Molodonts of the Early Ultimocene: Part 1

Sometimes in natural selection a single trait can lead seemingly insignificant life forms to incredible success. Such an adaptation, evolved first for one specific purpose, can sometimes be repurposed in a myriad of ways - the feathers of dinosaurs that went on to become birds for example. Such is also the case with what are now the most morphologically varied and specious grouping of all tribbets, the molodonts, who owe all of their success to an extraordinarily specialized set of teeth.

All tribbetheres are allied by their remarkable jaws, which come in many variations. The most basal is a simple extensible mouth similar to still-aquatic teleost fishes and still present in the tribbats and canitheres. The molodont clade though, which diverged around 50 million years ago, shortly after the Thermocene-Pangeacene boundary, has sacrificed this length for increased jaw strength. These tribbetheres evolved robust muscles that wrapped around the top of their snouts and powered a crushing top-down bite force to crack open hard seeds, becoming living nutcrackers. Over time most of the teeth in their upper jaw fused into what was effectively a singular massive tooth, forming a singular pestle-like grinding surface against a similar tooth plate that extended forward from the lower jaw like a mortar. By extending the upper jaw slightly, the molodonts were able to slide their upper grinding tooth against the sturdy lower one, not only opening seeds but pulverizing them to a paste, shells and all, and consuming the entire thing. This is the ancestral molodont state - a general sort of tribbetherian rodent - and one which remains widely successful in the early Ultimocene.

This diagram shows how the ancestral molodont jaw operates in order to process food. From this base form, shared with only minor deviation by all the species shown below, have come many more extreme specializations.

Simple Seed Eaters with a Big Impact

Molodonts evolved as specialist seed-eaters, overcoming the defenses of their plant prey with the most powerful bite forces, for their size, of any animals. Over the past 50 million years of their evolution they have been one of the most pivotal players in the game of life, directly influencing ecological trends on a global scale. The early molodonts were almost exclusive seed-eaters and proliferated so abundantly through the Pangeacene that they displaced whole families of seed-eating birds, reducing sparrowgull diversity considerably. Molodont seed-predation, utterly destructive to plants perpetuating their species, has also changed the course of tree evolution in several major ways. Early molodonts reduced the extent of many tree species and over millions of years resulted in the decrease in wooded habitat across Serina, aiding the spread of grasslands in the Pangeacene. Their feeding strongly selected for some trees to reduce the size of their seeds, producing many more smaller ones of less appeal to seed predators, either hiding them in fruit for animal dispersal or adapting toward increased wind dispersal, and for some ant trees to forgo bearing seeds at all, instead germinating their embryos immediately while still attached to the mother plant, which are then planted by ant symbiotes, in order to successfully reproduce; these groups then rebounded. A few trees however, destined for less long-term success, have found themselves locked in an endless arm's race, growing larger and ever more extreme seeds in virtual fortress-like hulls while some molodonts match them at every step and grow even stronger jaws to compensate, resulting in the development of the largest seeds ever known - yet which are so large, they are impossible to disperse, and can only grow in their parent's vicinity; unable to spread, such aberrant forms now lie in increasingly fragmented pockets of a former range.

Yet most molodonts have responded to these ecological changes a little less dramatically; as trees adapt to avoid their predation, most have simply become a little more generalistic, able to feed on a variety of foods including seeds, fruit, and small animals - and as they became less intense feeding on trees, stability returned to the forest ecology. These more generalized molodonts, searching for alternative food sources, also took to feeding heavily on birds' eggs and in doing so provided an intense selective pressure that resulted in several clades of birds evolving to carry their eggs with them and regularly change brooding sites, and so protect them from nest raiders - another way these little animals have had far-reaching impacts on their world.

