Muridiungulate Strongholds, Part 1: Choeropican Woodlands

After the recent infilling with sediment of its central sea, Choeropica is now Apterra's largest island continent (not counting Ailuropia), with a land area just larger than that of Unciolis, or more than Post-Abeli, Aglirium, and the Northern Isle put together. Being humid and tropical, it's also the most biodiverse insular ecosystem, with only Aglirium coming close. It is home to the endemic sappybaras, a clade of Muridiungulates distinct from the rattaloxen and basketbucks that populate the rest of the world. Their first giant member, the sappopotamus, lived twelve million years ago and has no living descendants. In its place, over twenty species of Muridiungulates now inhabit Choeropica and its surrounding island chains, but this list will only include eight that live in the same area, the tropical woodland mosaic in the center of the landmass, where what was once a shallow sea has become a network of stagnant wooded wetlands, open lowlands, savanna foothills, and scattered peaks with fully closed canopies.

Section 1: Muridiungulate Ecology

With a slender frame convergent on large basketbeests and cursorial oxen, the Jadetooth (Dromaeotetradactylus viridens) gets its name from the permanent green stain that covers the front of its incisors. It lives on a diet of jade skystalks, sodstalks, sweetheart bushes, and other ground-level Saccharophytes, and it accordingly lives a high-metabolism lifestyle, fueled by abundant simple sugars in its diet. It feeds so selectively on the sweetest vegetation that its digestive system resembles something closer to a frugivore than to most other grazers, with only a small fermenting chamber for the portions of its diet that aren't so easily digested. 

Jadetooth troops are led by a matriarch, usually the mother of all the other adult females, who herself continues reproducing into her old age. At nearly a decade old, she has the knowledge to teach the youngest members of the troop how to find good feeding grounds, how to distinguish high- from low-quality grasses, and how to look out for predators while still getting a meal. To prevent inbreeding, the matriarch usually allows two unrelated males to reside with the troop - one to be her exclusive mate, and one to mate with her daughters. If she lives to see her granddaughters come of age around their third birthday, she will find a young male suitable for them. As for her sons and grandsons, they must leave the troop before they turn two, join a temporary herd without a territory, and eventually win favor with a new matriarch if they ever want to settle down again.

Like most Muridiungulates, the jadetooth has its own unique head ornamentation. Its snout is expanded into a large nasal chamber, which in both sexes helps to sift out dust and resist pathogens in a habitat where disease loads can be oppressive. So too can external parasites, but they can be removed using using a narrow gap between the incisors. Combing through one another's fur in this way is the jadetooth's main means of affirming social relationships, as it requires a level of trust that the recipient will return the favor. But there are times when a jadetooth must communicate not-so-friendly intentions, such as when males compete for acceptance into a new troop. They display their inflated noses for all the females, but it is ultimately the matriarch who makes the decision. She may choose a male who doesn't have the best display if he seems strong and healthy enough for her family. Meanwhile, the rejected males may still get the chance to mate with lower-ranking younger females while the matriach is distracted.

The Briarpelt (Aculeophorus armatus) is by far Choeropica's largest true frugivore, standing over two meters high and weighing just shy of a ton. Though it browses a bit on high-quality trees and bushes, most of its year-round diet comes from the abundant fruits of the island continent. Choeropica has become the center of global fruitgrass diversity, with over a hundred species. Some take the form of pseudrotrees, growing three to twelve meters high. Most pseudarborescent fruitgrasses still bear their inflorescences at ground level, emerging from a rhizome next to the main stalk. This prevents the foliage from being damaged by overzealous herbivores, and it leaves the fruits in easy reach of as many terrestrial dispersers as possible. Others are hemiparasites, stealing nutrients from host palm-grasses while photosynthesizing for energy. Epiphytes grow from one tree to the next, including high-powered bloatseeds that can shoot their ripened fruits across twenty meters to disperse to new areas of the canopy, assuming they aren't eaten and deposited somewhere by an arboreal animal first. 

Segmented Voidfruits (Polycavitofructus) are an endemic genus responsible for as much as 25% of all fruit biomass on Choeropica. Sister to floatseeds and bloatseeds, these plants have compound fruits that develop from 4-12 individual florets that fuse together shortly after pollination. Each fruitlet grows quickly, leaving a hollow space above the seed. Unlike in other void fruits, these chambers are not completely closed off. The air pockets grow toward the base of the fruit, where specialized bracts act as one-way valves. When pressure builds within the fruit, a puff of air is released, along with a cloud of volatile chemicals that alert fruit-eating animals of its ripeness. With over twenty species and niches varying from pseudarborescent to epiphytic to semi-aquatic, there is almost always at least one segmented voidfruit in season at any given time, and while their vegetative bodies may be diverse, their fruit morphology has little variation from one species to the next. This allows them to serve as an unspecialized staple food for many frugivore species, each of which may be an effective disperser for only one or two voidfruits. 

