Antarctica no longer lies over the South Pole. The Antarctic Plate has been moving northwards for 100 million years, gradually creeping towards the southern edge of Asia. This plate has carried the continent out of the polar zone, through the southern temperate zone and across the southern desert belt. Hard as it is to imagine, Antarctica now lies partially in the tropics.
The Antarctic icecap melted as soon as the landmass began to move into warmer latitudes, exposing the majority of Antarctica's soil for the first time in millions of years. The continent's northern portion now lies well within the tropic zone of Earth's climate, the Equator, where the converging trade winds bring warm rain all year round and the sun shines directly overhead. These are the ideal conditions for plant growth, and this is where the lush forests of the new Antarctica are located.
As a frozen continent, Antarctica was an almost inhospitable environment for life. In the Quaternary, it was home to a few indigenous species. Plant life consisted of almost entirely of mosses. Other similar life forms included lichens and algae. There were no strictly terrestrial vertebrates and the several species of seabirds which inhabited the coastlines of the continent were the most successful animals living there (other tetrapods included seals and whales). As it moved into more temperate regions, however, Antarctica became a much better prospect as a home.
Plants were among the first of the newcomers: winds brought seeds and spores from South America in the east. Those seeds which survived the journey gave rise to adaptive radiation, where a variety of species evolved from a single ancestral species, each specifically adapted to the conditions they found on the Antarctic continent.
Spiders and insects were the next to discover the new habitat. Being lightweight they were carried on the winds, just as the plant seeds were. They settled easily among the newly-evolving plant life. The first vertebrate settlers were birds, their powers of flight enabling them to cross the oceans to reach the isolated continent. And they brought with them yet more seeds and insects.
These new species of birds joined the descendants of the seabirds which had populated frozen Antarctica since previous times. Having inhabited the old ice continent, the seabirds were ideally positioned to exploit the changes in their environment. This new, temperate land was a paradise by comparison and offered numerous and diverse possibilities.
One group of Antarctic seabirds that fared particularly well in the new conditions were procellariiforms (or tubenoses), such as shearwaters, fulmars, and albatrosses. Dating back to the Middle Paleogene (and possibly the Late Cretaceous), tubenoses bred mostly on islands in the Southern Hemisphere, although some breeding grounds were as far north as the Caribbean. They also wandered widely at sea during the nonbreeding season. Already capable of adapting to different climates, such forms as petrels remained and diversified as Antarctica gradually moved north, evolving to suit the changing conditions. They became the most varied and widespread group on the Antarctic continent, radiating to fill new evolutionary niches and becoming increasingly difficult to dislodge.
Now, in 100 million AD, the Antarctic continent boasts many species of bird. There are birds with long, narrow wings that soar over the land, smaller birds with short, broad wings that can maneuver easily in confined forests, and even flightless, ground-living birds. The majority of these are procellariiforms. The most widespread group of petrel descendants are flutterbirds.
In the Antarctic Forest, there are some very large insects from the high oxygen levels which exist worldwide now (a similar phenomenon to the Carboniferous). There are different arthropods (mostly insects) here, like wasps and beetles, big enough to make light work of killing flutterbirds.
Here, the insects' time has come. Insects rival vertebrates in size and sometimes even surpass them. Whole new living strategies based on this reversal have evolved. Some insects are brash and arrogant hunters, while many birds have become small and furtive. Flutterbirds may still prey on small insects, but the forest canopy is full of powerful, predatory, larger insects evolved to prey on them.