The Feasters Below

This is a thought experiment, coming up with a semi-plausible explanation for cryptid monsters in a story. Will this hold up as hard science? No, of course not. I only seek to help suspend disbelief just long enough for people to enjoy the story. The premise for the story is a small town in Pennsylvania comes under siege by these beasties and the locals rally to fight them off. These monsters are not supernatural, do not have magic powers and are meant to be part of the natural world we've yet to discover.

Overview

Homo Chthonisis (Underworld Man, from the bastardized Greek chthonic/chthonian) A newly discovered member of the Homo genus in Hominidae, the great ape family. H. chthonisis replaces P. paniscus (the bonobo) as the closest extant relative to humans. Preliminary research indicates that divergence from the line leading to modern man must have taken place over two million years ago when H. habilis and H. ergaster were the dominant hominids. The extent of worldwide habitation within the deep world is unknown, nor is there even a preliminary theory of how the species has spread. Eusocial, subterranean, burrowing, this creature is every bit as much a marvel of evolution as is man.

Discovery

There have been a number of cryptid hominids claims over the years from yetis to Big Foot and skunk apes, all supposed survivals of ancestral human forms. Skeptics have argued against the possibility of such creatures given human encroachment into unexplored habitats, territorial needs for supporting a viable breeding population, and the lack of any supporting evidence within the fossil record. Because of the very habitat they live in, infrequency of visits to the surface and ritual cannibalism of their dead, it becomes very clear why we have had so little contact with them.
The biggest question puzzling anthropologists is why H. chthonisis has remained successfully hidden for so long but is now suddenly thrust into contact with human civilization. Early speculation on habitat destruction zeroed in on the process of hydraulic fracturing, aka “fracking,” used to increase the rate of oil and natural gas recovery from reservoir rock formations. While the wellbores never came near the deep caverns where the colonies reside, it is well-established that gases and hydraulic fracturing chemicals can migrate great distances, contaminating groundwater supplies. The prevailing theory is that the subterranean ecology has been disrupted, thus forcing H. chthonisis to come to the surface for forage.

Physical Characteristics

H. chthonisis is believed to have undergone incredible selection pressures in its underground environment with physical divergences from hominid anatomy that are radical and unprecedented. Many evolutionary biologists would have flatly rejected any speculative theories concerning the existence of such creatures and find their theories woefully inadequate to explain the incontrovertible evidence lying before them.

The bodies, while seeming hairless, are covered in nearly invisible fine hairs that can detect the subtlest of air currents. The skin is gray and leathery, able to stand up to the abuse of burrowing. Their limbs are knotted with muscle like chimpanzees, pound for pound stronger than humans. They are natural contortionists and can maneuver their bodies through gaps that defy belief, a necessary skill underground.

For subterranean-adapted creatures, it is surprising that they retain highly-developed, lemur-like eyes. The deliberate cultivation of bio-luminescent lichen in their colonies is the answer. The eyes have a fully-developed nictitating membrane, unknown in primates save for the Calabar angwantibo. The membrane is not only opaque but highly reflective and shutters the eye instantly when exposed to a bright light source. Needless to say, the result of a flashlight in a dark tunnel playing across a snarling face with eyes glinting mirror-like is enough to unnerve even the most solid researcher.

H. chtonisis’ ears are highly developed and almost seem as if they belong on another animal. They are almost bat-like, understandable given their reliance on a form of improvised echolocation. The ears are very mobile and can be raised out from the head to capture sound or tucked flat against it to protect the ear canal from debris when burrowing. The tongue is used to create a sharp clicking noise, the “ping.” While the auditory cortex is not nearly as developed and specialized as with chiroptera or cetaceans, it is more advanced than with blind humans who have developed similar techniques for coping with a lack of sight. For H. chtonisis, there is no primary sense, all are used together.

H. chthonisis possesses a more pronounced muzzle than any other ape and the jaws are used intensively in fighting. The mouth contains powerful fangs and the jaw opens to a larger degree than with any other known hominid. In combat, the attacker will instinctively maneuver for the throat and a quick kill.

The hands are well-articulated allowing for fine motor control. When the fingers are held together with hardened nails at the fore, the hands now become an excellent digging tool. The paddle-like feet help push dirt behind in tunnels and provide excellent leverage against loose material. The toes remain very nimble.

Locomotion is varied; individuals are equally at home with a bipedal gait, a kind of scurrying on all fours, and a frog-like crawl used for digging and shimmying through tunnels. They are also adept climbers and can swarm up a rock face as quickly as they move across level ground.

