Apterra is not currently a world with permanent polar ice caps. Climates remain chilly but temperate all the way to the poles at low elevations, and sea ice is present only during the coldest months of the polar winter. However, tundra conditions are not entirely absent on the planet, even during this warm epoch in its history. In the northernmost regions of Ailuropia's mountains, truly arctic climates exist, overlooking the frigid steppe below and being themselves overshadowed by glaciers that dot the peaks. In this thin band, scrubby turfgrasses are the dominant flora. Descendants of the Dawn-Muricene grasses once found capping the Loxodian hills now populate the area. These are short, tough, and thorny, with each nearly-conical leaf ending in a sharp needle. These spiny-grasses are low-lying but not entirely stemless, and they fall on their side when they grow too tall to stand up to the brutal wind, the old culm now forming the beginning of a new rhizome. Boreal basket-grasses of the reed-like subgroup can be seen scattered across the hillside. These are shorter than their cousins but similarly moisture-dependent, growing along the banks of mountain streams during the springtime when they run with meltwater, then dying off when their habitat dries. Cold-tolerant rat-grasses are also widespread here. As rats tend to bury their seed caches near obstacles or recognizable landmarks, these grasses often enjoy a degree of protection from the wind, growing to nearly a meter tall as a result. The shortest and most abundant local turfgrasses are also descendants of the spiny-grass, reducing further in size and spreading widely through their underground stems.
The majority of herbivore species in the region are grazers, members of the same radiation as R. migratorius. Rattus borealis, for instance, follows a similarly nomadic herd structure. It is, however, quite a bit bigger than any of its relatives, a result of the need to conserve body heat and the fact that its large body size has a lower surface-area-to-volume ratio. Sedentary grazers live here too, coexisting with their wandering cousins due to the relative abundance of suitable food. If a rat-grass species were ever to outcompete the more nutrient-dense spiny-grasses as the dominant turfgrass in this biome, the resulting food shortage would likely result in the extinction of non-migratory forms such as R. cuniculonyx. As things stand, the scattered tall rat-grasses only support a single species of specialist seed-eater, the diminutive Rattus brevipes, which spends the long winter huddled in its deep burrows in colonies of up to 100 in order to conserve heat. They sleep and wake intermittently, making use of the downtime for reproductive purposes. Mating, pregnancy, birth, and weaning all occur during the mid-to-late winter months, just in time for a new generation to emerge into the springtime world of plentiful young shoots ripe for the taking. If the colony did a good job collecting seeds last fall, the members will supplement their diet with a modest post-winter surplus. When the first crop of the year arrives around five weeks later, they will abandon last year's leftovers, promoting the growth of future food sources.
These rodents are themselves the food of Rattus acudens, a carnivore smaller than most of the lowland hunters but no less ferocious. Its jaws are short and robust, allowing improved leverage and consequently a greater bite force. This pressure is focused on the sharp cutting edges of its incisors, clipping through flesh easily. They are especially well-adapted to severing the limbs and tails of their prey by gripping the appendage between their jaws and shearing it off between the two cutting surfaces. This mechanism will be further refined in future generations, and it is just one of many examples across Apterra of herbivorous features being repurposed for a meat-eating lifestyle.