Molodonts of the Early Ultimocene Part 2

Insectivores

If there were one reason molodonts today are so successful, it would be the ease with which they switch which foods they rely on. A diet of high calorie seeds placed the first molodonts in a perfect baseline position from which to specialize on most other possible food resources - be it fruit, foliage, or animal protein. The mashing molodont jaw was effective to process all manner of food, not just seeds, and further the structure of each tooth plate comprised of many fused teeth was highly malleable to selective pressures, forming into more complex shapes suited to specialist tasks.

One such particularly noteworthy aberrant group of molodonts have evolved as a sister clade to the seed-snatchers. Similarly arboreal, this is where the similarities end; they have become insectivores nearly to exclusion, with their teeth having deviated highly from their ancestral shape and function to let them catch and process small prey animals and the rest of their anatomy followed suit as they adopt radically different niches than their fore-bearers.

Iunctaurans

The iunctaurans ("jointed eared") are a clade of specialist nocturnal carnivores that feed mostly on arthropods and other insect-like animals including bird larvae. They are highly adapted for arboreality, with long fingers tipped with recurved claws for clinging to bark, and the forearms large and generally dominant at locomotion versus a reduced hind leg. Their teeth are angular, formed into a beak-like arrangement adapted for pinching prey and include some of the most derived jaw structure of any molodont. Yet it is not for any of these traits this group is named, but for the adaptation they have developed in their ears, which have evolved a new joint at their base. This allows the entire ear to flex independently of the motion of the mandible, permitting iunctauran molodonts to maintain an unwavering position of the ears when chewing, which is of great benefit for nocturnal hunters that often locate insects moving beneath the bark of trees by sound. With the upper part of the ear bone fused to the braincase and the lower jointed to move freely from the lower jaw, iunctaurans hold their ears motionless and fixed on the sound of a feeding insect all while gnawing it out with their sharp teeth; a feat impossible for other molodonts whose ears flex back and forth with each motion of their jaws.

The ancestral iunctauran form is that of an percussive forager, a creature which relies on sound echos produced by tapping to listen inside tree bark to locate hidden prey. On Earth, this is notably the tactic employed by the aye-aye, a strange and nocturnal Madagascan lemur. One such species alive today is indeed very similar to the aye-aye. The largest iunctauran, that would be the split-wristed chiseler.

Chiselers

Several species of chiseler have evolved to live in the tropical forests of central Serinarcta in the early Ultimocene. Strictly nocturnal, and furthermore living in the depth of forests where planetlight is almost totally blocked by foliage, these cryptically-colored creatures spend the day in dark tree hollow nests and emerge in the dark of night to forage in the high jungle canopy. They are spectacularly strange-looking animals, with humongous eyes and ears, disturbingly elongated digits, recumbent buck teeth and yet a curiously endearing quizzical expression plastered permanently on their faces. The split-wristed chiseler, a creature a little smaller than a cat, is probably the funniest looking of all, for it has evolved very strange and almost spider-shaped hands, jointed in the middle of the palm so that four fingers can fold to meet the other three and lending them the descriptor to both their common and latin name. The arrangement is to do with climbing, and allows a sturdy grip on branches; the inner three digits and the adjacent palm now function like opposable thumbs.

But it is not with their fingers that the split-wristed chiseler produces echos with which to locate prey; for this, they have adapted the central digit of their hind leg. Like the grossly stretched tapping finger of the aye-aye, the chiseler clings to the bark with its forearms and uses this highly elongate toe to tap the bark around them in a grid pattern, their ears pressed against the tree, until they find the telltale echo of a prey item burrowing within. To dig it out the chiseler uses its angular upper tooth to both pry up bark on the upstroke and saw through the lower layer on the downstroke, quickly opening a hole in the tree to uncover the insect beneath. The jaw is very similarly constructed to that of a circuagodont, even though the role it serves is not identical and two clades are of only very distant relation, in an example of convergent evolution. Unlike most modern molodonts, chiselers retain several un-fused molars in their lower jaws and it is against these which the upper tooth grinds on the back-swing, rather than against the lower tooth plate as in circuagodonts. The mechanism however is the same; chewing and food grabbing in a single cycle of jaw rotation. With their saw-like mouthparts and the unusually wide gape their bark gnawing has resulted in, chiselers also occasionally attack and feed on roosting birds and other vertebrates found incidentally during nocturnal foraging, already showing the behavioral flexibility that their circuagodont-like jaws allow them in the very same way some circuagodonts rapidly evolved from herbivores into active predators after adopting a similar tooth arrangement.