The last major component of Choeropica's fruiting flora is the Ramblingvine (Neoacuphyllum), a group containing five species on Choeropica and another three throughout Ailuropia. Individually, its fruits are less than a third of a centimeter across, with a seed the size of a sand grain. Over a hundred may grow together in a single aggregation, and 20 to 50 of these clusters are borne at the end of every fruiting stalk. There is no internal hollow space, as this genus comes from the other side of the fruitgrass family, descended from drunkgrasses. Fermentation is no longer part of its strategy; in fact, it seems more adapted to keep away potential dispersers than to attract them. It grows as a thicket, with long thorns protecting every leaf node. Vines can support their own weight up to three meters or so off the ground, and after successive years of growth, old stems can support new ones, allowing the thorny mass to reach five meters tall and thirty across. Ramblingvines grow best well above the water table, on the heavily wooded hilltops that experience less disturbance from floods and herding animals. Long runners travel across darker areas of the forest, searching for clearings to expand the colony. A single clonal stand can stretch for kilometers, producing a yearly mast measurable in the hundreds of tons across the many hectares it covers. Some smaller fruit-eaters are specialized almost entirely for this one food source, living most of their lives in the labyrinth of vines. Even they cannot keep up with the height of fruiting season, which peaks first in mid-spring and then again at the end of summer. Animals much bigger than a kilogram are unable to navigate the thorns, frequently dying as a result of being caught in their barbs. Only the briarpelt can clear a path; its skin is thick enough that it isn't bothered by the thorns, even as they dig deep and permanently embed themselves in its fur and epidermis. It welcomes the ramblingvine as a form of body armor, especially important during its early years, when it is not yet big enough to ignore most carnivores. It eats its fill of the fruit, downing entire infructescences and thousands of seeds in a single gulp. It soon leaves to return to its normal stomping grounds on the lowland plains, and the other frugivores of the forested hills move in. Following in its footsteps, they can see the sky through what was previously a solid tangle of vines. They know they are safe to walk where the briarpelt has already trampled, and they reach at their leisure into the interior of the stand, where untouched clumps of fruits are likely to remain throughout most of the year. 

Though the jadetooth may be the earliest-branching spappybara lineage to gain cursorial adaptations, it's far from the largest. The closest living relative of the sappopotamus is the Muritaur (Longicornomys cervicornus), a towering grazer that outweighs the jadetooth five to one. At a ton and a half, the oldest bulls are unassailable except by other males of their species, and even the young have only a handful of regular predators. Pregnancy lasts for over a year, with an average of three calves in a litter. They take half a year before they can digest solid foods, and another year before they're completely weaned and ready to fend for themselves. At full size, a muritaur's digestive tract alone is nearly the size of an entire jadetooth, so it doesn't have to be choosy with its diet, but a juvenile is more sensitive, and its mother will have to spend much of her time finding higher-quality vegetation for it. This leaves no energy to gestate another litter until finally, around their second birthday, her previous calves adopt their mature diet. Females can thus only mate once every three years, though many choose to wait four or five to better regain their fat reserves between litters. 

Males, on the other hand, compete for females every year, starting the spring after they turn three. It may be a few more years before a young bull sees any success, as dominant males can hold long-lasting harems for a decade or more. Yet these newly independent bachelors can still find limited success at the fringes. Young females leave their fathers' harems at around age five to seek out unrelated males, ultimately hoping to become part of a stable harem with a well-proven male. On their travels, though, they sometimes accept wandering males. When an already pregnant female muritaur joins a harem, her calves, though unrelated to the dominant male, will be accepted until they come of age. The bull bides his time; if he harms them, it will still be years before the female is ready to breed again. It's better to wait; he can make his move on their mother after they've gone away on their own. He can afford to take his time, for he lives a relatively safe life, with little risk of being usurped. He has been chosen by every cow in his harem for his strength and his ability to defend them and their calves from predators. In exchange, they drive away or even kill other males in their territory. This is to their own benefit; if an unrelated male takes over an entire harem, he will kill all of their existing calves, giving himself the chance to mate with more than a dozen females over the next three years. 

But killing a dominant bull isn't the only way for a new male to secure himself a harem. Around his sixth birthday, he is large enough to keep the attention of young females. Instead of simply meeting once and going their separate ways, they start to consider him an option to settle down with. He will have to prove himself capable of killing any predator that might threaten newborn calves, and he will have to face other bulls competing for the same females. His fragile horns are just for show, emerging not from his skull but from the neural spines of his third neck vertebra. The real weapon he carries is his hooves. Like most sappybaras, he has four digits on each front and hindlimb, lacking thumbs or big toes. In this species, only digits 3 and 4 bear weight, while 2 and 5 are conical, spike-like, an held just off the ground in a backward position. They deliver puncture wounds up to fifteen centimeters deep, while the blunt force of the leg impact itself is similar to a small car collision. Fights between bulls rarely take over a minute. As soon as one muritaur manages to land a blow on the other, the wounded male has little chance of survival. Once knocked to the ground, it can't quickly rise again, giving its opponent the chance to strike at its head or vital organs. 

