Rapid global cooling during the mid-Ultimocene ice age has decimated entire ecosystems across Serina. Plants and animals which had evolved during the warmer age of the early Ultimocene were left blindsided by a sudden drop in global temperatures, leading to a mass extinction of life and lineages. But as with all change, even the most calamitous, there are organisms which are pre-adapted to respond favorably to the new conditions. Cactaiga, a clade of boreal sunflower descendants which previously occupied cold, dry regions, have experienced sudden and prosperous success in a colder world as they have now spread across the remaining unglaciated land of Serinarcta and formed a new dominant floral community, creating a new biome that shares the name of its primary producers.

The Cactaiga as a clade are a family of sunflowers which diverged from the better-known sunflower trees early on in Serina's history, adapting first into small perennial shrubs of dry environments, filling a niche between small conifers and cacti. This group survived through the ages both hot and cold, producing large tree-like species during the Cryocene, and small species survived the end-Thermocene extinction to which they were well-adapted as a result of their tolerance for drought and poor soil conditions. These survivor species were primarily shrubby, branching plants. They no longer grew leaves (or grew them only briefly during a short summer season), instead photosynthesizing with fleshy green stems. They grew low to the ground to avoid desiccating winds and conserve soil moisture, but during the early Ultimocene gave rise to a new group of trees known as towertrees [no post yet], redwood-like succulent trees which grew larger than any plant on Serina before them and reached upwards with their specialized photosynthetic branches in unique spiraling patterns around a central trunk. This clade survived until very recently, succumbing to climate change within the last ten thousand years. Now smaller, hardier species from the north have replaced them, low-growing and thicket-forming bushes and small trees which survive the harshest chill. These grow tightly together in impenetrable stands to form a weight-bearing lattice between their many individual stalks, becoming cooperative to survive. Limited to cold, dry climates in the northern continental interior and along mountain slopes during the early Ultimocene, cactaiga now grow widely over the northern continent everywhere that the soil is freely-draining. Though they are short, never able to grow more than eight feet tall due to the cold climate, they form a forest - the very last one during this period - and like the trees of any forest, many animals have evolved to depend upon them for survival.

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The largest and most obvious fauna of the cactaiga are the thorngrazers, ox-sized molodonts with fierce horned faces and gigantic grinding jaws that can break down nearly anything vaguely organic into nutrition to survive in even the most inhospitable places. Known as omniphages, thorngrazers fill a very broad niche that no modern Earth animal does as both the primary herbivore and the primary scavenger, as they can digest both coarse plant materials and flesh and bones. In the cactaiga multiple species have evolved, all well-insulated from the cold with thick, shaggy fur coats unlike their earlier desert ancestors, and they are the only animals which can control the growth of the plants which are extremely well-armored against herbivory with massive silica-edged thorns. Thorngrazers are the eco-engineers of the cactaiga just as the antlears were in the broadleaf forests, and the trails they clear via their grazing opens up the environment, allowing other plants to grow between their sheltering thickets and ergo building protected microclimates for smaller animals. One of the animals that lives in these clearings is the strange and small burrowing antlear, no bigger than a fox, which has adapted to the extinction of broadleaf forests much better than its sapient relatives and learned to dig itself underground shelter to stay warm with its antlers, now more leg than arm. It feeds on grass, twigs, and herbs, foods too poor in nutrition to support the specialized woodcrafters but adequate for this smaller-brained and solitary animal to maintain itself upon. Hunting the aberrant antlear is the hugger, a carnivorous descendant of the chiselers belonging to a new clade of hunters called cutthroats, which have left the trees to hunt larger vertebrate prey. One of the smallest and most basal species, the aptly-named, cat-sized hugger ambushes its prey by pouncing upon the back and grabbing tight with the forearms which are armed with three hooked, opposing talons. Once it is restrained, the hugger uses its large, serrated teeth like blades to sever the spinal cord in the neck of its victim. Larger cutthroats, on the contrary, usually kill by cutting out the throat, thus leading to the common name of the greater clade.