The split wristed chiseler and a diagram of its jaws, showing the stabilized, jointed ear and wide gape.

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Vellicodontids

Related to but even more unusual than the chiselers are the vellicodonts. Also iunctaurans, this clade have seen their jaws and indeed much of their anatomy even more extremely altered by evolution, becoming some of the most distinct of any tribbetheres. Vellicodonts are also nocturnal insectivores that hunt in the forest canopy in Serina's tropics, but they have switched from percussive foraging to probing and gleaning, using an even more elongate, pincer-like tooth beak to snatch small climbing insects off of surfaces and out of holes in wood. The way this beak operates is highly derived; both jaws move in tandem, and the upper and low jaws are fused with cartilage, making a wide gape as is seen in their nearest relatives impossible. The premaxilla is extremely flexible and bends considerably with each cycle the jaw operates as it powers the movement of a dramatically altered upper tooth, which has evolved one very long, pointed cusp that forms the top of the beak. Chewing ability is very minimal in these tribbetheres, and insects are just lightly crushed before swallowing - a muscular gizzard-like chamber above the stomach aids in grinding them before digestion. The jaw muscles store energy as they retract and release it on the forward stroke so that the mouth is more powerful when opening; this lets them easily probe and widen insect holes in the bark to reach in and tweeze out their prey; on Earth, this same mechanism exists in a bird, the European starling.

Vellicodonts are all very well adapted to leap through the branches; the forearms are still the powering force in their climbing, but in this group the tail is relatively large and shows a unique anatomy where weight is born on all three digits, but now not only is the central digit lengthened but all three so elongated as to function almost like legs themselves. When scurrying on vertical tree trunks, each long digit grips the bark independently, and the posture is effectively pentapedal. With effectively five clinging limbs, vellicodonts move freely in all dimensions both up and down the tree trunk as they probe nooks and crannies for insect prey. The most remarkable species of all, however, no longer merely climbs around to find a meal - it floats on air.

The tweezertoothed glider is indisputably among the strangest of all tribbets. Only as large as a hamster, the tweezertooth is cryptic and nervous, coming out of the crannies it sleeps the day away in only after sunset to run up and down the trunks of tall forest trees, bouncing from branch to branch at a frenetic pace and dancing on tiptoe with its long tail digits, many meters from the ground below. It pries beneath the bark to find insects and especially beetle grubs much in the manner of a bird, and when the time comes to move to a new tree... it makes a leap of faith, launching itself into the open air between trees with its two powerful, backwards-oriented outer toes.

What happens next is not quite powered flight, but a long, slowly descending glide. Paper-thin skin patagia unfurl from between its forearms and its outer two toes, producing a wide parachute to provide lift and carry it up to four hundred feet or 121 meters. In flight, the center toe in the hind leg becomes a balancing tail as long bristle-like guard hairs are extended to form a wind vane to aid in steering the course to the next tree trunk. To land it catches itself with its arms and grips simultaneously with all three hind toes. Then, however, the center toe is lifted, the tail fan furls up, and the digit, with only a small claw, is not used in walking. As a facultative quadruped - the first in any tribbet - the creature scurries off on its way into the night.

The tweezertoothed glider and a diagram of its jaws, showing the narrow gape and highly flexible premaxilla bone (green) that powers its strange, pointed upper tooth forward in a pinching and prying movement.