Stottmice from a cold paradise

Apart from tramplerats, another ubiquitous and abundant presence in the trample steppe are stottmice, a group of medium-large rodents. The treeless environment of the trample steppe has evolutionarily pushed these animals to sprint instead of hiding, resulting in the evolution of the fastest mammals ever to have emerged in Antarctica. Among the three currently existing species, two can be found in the trample steppe, both belonging to the same genus, Longiomys.

Both species possess relatively large skulls in proportion to their bodies, similar to tramplerats. However, their snouts are notably shorter. Stottmice have a reduced number of molars (only a pair per dental arch), occupying a smaller surface area of the snout. This relatively flat snout adaptation is attributed to their foraging method: unlike uprooting plants, stottmice are superficial grazers, consuming the youngest and most tender parts of plants. Unlike tramplerats, their dental structure doesn't exhibit the same resistance to abrasion. Consequently, their diet is less specialized, especially in the case of the smaller species: the dwarf stottmouse (Longiomys capreolus). Due to its dietary flexibility, this medium-sized stottmouse is among the most widespread mammal on the continent, inhabiting both coldvanna and trample steppe environments.
This species mostly thrives in flat terrains, except for the L. c. alpinus subspecies, who has adapted to move on rugged territories in mountainous regions: their adaptations include notably enlarged paws and proportionally reduced leg length relative to the body, typical characteristics of a rocky-adapted species. Despite anatomical differences, these two subspecies can still interbreed, although an evident evolutionary divergence is ongoing between the flatland and mountain forms.

In flatland areas, but rarely in mountainous regions, another stottmouse species can be found. Weighing six times more than its relative, it's known as the steppe stottmouse (Longiomys cervus). This species largely resembles its smaller counterpart, except for its teeth, which have a sturdier structure with multiple crowns. This adaptation likely suits a mixed diet with a preference for grasses. Their high abundance in the trample steppe makes these species one of the most preferred prey for many species of carnivores, from the terrestrial sheardogs to flying pinpiercers.
Both stottmice species exhibit a digitigrade locomotion that has not fully transitioned into unguligrade. Their digits have two phalanges that make ground contact, with a semi-webbed condition. This somewhat unusual evolutionary "stagnation" of not fully developing hooves (which is a common trend for many cursorial herbivores) may be explained by the lack of evolutionary pressures: many Antarctic carnivores in fact have specialized in ambush or endurance hunting (like a wolf or a hyena) rather than high-speed pursuits (like a ceetah). Last but not least, a broader foot is less likely to sink into the snow during the extended Antarctic winters.

In terms of behavior, stottmice of the Longiomys genus are much more gregarious than their ancestors, forming family groups consisting of a breeding pair and their first and second-year offspring. The steppe stottmice are also known for their social migratory behavior: as temperatures drop below freezing, thousands of stottmice gather together to migrate towards wintering sites, typically located along the coast or near large lake basins where temperatures are milder, and snow accumulation occurs later. These mice tend to graze in proximity to tramplerats, albeit at a safe distance due to the aggressive behavior of these large rodents: monitorings indicate that foraging usually occurs around 100-30 meters away from tramplerats.
Like many other herbivorous species, this tendency to approach tramplerats is easily explainable by the (unintentional) protective effect they offer, as tramplerats deter large predators through their intimidating behavior.