One of Serina's most vast regions, savannahs with sparse tree cover now cover most of the former extent of the central soglands throughout south and central Serinarcta. These new lands are now home to some of the largest land animals ever to live on Serina.
In the late hothouse, the cygnosaurs - a lineage of extraordinarily large, plant-eating gantuan skuorcs - are now among the largest animals ever to walk on Serina. These giant animals have completely transformed the landscape of the late hothouse, displacing destructive thorngrazers with the result that much of the continent has grown drier, and non-cementree trees are now able to set seed and grow, albeit sparsely. These animals are ultimately responsible for the creation of an entirely new biome, the savannah woodlands, now home to thousands of smaller, endemic species dependent on them for their continued survival.
One of the most distinctive, largest cygnosaurs of the late hothouse savannahs is the ridgeback cygnosaur, with a huge triangular crest and dorsal hump. These great animals are the hybrid descendants of the cline that included baronial, fiendish, and draconic cygnosaurs, and now weigh 20 short tons and reach lengths of 80 feet, a size greater than the sauropod dinosaur Diplodocus. Like mountains of flesh, they roam the northern plains in herds of hundreds, greatly affecting the landscape around them. Long craning necks reach up the crowns of isolated trees as the browsers strip them of their leaves with rake-like bill pecten that leave only bare twigs in their wake. Dominant males turn from a dusty grey into a brilliant tapestry of red, with rich black underparts, becoming an utterly unmistakable beacon on the plains which draws in females from miles around, as well as rival males. These animals may be herbivorous, but they are not gentle giants. Males savagely fight, becoming battle-scared and bloodied to maintain or win control of female harems, and even females are aggressive, forming strict pecking orders within their herds.
Gantuans, the broader group to which cygnosaurs belong, have many adaptations in common with the physically-similar sauropods of ancient Earth, owing to a unique combination of traits retained their distant avian ancestry and others acquired through more recent metamorphic ancestry, and these attributes have allowed them to rapidly increase in size over a relatively short timespan in the hothouse. A sac-based respiratory system, typical of birds, incorporates hollow air pockets throughout bone and muscle tissues, reducing their body weight. A long balancing tail, absent in all terrestrial non-skuorc birds, allows far greater body length than the tailless boomsingers of the early Ultimocene which approached these weights and even surpassed their heights, and this tail balances a long, horizontally-carried neck up to 28 feet long. Adults of the largest gantuans frequently have a large hump over their backs - a huge bank of muscles which anchor both neck and tail to elongated projections of the spinal vertebrae, and also keeping the center of balance right in the middle of the body. The tail is prehensile and whip-like, incredibly flexible and useful as a defensive weapon and as a manipulator to hold objects - or to swat pests, or even pick up and fling pesky smaller animals.
The few largest, healthiest adult ridgebacks have little to fear even from the largest land predators. At full size they are more than capable of killing their enemies, swatting sideways with their tails with enough force to shatter bone and or break their jaws or kicking out with two-foot-long ankle spurs that can gouge straight through an eye and out the other socket. Particularly agitated adults may even rear up and drop their full weight onto predators, crushing them to a pulp. Even a simple bite from a serrated plant-clipping jaw four feet long is enough to leave a bloody wound liable to become infected, making the ridgeback an extremely formidable animal to deal with. Hunters such as giant sawjaws thus focus their efforts upon the far more numerous juveniles and subadults, and so ensure only a few of the fittest individuals per generation ever reach their greatest size and outgrow their predators' ability to hunt them. The biggest animals still don't live lives of total leisure however - in addition to battles against their own kind, they are fed on by agile flying parasites - butterbirds and tribbats - that not only drink blood, but tear mouthfuls of meat from their hides with specialized cutting jaws. That flyswatter tail swings around all day and night, and sometimes makes its mark, but vertebrate parasites are smarter than insects and know which places their host can and cannot quickly swat. The chest and lower neck are difficult to quickly reach, and so these are where the pests focus their attentions, leaving messes of wounds and scabs that never get the chance to heal properly. Ticks and smaller blood-suckers likewise gather in numbers on the belly and near the legs, too small and tightly-stuck to pry loose. Some specialist insect pests of gantuans can reach sizes as large as rats.
