How to escape from the permafrost
The new bellydruggers

The ever increasing permafrost layers is posing significant challenges for fossorial animals in Antarctica: although the ecological dynamics of the trample steppe can lower the upper summer permafrost layer from 10 to over 50 cm compared to a typical tundra environment, this layer is still much thinner than the ice-free soils of the Cambiocene. Some rodent species have adapted by digging small burrows for shelter or hibernation, while other non-hibernating species, like modern-day snow vole, have found ways to live within the snow layer during winter.

Ground tyrants have experienced a substantial loss of biodiversity due to these soil changes and the emergence of other ground bird-like species, such as several lineages of eggpuochers, which are more physiologically suited to cold temperatures. Meanwhile, other small fossorial birds have managed to survive the rapid climate change by partially abandoning their underground habits and adapting to new ecosystems. For instance, the remaining species of bellydruggers, the last lineage of penguins in Antarctica, have adapted by reducing their ability to create extensive underground tunnels. These tunnels are now primarily used for defensive purposes rather than foraging underground and they are no more than one meter long usually.

Bellydruggers now feed mostly above ground, with some species foraging on insects and plants, while others hunt invertebrates and algae in the water, such as the plantigrade bellydrugger (Marmotaspheniscus riparia). Comparable in size to a quail, this bird has adapted to make short burrows in the riverbanks of the continent's warmest rivers. Some subpopulations are gradually expanding southward, extending their range along trample steppe rivers.

As its name implies, the plantigrade bellydrugger does not always crawl on the ground using sprawling quadrupedal movements but, instead, it moves by standing on two legs in a plantigrade manner. This trait is shared across all current species of bellydruggers in Antarctica, all of which are descended from a single semi-aquatic Cambiocene ancestor. This gives bellydruggers a human-like gait, less swinging compared to a holocenic penguin and more adapted to relatively long walk: these species can travel several kilometers per day, in search of new food sources or for a mate.
In order to not face predators, bellydruggers are usually nocturnal; because of this, they have developed large eyes with a high number of rods photoreceptors, which enamble to see well in complete darkness, altohugh reducing the capacity of recognize colors. This adapation is in part the result of their past fossorial ancestors, which were almost colorblind; now, actual bellydruggers have partially recovered some color vision although they cannot see properly ultraviolet, like most birds. Biancocenic bellydruggers have only two photoreceptors, therefore their color vison would be comparable to the one of a cat or dog.