Taking the bronze medal for body weight among sappybaras, the Tusktrap (Octolongidens incarcerator) tips the scales at a little over 400 kilos. This omnivore lives in herds numbering no more than ten, as dominant males will only accept newcomers until there are enough adults to protect the calves from predators, with the exception of receptive unmated sows, who are always welcome. A litter of up to six small, well-developed young are born after a seven-month gestation, and they grow quickly, reaching independence in under half a year. As they mature, most of their molars begin to grow long, losing their grinding function. Only the rearmost stays short, and once it is shed and replaced by its adult counterpart, the new hind molar is broad and ridged, allowing it to pulverize large amounts of food without help from the first two pairs. The middle molar grows to about eight centimeters long and takes on a caniniform shape once its tip gets worn down from usage. The frontmost pair eventually begins to grow continuously, arcing forward until they emerge in front of the cheeks. The incisors are of around average size for a rat this massive, serving to clip vegetation and cut through meat alike.

Hunting is not a cooperative effort; this species gets only around 25% of its calories from meat, so individuals can get by on what they catch for themselves. The tusktrap usually eats animals around a tenth its own weight, only going after big game during times of desperation. Its long head can reach into thickets and crevices far too small for the tusktrap to fit its whole body inside. Sometimes it even positions itself just above the horizontal opening of a burrow, a bit too high for its fossorial prey to see it from inside. As soon as it emerges, the trap slams down upon it; the robust upper tusks dig into the ground, blocking the smaller animal's escape, while the gently curved lower pair scoops it off its feet, right into the waiting incisors that make short work of its muscles and bones.

The remaining Muridiungulates of Choeropica all fall into a single clade - the Murimaras (tribe Dromulomyina). These are small ungulates with a shared set of adaptations for short-distance running in unfavorable terrain. They've all reduced their number of digits to varying degrees, shrunk their tails to less than half their height, and gained a greater degree of spring-like spinal flexibility. They are some of the most common prey for megafaunal predators, as they're mostly defenseless once caught. But even the slowest murimara is far from easy to catch.

The Pocketbolt (Dromulomys arborealis) is the world's first climbing Muridiungulate. It has only three digits on its front paws, but they have become less hoof-like, bearing little weight and curving strongly downward. It usually doesn't climb particularly high into the trees, as its preferred food is not to be found there, but it uses pocketwood cavities for shelter and to raise its young. Some pocketwood trees grow many meters tall, with suitable pockets reaching well into the upper layers, but the pocketbolt is safe enough in the lower storeys, between two and five meters up. It takes care not to disturb the resident isopods, and it actively dispatches smaller vertebrates that try to intrude on its nest, including many that would be damaging to the tree if left unchecked, so it goes unbothered by the swarms of crustacean symbiotes. 

Its diet consists of large seeds, fruits, and foliage from bushes and small trees, though never pocketwoods, not even saplings too small to support a den. This is the only murimara that isn't exclusively herbivorous; it may also eat a small percentage of meat, sourced from would-be nest invaders, though this is only common among pregnant females looking to increase their protein intake for the health of their developing calves. Otherwise, any carrion will be hauled away by woodlice and brought to the highest fully-developed cavity on the trunk, where it will be inaccessible to most kleptoparasites. There it will feed tens of thousands of isopods, and its nutrients will eventually feed the tree itself by way of the arthropods' waste and corpses.

On the low-lying grasslands, kept free of trees by megafauna like briarpelts and muritaurs, lives another herbivore with a far less imposing stature. The Prairiebolt (Dromulomys velox) belongs to the same derived genus as the pocketbolt, but with an even more extreme reduction in its fingers and toes. All four limbs now end in just two digits, though they are rather wide-splayed to keep the small ungulate from sinking in areas with soft soil and regular flooding. Larger sappybaras can simply trudge through the muck, allowing themselves to sink until they hit solid ground below, but their three-kilogram cousin must walk atop the soft ground or mats of vegetation. It is more nimble in flooded-out areas than any land predator, so these are its places of refuge, just like tree cavities are for the pocketbolt. 

