The Sonicorn and The Snowdevil

300 million years PE, the climate is becoming more inhospitable across the world of Serina. Equatorial regions become hot, scorched deserts with a deadly UV index, while closer to the poles the world is gripped in a new, powerful ice age. With the sanctuary craters now also becoming colder, the life that sought refuge in those lower elevations will eventually be lost, too, even if that time has not yet come. But conversely, animals that continued to hold out in the outlying regions at higher elevation may last far longer, for they have had the time to adapt to the worsening conditions gradually rather than all at once. It is so that while the lowland unicorn is now extinct save for its highly modified, tamed descendants, the hardier highland species remains, and has split into multiple descendants. Among them is the large, bizarrely ornamented sonicorn of the frigid north. With the extinction of many megafaunal groups in the last ten million years of severe climate change, these once alpine creatures have now spread over the land and onto the plains and vast deserts of the continent. 

Sonicorns still resemble the highland unicorns they arose from - and the crater population that survives little-changed even until now - but have doubled in size, with larger curved tusks and much thicker, paler fur. They have massive lungs for their size, and like birds can benefit in the thinning air at elevations outside deep craters from their unidirectional respiration. They live in large groups, nomadic across the plains where they feed on anything they come across, mostly sparse, often dry grasses but also carrion, bones and other organic matter. Dense, long hair shields from harsh northern winds and strong sunlight on clear days, while the eyes are dark for protection from radiation and shaded by brow-like extensions of the head crests. They most noticeably sport more robust spiraled horns that have evolved their disc-like structure into a pair of massive resonating chambers near their tips, and through these they now produce among the loudest calls of any land animal which has ever lived, producing brief ultrasonic pings of noise in excess of 180 decibels, that are felt much more than heard. Crests are present to a similar degree of development in both sexes now, though largest in the male, and serve a function of defense: sonicorns have evolved to utilize their great voices as a deadly sonic weapon against predators. By producing powerful, extremely high-frequency bursts of sound in the direction of threatening animals, sonicorns can induce severe injury, explosion of ear drums, and at close range even death through brain damage to enemies, and so keep even the most dangerous animals that still stalk the surface of the changing world at bay. Sonicorns live in groups for protection and alternate feeding and resting with a system of sentries that patrol the perimeter while the rest relax, so that the herd is never caught off-guard. 

Their fatal songs render the sonicorn almost immune to predation, especially from such formidable hunters as the leucrocotta that now roam over almost the entire northern continent, and this has allowed them to become among the most numerous land animals in these northern wastes. They also use their calls offensively, targeting them at small animals such as passing birds and small molodonts to stun them so that they can eat them. To protect its own hearing, the skull of the sonicorn has thick sound-absorbing fluid pockets which can be pressed together with the jaw muscles to completely seal the ear canal, while extraordinarily fluffy hair - as dense as a sea otter's coat - lines the entire inner surface of the outer ear, which can also seal up, providing further sound dampening. When not calling, a sphincter-like muscle valve seals the openings of the nasal crests to keep them free of debris and keep out the chill.

But there is one thing that their call cannot protect them from.

~~~

The destructive, localized sound waves produced by the the sonicorn render these thorngrazers almost immune to predation. But the almost is not to be overlooked. Sonicorn ancestors evolved their defense to fend off pack-hunting ground hunters like leucrocottas, animals very vulnerable to directed ultrasonic burst calls. They never had to contend with a threat unable to hear at all, lurking right beneath their feet. With a defense that relies on knowing exactly where your enemy is coming from, the sonicorn has no counter-attack to the ambush of the snowdevil, which has become its sole significant predator.

Snowdevils are burrowing strikeworms that make their homes in the ground of the northern desert and hunt grazing animals. Like other and earlier species of this group of extremely strange metamorph birds, they are extremely sexually dimorphic, with males being small, short-lived flying birds that do not even feed during the short northern summer, while females are massive and sedentary, growing to lengths of 10 feet and sometimes reaching weights of almost a thousand pounds after a large meal. They live in a single burrow for their entire life, digging it out in their first summer when the desert briefly thaws and then slowly expanding it with shovel-like hind leg claws over many years, with a potential lifespan in excess of a century. The female snowdevil never turns around in its den, and never leaves it by more than half a body length, always keeping its deadly pronged jaws upward to face any foe or strike any potential prey; as for all bumblebirds, the larger set of jaws is actually derived from their wings, with the real jaw smaller and located between them.

The snowdevil lies in wait for weeks and sometimes months at a time for prey to come near, living most of its life in a dormant state. Yet even if it appears dead, down below the ground and its den entrance covered with snowfall, antifreeze chemicals course through its blood, preventing frostbite, and it is always perceptive to ground vibrations that hark the arrival of food. The snowdevil cannot hear - not really - for it has no external ear, or any ear drum at all. Its entire body instead feels the movement of footsteps and vocalizations coming from above, and so it reacts by vibrating muscles down its body length to rapidly warm itself and ready for attack. The success of the snowdevil lies in surprising the sonicorn as it steps above the burrow, focusing its jaws against its target via its heat-sensing organs, grabbing it with enough force to stab its chest and puncture its huge lungs to deafen it, and drag it below ground before its fellows can react. An attack takes place in seconds: the snow seems to explode in a white cloud that temporarily obscures visibility, as one member of a herd simply vanishes into thin air without time to call out. An adult snowdevil can survive for a year on a single kill like this, slowly gnawing on the carcass over months, which does not decompose in the cold. Once sparsely distributed over the land, the snowdevil now is widely abundant, sometimes occurring in aggregations, rendering the seemingly barren plains a mine-field of danger to an animal with little else to fear - and keeping the numbers of even the most seemingly invulnerable animals in check. 

They never know what hit them.