Mature female ridgebacks give birth to huge litters of live, placental offspring. While it is common for larger animals to evolve to have fewer, bigger young, gantuans have maintained the strategy of their small ancestors. In fact, large cygnosaur chicks are not born significantly larger than those of the primitive soggobbler, instead being born in much bigger litters; a full-sized female can produce more than a hundred nine or ten pound chicks at a time and become pregnant as often as four times each year. Giving birth is a very easy process for such a giant, which does not even seem to notice the process as chicks are dropped, one by one, to the ground under cover of night, still in their placental sacs. They are abandoned from their first moments, scurrying away to hide in the tall grass a matter of minutes along with many of their peers, as females within a herd have a way of timing their births so that all litters are born within a few hours of each other. This helps swamp local predators' appetites, though the vast majority of gantuans are still killed before even their first birthday, and less than one in ten thousand will reach its full size, attained around 35 years old, and only those will find themselves truly safe from threats. Though both sexes can begin breeding much smaller, as young as their teens in the case of females, males will only get any chance once at their full potential, meaning far fewer males than females get to reproduce in a population and meaning that male dispersal, rather than female, is critical to maintain genetic diversity. Males which cannot find a harem nearby can therefore partake in incredible cross-continental journeys lasting years and covering thousands of miles, in order to find a mate.
As gantuans and their relatives become the biggest land animals of any kind in Serina's long history, it is inevitable that unprecedented predators evolve in turn. 290 million years PE, the cutthroat subjugator is now among the most formidable land predators Serina has ever seen. Growing to some 30 feet in length, this extremely robust bipedal predator can weigh as much as six tons, and likely approaches the size limit for a biped animal without the inherent weight-reducing air sac systems of birds and their relatives. Not even this beast can typically expect to bring down a healthy, titanic adult ridgeback cygnosaur, or even to separate it from its herd. But it is able to kill them up to and including those at 85% of full adult size, past the age of sexual maturity, and long after any other enemy poses them threat, and for this reason, it is their most feared predator.
Because it is now so very heavy, the cutthroat is no longer able to run fast after prey. But it does not need to. Large subadult cygnosaurs, neither, can run fast, and it is this which the hunter seeks to subdue. With flight out of the question, every predator must be faced head-on with a fight, and the cutthroat subjugator is an extremely strong opponent. A robust skull as big as a refrigerator holds the strongest jaws of any land predator which has ever lived: its arcing, immense jaw muscles can deliver a bite force of nine tons per square inch - stronger than that of a Tyrannosaurus rex, but still weaker than the grinding jaws of some extinct ice age molodonts which fed exclusively on large bones. The cutthroat often hunts singly, for it is so large that each individual needs a lot of food and territory to sustain itself (but not always.) It's strategy entails seeking to single out an individual and get a hold of its throat to crush the windpipe - a difficult process, as their prey group up together when threatened and can brutally whip with their tails and slice with defensive claws, or even plow their predator down and crush it under their own weight. To succeed these huge carnivores rely on brute force. It is hard for the cutthroat to get a bite in, but once it can, it takes just one to do the job. Skin up to 9 inches thick and armored skulls provide superficial protection from tail whips that would maim smaller predators, letting them rush in and make their move despite the attacks of their targets. Their extraordinary jaws let them bite and retreat, causing instant and catastrophic damage and letting them back up and get out of harm's way as their prey suffocates with its throat destroyed or falls to the ground in earth-shaking spasms as its neck is broken. The other cygnosaurs - aggressive but dim-witted - often become distressed at the sight and abandon their stricken companion as they become more injured, sometimes even attacking them in their confusion and only making the hunter's job easier.
When their quarry is disabled and lay dead or dying, blood gushing from its arteries or out of its mouth, and as the herd moves on, the cutthroat at last can come in to feed. With their powerful mouths they cut through the thickest bones as if they were carrots, chopping off limbs as wide as tree trunks. They first shear off the muscle meat in neat, fluid movements with the pointed tip of the jaw, and then roll the cleaned bones toward the back of their teeth to shatter them and access the fatty marrow, which is one of their favorite foods and - unusually - one of the first things they eat on the carcass as it is extremely rich in calories. Conversely the softest parts - organs especially - are largely picked over or dropped to the side of the kill, being taken quickly by a wide variety of associated scavenging birds and tribbetheres that could never kill such huge prey on their own. Like many of their order, the largest of sawjaws has very specific food preferences, and smaller non-targeted opportunists know that, trailing hunting pairs and darting right under their noses to snatch scraps with very little fear of harm - some species of pickbirds work actively with the predator to distract prey and let the killer approach from behind unseen, the resulting food benefiting both parties. With an open septum that forms a single nostril hole on the front of its wide, bulldog-like snout, the cutthroat subjugator has a keen sense of smell and is also quick to find any carrion on the plains, being one of the first on the site of gantuan-falls - temporary buffets that draw in all manner of life and occur rarely when the largest and oldest cygnosaurs die of old age, providing enough meat to feed hundreds if not thousands of smaller animals for a number of weeks.