Of course, there is danger below the surface too; geckodilians, descended from Gekkosuchus of the Early Arthrocene, prowl the open channels, and their half-grown juveniles are the perfect size to see prairiebolts as easy prey. They live in the shallows, away from free-flowing waterways dominated by the adults. A prairiebolt rarely sees the predator coming; in many cases, it can approach from directly below the little ungulate, weaving through submerged stalks of plants until it can shoot upward and grab the hoofed rat from its perch above the waterline. If the prairiebolt dodges the initial bite, it may try to break for a higher patch of plains, as it can run above the flood faster than the lizard can swim beneath. Its survival then comes down to whether or not any terrestrial carnivores are around; many a prairiebolt has fled from one species of hunter into the waiting jaws of another.

The Berrybolt (Paradromulomys acuphyllophilus) is at once the most anatomically conservative and ecologically specialized of all murimaras. It has four fingers and three toes on each side, more than any other member of its tribe. Its diet is more than 80% ramblingvine "berries" - a consistently abundant food source, if one can access them. Though ramblingvine can create clonal colonies across a huge area, it tends to clump up in individual thickets just a few tens of meters across, joined only by tenuos runners that frequently become disconnected. Unless exceptionally sprawling, each stand supports just a single full-time berrybolt inhabitant, who defends its territory against conspecifics. It moves in and out of the vines, relying on its ultra-fine, oil-coated hair to resist snags. Its claws are small and pointed, without hooves even on the hindfeet, granting them the dexterity to remove any thorns that get caught in its fur or skin. Its downturned nose ends in whiskers nearly 20cm long, which it uses to feel ahead of itself in the dark interior of the ramblingvine. 

A single cluster of fruit, a bit smaller than a human thumb, is a decent-sized snack for the berrybolt. On a good day, it will find around twenty of them in the thicket, a tiny fraction of the thousands hidden throughout its twists and turns. The only time it ever forages outside the vines is during the brief dry season, when production slows dramatically for a few weeks to conserve water. It mostly looks for other types of fruitgrasses in nearby wooded areas, especially parasitic drunkgrasses in the genus Noxiflora. These are the most calorie-dense fruits in the world, with simple sugars making up more than a quarter of their weight. Most frugivores leave them alone, though, as their florets and unripe fruits are deadly to mammals and birds alike. Then, after ripening, they ferment and spoil very quickly as a result of their high sugar content. The berrybolt must find them within a 36-hour window, whick luckily falls during the exact time of year that ramblingvines slow down. Its sense of smell is well-developed from spending most of its time in shaded thickets, so it can find and distinguish ripe Noxiflora from unripe and overripe ones from a great distance. Each fruit on a single plant matures simultaneously, but different plants may differ in their timing by up to a month, so the berrybolt can rely on this resource throughout most of the dry period. Meanwhile, males and females begin to search for one another, taking advantage of their time away from their isolated homes.

When the rains return, berrybolts return to their stands of ramblingvine, but they aren't alone for long. Driven by the sudden flooding, briarpelts head for the hills, and they turn to the most abundant fruit in the uplands. They plow through the vines, undeterred by thorns shorter than their skin is thick. In their wake, other frugivores enter the ramblingvine that would normally find it inaccessible. The smaller but more easily-ensnared pocketbolts, along with many species of small and medium-sized birds, reach into the vines from the safety of the pathways cleared by the giants. They draw in predators from all around, and the berrybolt is forced into hiding. It cowers in the few untouched fragments of the stand, feeding on berries still too deep in its structure for the others to access. Finally, once the colony begins to regrow, the other fruit-eaters are driven away, and the bounty once again belongs to the berrybolt alone. A litter of six to ten calves is born in early or midsummer, and they will grow quickly enough to set out in search of their own territory before the dry season returns. 

The largest murimara, reaching nearly the size of a jadetooth, is also the largest full-time resident of the upland canopied areas. The rolling hills see visits from briarpelts twice a year and from nomadic tusktraps far more frequently, but the Fawngarde (Bilongidens alburus) lives here its whole life, only crossing the grassy lowlands during the dry season in search of scarce water. It browses from the ground up to its own maximum head-height of 270 centimeters. It can also pull down higher vegetation if it comes across a convenient low-hanging branch or vine. Sister to all other murimaras, this tall and gracile animal descends from a body plan similar to the berrybolt, but with more typical hooves and short, unspecialized fur. All of its limbs now bear three toes, though only two of the front ones touch the ground. Its body is narrow to move between trees, which on the steepest slopes may reach staggering densities (this would be the case all over the continent without megafauna), and its hooves are small and fully upright, reflecting the stability of the ground it walks on. 

Males reach full size and sexual maturity around their second birthday, approaching a third of a ton in weight. They ritualistically spar with their overgrown first upper molars, which are too thin to actually deal damage without breaking themselves. On the rare occasion that a fight escalates to life-or-death stakes, fawngardes switch to using their forelimb weapons: giant downward-pointing claws, held just above the ground by the innermost digit. They rear up and aim for their opponent's chest, shoulder, or back. If one can sink a claw in, he drops his full weight onto it, driving the other buck into the ground. A downed fawngarde may still kick out with his legs, so the soon-to-be victor twists around until he stands over the other's head, their bodies pointing in opposite directions. Finally, he lines up a single bone-breaking kick to the loser's spine.