Generalist seed-eating molodonts occur almost everywhere on Serina today, save the most isolated volcanic islands, and belong to several groups both basal and derived, the distinctions between being minor and all sharing similar attributes. Many of these animals are arboreal or climbing at least to some extent and adapted to feed on tree seeds, though equally if not more abundant are burrowers that feed primarily on the seeds grasses and herbs. In all cases molodonts continue to compete intensely with birds and now limit them almost entirely from specializing to feed upon seeds as, at one time, every Serinan bird was adapted to. This loss is notable, as these basal finch-like canaries had persisted in relative abundance on Serina for its entire history, through everything else circumstance could throw. Today these birds are at last all but vanished from the landscape.

Seed-snatchers

One of the most cosmopolitan seed-eating molodont families are the seed-snatchers, arboreal squirrel-like forms ranging in size from about one ounce to ten pounds in weight at their extremes but most at one or two lbs. With limbs well adapted to climb, they spend their whole lives in the trees and rarely descend - this habit, different from squirrels, is partly why molodonts over time evolved to contribute so little to trees; while squirrels bury their seeds in the ground and so disperse some to sprout, molodonts usually stashed food in gnawed out tree hollows where they will never germinate. The seed-snatchers' teeth are indeed sharper and a little smaller than the first molodonts, adapted to exploit many different food resources, though seeds are favored, and to chew dens and cache sites into trees.

Seed snatchers are social to an extreme, living in related groups of bonded pairs, usually related as siblings, cousins, and parents and grandparents, all of which cooperatively forage and raise their young. For such small animals the young spend a long time with the parents, nearly an entire year before independence. The seed-snatchers, though small and seemingly vulnerable, are indeed surprisingly long-lived - they are one of just three tribbethere clades, and two within molodonts, which can lower their metabolism and hibernate in cold weather, making them particularly well suited to endure the looming threat of global cooling. This also has the effect of slowing the process of oxidation in their bodies, lengthening their lifespan. Most such small animals are heavily preyed upon, yet seed-snatchers seem especially skilled at predator evasion; they are small, yet they live in very cohesive family groups that can help watch for danger, with each adult individual alternating duty as a lookout, and individuals will gang up on threats to protect their own so that small predators such as eelsnakes, perhaps able to easily kill one seed-snatcher, will avoid doing so as they can be overwhelmed by a family group. By combining such complex social behavior with physical camouflage - their fur very often blends into bark or the branches of trees and the nearly bare skin along their snouts and ears can lighten or darken under different emotional states to aid in blending in - seed-snatchers have surprisingly subverted the expected role of such small animals in their ecosystems. With few losses to predation, lifespans can exceed ten years.

Seed-snatcher social groups can grow to hundreds where food is sufficiently abundant, and such cooperative groups of animals make for a very safe environment with so many eyes very little can infiltrate. Yet there does come a time where groups could become so large as to be a hindrance, and so population is limited by male dispersal; around six months after sexual maturity young males leave their natal clan to pair with a mate in another in an adjacent territory. This also limits harmful inbreeding.

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Dietary Divergence

During the arms race between the molodonts and the seeds of trees, some molodonts dropped out entirely. Instead of becoming more generalistic, they specialized in other directions. All descended at one time from the seed-eaters. It is these more divergent molodonts which today have come to dominate terrestrial landscapes. All of these species and the wider clades they have produced have switched diets, and have adapted their seed-smashing jaws for new, novel uses.

Poppits

Some of the earliest divergent molodonts were those species which transitioned from seeds to the green parts of plants. The most successful clade today to have done this were a group of secondarily-terrestrial burrowing forms belonging to a clade known as the Oxyminodonts ("pointed-lower-toothed"), which early in molodont evolution dropped back to the ground from the treetops and evolved an elongated lower tooth plate to aid in burrowing and to uproot entire plants, first to reach their out of reach seeds and then to eat directly. The distal edge of the upper tooth became sharper and could be clipped against the elongated lower tooth to crop plant matter. The most basal representatives of the oxyminodonts alive today are a genus of small burrowing vegetarians found on the grasslands of Serinaustra known as poppits, for their "popping up" behavior where they peer out from burrows to scout for threats before emerging to feed.

