Rumbling and tra(t)mpling
The trample steppe fauna is extremely biodiverse, but one species in particular contributes immensely to the maintenance of its typical grassy environment: the woolly tramplerat (Columnomys plantigradus). This massive rodent is undoubtedly the largest terrestrial mammal that Antarctica has ever seen, boasting an astonishing length of 5 meters and a weight of 3-5 tons.
Derived from a branch of heavy tramplerats, the woolly tramplerat is perfectly adapted to withstand the cold climate of its biome, thanks to several metabolic and behavioral adaptations. Its brown thick fur, layer of fat, and short legs prevent heat dispersion, while the large nasal cavity allows it to warm up the cold air.
The toes of the woolly tramplerat are greatly enlarged compared to its ancestors, and its feet possess a fatty cushion that helps distribute the weight of its body, thereby reducing sinking in the snow. However, their unguals (hooves) are short and flat, rendering them unsuitable for digging in the snow to find their main source of food, grasses and sedges. In response, woolly tramplerats have evolved a large head that functions as a shovel for foraging.
Their skull has undergone significant pachyostosis, a condition in which bones become thicker, which in marine mammals is an adaptation to handle strong water pressure. In tramplerats, this adaptation reduces bone stress from their foraging method.
The enormous head, aided by its short but relatively mobile neck, can also serve as a formidable weapon against predators. The neck vertebrae possess a discrete capability for lateral movements, allowing the tramplerat to deliver fast and powerful blows that can easily break bones of any nearby animal. If predators do not retreat, tramplerats can also defend themselves using their strong incisors.
Even under normal conditions, woolly tramplerats are highly aggressive and combative herbivores. Because of this, they rarely tolerate the presence of other large herbivores within their herds, with very few exceptions.
Social groups are dynamic, often separating and fusing together depending on the season: during the summer, herd sizes can reach up to 80 individuals, which then expands to approximately 400 during the winter months.
Similar to deer, tramplerats engage in rutting behavior during the breeding season. Males become very communicative to attract females and intolerant of other bulls. Male battles can be bloody but are rarely fatal due to the only use of their incisors, which leave however significant scars on their bodies. These scar are useful in body comunication: the more scar you have, the stronger and older you are.
Without tramplerats and many other large herbivores, the trample steppe would be much less biodiverse than the actual one. The inferred herbivore biomass in this tundra would be just 2 tons per sq.km in normal condition: however, the high nitrogen production and grazing/trampling action of herbivores reduce the abundance of low-energetic food such mosses and lichens, in favor of a grasses-herbs dominated environment, which can now sustain locally even 12 tons of large mammals and birds per sq. km. This outstanding productivity is comparable if not higher than the pleistocenic Mammoth steppe, although its faunal composition is only partially analogous to the one found in the tramplesteppe.
Portrait of a fully grown male tramplerat.
The individual has barely reached sexual maturity, yet it already possesses battle scars on its face.
Confronting males. Instead of developing horns, clubs or tusks, tramplerats use their incisors as an offensive weapon, like most rodents do.