H. chthonisis is able to deal with anoxic environments that would cause a human to pass out and can slow respiration and metabolism so that even the foulest air can sustain them. This is an adaptation shared by the naked mole rat.

H. chthonisis is unique among known hominids, living in a eusocial arrangement similar to naked mole rats, possibly driven by similar selection pressures. There are three roles in the colony: breeding female (queen), worker, and soldier. Fertile males and females are considered part of the queen’s court; the males compete for breeding privileges and the females serve as nursemaids for the babies. Sterile males and females serve as workers with larger examples of either sex also doubling as soldiers. The species is wildly dimorphic with queens being considerably larger than members of her court. Pheromones released by the queen will keep the fertile females in a state of induced sterility. The death of the queen allows fertility to return and will precipitate a power struggle among the incipient queens until one finally asserts dominance.

All H. chthonisis pregnancies seem to result in multiple births, litters of four or five undersized and underdeveloped babies.

Despite rumors of humanzees, it is generally accepted that human beings and other great apes cannot interbreed successfully. It is accepted that human ancestors such as Cro-Magnon and other hominids such as Neanderthal were capable of interbreeding. Reports of abductions of human victims seem to follow the pattern of one colony raiding another for breeding stock. Usually juvenile fertile males are abducted but females have also been documented. Fresh sources of genes are required to keep the colonies from becoming inbred. While there are no documented cases of hybridization, the level of chromosomal similarity is greater than that  found in equines who are well-known for hybridization.

Habitat

The deep world cave systems represent an entirely new biome, more reminiscent of the deep sea thermal vents than anything on the surface. The base of the food chain relies on chemosynthetic microorganisms and strange species of symbiotic lithovore lichen. The sun holds no power here. Once the energy is in the food chain, we see vaguely recognizable cave-adapted species predating on each other. There are a mixture of fish, lizards, arthropods, and mammals.

Major competition mainly comes from rival colonies.

Diet

H. chtonisis’ efforts are split between hunting, forage, and fungiculture. They are indiscriminate omnivores and will eat anything they can catch.

H. chthonisis will farm fungus in a mix of colony feces and vegetative material carried in from the lakes. This fungus represents a major dietary staple and also an emergency food supply when the hunting is scarce.

Cannibalism is a way of life in the deep caverns. Warfare with neighboring colonies is constant and raiding for territory and fresh meat is routine.

Tool Use

H. chthonisis has been observed making use of simple tools. Equipped with formidable natural weapons, they’ve not had any need to develop handmade weapons. There is evidence of the making of ropes from plant fibers, the weaving of baskets from dried plant material taken from the lakes, crude water skins, and the construction of bone and hide boats. They do not ride in these boats but use them as floating baskets when fishing. They deliberately propagate bio-luminescent lichen through their colonies.There is also evidence of fire use but it seems to have more of a ritual use than for anything practical. Any part of their behavior whose purpose cannot be immediately divined is usually attributed to religious or ritual purpose; this may simply be a deficiency of imagination the the part of the observer.

Colony Construction

Due to the lack of weather underground, construction efforts are not so much about protection from the weather but defensive structures. Rocks will be stacked into unmortared walls to create choke points or enhance the defensive character of a location. Natural galleries will be expanded upon for living space. Fungiculture is carried out near the latrines. Colony stink is very important for identification and any individual who does not smell right is subject to attack.

The inner chambers are where the queen and her court reside. The breeding chambers with creches for the young are located adjacently.

A considerable question arises from the digging proficiency of H. chthonisis in the loose soils of the surface world. Considering the rocky conditions of the deep world and the lack of any previous knowledge of their existence -- excepting wild tribal folklore of vaguely humanoid monsters -- there are many questions raised. Why have we not seen them before? How were they able to keep themselves so well-hidden? What else might be lurking down there that we’ve yet to discover?

Psychological Characteristics

H. chthonisis represents a sidetrack on humanoid evolution, an alternative take on the human template. They are intelligent, tool-using, have speech (though difficult to recognize as such since half of what they say is beyond the range of human hearing.) The eusocial society puts most of their brainpower back in the breeding chambers of the colony; the workers and soldiers commonly encountered are clever but lack the mental acuity of the queen and her court.

While proper studies have had little chance to show progress, it is suggestive that H. chthonisis workers are smarter than chimps and the queens could be on the cusp of human-level intelligence. There is much empirical evidence of planning, strategizing, and implementation of complex actions. These are not dumb animals operating on instinct.