The Treeskinner

Circuagodonts of the Ultimocene so far include some of the the largest molodonts, only rivaled in size by the thorngrazers. Though some very notable circuagodonts are now entirely carnivorous and very far removed from their original diets, most species are primarily herbivores. Their rotating upper jaw is blade like at the distal edge and rotates to cut plant stalks against the elongate lower tooth, then rolls back to pulverize them under the wide hind portions of both teeth. Their feeding cycle is highly efficient as each new bite rolls the last bite further back into the mouth to be pulverized before swallowing. The jaws of circuagodonts are built to consume the roughest and most unappetizing plant foods available.

Combined with a large fermenting stomach, the tree-trimmer shaped jaws of these spectacular tribbetheres allow their owners to make a healthy living on some of the least desirable food sources around, for which they might even have no competitors. The treeskinner (Bratacutidon magnificus, the "magnificent tree skinning tooth") is one such species whose sole diet is something so hard to eat that other animals only consume it in desperate times - tree bark. And far from suffering on this seemingly sparse diet, this species has evolved to be the largest of all circuagodonts, usurping the armox of ten million years prior, and weighing as much as 1500 lbs: the size of a bull moose.

Found now across the southern Serinarctan forests, treeskinners are descended from much smaller forest circuagodonts that had begun using long forelimb claws to pull down branches. The claws of their immediate ancestors grew so long and hooked that to keep them sharp, they adapted to walk on their knuckles. Treeskinners now spend much time feeding while standing on their hind legs, keeping the claws sharp and off the ground, yet their long claws no longer serve to pull down branches. This is because they are now obligate bark feeders and do not consume anything else. Their lower tooth is hypertrophied and more than three times the length of the upper one, extending from the jaw like a tusk. Its upper surface is very narrow at the protruding edge, serrated and blade-like. To feed the treeskinner simply wedges this blade up against the trunk of a tree and, with its powerful neck muscles, shoves it upwards and against the surface, peeling up the bark in long narrow strips which it then pulls away and cuts free with its upper tooth. As in some other cirguadonts with highly exaggerated teeth, lips that open outwards and then forwards assist to pull the food into mouth so that it can be thoroughly chewed.

Bark may not seem like a nourishing diet, and it is true that the hard protective outer coating is little more than fiber, but the cambium layer which can be found just next to the dead wood of the tree is fairly nutritious. This inner bark contains a surprising amount of digestible starches, sugar in the sap, and a variety of vitamins and minerals that the tree has painstakingly pulled up from the soil. During the growing season this bark layer can contain as many as 800 calories per pound; requiring an average of fifteen thousand calories a day to maintain condition, the treeskinner can get by on just nineteen pounds of forage a day during the summer months. In winter when the tree is not in active growth and the animal has to keep warm however it may require four times this much food. Because the treeskinner begins feeding from near the base of the trunk and girdles all of the bark off as it goes up, preventing the tree from taking up water or nutrients, it is highly destructive to stands and can kill off entire tracts of forest over time, a force mitigated somewhat by a nomadic habit that means it rarely spends too long in any one area.

This destructive feeding manner is unusual for a circuagodont, and the evolution of a species like the treeskinner is indicative of a big problem in Serina's ecology. As a result of the rapidly cooling climate and the rapid shuffling of temperate forest ecosystems to lower latitudes in place of tropical ones, the intricately connected system of the ant forest is breaking down. Until recent climactic stress such a specialist feeder would be inhibited by the symbiotic ants which protected most sunflower trees from intensive browsing in the past. The rapid cooling of the world over the past ten million years, resulting in the upheaval of entire ecosystems and the loss of many entirely as the tropics dwindled and the cold northern climes moved steadily southward, has resulted in an ongoing collapse of the ant forest's once highly efficient and integrated system. Many species of both symbiotic ant as well as formerly ant-hosting tree have died off, leaving most of the remaining trees in this region poorly protected from intensive browsing. The treeskinner's ancestors were quick to capitalize on this chaos, as as soon as a resource is available, something will evolve to make use of it. Yet the very existence of such a creature is a harbinger of even more extinctions to come, as intricately cooperative ecosystems that took tens of millions of years to develop all begin to unravel.

Yet while some old partnerships are breaking up, new ones form. The treeskinner is solitary, only forming loose and incidental groups occasionally and pairing to mate, yet they are never really alone. Virtually every treeskinner is always in the company of another, much different molodont with which it maintains an intricate mutualistic relationship. Hamster-sized descendants of the tweezertoothed glider called ripgleaners (Vellicodon ascensor, "riding pinching tooth") shelter in their furry coats, roosting while clinging between their forelegs. They have evolved to take advantage of the constant stream of insect larvae which are exposed as the treeskinner pulls away the bark of forest trees, leaving the barren trunks called rips which are instantly indicative of a woodland with treeskinners resident. Each individual ripgleaner claims one entire treeskinner as its territory, rather than a given area of forest as in its ancestors, and never strays far from its host. When the treeskinner feeds the ripgleaner hops off and snaps up all the insects left scrambling for cover as the tree bark is pulled away. When the host moves away the little guy quickly hops back on. No longer reliant on gliding long distance to find food, their wing membranes are beginning to reduce in size while they are now too heavy to glide well.

Ripgleaners are generally not even acknowledged by the treeskinner, but do perform a beneficial service by removing ticks from its skin. The species began its association this way, by incidentally removing parasites from the skin of large herbivores they jumped onto at night, a habit that it shares with several other extant species. In no other has such an obligate partnership formed, however, where the ripgleaner is no longer alert and agile enough to survive for long without its host to regularly take it to food sources and protect it from predators. Ripgleaners only meet one another when their hosts make close passes; primarily they mate only when the treeskinners do, which may also account for male ripgleaners being found much more frequently on male treeskinners and likewise with females, perhaps to maximize their chances of finding a suitable partner the few times their hosts meet up and facilitate a tryst.