A precarious life in Centro Island

During interglacials, the rise in sea levels triggers the reopening of the Fire Bridge and submerges the Great Depression, resulting in the reformation of a large island we call Centro Island. This island, much like others, becomes a hotspot for endemism due to the isolation created by the shallow sea separating it from Neopolarica.
The fauna of Centro is notably dynamic and has formed countless times in various, often drastically different, ways. Here, we discuss just one of the numerous endemic biotas that have developed on Centro, possibly the most ecologically intriguing. This particular biota emerged during the "Centro interglacial period n.33," characterized by a much warmer and more humid climate compared to other variants, which has fostered the expansion of forests across 60% of the island (for comparison, continental coldvannas never exceed 40% forest cover in flatlands). These forests are moderately open, because of the presence of relatively large herbivores due to the island's considerable size that transform the natural closed environment in a wood-pasture. This unusually long interglacial period, lasting 100,000 years (typically, late Biancocenic interglacials last less than half this time), has given evolution enough time to produce some insular oddities, listed below.

Some animal species have undergone insular dwarfism, such as the descendant of an insular brumblestilt population, which is one-third the size of its continental relatives, known as the brumblesstilt (Ornithotitan minutus). The higher frequency of trees causes a higher snow retention on the branches and lower on the ground, which has lead to a reduction in leg length for the brumblesstilt, since longer legs became unnecessary in this environment. The now much sturdier legs are used by these birds to better dig out tubers from the soil and to defend themselves from the island's only large predator, the long-legged lone barkdowner (Dendricyon cursorium), which evolved from a barkdowner of the Dendricyon genus. This insular predator has more than quadrupled in size in just 40,000 years and has developed several autapomorphies, such as a slightly stronger bite force and longer legs. Unlike its continental counterparts, this barkdowner is much more adapted to pursuit hunting, although ambush hunting remains their most frequent method (comparable to the running adaptations of a leopard versus a lion). Its claws are only partially retractable, another trend seen in persistence hunting predators.

Long-legged lone barkdowners prey on medium-sized vertebrates like otterwatchers, young brumblesstilts, and stottmice, though they rarely target mammals as large as the hefty stottmice (Cuniculungulatum robustus), a giant descendant of burrowing stottmice. While the continental counterparts do not exceed 30 kg (66 lbs), the hefty stottmouse can reach up to 250 kg (550 lbs), making it the heaviest mammal on the island, having nearly doubled in size every 10,000 years since Centro's isolation began. The species has completely lost the burrowing habits of its ancestors, now living in the forest meadows of the island and feeding on both grasses and leaves. However, they have maintained the same social organization as the continental burrowing stottmice, living solitarily for most of the year. They still retain a red inflating nose skin, used for sexual dimorphism and displaying dominance.
Hefty stottmice often seek protection near large herds of turret hoofpoles (Avipalus palus), a species of hoofpole that has entirely lost its flight capability in adulthood. They are characterized by an absurdly long neck, which can reach 1.5 meters in adult males, allowing them to feed on fresh leaves up to 4 meters high. Despite their fragile appearance, few terrestrial predators dare to attack this walking tower due to the high position of its vital areas and the risk of being struck by its lethal kicks. While incapable of flying when fully grown, they retain relatively long wings (but vestigial tail feathers), which are useful for providing an extra burst of speed when running.

Despite the uniqueness and astonishing species of Centro, we must not get used to it: like many other insular species around the world in the past, this ecosystem will be wiped away in the next glacial phase with the drainage of the Weddell Sea. With the ongoing cooling trend, even the reappearance of Centro Island is becoming increasingly rare, condemning most of the endemic species of the coldvanna to eventual extinction.