But it rarely comes to that, and even the biggest fawngarde bucks are peaceful to one another outside of a short rutting season in the early spring. The rest of the year, two to five of them live together, along with up to a dozen does and their fast-growing young. Unique among sappybaras, the fawngarde has only one baby in a litter, born around one tenth its mother's weight. It doesn't have to worry about competing for milk, so it soon reaches a size large enough that it doesn't need to worry about most predators in the forest, either. The times of plenty last for exactly one year; around a fawngarde's first birthday, its mother gives birth again, in sync with all the others in the herd. The previous year's cohort is then forced to leave the herd's territory. This is the true reason for the fawngarde having only one offspring per year: it ensures the yearling cohort is never more numerous than their parents, in which case they might drive the older generation out instead of leaving peacefully.

Forced to disperse, the young males and females split off; they see each other as family, so they would never attempt to form a breeding herd together, even those with different mothers and fathers. Instead, the males go into the lowlands in search of an unrelated hemi-cohort of yearling females, and vice versa. They form coalitions with a roughly equal sex ratio. This exploratory period lasts for only a week or so at the very end of winter, but the pair-bonds established at this time can last a lifetime. When rain returns to Choeropica, they start looking up again, retreating to higher elevations around the same time as the briarpelt. Though their typical diet is fibrous vegetation, they won't turn down a sweet treat when it's freely available, so they take full advantage of the broken ramblingvines. There they may meet other coalitions or members of established herds. If unoccupied territory exists nearby, they will quickly be claimed by the first-arriving pairs of fawngarde half-cohorts. But there are likely to be many more coalitions than available space can support, so the majority are forced to the edges of the forest, where they are far more exposed to predators, and where most of the low-lying vegetation is of lower quality. 

Coalitions launch forays into the "islands" of dense forest from the sparser semi-canopied foothills. There may yet be unnoticed pockets of good habitat for the taking. Still, thousands more juvenile fawngardes grow restless. Some break away from their groups and attempt to gain entry into existing herds. Some coalitions remain strong and seek to usurp weaker herds with territory. To avoid this fate, herds with dwindling numbers may preemptively welcome entire coalitions into their ranks. In good years, this type of alliance can account for most or all of the anxious youngsters. But if the old guard proves too numerous to accept new members and too strong to topple, more than a thousand yearlings can remain at the periphery to be picked off by lowland predators. Desperate, they form mega-coalitions to provide themselves safety in numbers, but they pick the entire landscape clean of food so quickly that they have to trot to keep up, circling the forest islands until they come back to where they began. The weakest juveniles wander out into the drenched basins. A few very lucky ones might reach another highland area many kilometers away; this is how their species maintains gene flow between isolated patches of forest. 

Other yearlings do not venture out; they continue fighting amongst themselves in the foothills, with males in particular whittling down their numbers by casting out the losers of ritualized practice battles. This coincides with the rutting season that sweeps through the adult population further uphill. A small number of yearling bucks are soon invited into established herds to replace the few casualties of the rut. With their numbers reduced yet again, the remaining juveniles in the foothills are able to find ample food for the next few months, though they still face a higher predation rate than the herds in the forest. Smaller coalitions reform, often after exchanging a member or two with a different group, and launch cautious raids into known territories. Those who strike early can clear an area of its former residents, then become vulnerable to attack themselves due to being unfamiliar with the new land. A single territory can change hands a dozen times in a summer if it is toppled once. 

By late fall, the population of the outskirts is two-thirds yearlings and one-third older adults who've been expelled from their territories. The experienced outcasts gather new mega-coalitions around themselves of fifty fawngardes or more. They sweep through large tracts of forest, killing or expelling multiple herds at a time. Once in charge of a large area, mega-coalitions rarely stay together for long, disbanding without conflict into as many as five different herds. When the short winter drought arrives again, any fawngarde that remains in the foothills gets one last chance to gain entry into a herd. Thousands of adults, including heavily pregnant does, descend to drink from the few remaining water sources in the lowlands, and if any of them dies on the trip, a new yearling will be accepted in its place. 

That leaves a total of perhaps 100 yearlings and 50 adults without territory around the edges of a typical mid-sized forest island. Most plant life is dry, dead, or dormant, and the predators are growing hungrier and moving uphill. The stragglers stand little chance of winning a fight in their weakened state, either over territory or against carnivores that exceed their own size. Most years, no fawngarde outside the closed forest survives to see the next year's cohorts emerge from the treeline at winter's end.

Section 2: Surprise! It's also a Downling Stronghold!

