Swattermice

The Muscivorattids are a somewhat early-branching family of rats that evolved during the Muricene to fill insectivorous niches, specializing on small, flying prey. Their defining characteristic is their long, sturdy tail, which can flex up to 120 degrees at its base. This allows them to control their trajectory with great precision, making them quite effective hunters. They also tend to have acute vision and quick-moving eyes that let them track their prey as it moves. In their heyday, they were ubiquitous across the rat-grassland, feeding on vast swarms of bloodsucking flies that followed the Muridiungulate herds. During breeding season, they'd migrate into pseudoforests to find a safe place to raise their helpless young, then return to the plains en masse once the pups had matured. Their small size allowed them to survive the decline in oxygen levels following the Great Decarbonisation, but many species later went extinct during the ensuing rat-grassland collapse. Three million years later, however, the clade has recovered its former diversity, creating a place for itself in the new epoch.

The most basal swattermouse genus is Abelitherium. The ancestors of the Abelitheres were the dominant lineage pre-Ice Age, with dozens of species by the end of the Muricene. With a strategy largely unchanged from the first swattermice, they were hit hardest by the mass extinction, and only one ended up surviving. It was a desert specialist, able to survive periods of food scarcity by reducing its metabolism. The Desert Swattermouse (Abelitherium antecessor) then spread across Panapterra once warmer conditions returned. However, with new forms of grasslands replacing its old habitat, the genus would never again reach the level of dominance it once held. About half a dozen species of Abelitheres exist today, all with body plans nearly identical to their ancestors.

Tiptoe Swattermice (Capiodocus) are another group whose diet has changed little over the years. Their bodies, however, have specialized for more efficient prey capture. Their hand claws are long and sharp, and the hands face inwards in their neutral position, with strong shoulder muscles that allow them to snap shut in a fast, pincer-like motion. Capiodocus walk on their hind legs, with their extra-long tail balancing the rest of their body. This lets them avoid wearing down their fly-catching claws, improving their rate of hunting success. Two dozen or so tiptoe swattermouse species live across the world, with their greatest numbers being found in temperate grasslands.

The Climbing Swattermice (Loxoditherium) have undergone the most modification since the end of the Ice Age. They descend from a group of swattermice that evolved to live full-time in temperate pseudoforests instead of migrating back to the prairie each year. Before the Arthrocene, they were a rare and geographically restriced taxon, existing only in the tree-mycad woodlands of southern Loxodia. When hybrid trees took over the world, these arboreal rats came along for the ride, expanding into every type of woodland ecosystem. By far the most speciose swattermouse clade, there are now over fifty species of Loxoditheres.

Climbing swattermice have always been above average in size, as trees and pseudotrees can support larger climbers that herbaceous grass stalks. Today, even the smallest members of this genus are thrice the weight of their forty-gram ancestors. One such species is the seed-eating Loxoditherium sciurimimus. Like many of their congenerics, these Grainhatches have abandoned a mosquito-based diet, as that niche is now filled by skeeter-snappers in this ecosystem. Arboreal woodlice, on the other hand, are fair game. The closely-related Palmscratcher (L. picimimus) can eat up to 200 a day, harassing isopod colonies and picking off the weakest members. Their family's jumping abilities come in handy, as they often must make a quick escape when the swarm launches its counterattack. The Squoth (L. lentiscansor) eats exclusively foliage, browsing on the rich leaves of palm-grasses. This energy-dense plant matter allows the rat to maintain a basal metabolism typical for rodents of its size, though it still must conserve energy by moving slowly. By carefully grooming itself for up to six hours a day, it can wash away its scent, avoiding detection by woodlouse colonies. If this fails, the squoth can drop to the ground quickly, as its lightweight body can survive a fall at terminal velocity.

The largest and most derived swattermouse is the Glirrel (Loxoditherium cryptocursor). Though other meat-eaters like the terror kiwis that prowl the forest floor may outweigh it by a factor of fifty, they rarely attempt to climb into the canopy, making the glirrel the apex predator of the treetops. Arboreal birds and rats make up around 60% of its diet, the rest being mostly seeds, eggs, and carrion. This two-kilogram, low-slung omnivore can move quietly through tree branches because of the thick, soft fur on its feet. It sits patiently on a high branch, waiting for a potential target to walk by. When the time is right, it leaps without a sound, grabbing tightly onto its prey. The two then tumble to the ground below. In the brief moment when they're both airborne, the glirrel uses its bushy tail to change its orientation, maneuvering the smaller animal underneath itself. This cushions the hunter's fall and delivers a killing blow simultaneously, after which the carcass is hauled skyward again to be eaten at a safe height.