Sharkanthers and Spiderfish: Hunters of the Darkest Depths

295 Million Years Post-Establishment

The apex predator of the polar basin's inland sea remains the darkshark, now shaped by its surroundings over another 5 million years into an even larger and highly distinct descendant known as the sharkanther. A predator of sea horses, this fearsome whiskerwhale grows to a length of 26 feet. Its dorsal fin is reduced to a nub, to facilitate travel beneath ice, while its teeth are fused into catastrophically powerful cutting blades on each jaw, designed to tear mouthfuls of flesh and muscle from even larger prey animals in debilitating bites. The upper jaw is now highly modified, with a cleft upper lift through which forward-facing recumbent 'teeth' from both sides of the upper jaw converge into a saw blade-like structure. This is used by the sharkanther to further slice into and dismember its prey, but it has evolved primarily in response to a need to keep open breathing holes beneath the sea ice during the winter, something that this species must do constantly to survive, and must do with its teeth. The blade-like structure of its "teeth", still formed in early embryonic development from keratin, is now ossified into a matrix of bone by the time the animal is born, and protected by a layer of dentin; this lends greatly increased durability and the ability of the sharkanther to wear off the worn outer layer of its teeth faster than the bone beneath it, keeping its bite sharp. A skuorc which has convergently evolved to resemble a sawjaw under totally different environmental conditions, there is now no other bird quite like it in the world.

Solitary animals, sharkanthers have the capacity to slightly lower their metabolic rate in winter, reducing their need for oyxgen and their caloric requirements so that they can remain under the ice for as long as four hours - this is longer, though only marginally, than the longest recorded dives by any whale. This comes at the expense of being capable of sustained bursts of speed, so that in winter sharkanthers are sedate, slow-moving ambush predators. They travel distances of several miles from their breathing holes in the search for food, maintaining a remarkable mental map of their movements in space even without landmarks and being able to return to where they last took a breath hours later; magnetic particles in their brains likely serve as navigating beacons, sensing what still remains of the magnetic field and allowing the animal to align itself in its prior location with a high degree of accuracy. They have keen sight, an acute sense of smell, and sensitive whiskers on their faces which they use to feel the sea ice overhead and avoid crashing into it. They also navigate crudely by sound, producing sharp clicks with their teeth which will echo against prey animals that may be hiding in the darkness out of range of its vision. 

They hunt for prey not by searching the depths in hope of coming across one, but by seeking out their own breathing holes through their simple sonar; the echo that returns to them from the sea ice will be very different if there is an opening in it, and an opening means that another animal will return here to breathe within a short time. Once they successfully locate an active sea horse breathing hole, they can also use it to refill their lungs and re-start their dive timer, giving them an advantage to strike it and take it down before it is able to breathe. Sharkanthers can identify the species which has made a hole in the ice by its structure; sea horses push upwards and smash the ice out of the water, while snagglejaws - potentially dangerous - will punch down, producing holes surrounded by ice chips stuck beneath the ice around the puncture. Other sharkanthers, in contrast to both, saw their breathing holes, producing a neater, rounded structure. Sharkanthers in winter do not tolerate intruders and will fight savagely; upon coming across another's breathing hole, a sharkanther will quickly divert its route far around to avoid such a confrontation. Even so, adults are usually marked with numerous scars from the raking teeth of rivals that have bitten them in such territorial contests. When the ice of the basin melts in summer, food is no longer scarce, and sharkanthers no longer aggressively fight; having mated in the fall, young are born with the first light of spring, and will grow quickly hunting seasonal prey in warm, sunlit shallows.

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Though it is not as imposing in size as the sharkanther, the sabertooth spiderfish is just as frightening and most fascinating in its own ways. A large predatory bannerfish that hunts the depths of the polar basin in the early final stretch, when this vast inland sea is covered with seasonal ice for up to half of each year. Growing to a length of 6.5 feet, it is over three times larger than its hothouse ancestor, having moved into the vacated niches of other predators which did not survive the cooling of the basin at the hothouse's end. Sabertooth spiderfish descend from benthic foragers which used their paired extensions of the anal fin as feelers to probe beneath rocks and substrate and located hiding prey animals. Now they are pelagic, streamlined and quick, spending much of their time in the water column, but these specialized fins still serve an important use in navigating as feelers, preventing this hunter from hitting the uneven sea ice, which it often hunts just beneath in the winter season. These spiderfish, having no need for air, can monopolize the entire under-ice surface including in the most northerly regions of the basin where it becomes difficult for other animals to break open breathing holes. Their diet is comprised of other fish almost entirely, which they strike almost always from above, hiding against the ice. Living in a world without light, the blind spiderfish navigates through echolocation, with a small hump on its back, just above the head, being full of an oily substance which focuses their clicking calls and likewise absorbs returning echos efficiently from all directions, transferring sound waves into the bones of the jaw. This way, the spiderfish can hear in all directions at once.