Choeropica's native clade of predators are all descended from zipperbill downlings that island-hopped here before the Ice Age, coevolving with sappybaras for over fifteen million years. In that time, they've evolved to become everything from apex predators to insectivores to durophagous omnivores. Most are still carnivorous in some fashion, though many have adopted new ways of securing prey. This includes the species most distantly related to all others on the island continent.

Sipperbills (Titanocadavoris) comprise four species of small-game predators with a talent for scavenging much larger carcasses. They travel in groups of three to eight, guided by their keen sense of smell. They hunt small burrowing rodents by flushing them out of the ground. With their two long toes, they probe until they disturb the rat underground, in hopes that it will flee out a neighboring exit, where another sipperbill is waiting to deliver a killing stab with its narrow lower beak. Individually, they won't go after anything bigger than a berrybolt. But with a pack, larger muridiungulates are on the menu. Sipperbills frequently take yearling fawngardes, who are easy to separate from their disorganized megacoalitions, and young jadeteeth up to around 125 kilograms, equivalent to three or four of these carnivores put together. The latter is a more difficult task, as their troops will rally to protect them, but it only takes two or three sipperbills to create a distraction and allow the rest of the pack to dispatch a juvenile while the adults aren't looking. 

The sipperbill also scavenges on anything it can safely access, up to and including the largest muritaur bulls. This requires most of the pack to stand watch and defend against other carnivores at the carcass. When feeding, they drag the cutting edges of their lower bill along the flesh, cutting cleanly down to the bone. They carve off large chunks at a time so that, if they hear the guards give a signal, they can quickly haul away a large amount of meat to safely eat elsewhere. 

This genus gets its common name from the way it drinks at watering holes: it places its tongue atop the thin gap between the two sides of its lower beak, creating a straw. Muscles at the back of the tongue draw water into the opening, and then the bird tilts its head back to swallow. This allows the sipperbill to keep its eyes high above the waterline, making it easier to spot larger predators approaching from land or water. In a pinch, many sipperbills have learned to perform this same trick on carcasses, especially very fresh ones, allowing them to drink blood instead of trying to cut away solid meat. 

The largest carnivore of Choeropica is the Quadrannulus (Quadrannulus fortis), so named for the four "rings" on its body. Like scythesnouts, zipperbills have down-curling beaks; if left untrimmed by normal wear and tear, these would grow into a circular or spiral shape. In the quadrannulus, both the upper and lower rhamphothecae have this growth habit, though the top beak is usually so heavily worn down that the curve is barely apparent. Meanwhile, each foot has a robust, curling claw useful for foraging for buried plant matter (around 10% of its diet) and for sparring with other quadrannuli. Held aloft by the backward-facing first toe, this claw is too curved to be useful for slashing and jabbing, and its digit lacks the musculature to drive it deep into its enemies' flesh. Instead, when two individuals fight, they each stand on one leg and reach out with the other. Their big-toe claws interlock, and they both pull until one can no longer keep its balance. This requires both brute strength and coordination, so it's a reliable indicator of which individual would win if they actually decided to fight to the death. Thus, the loser rarely goes for a rematch, and fights don't tend to escalate to the point of drawing blood.

Quadrannuli are born helpless, blind, and bald, with a bill yet to keratinize. As time goes on, the tip of the jaw turns downward, making room for a developing beak with a concave V-shaped cross-section. In the rear, its twin cutting surfaces are constantly refreshed by grinding against the back of the upper beak, while the tip is allowed to grow almost freely, letting it take on its mature curled shape. Unlike in grimbills, the hooked lower jaw isn't used in hunting. Rather, the more traditionally raptorial upper beak serves that purpose, while the wide-flared back of the lower beak can cut through tough tissue and even snap the bones of medium-sized animals. By the time a quadrannulus reaches its maximum weight of 175 kilograms around its fourth summer, it can take down all species of prey (or at least their juveniles) on Choeropica, and its range may be as vast as a hundred square kilometers. It won't tolerate any other quadrannuli in its territory outside the breeding season at the end of fall, after which the enormous egg is left under the care of its father. Following an incubation period of 30 days, the chick hatches just as the winter drought ends, so it grows up with abundant food and low predation pressure. 

The remaining Choeropican zipperbills are grouped in a tribe called Knife-Gnathes (Ankylotomiini), who get their name from their fused jaw and beak structures. Instead of splitting along the sides of the mandible, the lower rhamphotheca emerges as a single blade down the center of the jaw, slotting into a groove within the larger upper beak. This means knife-gnathes can cut into their food face-on, instead of twisting their heads sideways to use a cutting surface further back in the mouth. Members of this tribe also have more forward-facing eyes than more basal zipperbills, making them more effective hunters, especially in the trees. These two traits evolved in tandem, giving all knife-gnathes a decidedly forward-focused lifestyle, though one still uses a sideways shearing bite to finish off its prey.