The cutthroat subjugator is brightly ornamented with a retractable, blood-red dewlap which can be spread out from under its throat and connects to the back of either ear. This feature is present and equally large in both of the very similar sexes, its purpose being species recognition and intimidation of competing predators. Pairs, which only meet briefly and then go their own ways, flare their dewlaps in ritualized courtship displays and raise them against unfamiliar pairs to make themselves appear larger. Yet the cutthroat is not always an absolutely territorial animal; individuals sometimes share kills with others of smaller size, especially juveniles, including those unrelated to themselves, and in doing so aid their own species' survival against competing predators, at a time before they can hunt the largest prey on their own. Sometimes pairs will form to hunt, and rarely as many as four adults will work as a team to kill prey, making easier work of it. Where multiple of these supersized sawjaws come together to hunt, they will hunt over a much wider range than would singles or pairs would, and so their total effect on their prey's population is not significant. Gantuans respond to larger group sizes of their predators by forming larger protective herds than they do in less dangerous habitats, however, even though this may mean each individual can eat less, and so their growth is slowed where this sort of predation exists.
Like all sawjaws, young pups are carried on their parents' long, horizontally-carried tails, which are perfectly shaped to accommodate their grasp. When not fulfilling this role, however, the tail is another weapon, heavily muscled and forming a meat-hook with its large distal talon that can be used to swing out at prey while keeping the face away from danger, helping to weaken it with slashing wounds before delivering the killing bite, or even knocking it off its feet.
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Though the ridgeback is safe from even these giant hunters if it can reach its maximum size, all smaller cygnosaur species face predators at all life stages, and so these - not the most massive forms - are the most aggressive of all. A predator needs only to be fierce enough to get a single meal at least some of the time, but for prey, each and every battle is life or death.
A great spectacle is unfolding on Serinarcta's plains as great numbers of 60 foot long male bristleback cygnosaurs (Saurocygnus spinacristus - spine-crested lizard-swan), weighing as much as 14 short tons, migrate toward open clearings in the savannah. They seek a landscape without trees to block the view, as the first males begin to claim a spot to display as the breeding season begins with the first powerful rainstorms of the summer. Soon the females will arrive in number - a few have already begun to linger in the distance - and within a week the plain will be deafened by the rumbling calls of males seeking to attract a group of them for themselves. Being the first to join the gathering has benefits - these males will get first dibs on the best places to display, near the center of this particular plain. It is an ancient gathering place that stretches a few miles between two stretches of forest. Once cleared by a brush fire centuries ago, the growth of new trees has since been prevented by their annual trampling. Yet dangers come with being early, too - as these first males begin calling and displaying without any safety provided by a crowd. For unlike their larger relatives, even the oldest bristleback cygnosaurs do have enemies.
A pair of sprinter subjugators (Curserradon longicollus - long-necked running saw-tooth) has been drawn in by the activity, and they begin to circle one male which, while still very large at some 10 tons, is not yet fully grown. These gracile 23 foot long, 2 ton sawjaws, unlike their more robust relative, are very fast on their feet, and sometimes able to outmaneuver large, heavy prey like these mid-sized cygnosaur species despite a smaller size. They are also more consistently social, hunting in pairs and packs with a great degree of coordination. The male, with bright yellow bands below its eye, charges from behind the animal as it is distracted, grabbing hold of its flank with its huge jaws and slashing one of its hind legs as it tries to get a hold with its right set of sickle claws. The injured beast roars and turns to face its attacker, but the hunter holds tight, staying out of reach of the full force of its powerful, lash-like tail, which cannot get enough momentum at such a tight angle to hit it with enough force to dislodge it. The female now runs in while the cygnosaur is focused on the male, and seeks to get a bite on its neck to pull it off its feet. But she is young and inexperienced compared to her mate, only a few months independent of her parents, and when the lumbering animal spins toward her suddenly as it tries to shake off the male's jaws, she makes a fatal mistake and hesitates. It takes only an extra second for the prey to take note of her and raise up, pushing her to the ground with a brutal kick of a front leg that knocks the wind from her, throwing her to the ground with a pitiful yelp. The male, concerned for his partner, makes his own mistake of loosening his teeth just enough that the leviathan pulls itself free - leaving a massive bloody slash, but one which has just missed primary arteries deeper in its muscular body. Now enraged - and with new leverage with its tail free of the predator's maw - it strikes the male across the side of the face with enough force that it cracks the air like a whip, missing an eye by less than an inch and leaving its own mark that almost immediately begins to bruise, and may have even cracked the underlying bone of the jaw. The male, blinded by pain, runs off and leaves his mate behind. Seeing this, the cygnosaur turns back to its original antagonist, and as she tries to stand, it rears up and crushes her torso under its full weight, killing her instantly. These great skuorcs are no easy prey.
Moments later the male back toward the fight as the world comes back into focus despite the aching pain, and sees how everything has changed in seconds. With the female's body laying limp and broken, the cygnosaur begins to turn away, bloodied but victorious. The male sawjaw will do the same, retreating to some secluded place in the woods to heal. He will not breed this year. His would-be victim, however, has now attracted the attention of several distant females who had formerly been spending time with a somewhat larger male. His impressive show of strength appeals to them, and demonstrates his fitness. Just meters away from the vanquished killer, the giant herbivores will consummate their relationship, as this male becomes the first of the season to amass a harem.