Poppits are the Serinan equivalent to marmots, pikas, or some mole rats; burrowers that feed mostly on the surface, eating primarily grasses, though they also eat a lot of subsurface roots. Their skull anatomy is quite specialized, their eye sockets having moved very high while the braincase has moved low, which allows them to peer from their burrows while keeping as much of their body below the soil line as possible. They are social and cooperative, communicating warnings of danger at a distance not through sound but conspicuous visual signals provided by brightly colored inner ears that flare and retract in a crude language of gestures, yet even with a social system to watch their back they are nonetheless nervous and easily spooked. They take that step of faith outside their shelter only with great hesitation and move at a frantic pace, never resting as long as they must remain on the surface, for they are defenseless in the open.

With a long lower tooth useful as a pick axe to tunnel as well as to loosen tubers out of the earth, they also utilize it as a scythe. Hastily scurrying from their tunnels to crop grass from the surface, taking mouthfuls and clipping the shoots near ground level, they lay them near the burrow entrance and then dash back to safety, carting the resultant hay below ground later after it has dried. They still feed on seeds when they come across them but their gut is much enlarged and built now for a much coarser diet of foliage, and rather than selectively eating seeds when they find them they are more apt to chew up the whole stem. Being small and highly fecund, poppits - unlike their distant relatives - have not avoided the fate of being small prey and are heavily preyed upon by carnivores such as repandors and spearrunners, those aberrant predatory serezelles that still persist on these southern plains, and thus play a pivotal role in the ecology of these environments.

Tolerant of the cold, they are the second molodont clade capable of winter hibernation - vital in the cold, wind-swept steppe habitat they prefer. Huddling for warmth, they retain their limited body heat very efficiently deep below the ground and lower individual metabolic costs. There is risk to clumping together, though, in that the motive for predators to find you in your sleep is increased the more of you it may find together, and so some polar bumblebadgers seek out dormant colonies by scent, dig them out, and eat them in their torpor; such concentrated food resources indeed sustain these predators in Serina's coldest southern regions in winter, when other prey on the surface may be nearly nonexistent.

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Circuagodonts

The closest relatives of the poppits are the circuagodonts, themselves a molodont clade but a highly divergent one also allied with the poppits in the oxyminodonts. Circuagodonts share the elongated, projecting lower tooth morphology but further specialized their upper tooth from a purely masticating structure to a complex wedge-shaped cutting tool that clips plant matter in front, against the narrow lower beak, and widens in the rear to pulverize it against a broader interior plate inside the mouth as the jaw opens and closes. Circuagodonts, in effect, are molodonts that transformed the ancestral griding, mortar and pestle jaw structure into a set of tree trimmers. Circuagodonts are themselves so large and varied a clade, which have experienced their own dietary shifts and niche swaps to such a remarkable extent that they will be covered in detail in a following chapter - their mention here is only to show their relationship to the other molodonts.

Omniphages

Upon Serinarcta can be found an interesting branch of the molodonts, a group of animals of particularly massive size and strange appearance, which are despite this considered to be among of the most basal of all living species, having diverged nearly 45 million years ago from all other forms alive today. These are the Omniphages, ("everything eaters"), immense megafaunal molodonts which have evolved hugely wide, smashing jaws to indiscriminately consume food resources typically viewed as undesirable to other animals, including rotting wood, thorns, and bones.

