Tribbetheres: Meet the Molodonts and Circuagodonts

Molodonts

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Molodonts (meaning "grinding tooth") are a highly diverse group of very mammalian, largely rodent-like tribbetheres of the Pangeacene era which have evolved into seed-eating specialists. Their dentition is highly derived; it appears that only two teeth are usually functional for feeding in a molodont's jaw - one upper and one lower - but each tooth is actually a plate formed from the fusion of most other teeth in the mouth. These plates are enormous and have become distinctly modified into a smoothly operating mortal and pestle-like device which is very effective at crushing and grinding hard-shelled nuts and seeds. While the upper incisor is modified into a heavy squared-off pestle, the lower incisor projects forward from the jaw and has flattened into a hard plate, against which the upper tooth can grind. Molodonts feed by grasping a seed in their jaws and closing their teeth over it in a clenching grip, then extending their upper jaws forward in a biting motion. The frontal edge of the upper tooth is attached via a muscular hinge to the tip of the jaw, so that the process causes the tooth to rotate back and forth as much as 90 degrees, with the portion initially gripping the seed rotating rapidly up into the back of the mouth and forward again. The result is that the seed is repeatedly abraded until even the hardest protective covering is broken up and the entire seed is macerated to a pulp, which is then drawn to the back of the mouth and swallowed.

above: a chipmunk-like molodont adapted to burrowing and living on the forest floor.

Because they are so heavily used, the teeth of molodonts have adapted to grow continuously throughout the animals' lives, compensating for the heavy wear put upon them by the process of feeding. Molodonts are therefore exceptionally efficient seed-eaters and have specialized to feed on a great variety of such food sources and to live in all environments where they are abundant. Groups have evolved which burrow like chipmunks, which run along the ground like agoutis, and which leap agilely through forest canopies in the manner of squirrels. Many species are nocturnal and thus the group as a whole is fully covered with a pelt of insulating, mammal-like hair, covering most of their bodies except the pads of the feet, the ears, and the snout, which are frequently bare to facilitate the loss of excess heat. All molodonts have seven digits on their forearms ancestrally, with three on the singular hind limb, but some derived lineages exhibit fewer digits.

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above: a simplified diagram of the "mortar and pestle" grinding system of a molodont's jaws. The chewing cycle involves the extension and contraction of the jaws, as in all tribbets, but the visible change in the length of the snout through the cycle is especially obvious in the molodonts, whose snouts are therefore composed of folding and highly elastic muscle tissues well-adapted to withstand such stretching.

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Circuagodonts

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Not all molodonts feed on hard-shelled foods, however. Circuagodonts (meaning "wheel-toothed") are a highly specialized group of grazing molodonts which have abandoned a diet of nuts and seeds for one composed almost exclusively of vegetation, including well-defended razorgrasses. The teeth of these tribbetheres are even more specialized. The upper incisor has become even more massive, to the point that it projects from the mouth even when the jaws are closed, and is now vaguely wedge-shaped, flattened lengthwise into a sharp cutting blade at its front but widening and becoming blunt and toward the back, while the lower incisor is greatly enlarged, forming a hard plate over most of the lower jaw, and coming to a sharp upward curve at the front of the mouth. The sharpened blade-like front of the upper tooth grinds smoothly against the edge of the lower incisor as the jaw is extended and retracted, functioning like a set of pruning shears to cleanly cut twigs, branches, and blades of grass. As the upper tooth rotates backward and the jaw is closed, this freshly-cropped plant material is then immediately pulled back toward the wide rear of the tooth and pulverized against the tooth plate on the lower jaw until it is broken down enough to swallow. By grinding the upper tooth back and forth against the lower like a wheel, the creature can thus simultaneously crop new mouthfuls of food while masticating the previous bite, allowing it to take in a steady stream of nourishment continuously and process it at high speed. Because their jaws taper from wide and broad in the rear to narrow and angular at the leading edge, their heads typically take on a distinctive triangular appearance, and forward-projected state of the lower jaw, positioned as it has become to meet the upper incisor in a smooth cutting motion, also gives most circuagodonts a noticeable under bite. Combined with the often large, mobile ear pinnae, large fleshy cheeks and protruding incisors, the result is an animal that is very strange looking indeed, like some eldritch hybrid of rodent, ornithopod dinosaur and bulldog.

above: a large circuagodont grazes on razorgrass.

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Because their teeth grow continuously and are thus well-adapted to compensate even for heavy wear, circuagodonts easily feed on the abrasive leaves and stems of razorgrass and can thus thrive where herbivorous birds cannot survive. Some forms are small, leaping over the grass like hares and sheltering in burrows, but on the razorgrasslands, without competition others have become large and ungulate-like, bounding gracefully on three stilt-like legs and moving in large herds. The limbs of these forms are modified substantially to allow for such a lifestyle, being elongated and digitigrade and with many of the fingers now absent or vestigial.

As the tribbetheres whack away at the newly-evolved vegetation and begin to enact a controlling effect on its spread, the invasive plant steadily loses its short-lived monopoly on the savannah ecosystem with the result that other plants are again able to compete and a more diverse ecosystem is restored. The damage may well already be done for the serezelles, however, as the circuagodonts are notably more efficient feeders even with more palatable food plants. In the end, they will successfully usurp and displace the serezelles on the plains, the ease of traveling across the current supercontinent allowing them to spread and conquer and leaving few refuges for the grazing changelings. It is the first time that the birds will have been so displaced by another group in Serina's history on such a scale, but it will not be the last.

above: a simplified diagram of the highly specialized cropping and grinding, wedge-shaped jaws of a circuagodont, adapted to crop food like a set of pruning shears at their narrow front and simultaneously to grind it down at their wide back ends.

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