above: a lone lumberbeest browses in the deepest depths of the equatorial jungle.
The warmer forests near the tropics across central Serinarcta in the Ultimocene, 250 million years PE, support incredibly high numbers of ants, which live symbiotically with most of the trees of the time, providing protection from browsers in exchange for nest sites and food. Here, it seems that nearly every tree is covered in a constant stream of tiny moving bodies, running to defend their hosts whenever they are threatened with a barrage of irritating bites or stings. Most of the ants are not particularly aggressive, merely irritating, but they are nonetheless enough of an inconvenience as they gather in swarms to keep the various large browsers of the forest moving from branch to branch, never lingering long enough to cause significant damage to any one tree. Most symbiote ants are selective defenders, paying no mind to a carnivore brushing past or a fruit-eater leaping through the branches; they concentrate their aggression on active plant predators, herbivores physically damaging their host trees, which release volatile organic compounds into the air when physically damaged - pheromone signals which the ants have evolved to understand and respond to as a cry for help. Within a minute of a browsing bird or molodont starting to chew on its stems, the sunflower tree will have called its armies; in another minute or two, the ants will have gathered at the site of the attack in sufficiently large numbers to drive off the hungry animal, climbing into feathers or fur and biting at the exposed skin of lips, noses and eyes. Herbivores must be very attentive when browsing, as not only will the ants of a single tree respond to the cries of their host, but ants in adjacent trees downwind will also pick up the alarm and be ready should the browser come chomping in their direction. They must approach all food sources downwind and move into the breeze as they go, spending just a few minutes nibbling at each branch. Some herbivores cheat the system by adopting new methods of browsing without leaving time for the swarms of ants to reach them, such as breaking off single large branches, shaking them vigorously to dislodge any of the insects, and carrying them away to strip off the unprotected leaves. The vegetable food resources of the ant forest are still attainable enough to support many herbivores, but require considerably more ingenuity to obtain than unprotected vegetation that may be nibbled at leisure. The complex relationships between symbiote ants and their host trees thus produces a selective pressure for more intelligent herbivores than were formerly required to reach the same food sources, ones better able to solve the problem of circumventing the insects' defenses. Highly intelligent rhyncheirid birds, with big problem-solving brains, thus come to monopolize herbivore niches in the broad-leaf forests over their main contemporary competitors, the circuagodonts which conversely dominate the grasslands and cool polar forests where insects are far less numerous.
More intelligent feeding strategies, though successful as they are, are not the only way of dealing with the defenses of myrmecophyte trees, however. An equally viable option is physical toughness - the evolution of thick skin or otherwise protective body coverings that prevent insects from stinging or biting. Adaptations of armored snouts have appeared in various bird groups since the dawn of the ant forest, proceeding behavioral ant-avoidance adaptations, and remain effective though less common in the Ultimocene. Undoubtedly the most extreme example of an armored but slow-witted browser is the strange and rarely observed forest giant known as the lumberbeest.
The lumberbeest is the largest living muck on Serina, one of the last terrestrial representatives of this clade, and the only living member of a family all its own - others like it were formerly abundant in the early Pangeacene, but diversity has been in a steady decline since, largely due to the evolution of new, more adaptable competitors. Now found only in the densest, most inaccessible regions of the tropics, the last giant is a veritably enormous beast standing upwards of twenty-five feet tall and weighing two tons. It is a creature of marshy woodlands and swamps, where the densest jungles are criss-crossed by large silty rivers and broken occasionally by open flood plains. As it moves, it walks with a side to side waddle like a giant goose on large splayed toes that spread its weight out on muddy earth, its body carried at a forty-five degree angle and its tiny head resting at the end of a long curved neck that makes up half of its total height. Though it may feed far from water by night, it often spends the day retiring in the rivers or muddy swamps, freeing its squat little legs of supporting its hefty body and submerging until only its head peaks out from the water in the reeds along the banks. The lumberbeest will travel the wide rivers preferentially to and from feeding sites, swimming with strong kicks of its webbed feet and strokes of its large clawed forearms, always floating just under the water with only the hump of its back and its head and neck protruding. Its diet is broad, almost anything green will do, and it can afford to eat leisurely from a single tree at a time thanks to its armored skin and nictitating membranes that slide over its eyes to guard against even the fiercest ant bites. It lifts its neck high into the canopy, reaching leaves inaccessible to other ground creatures, and feeds unperturbed even while hundreds of ants swarm down the branches in defense of their homes and crawl across the hide of its face, stabbing their little jaws and stingers against the thick scales futiley and to no effect. They find few orifices to climb into - the lumberbeest can simply seal its ears and nostrils as it feeds. The horny keratin of its short, tortoise-like beak provides no surface to bite, and even the tongue is armored in a thickly protective covering of this keratin. Countless ants stream into the giant's mouth as it swallows and are carried right down the lumberbeest's gullet with the vegetation, to no harm to the animal, which simply digests them as well. Very little bothers the lumberbeest, for no predator exists that can harm it as an adult. They are mostly solitary but do not oppose company, and multiples may gather and feed together from a single tree or bed down in the same pool during the day.
