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The (not so) new antarctic stottmice

With the melting of the Antarctic ice cap, stottmice underwent a rapid and dramatic shift in both size and form. After a brief and tense period of competition with the newly arrived rompos, the group found space to diversify as the landscape of Antarctica fractured into a mosaic of new environments. Like many others antarctic organisms, stottmice reach their diversity peak in the Great Depreasseaon, but their range now comprise nearly the entire continent (except some insular regions), stretching from thick forests to barren tundra.
The most widespread species today are the pompomouse (Microungulatum pseudocavia) and the round-headed stottmouse (Almacavia pratensis), both still reminiscent of their ancestor, the triple stottmouse. While similar at first glance, the two species show important differences, both physically and ecologically.
The pompomouse has a compact, fuzzy tail, more like a bunny’s than a rodent’s, and a bulkier snout, which help feeding on hard food like bark, branches, seed, but also tough foliage. The round-headed stottmouse, by contrast, has a lighter, longer and narrower skull ideal for poking into grass clumps and shrub layers in search of tender growth.
Their ecological divergence can be seen even from their leg proportions: the pompomouse, with its stocky and compact body, prefers more closed environments or rough terrains, like the ones found in the old-growing lowland forests or in mountain ranges . The longer legs of the round-headed stottmouse help instead at sustaining high speed in more open environments found in more arid region, like the Great Depresseaon. Their niche separation helps keeping direct competition to a minimum, even where their ranges overlap.
The social structure of the two species is also pretty different, with the pompomouse being mostly solitarily except during the breeding month, when a reproductive pair forms, while round-headed stottmice live in gigantic herds that can exceed half a million of individuals during the migrating season.

Despite the evident differences between the two species, an even more dramatic evolutionary branch has split off from the classic stottmouse body plan: the groundlifters, currently represented by the genus Pachypes.
These animals are stottmice in name only: bigger, bulkier, surely not cursorial, groundlifters’ve gone fully graviportal. Size ranges from the 100 kg highland types to the peninsular groundlifter (Pachypes musculus), which, at over 400 kilograms, now stands as one of Antarctica’s heaviest land vertebrates (but not the tallest, which is the crowned hoofpole).

Thanks to their relatively large size, groundlifters are the only keystone species of the currently depleted antarctic ecosystems. They clear undergrowth, rip up shrubs, and create pockets of light and space in the dense forest, allowing countless smaller creatures to thrive. Their size also puts them on the menu of the few large predators present in the continent, likely what has driven their rapid size increase as an evolutionary countermeasure: some species, like the peninsular groundlifter, increased their body weight twenty-fold in just 5 million years.

Unable to run through the thick forests they inhabit, groundlifters rely on gregarious habits and brute force. Groups of 50 or more aren’t uncommon. When danger strikes, they don’t scatter; instead, they stand their ground and help defending each other. A predator that dares to lunge may find itself battered by heavy feet or torn open by their chisel-like incisors. Currently, only onegroup of predators dares to hunt a fully grown male groundlifter, while most current predators prefer harassing young and females.
Unique among Antarctic rodents, groundlifters have developed a prehensile upper lip similar to a horse, that lets them grab foliage with precision. They’re mostly browsers and with an upright feeding posture they are capable of reaching branches up to three meters off the ground. Their deep, resonant calls are used to maintain contact through the dense vegetation, sounding close to those of a Cape buffalo.
In just a few million years, stottmice have gone from survivors to potential rulers of the continent. If nothing catastrophic intervenes, it’s hard to imagine they won’t be one of the dominant forces shaping Antarctic life for the foreseeable future.

Well, if it goes all right.