Slashing pouches
The borax domain

With the increasing complexity of Antarctic environments, herbivore diversity steadily rose, and alongside it carnivore diversity also expanded undirectly. Carnivorous geotters, which currently include wonderlonts and ragos, still maintain a very high level of diversity, but none of them currently occupy the niche of an apex predator. That role is now in the hands (or better, paws) of borax, the large marsupials that first arrived in Antarctica and triggered the beginning of the Incertocene.

While some borax species have become slightly dwarfed compared to their ancestors, rarely exceeding 50–60 kg, most species retained or even increased their size, with some weighing over 100 kg.
Their anatomy has changed profoundly, abandoning the heavy graviportal build of their semiaquatic ancestors. Modern borax are still far from cursorial, but they possess longer legs and more elongated bodies, allowing them greater mobility on land and short bursts of speed to catch prey, like a stoat or a feline.
Their locomotion remains primarily plantigrade, similar to that of bears or humans, which limits their top speed. However, some species have shifted toward a more semi-plantigrade stance: the greatest example is the greater borax (Thylacotitan unicum), the largest living borax, comparable in size to a tiger. This formidable predator normally walks with most of its sole resting on the ground, but when running it raises the heel and shifts weight to the digits, gaining extra stride and speed.

Greater borax are the largest terrestrial predatory mammals in Antarctica and dominate the trophic chain in their large range, though they have not successfully expanded yet into the most open environments of the Great Depresseaon. Their hunting strategies rely heavily on cover, such as bushes, rocks and tall grasses, which are found mostly near the large endorheic river systems of the Great Depresseaon basin.
The greater borax thrives mainly in closed tropical habitats, including dry forests and rainforests, and only rarely ventures into semi-open environments. In these ecosystems it preys on medium to fairly large mammals, such as pompomice, sturdy stottmice, and groundlifters. Large brumbles are less frequently hunted, primarily because of their sharp vision, which makes ambushes difficult.
Like many other borax, the greater borax possesses serrated saber-like canines. Contrary to popular belief, these teeth do not allow them to kill larger prey than normal carnivores, but they do speed up the killing process. The prey is subdued first with brute force thanks to its exceptional built, greater than any geotter, and only then are the saber canines plunge into the neck to damage major blood vessels and the trachea. This method is especially effective in dense habitats, where ambushes can be launched from very close range, requiring only a short sprint. In more open areas the same technique can be used with the help of shrubs or grasses, but the large size of most borax makes them much easier to spot before the attack.
Prey typically ranges between 40 and 400 kg, though some individuals specialize in hunting larger game. Certain populations of greater borax have been observed targeting groundlifters far larger than themselves. Taking down such prey is dangerous, but the payoff can outweigh the risks. Still, very large and healthy adult stottmice, such as the greater groundlifter, are generally avoided. There're limits that even a formidable predator can't cross.

Unlike some geotters, borax are not social hunters and pursue prey individually. However, they show a surprising degree of tolerance toward neighbors, especially among females. Females may even assist each other in raising young, though such cooperation is rare. Males are far more territorial, and encounters between two males are usually hostile, though rarely lethal. Despite this, males do take part in raising offspring with his partner: after mating, they form short-term breeding pairs lasting around four months.

Like all marsupials, borax give birth to extremely underdeveloped young. In the greater borax, newborns weigh barely 50 grams (which are actually pretty heavy for being marsupials) and are born after only 2–3 weeks of gestation. They then crawl into the mother’s pouch, where they remain for at least four months before venturing outside. During this period, the male provides food for the female and her offspring, gradually reducing his support after the third month. Litters can contain up to seven young, but usually no more than two survive their first year.