The lumberbeest's metabolic rate is slow but even so it must spend most of its waking hours feeding. Like most mucks, it also has a poor ability to control its body temperature. Young individuals must stay comfortable by environmental means, sunning themselves if they become chilled or seeking shade if they are overheating, though adults are large enough to stay warm without much effort and are mostly only concerned with keeping cool in very hot weather, which they do by retiring to the water. Nonetheless, the amount of warmth generated by gigantothermy is finite and so the temperature range tolerable for the lumberbeest is still thin, restricting them to the tropics where temperatures never drop below freezing. Though they do most of their feeding on land, lumberbeests will also feed whilst in the water by extending their necks to graze on waterside vegetation. Occasionally they may even submerge completely and graze on algae and water weeds on the bottom of the water just as their distant ancestors did.
To reproduce, the female lumberbeest buries a clutch of eggs in a patch of soft, silty soil in a clearing near a riverbank, where the sun will warm them. She lays upwards of thirty at a time, producing three per day for one to two weeks and storing them together in an internal tract, only depositing them when the clutch is complete. She digs out the hole with her long forearm claws that work like pick axes to cut into the earth and lays her eggs in layers, between which she fills in the hole with soil. Mucks are noteworthy in that unlike most birds, they have temperature-dependent sex determination; each egg laid is sexless, and will only develop into a male or female if conditions are right. In normal conditions, the eggs higher in the nest, exposed more directly to sunlight hitting the soil, are kept slightly warmer and mature into males. Eggs lower in the nest, kept cooler, mature into females. This differentiation may serve a purpose in that if nests are raised by predators, the eggs containing the less valuable male embryos will be more likely preyed upon than the more important female embryos (as only one surviving male is need to fertilize many females in mucks, which have no pair bonding.) The mother lumberbeest provides no further care to her brood once she lays her eggs, and their fate is left to luck.
If all goes well, the eggs hatch several months later into several dozen very precocial infants, more or less identical to their parents but much, much smaller - only about one pound each - and also much more agile. Just seconds out of the egg, they scurry for cover. The chicks are on their own from the start and are arboreal, climbing into the nearest tree with well-developed claws and grasping talons as soon as they leave the soil to avoid becoming a quick meal to a passing predator. Their hind toes are initially suited to grasp branches and are opposable in a zygodactyl form, which they lose as they grow and their feet change into a pillared structure better suited to supporting great weight. They take ten years to reach sexual maturity and as long as thirty years before they are done growing, and until the age of six or seven years they will rarely leave the treetops. While almost totally vegetarian in adulthood, excluding the insects they swallow incidentally, the lumberbeest starts life with a ravenous appetite for insects and is mostly carnivorous in infancy to allow for the rapid growth it must put in to reach its adult size. Individuals gradually begin to consume more plant matter from the age of one year on and are mostly weaned onto a plant-based diet by the time they become too large to easily move through the branches, though they will continue to eat small amounts of insects, mostly accidentally, throughout their lives. Very young lumberbeests are vulnerable to a number of threats including birds of prey and tribbats, while juveniles just coming to ground are often taken by grapplers. Mortality is high, and only one in two hundred chicks can usually be expected to reach sexual maturity, though if they can get to the point that they are too large even to fall prey to the greater grappler, the odds are in their favor that they will experience a long life - a hundred years is not unattainable.
I am open for commissions! Note me if interested!