Unexpected successes
The new small ground birds of Antarctica

The increased seasonality, lower temperatures, and higher snowfall frequency have severely impacted the delicate avian fauna of the Cambiocene, leaving very few survivors, especially among the small species. Ground tyrants were severily affected by this event: while during the Lentocene several species were adapted to rigid temperatures, all modern day ground tyrants derive from temperate/subtropical ancestors, which were not fast enough to adapt to cold habitats like the coldvanna and the tramplesteppe.
Rostrids were among the few terrestrial birds to take advantage of this climate change, becoming the dominant birds of Antarctica. While brumbles and terrariders occupied the niches of medium to large size, other groups of rostrids filled the small-sized niches.
Closed or semi-closed environments are dominated by woodclimbers, while open areas have been colonized by a group of birds once restricted to alpine tundras of the continent: the trenchcrawlers. These small but sturdy parrot-like ground-dwelling birds are among the best-adapted to thrive in harsh climates, aided by their ability to enter a state of hibernation for several months of the year. Despite lacking a chewing apparatus like their brumble cousins, trenchcrawlers are well adapted to digest cellulose fibers, especially the grasses, which make up the majority of their diet.
When threatened, the trenchcrawler retreats into its burrow by walking backward, ensuring that its primary offensive weapon, its enormous beak, faces the attacker. The audacity of this bird is remarkable: social species of discrete size, such as the polar trenchcrawler (Microrostris polaris), have been observed driving even large herbivores out of their territory.

However, trenchcrawlers are not the only hibernating birds in Antarctica, nor are they the first to develop this evolutionary adaptation. That title belongs to the armadrails, the group of armored rallids originating in the Lentocene.
These birds are a classic example of evolutionary stasis, as they have retained their bauplan virtually unchanged for nearly 40 million years. Only recently, with the hardening of temperatures, a drastic evolutionary trend has been observed: since their protective scales provide little insulation against the cold, the biancocenic armadrails have gradually reduced the size of their cutaneous armor. The scales are no longer overlapping like those of pangolins but form a superficial pattern across the animal's body like osteoderms. The interstitial spaces between scales are filled with dense downy plumage, providing the animal with some degree of thermal insulation. While early lentocenic armadrails had a simple exposed carapace, today's armadrails appear to be typical ground-dwelling birds, but they conceal an impenetrable shield beneath their plumage.

The most widespread species currently is the overscute (Panoplia omnifaga), which exhibits the most derived characteristics among all biancocenic armadrail species. This bird has recently established itself in the tramplesteppe, where it feeds on anything it can swallow, from small lizards and bird eggs to fruits and plant parts. Due to its low metabolic rate, overscutes must employ strategies to endure the cold polar nights of the tramplesteppe, taking advantage of microclimates, such as the ones found in caves and underground shelters (often sharing hibernation burrows with trenchcrawlers).