The Threeshear (Triplotomia) houses its knife within a narrow space between two others. As the earliest-branching knife-gnathe, its lower beak still splits at the very back, running along the two sides of the jaw for about a centimeter. These side-branches are worn down by the upper beak, which is barely even wide enough to accomodate the thinner part of the knife. Its twin walls almost completely cover the knife when the jaw is closed, a trait common among knife-gnathes.

Five species of threeshears can be found across Choeropica; they become reproductively isolated rather easily, as they refuse to venture across treeless areas. In the forests, however, this is one of the most mobile animals on the continent. It hangs upside-down when it crosses horizontal branches, so it doesn't need to worry about balance. It only has to focus on holding tight with its toe-pads, which splay out in a zygodactyl arrangement. The claws are used sparingly in climbing, as the threeshear has no desire to damage the trees and invoke the ire of their arthropod inhabitants. In fact, many of its prey species are enemies of the palm-grasses, such as arboreal swattermice and smaller downlings, whose diversity remains strong on the island continent for now. 

But at thirty kilograms, the threeshear sometimes gets an appetite for larger prey. Newborn fawngardes aren't unheard of; they're just barely light enough to be carried into the canopy, safe from kleptoparasites and retaliation by the rest of the herd. But these Muridiungulates are only a seasonal food source, as they soon grow far too large to risk attacking. Smaller sappybaras like berrybolts and pocketbolts are also on the menu, but only if they can be caught far from their refuges. Despite its bulk, the threeshear can survive a drop of five meters without injury - more if it can successfully land atop a prey item to break its fall. This is its method of killing Muridiungulates, even the slowest of which are far too quick to be caught on foot by a predator that almost never walks, let alone runs, on the ground. 

Finally, the majority of knife-gnathes have yet another feeding adaptation, one that has allowed them to broaden their diets more than any other Choeropican zipperbill. Sheathheads (Ankylotomiina) are a subtribe with three members living in central Choeropica, all sharing an upper beak that curves so far downward that it obstructs the lower knife. How, then, can sheathheads open their beaks at all? The jaw is able to slide forward and back several centimeters, granting it the clearance to open all the way. This movement also allows new forms of food processing and thus new niches for sheathheads to fill.

The Pleated Sheathhead (Parvitomia plica) is the most distantly-related of the sheathheads, and it has shifted to a diet of Scansoriarthriform isopods. The jaw has only a few degrees of motion at its hinge, but it can slide horizontally about three centimeters back from where it meets the upper beak. This allows it to hold an isopod still with its hooked top beak, then cut it apart by sawing with its mandible. At ten kilograms, this zipperbill is nowhere near large enough to be immune to counterattacks, so it relies on the heavily-folded skin on its bare face to repel bites. Even still, it has to move constantly, rarely returning to the same tree twice. Its scent is instinctively known to many species of symbiotic woodlice, who pursue it even in its sleep. Luckily, it can retreat to the semi-open ground of the foothills, where tree cover is more sparse, making it harder for swarms to chase it over long distances. Some pleated sheathheads spend their whole lives in these mid-elevation savannas, where predation is higher but foraging isn't a constant race against counterattacks by its own prey.

Others, especially mature females, stay in denser forests where their young are less vulnerable. Each egg takes a month to form, a month to incubate, and a month to rear the chick to independence. Thus, an experienced mother can comfortably maintain an average of three per year, with a rest period during the winter when food is scarcer. For her first few years, she will lose most of her offspring to isopods, who have evolved to target the young in an effort to prevent future generations of their predators from reaching maturity. With adults, they usually seek only to chase the sheathhead away, as their odds of killing it are low. This means each female will get many chances to try again; a lifespan of twenty years isn't uncommon. 

Next, the Shuntblades (Cryptotomia) are the smallest of all knife-gnathes, reaching around seven kilos in their largest member, the Common Shuntblade (C. continentalis), which is also the only one that lives across the interior mosaic. It is the second-most arboreal Choeropican zipperbill, but it runs instead of dangling from branches. Outside of breeding, it is mostly nomadic, as it can find food almost anywhere. Its diet is omnivorous; like the ancestral sheathhead, it kills by pinning and slicing through small prey, but it also eats plant matter for about 2/3 of its energy. Its jaw joint is capable of translational movements both horizontal and vertical, so its beak is more versatile than that of any other bird on Apterra, though it still can't compare to the cranial kinesis of Earthly Neognathes like parrots. 

Shuntblades break open seeds by holding them inside the curve of the upper beak, then using the knife as a wedge. The jaw slides forward and down, opening slightly as it reaches the front of its range of motion. This also works on some bones, which would normally be an inaccessible food source to a bird this size. Fruit makes up a large portion of the common shuntblade's diet, especially segmented void fruits, which it expertly cuts into individual segments without breaking the skin. This doesn't improve the quality of the food, but it's a good way to show off around other shuntblades. Youngsters can frequently be seen making a game out of it, and mature males may use this exercise to display their fitness to potential mates. 