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Without the thorngrazer to open up the environment, the cactaiga would be a much less biodiverse place. Yet one animal is more dependent on the thorngrazer directly than even the rest. The siphontooth, a mouse-sized molodont descended from the tweezertooth glider, is now a dependent parasite to these large hulking herbivores. Over millions of years the tweezertooth began associating with various large herbivores to take advantage of catching the insects their browsing disturbed from their hiding places, leading to species such as the ripgleaner. The siphontooth's ancestors took the association further, feeding directly on blood-sucking parasites from their hosts bodies, before developing a taste for blood itself and becoming them. Working off of pre-adaptations it first evolved to pry and pincer grubs out of tree bark, the siphontooth's jaws have now evolved into a remarkable apparatus - a biological syringe. They now feed by sliding a needle-like upper tooth into a much longer, tube-shaped and hollow lower tooth. Poking the bottom one between the thick hair of its host and into its skin, the creature then retracts its upper tooth from the tube, producing suction to pull blood into its mouth. It has become a vampire, and now spends its entire life on the bodies of its hosts, jumping and weakly gliding from one to the other and taking advantage of the fact that while social for convenience sake, thorngrazers do not groom each other, and thus cannot easily remove the pest as it clings to their bodies in places they themselves cannot easily reach.

The needle-like teeth of this animal may appear fragile, but they are strengthened by incorporating iron (taken from its blood diet) into their structure, turning them dark red. As the teeth grow continuously from the root, the needle does not wear down and become blunt. Passing through the thick epidermis of the host is all that is required to wear away jagged edges and keep the tool sharp.

Siphontooths are also truly quadrupedal tribbets, as the two outer fingers of their hind leg have become highly elongate. They face backward, like the legs of a grasshopper, and allow this mouse-like animal to leap great distances between hosts, while the middle digit serves as a balancing tail with only a small gripping claw. They have a much reduced gliding ability compared to their ancestors, as they now rarely need to cross large distances as their hosts live in large groups.

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Cactaiga plants barely resemble sunflowers any longer - hundreds of millions of years of changing conditions has reshaped almost every aspect of their biology. But they still must flower to set seed and reproduce themselves, and if you look closely enough, you can still see some resemblance in the structure of their blossoms. Sunflowers are in the daisy family, and so the large bloom that what we generally called their flowers were actually a composite of many individual five-petaled flowers born together in a cluster, surrounded by a set of large and flamboyant petals. The real flowers were tiny, visible within the cluster only on very close inspection. The cactaiga plants long ago lost the large petals, but still bear the small true flowers in a cluster, on top of a large swollen stem that is in fact a huge nectar reservoir, holding up to a cup of sweet sugary water. The whole structure is very long-lived for a flower, lasting several months during which time the nectar is continuously refilled by glands in the stalk while new flowers develop insulated inside the top of the swelling, out of the chilling wind. Each night, just after sunset, a few short-lived flowers emerge from the protection of the stem and bloom into the cold air. They last only an hour in the frigid temperatures at the equatorial night and a little longer during the northern summer, but this is enough to attract their pollinators.

Butterbirds, a group of hummingbird-like metamorphs whose larvae live underground sucking the sap from roots for years before maturity, emerge from daytime hiding places to feed after dark. These little birds can go into a low-energy state of torpor for more than twenty-two hours every day at the equator, or for months at a time during the northern winter, in which they use almost no energy, allowing them to survive on remarkably little food. Only when they know that the flowers they need will be open do they wake up and fly over the thickets, using their acute eyesight to search out the stark white flowers against the dark backdrop. The plants hide their precious blooms deep within their thorns to protect them from large herbivores that would eat them entirely and ruin their chance of reproduction, but the little butterbirds easily climb through the spikes with their grasping toes and tiny wing claws to reach their prize. Using their extraordinarily long brush-like tongues, they reach through the flower and into the deep nectary to feed on the sweet, energy-rich reward they find there and inadvertently brush the stamens of the blossoms with their chins, thus carrying pollen to other flowers as they move about and feed and thus pollinating the cactaiga. Only much later on after all the blossoms have died and the nectar been depleted does the flower stalk lengthen enough to push it out of the thorns and into the open. By now it has swelled further and ripened into a seed-filled fruit, which is advertised openly to all passers-by, eaten by animals of many kinds, and thus their seed dispersed in their droppings.

