Rise of the Cygnosaur

285 MPE, the huge descendants of soggobblers  now roam across the northern continent, as this ornery, super-abundant herbivore diversifies into many new species that reach body lengths unseen before in land animals on the world of birds, thanks to their impressive necks and their even lengthier tails. These giant skuorcs, now some of the biggest ever birds, have reclaimed the avians' dominion over the land. Gantuans, despite being herbivores, are often fierce, and few may be more so than the draconic cygnosaur, a 7 ton, 50 foot long browser which has no patience for interlopers in its space. Males of this species sport prominent dewlaps, colorful snouts, and three incredibly long, specialized head feathers that form a crest up to nine feet above its head. These unbranched quills are the longest feathers of any bird, and are supported as they develop by a calcium shell, so that the mature structure is like a hollow horn that remains flexible to avoid breakage due to its thin diameter and great length. Hair-like plumage still remains on the neck and the back, now stark white, and serves a purpose in keeping cool under the beating sun by reflecting solar radiation. 

Male cygnosaurs, if their displays don't do enough to show their strength, fight amongst each other for breeding rights over large female harems. They bellow and roar as they slam their necks into one another and even rise up on their hind legs to try and topple their opponents. Only the biggest and meanest males can hope to breed, which not only selects for increasingly large and aggressive males, but also means that the majority of males that don't make the cut will never breed at all. Frustrated and cast out of the herds, they take out their aggression on creatures even weaker than themselves, and too slow to run away: the thorngrazers. 

On four legs they not only tower over all tripods, but can run them down at a faster pace, and kill those which don't give them a wide berth: it is a concept alien to creatures such as monstrocorns, which evolved as the toughest animals around, but now find themselves swung around like living ragdolls by gigantic aliens beyond their comprehension, often to fatal results. These tribbetheres, limited to comparatively small sizes by their leg arrangement, will never again roam the continent uncontested as they did for millions of years. The age of thorngrazer domination of the land comes to a harsh and sudden close as the age of dinosaurs returns in full force with the success of the sauropod-like gantuans and their relatives.

Using their superior size and a propensity for aggression to dominate even the once indomitable thorngrazers, gantuans such as the cygnosaur now impact nearly all land habitats on Serinarcta in a big way. Even when they are not angry outcasts, gantuans are often territorial and intolerant of competitors in their feeding grounds, bullying smaller and slower animals out of their way. So as thorngrazers now grow smaller and faster to avoid the threat these competitors pose, plant communities change as their grazing pressure is reduced, and a trophic cascade occurs as one thing leads to another. No longer grazed down to the soil as seedlings, forests of broadleaf clover trees have popped up all across the continent, competing with established spire forests, and forcing these to become more aggressive to defend their habitat. Cygnosaurs, a relatively aquatic group of gantuans, are good swimmers and often move along rivers in the soglands where they meet forests, moving through this mixed environment and keeping the tree cover more open with their feeding, forming new biomes: savannah woodlands that follow the rivers along their banks, allowing new plant species to colonize and thrive. Yet while plant diversity goes up, animal diversity declines over Serinarcta overall as gantuans with niche-partitioning life stages replace differently-sized species in the ecosystem. Even so there are some net benefits brought to some animals by these new mega-herbivores: thorngrazer parasites jump ship from their former hosts to a much bigger buffet, while a significant increase in dung in the environment favors larger forms of insects that make use of it as a food source. Predators by now have also evolved in time with the gantuans and begun to prey upon them, in the form of giant bipedal sawjaws, now the largest ever land predators.

abov : a male baronial cygnosaur, Saurocygnus augustus (grand lizard-swan), tries unsuccessfully to catch a pair of 2 month old chicks of the same species that have sought shelter in a cementree canopy just beyond his reach, even rearing on his hind legs. The earth shakes beneath him as he presses a massive clawed hand against the trunk, which sways slightly but doesn't topple or break, being tapered to a thick bulb at its base and built of a material more flexible than concrete due to the inclusion of plant fibers into its structure. The chicks are safe... for now, and the adult quickly loses interest and turns away to browse in a nearby patch of shorter trees. 