Shorter but heavier than sipperbills, the Siegemouth (Ankylotomia robusta) is the second-biggest bird on Choeropica. It can climb to nest, stash its kills, and keep safe from larger predators, but it hunts at or below ground level. Sometimes it fishes, and sometimes it digs for burrowing animals, but small game makes up less than a quarter of its diet. By weight, most of its kills come from animals larger than itself, including all but the largest Muridiungulates. Even adult briarpelts and tusktraps are taken in times of desperation, though jadeteeth and fawngardes are more typical. This species is the main predator of full-grown fawngardes, as tusktraps and quadrannuli find it too difficult to chase them through the forest. The siegemouth can find food and make itself at home anywhere with at least a few trees, and it is happy foraging on completely open ground, so it ranges across the whole of Choeropica, even venturing onto the coastal matkelp, though it doesn't live there full-time like some other predators. 

The siegemouth's heavy and cavernous upper beak can easily stop prey from getting up and fleeing, but the pinned animal is likely to flail and scratch at its attacker's face. In response, siegemouths have evolved keratinous pads all over their heads, keeping most areas safe while the knife does its job in dispatching its target. Fish and small rodents can be swallowed whole, as the bill conceals a massive internal volume for holding prey. Anything bigger than a few kilograms will need to be cut into chunks, an easy task for an animal with a ten-centimeter knife on its face.

Section 3: New Arrivals

Though many clades of animals have walked, swum, or rafted to Choeropica, the island continent has seen fewer and fewer migrants over time. Its two dominant tetrapod lineages both arrived before the Arthrocene began, and there have been nearly no new arrivals for over seven million years. But times are changing, rafting events are becoming more frequent due to the expansion of matkelp. And the rafts are getting bigger, carrying bigger species to unfamiliar lands..

Well, big for a bug. Bunkerbugs (Lardariarthrus) are a genus of castlebugs second only to the geoglyph in size. Adults can weigh over a kilogram, though their armor isn't as extensive as most other Thyrearthrids. This is because they spend much of their time in or near a protective burrow, where they store food and rear their young. The food supply mostly consists of small seeds, though this isn't the bunkerbug's exclusive diet; it just stores better than the fruits and foliage that make up the rest of its intake.

One species made it to Choeropica around a million years ago, and it seems to have made itself comfortable, evolving into the Trapdoor Bunkerbug (L. omnivorus). In this species, the burrow is itself protected by a rock, sometimes weighing five times as much as the adult, which prevents most nest-raiders from picking off its offspring or its grain supply. Its ancestors used fallen leaves for a similar purpose, but when their raft landed on Choeropica, they gained access to new materials. They also grew larger due to reduced competition, requiring more heavy-duty fortifications. However, trapdoor bunkerbugs do still use leaves to hide smaller secondary larders without precious mancae to protect. These smaller dens are funnel-shaped to trap any smaller animal that falls in; once a day or so, the bunkerbug checks each trap and finishes off anything that has stumbled its way inside. 

The Prong-Faced Portent (Prophetornis simpliplumus occidentalis) arrived even more recently, less than 100,000 years ago, and is still considered a subspecies of the Whisker-Faced Portent (Prophetornis simpliplumus), which has three other subspecies along the west coast of Ailuropia. The prong-face is the largest of its species, representing another case of insular gigantism. Its evolutionary path over the last hundred millennia has been broadly similar to the first portents that escaped Ailuropia to the eastern continents a few million years ago: it has grown bigger and stronger, with a more robust bill, and it spends more of its time on the ground. However, it also has traits that aren't seen in eastern portents or their descendants like the omniportent. While some Prophetornis were off conquering other continents two million years ago, those that remained in Ailuropia were innovating in order to compete with a higher diversity of other local pouchwings. 

Like all whisker-faced portents, the prong-face has large feathers at the front of its head, derived from ancestral feeler-like feathers common among kiwis. There are still a few small whiskers at the base of the keratinous beak, but the three largest whiskers now serve a display function. In the prong-face, these feathers are even more developed, each bearing a sheet of rippled keratin behind its single filament. Other than these novel structures, most of this species' feathers are simplified even compared to those of other kiwis, with no side branches and a hair-like texture. Only those on the tail remain downy, with branching filaments along their length. Another Ailuropian innovation was the splitting of the pouch into two distinct chambers, one attached to each wing. All subspecies of P. simpliplumus are able to raise two clutches of eggs simultaneously at different stages of development, which doesn't increase their overall reproductive output, but it does provide insurance against predators or disasters that might wipe out one entire age group.