Notably, members of this clade are thought to have never been arboreal; having never lived in trees, they represent an herbivorous molodont that switched directly from grass seeds - likely the first food source adopted by the molodonts' terrestrial ancestors - to the grass itself and from there to a variety of other things which could incidentally be found among grass. Omniphages represent effectively the opposite extreme from the small arboreal molodonts that pick and crush individual seeds; they are broad, indiscriminate eaters that evolved to pick up, crush and devour anything in the vicinity, plant or animal, in wide gnashing mouthfuls. This let them get the maximum nutrition they could find in low-productivity environments like dry plains yet required a large fermenting stomach, and so the omniphages became giants, the heaviest of all tribbetheres on land and approach the theoretical maximum weight for a tripodal tribbethere, which must bear all of its weight on the single hind limb during part of the walk cycle - up to 1,500 lbs. They are heavily built, with stocky, straight limbs and elephantine feet, but their enormous heads are the most noticeable feature, supporting immense pulverizing jaws that can grind virtually anything, even small stones taken incidentally in feeding, to a crumbling powder or a paste that is swallow-able.

Omniphages include preferential grazers, scavengers, and browsers; most species though will readily consume any sort of organic matter however and have a flexible digestive system to allow them to survive on a wider variety of food, and lower quality of food, than almost anything else alive. Meat digests quickly in the foregut and so nutrients move through the stomach in a short time, while coarse ground plant matter collects in a large fermenting hindgut for up to several days before being thoroughly digested; symbiotic bacteria let all species digest cellulose. The stomach, combined with the digestion that occurs in the mouth via saliva, is so efficient that almost nothing is wasted; the feces produced afterwards is predominately their own dead cell waste and a sandy powder of minerals - even traces of organic matter in dirt and mud can be digested.

One of the most visually unique omniphages is the thorngrazer, a mostly herbivorous species native to the dry scrublands of northeast Serinarcta that has become a specialist in eating thorny desert plants. In another evolutionary arms race, the thorngrazer evolves to feed on ever more fiercely defended foliage, while its prey responds with increasingly extreme defensive measures. Currently the thorngrazer is winning this race, able to engulf huge mouthfuls of foliage with spines long and sharp enough to skewer a man through the gut and out the back, but it has only achieved this tolerance with extreme physical defenses of its own. The lips, the eyelids, the inside of the mouth, the nostrils, the throat, and even upper stomach of the thorngrazer is lined with hard, bony spikes, which protect its own tissues from the deadly defenses of its food. Originating from inside the creatures's mouth tissue and out and over its face, these structures are actually specialized teeth. As the sole species able to access the liquid water found in these plants, which is after all what they ultimately strive to protect in the arid climate, thorngrazers are a keystone species that allow many invertebrates and birds to survive in climates which may lack free standing water for 90% of the year. Small animals follow the solitary thorngrazers like a small entourage, quickly drinking the oozing sap or chewing the soft inner flesh of the plants to quench their thirst in the mere minutes before the sun dries the wounds and the plants begin to cover their injuries with woody scabs.

Due to the extremes of their diet and the specialization they must grow to handle it, thorngrazers - born without teeth and by extension spikes - have a very long period of infantile dependency on their mothers and cannot feed themselves for as long as eighteen months. To nourish her young when she herself eats only the most low-nutrition diet, she as well as others of her clade bear a milk-like food source for their young; this is actually a fatty slurry of cells that sloughs off of the lining off the foregut; rich in fat and protein, the young eats almost nothing else but this sticky, pus-like slurry of cell tissue regurgitated by its mother until it is mature enough to begin handling the coarse adult diet. To lick this substance from the mother's mouth, the young thorngrazer, as well as some other omniphages, uses something no other molodont still has - a tongue. While most molodonts lost their tongues, as they are useless and a hindrance in their crushing mouths, this basal clade retains them in infancy as the spines on many of their faces as adults prevent the adults from locking lips with the young to transfer food as other tribbetheres do.

Mostly hairless, the thorngrazer is able to fire up or down the pigment in its skin to help regulate its body temperature, varying from pale tan to almost black depending on the time of day, for nights and days in the desert can bring incredible temperature swings. Males also sport bright red and orange patches of pigment which can be flared to high intensities during combat or courtship and muted at other times.