As for the cementree, these plant-animal symbiotes continue to persist despite the broad replacement of thorngrazers by gantuans, but their growth patterns have shifted. They now form more isolated clusters that build upon older spires over many years, forming raised ridges on the plains, and seedlings disperse only rarely to new ground. Towering cage-like spires are constructed to protect upward-growing saplings from browsing until they extend beyond the highest reach of any animal, and then the tree branches and grows a lush canopy like that which the cygnosaur chicks here have climbed up to to escape their hostile elder. These huge structures can be constructed before the tree that will use it is large enough to support the ant colony because the cementree spires themselves are grown in cooperative colonies. The builders borrow resources for the job from the more mature trees until the new tree is able to pull its own weight and provide food to the ants. 

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Gantuans undergo significant changes in morphology as they age, mirroring their own evolutionary history as they do so, in a less extreme way than earlier ornimorphs but one which still reflects their skuorc ancestry. Newborns are rat-like, weighing only a few pounds, and eat mostly insects and small animals in densely vegetated areas, often near water. They climb well in their first year, only losing the ability entirely as they exceed a weight of five hundred pounds. Over their first couple years of life they grow taller, longer, and more omnivorous, coming to resemble the scrunge, and at this size can still walk on two legs for periods of time to keep watch for distant danger. From there they gradually reach greater and grander heights as they become more fully quadrupedal and mostly plant-eating, but they never lose the inclination to catch a bite of meat if they can do so to supplement their diet - and this omnivory means that these enormous animals influence their surroundings in even more complicated ways, for cygnosaurs can also be predators, and even cannibals. Whether young are their own or not isn't a factor in this behavior; cygnosaurs practice no parental care and have no kin recognition of their offspring. While predominately herbivorous browsers, all cygnosaurs are opportunistic omnivores and will eat small animals of any kind. Baby cygnosaurs have advantages that help them avoid becoming their parent's midday snack however - they are small and fast, able to hide in thickets and to climb trees - things that other animals, like most thorngrazers, cannot. 

above: a fiendish cygnosaur, Saurocygnus avorsus (evil lizard-swan), feeds upon a crested thorngrazer that it has killed in a predatory behavior pattern. 

While cygnosaurs are by necessity primarily herbivores - this is the only food abundant enough to maintain their huge mass - these animals, like the thorngrazers, are not strict vegetarians. Cygnosaurs begin life with a diet leaning highly toward carnivory and are still opportunistic in adulthood. They will eat carrion readily, but will also occasionally kill smaller animals for the express purpose to eat them. The behavior is most pronounced in pregnant female cygnosaurs in order to supply their developing young with protein, but can occur in either sex and in all gantuan species. Predatory behavior is most often directed at thorngrazers and can be distinguished from territorial-aggressive behavior by the silence and calculated approach of the cygnosaur when hunting, compared to loud vocalizations and threat displays of territorial individuals. Hunting cygnosaurs approach their prey consistently in a chained behavior pattern which is always performed the same way. It begins with silent stalking, during which the animal approaches a smaller prey species from the side without obvious malicious intent, becoming faster and more purposeful if it flees. It is followed with a powerful sideways kick of a hind leg to knock the animal off its feet and finished by raising the front limbs off the ground and stomping the prey's abdomen. The hind claws are used to cut the carcass open. Cygnosaurs can only digest small quantities of animal protein in one sitting, and so are selective in only eating the most nutritious parts of the carcass. Lacking anatomical adaptations to feed on meat, the animal grazes on only the skin and fat, and then removes soft viscera of the body cavity, leaving behind most of the tough muscle meat that it is unable to easily remove from the larger bones. Thin leg bones are usually consumed by crushing them with the foot before swallowing, and provide a vital source of calcium that the vegetation of soglands often lacks in enough quantity.   

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The cygnosaurs represented here form a complicated cline across Serinarcta, with the draconic cygnosaur falling at one end and the baronial at the other. While these two species at either extreme of their north-south distribution are physically and behaviorally different from each other, with the southerly baronial being larger but the northerly draconic being more aggressive, they intergrade in between where most individuals exhibit intermediate traits. Further complicating their taxonomy is the smaller fiendish cygnosaur, mostly found to the east, which hybridizes with both forms where they meet, as the males of the two larger species often mate with fiendish females. All of these species have diverged so recently in evolutionary time that barriers to their hybridization are incomplete.