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For cygnosaurs, size is everything: only the very biggest among them escape the ever-present threat of predation. For their sawjaw predators, they must increase in size in turn to still be able to kill their prey and so remain fed. But the savannahs are wide, and home to far more animals than only these two lineages. And for one other relative giant of the grasslands, size is not all it's cracked up to be.
A descendant of the stormshadow lives at the end of the hothouse, on the same plains as the cygnosaurs and their enemies play out the battles of their lives. It has no stake in their stories, for it is the protagonist of its own tragic tale. It is the least common of any surviving giant aukvultures. Though it may not seem it, it is much more specialized than either the mountain-dwelling thunderbird or the flightless gigagret. It is the tallest of them all, at up to 18 feet at the top of its brightly colored, featherless head, and a couple feet more to the tips of its elaborate head crest. But unlike the gigagret, it is still trying to be a flying creature; its body is thus much lighter as a result, and it weighs barely half as much. Yet nearly a thousand pounds - a weight rivaled in all of Serina's history only once before, by the even taller stormsonor of the mid-Ultimocene - is still an immense load to lift off from the ground, and made all the more difficult by the gigantic, branching crest that projects from the head of the male, extended up to 15 feet across and weighing some 230 pounds by itself. Combined with a much shorter wing loading than the stormsonor, and the male culminant crown of today no longer flies well, and is an animal caught between the ground and the sky, ideally suited to neither. But this is a very recent condition - it was not always this way. And how it got to this point is perhaps a lesson in just how opposed the selective pressures of natural and sexual selection may be in a single organism, sometimes to its downfall.
The ancestors of the crowns evolved in the middle hothouse, large scavenging birds with spiked head crests which, like those of the cygnosaurs, evolved as males used them to attract mates. They used their height, in excess of any other aukvulture, to frighten other predators - like earlier subjugators - off of kills, and then stole them as an aggressive mob, and so avoided needing to hunt on their own. The bigger they became, the more effective they were at taking food, and the larger the head crest of the male became, the more attractive they became to females. Soon one lineage, the pinnacle of them all in size and grandeur, out-competed the rest; it was the immediate ancestor of the culminant crown, a social bird that appeared immensely large and ornamented that no enemy would dare to fight it, letting it monopolize the large carcasses that it found while soaring over the open plains of Serinarcta. Had it stayed as it was then, all might have been well. But without other rivals to oppose it, and no enemies, the species found itself in a cycle of out of control sexual selection as females continued to prefer ever more convoluted and massive head crests that became heavier and more difficult to get off the ground with, for not only were they large, but also very heavy - males would batter one another with them, and a hollow crest would simply break off. Without enemies, there was not enough counter pressure to prevent the male's crest from growing to absolute extremes; furthermore, as a species which breeds polygamously, rather than in pair bonds, a single especially well-endowed male could sire a majority of chicks in an entire population, causing rapid change to the crest size of all males within it in just a few generations. Sometimes, this fast spread of a trait can benefit a species. Other times, however, it can doom it.
This low genetic diversity and strong selective pressure for crest size has resulted in a meltdown of the genetic health of the culminant crown, as their head crests have become so ungainly that it becomes very difficult and ultimately impossible to fly with them. Once keratinous, they are now almost solid bone, and weigh up to a quarter of their entire body weight. The male of the species has also experienced a dramatic reduction in wing length in just a few tens of thousands of years, which may directly correlated to their putting an excessive percent of their energy into growing their head crests, at the expense of other skeletal development. This has produced a situation where adult males become increasingly unable to fly as they mature - and entirely flightless by the time their crests are big enough for females to even consider mating with them. For an animal which must cross many miles every day to find scattered carrion on the grasslands, the loss of flight is a major handicap - it is not adapted to it, like the gigagret is. While females fly easily and dominate carcasses, lone males wander the ground and exert far more energy just to find food, for they do not know how to hunt live prey any longer, and will starve without suitable carcasses available to feed from. Adaptations to stride over land already existed in earlier crowns, including hoof-like toe claws which make them faster runners, but these birds still relied on the ability to take off and soar in order to locate food from above by scent and sight. Reproductive success in the culminant crown now depends on walking a narrow line between life and death; the size of their crests and the preference of the female who is herself unaffected by its encumbering size is literally driving their species as a whole toward extinction. The culminant crown is the tallest and most extravagant of all the crowns, but it will also be the last of them, a victim of its own short-term success whose evolution has been pulled in a direction that is already proving unsustainable. The slightest change to its stable environmental condition, reducing the availability of food even slightly, will surely push it to the point of no return - even if it has not reached it already.
The culminant crown demonstrates the principle that in nature, even in a land of giants, bigger is not always better.