All butterbirds supplement their nectar-based diet with animal protein for their growth and the development of their eggs. Most species catch a few nocturnal insects during their active period, usually various beetles or flying ants which fly by night and insulate themselves with moth-like fuzz. They catch them punctured on their upper bills (they have no lower ones, a result of the larva's specializations to puncture and suck sap from roots) and eat out their soft innards. But for some just insects are not enough - they have become true predators. The skewer is a very large butterbird, about as big as a thrush, which hunts other birds - mostly its smaller relatives. It, too, emerges from sleep at sunset and lifts off from the ground where it hid by day via its cryptic markings to search for food. Like them, it seeks out the white blossoms of the cactaiga and enters the thicket to reach them. But it does not want the flowers. Instead it finds a perch nearby, freezes and hides in plain sight, and watches and waits for another bird to come for a drink. Smaller butterbirds are faster and more agile in the sky, but when caught by surprise the predator can snatch them as they are crawling through the thorns around the flower and unable to take flight. Using a highly mobile upper beak this group is known for, they reach in and skewer their prey, then pull it still struggling out of the thorns to feed. The upper mandible is barbed, rendering the prey helpless to pull free as the hunter injects its own tongue into the wound. Unlike the nectar-collecting brush of other butterbirds, the skewer's tongue is covered in keratinous hooks and blades which it uses to cut and pull out out the prey's internal organs as well as drain all of its body fluids. When it finishes feeding, only an empty husk of skin and bones will remain with all of the flesh removed through a single small entry wound. Though the skewer still sometimes consumes nectar, it is so large that it merely pops a hole into the flower's nectar resevoir to get to it, bypassing the stamens, and drains all of the fluid in one go, effectively preventing it from reproducing. As such, it is no longer a pollinator but a plant predator.

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The skewer is not the only small-scale predator that other birds and animals need to worry about in the cactaiga. The bonebower bird, a type of sparrowgull no bigger than a sparrow, is a deadly effective hunter that lives here too, and it has learned to use the cactaiga's thorns as tools. Making up for the fact that it doesn't have a particularly sharply hooked beak like the skewer does, this very intelligent bird simply hunts other birds as well as tribbets and anything else small enough to bring down with weaponry, using thorns as spears and stabbing them in the head or chest, often while they sleep. The use of tools even allows this surprising little hunter to take down prey larger than himself. Male bonebower birds also use the spikes for another, arguably even more morbid purpose; he saves the skull, and sometimes other elements, of every kill he makes and hangs them for all to see in a meticulously maintained collection high on a branch over a clearing. Using this special place to sing and advertise to passing females, he demonstrates in the most fundamental way his success as skilled hunter and tell the female he would provide abundant food for her and her young. The males with the best collections have the highest mating success.

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Not all small animals of the cactaiga are vulnerable to the bonebower bird, for even the best strategies to hunt cannot render the fireslime lumpus edible to him. A tribtile with a very conservative anatomy almost unchanged since the very first tribbets left the water, at first glance the lumpus appears a docile and defenseless animal, fat and slow and very much harmless. And he is indeed most of those things, but only because he is anything but harmless. The fireslime lumpus is extremely poisonous, secreting a mucous when threatened which contains deadly batrachotoxin, a neurotoxic alkaloid which in high enough quanity forces open the sodium channels of animals' nerve cells and prevents them from closing, resulting first in total body paralysis and then death. Skin contact of this mucous of the lumpus is enough to cause a powerful burning sensation, which may linger for many hours, and thus the lumpus is free to go about its business lazily scooting along the ground and consuming small beetles (from which it synthesizes its toxicity), left alone by almost anything which might otherwise be inclined to attack it. - except for one. The spitfire sniffler, a very closely related species to, and likely descended from, the spiny sniffler, feeds upon lumpuses including the fireslime lumpus with impunity. Having evolved an immunity to the effects of batrachotoxin, this tiny trunko not only eats the deadly tribbets but steals their defense. By chewing the skin into a paste and grooming the resulting froth onto its quills, the sniffler renders itself deadly poisonous. For by concentrating the toxic skin secretions of so many lumpuses onto itself, the sniffler becomes not only highly painful to touch but downright deadly, poisonous enough to kill any animal it touches with its quills. Thus fully protected from predators as well as able to kill many competitors, the spitfire sniffler is frequently the only sniffler species to be found in the cactaiga. It warns would-be predators to avoid their deaths with bright warning coloration in black and gold bands along its body and is so confident in its armor that it has virtually no fear of predators, even boldly marching up to much larger carnivores and taking bites from their kills.