In the western rain-pseudoforests of Ailuropia, features of Apterra's pre-terraforming history dominate the landscape. A mesa-like feature stands more than a kilometer above the surrounding lowlands, towering over the otherwise low and hilly landscape. This rough terrain is the result of tens of millions of years of karst topography. Unlike most similar regions on Earth, though, these features are carved from quartzite instead of limestone. In the watery but dead world of ancient Apterra, there were no marine organisms whose shells could've fossilized into the soft sedimentary rock where karsts are generally formed. Instead, the normally tough and erosion-resistant quartzite was scoured by thousands of millennia of exposure to wind, water, and chemical weathering. By the time the planet had been populated with life, this process had produced Tepui Mons, a mountain that's become the home of a unique assemblage of living creatures distinct from their neighbors below.

Acrapteryx platyrostris, the sole living descendant of A. grandis, are the dominant herbivores. They can be seen cropping grasses with their blunt-ended bills and occasionally scampering up outcrops to find hard-to-reach foliage. While their ancestors were small and nimble enough to climb the sheer mountain, they rapidly evolved to become too bulky to return to the pseudoforest floor below, stranding them on the peak. These giants reach up 130 centimeters tall and possess long spurs on their heels, making them invulnerable to any potential predators. A crest on the male's head indicates his reproductive fitness, and his mate in turn displays her white tail feathers when she's receptive. They raise their young cooperatively, though little care is needed as chicks can feed and defend themselves just a few hours after hatching. All 1,500 or so of them live in a single herd that patrols the plateau. They travel in a clockwise direction as they migrate, making a full loop of Tepui Mons's fifty-kilometer circumference every month or so. 

Taller pseudotrees are subject to browsing by Petrapteryx scandens, a descendant of mountain kiwis of ages past. These are the only members of the community that regularly descend to the terrain below the mountain, where they feed and often mate, but they always return to the peak to lay their eggs. This species (and its predecessors that arrived here 500,000 years ago) is responsible for inadvertently carrying the seeds of many plants up the mountain; in many cases, these grasses would've otherwise had no chance of colonizing the area. In one notable instance, a dying Petrapteryx dragged itself up the slope before it perished, unknowingly bringing a pregnant carrion-isopod along for the ride. These descendants of Armadillidium dermestemimus have radiated widely on Tepui Mons, giving rise to about a dozen species that feed on meat, dung, and other animal byproducts like shed feathers.

The woodlouse diversity of Tepui Mons also includes herbivorous forms closely related to the Plague. Due to the limited size of their habitat, though, these have evolved to be less destructive than their cousins, a trait that helps them preserve their limited food source. They are pursued by the tiny bluish-grey Evellapteryx tepuicus, an insectivorous species in the Pillbird group. These measure no more than ten centimeters in height, and they travel in flocks that can number up to 200. A large group of Tepuine Pillbirds can collectively eat five thousand Skyplague isopods per day, unknowingly ensuring some vegetation remains for larger herbivores to eat. 

The top predator here is the Long-Clawed Ratweasel (Tondendens longinychus), a small but deceptively powerful hunter capable of killing prey up to triple its own size. While smaller than its lowland cousins, this species is still easily large enough to bring down Pillbirds, Mountain Kiwis, and even unattended young Acrapteryx chicks. Like Petrapteryx, it has the ability to travel between the mesa and the ground, but generally finds itself outcompeted (or sometimes even outright killed) by its larger congenerics if it attempts this. This species is more arboreal than most ratweasels, often catching its targets by surprise by dropping from a tall pseudotree. 

In the small pond at the center of the landform, an endemic population of sugarfly larvae swims alongside predatory wranglers and butcherflies. While they look similar in this state, their future lifestyles could not be more different. The Tepuine Sugarfly (Myzops caelensis) is a canopy-palm specialist, dodging attacks from the isopod Dendrarthrus pluvifugus as it attempts to drink the syrupy nectar the grass secretes high in its upper branches. Meanwhile, Skyplague woodlice find themselves picked off one at a time as the wranglers carry them away to some far-off perch where they can digest the pill bugs at their leisure. Like all wranglers, these are strong long-distance fliers, and this particular species (Flagelloculex ailuropiensis) is also widespread across the tropics of the western continent. The Cloudbutcher (Culicarnifex nimbophilus), on the other hand, lives nowhere but here. They exist in an arms race with the Dermestemimid woodlice, a group too strong to be preyed upon by other microraptorial mosquitoes. With their thick armor, muscular legs, and blunt, crushing jaws, Cumularthrus gives the cloudbutchers a run for their money in terms of sheer strength among Apterran arthropods. Battles are fierce; the butcherflies' strategy relies on turning the pill bugs on their back, leaving their underbellies vulnerable to envenomation, while the carrion-isopods try to secure a killing bite on the fly's head or thorax. Thousands of these fights occur each day on Tepui Mons, with both sides suffering similar losses as a result. This is a microcosm of the struggle for existence in this region and on Apterra in general. Life is equally brutal in every habitat the Quartzkarst has to offer, even at the opposite extreme of altitude.