athyrmatherians (and EXTREMELY unlike our own bovine mammals), Xenobos borealis is oviparous, though it has altered this method of reproduction in a manner that closer resembles live birth. Xenobos, along with a majority of Ruminantiformes, are semi-ovoviviparous, and rather than laying several eggs that hatch into larvae that couple together post-hatching, impregnated females produce a single, extremely elongated egg that houses four developing quadruplets of the same sex, which couple together as soon as their mandibles develop and partially metamorphose into a single "composite infant" while still in the egg. This quadruplet egg is incubated internally for about 250 days, and when the incubation period is finally complete, the gravid female lays the egg, which breaks open upon impact with the ground much like a mammalian placenta. From there, the newly hatched composite baby (or "calf") is cared for by its mother until it is old enough to live on its own, and rather than feeding her calf from a teat (Athyrmatherians do not lactate), the mother feeds them cud regurgitated from her foregut, simultaneously sharing the essential PLA-processing bacteria with her child. Despite part of their metamorphosis taking place while still in the egg, the composite infant and adult forms of Xenobos fully retain the nearly ubiquitous ability to separate and reattach their body zooids at will.

Xenobos borealis is a very social animal, with cows living in large maternal herds that travel and eat together. These maternal herds are highly altruistic, and the cows will occasionally even take turns looking after each other's calves. When the herd is threatened by a predator, the herd members will arrange themselves in a circular defensive formation and surround the calves and pregnant females, their spiny, armored backsides facing outwards to fend off the attacker. They are also migratory, spending a majority of spring and summer and in the grasslands and savannah but moving to the xeric shrublands further south during the fall and winter. Bulls, however, live largely solitary lives, and the only time bulls ever meet together is during the mating season in spring, where they will gather near herds of cows and compete for mates via intraspecific combat. Battles between Xenobos bulls tend to be rather gruesome, as it usually involves the two opponents trying to forcefully decapitate one another using their ceratopods until either one of them yields or gets decapitated. While Xenobos are naturally capable of dropping their own heads at will, having their heads be forcefully removed can potentially be devastating to their livelihoods, since it may irreversibly damage the nerve conduits or even break the coupling joint that connects the head to the shoulders. Due to this, if one bull ends up losing his head during a duel, it often ends up being his last.