Packs of sabertooth spiderfish live as cooperative hunters; groups are based on matrilineal lines, with mothers and their young forming multigenerational family units that are highly stable. These groups live together, protect their young as a group, and exhibit many hallmarks of the highest level of animal intelligence and social complexity, up to and including empathetic tendencies: group members will provide food and shelter to injured individuals of their packs, allowing them to survive injuries they could not on their own. Echolocation is not used to communicate, however; for this, the spiderfish speaks in weak electrical impulses produced in the muscles of its tail. These signals, imperceptible to prey and only understood by other spiderfish, let the hunters speak in silence when closing in on prey. The intensity, duration and pattern of individual clicks is varied to indicate different instructions to coordinate their hunting efforts, with these fish even being capable of back and forth discussion - the clicks have every indication of being a sort of rudimentary animal language. Further, this language is neither innate nor universal. At least two subcultures of sabertooth spiderfish exist in the polar basin. They differ significantly in their 'dialects' and cannot communicate with one another, which has led to total reproductive isolation. This language of electricity - speaking with metaphorical sparks - is learned in infancy. Young stay close to the adults for over 2 years before they are semi-independent, and babysitters alternate their role in attending the schools of vulnerable young which follow very close to them like baby ducks. Even females (the dispersing sex) don't leave their mother's pack until as old as six years. This very long childhood is necessary because unlike nearly any other fish in the sea, these spiderfish teach their young the ways of their life. This gives them a competitive edge in a changing landscape, for by being capable of learning new tricks for survival, the sabertooth spiderfish can more rapidly adapt its behavior in the face of new challenges. For this reason, it is thriving at a time where many basin lineages have faced significant declines.

The two groups of sabertooth spiderfish differ not just in their dialects but in their behavior. Unable to understand the other, but with virtually no genetic differences, they do not interbreed and would thus be highly competitive over the same food resources if they lived in the same ways. The more common group to be found in the basin is the "skaters", which spend their winters beneath the pack ice - very often flipping themselves upside down, so as to angle their mouths, which have longer lower jaws, downward in the direction of prey. Skaters slide inverted, their bellies almost touching the ice, as they patrol in packs, darting downwards suddenly and swiftly to catch their prey. In summer, they descend to great depths, where the darkness persists, and hunt near the sea floor, darting upwards to snag their prey. Most food taken by this subculture is small enough that a single individual can catch and subdue it, with the group working together to herd shoals of fish and prevent their escape.

 The second group, the "strikers", is strongly pelagic. They do not invert themselves below sea ice, nor do they winter at low depths. They are year-round active predators of the open midwater, and they favor larger prey animals. Their version of cooperative hunting is to bring down big game, sometimes animals bigger than themselves. Their winter diet is primarily other fish, but in summer they remain in higher water while their relatives retreat into shadow. So efficient is their sonar navigation and their electric language, that the strikers now hunt in sunlit waters throughout the summer, even though they are totally blind - and they hunt sighted animals in their own element. Strikers alone will ambush and kill air-breathers, including seahorses, savagely outnumbering and overpowering them in piranha-like swarms, using their huge teeth and a rapid spinning maneuver to rip and tear flesh from even the biggest carcasses. By so totally differentiating their habits and ways of life, the skaters and the strikers rarely meet and don't compete over prey. If they do come across one another, they are usually avoidant; they seem to find each other foreign and disconcerting, so alike, and yet utterly incomprehensible.

The sabertooth spiderfish's social complexity, capacity for learning, and behavioral adaptability make it, almost assuredly, the most intelligent non-tribbethere fish to have yet lived, and even then, it is smarter even than a large percentage of tribbetheres. Its brain is enormous relative to its body size, bigger in comparison than any bird or tribbet, though a significant percentage of its mass is dedicated to highly specialized use, particularly forming a map of its surroundings based on echolocation data and receiving electrical signals. This spiderfish has culture passed down generationally, and individual electrical impulse signatures acquired by each one as it grows are used as names both to refer to one's self and to direct communication toward others in the group. That this fish is a near-sophont species is certain. On land today, only a few subsets of tribbetheres, including savage unicorns and snagglejaws, can match its long list of hallmarks of intellect. Sabertooth spiderfish are probably smarter than a majority of life on Serina today, including most birds. Whether they should qualify as something more than animal, a person, could be debated endlessly, for the precise line where one ends and another begins is a long, gray road of possibilities. It is easier to regard something as someone when it shares traits in common with you, something with eyesight and lungs and perhaps hands or something like them to hold with, but the sabertooth spiderfish is alien, even to the most unusual of other highly intelligent animals it shares it world with. Exactly what it means to be a spiderfish, to live in its cryptic, shadowed world - or what it might itself refer to as a world brilliantly illuminated with sound and electricity - may never be known to us primitive land lifeforms living our own mysterious lives, blind to such senses we have never felt. Does ever a spiderfish, waxing poetic, contemplate fellow intelligent life somewhere out there, beyond the ice?

It is an unfortunate truth, no matter how bright it may shine, that whatever the spiderfish might be now, is likely all it will ever be. Confined to a shrinking aquatic world, it has no way to expand beyond its limited habitat, and no way to modify it. In this way, at least, it remains an animal ultimately at the whim of its surroundings. The polar ice and the stark line that separates sea from sky is as great a barrier to the spiderfish as the starry sky is for others, and none yet have broken through that ceiling. For now, at least, it is a success story on Serina. It has already outlived many species, including people. That it may never change the wider world beyond that it knows, or that there may be no grand epics told about its triumphs, does not diminish its importance simply for existing in its own right, for its own reasons, little-known and rarely seen by all others. It is, for now, still perfectly adapted in every way it needs to be. 

And long may it be so.