Extinct survivors

It's the year 5446.

Antarctica has been now legally off-limits for nearly three thousand years. Despite this, several scientific rovers freely traverse the icy continent for various research purposes, the only activity allowed according to the FAIT2050. The most advanced rover types, weighing over one ton, are employed for fossil searches, and as the past millennia has shown, numerous discoveries have significantly enhanced humanity's understanding of Antarctica's mysterious past. For years, the inability to study the geology of Antarctica beneath the ice and the abrasive action of glaciers over millions of years made it nearly impossible to find significant fossil remains. However, with the unfortunate (yet paleontologically fortunate) melting of the ice, new rocky areas have emerged, facilitating the discovery of new fossil sites.
On July 12, 5446, in a new geological formation known as the Fantiman Formation, an important discovery was made: the fragmentary bones of a large terrestrial mammal, the largest ever found in Antarctica. The holotype consists of an incomplete skull, a complete radius and ulna articulation, and an incomplete hip and femur articulation. The remains were transported by drones two years later to a European paleontological facility carried by the paleontologist Luke Turnwell, who managed to classify the fossil.

Although paleontologists did not give a vernacular name to the specimen (it was coldly designated as AVNMROTAS45), it was popularized due to its goofy and friendly appearance, leading to its unofficial nickname "Grunt", referring to the giant protagonist of the BFG*.
The animal was immediately recognized as an astrapothere (Astrapotheria), a clade of endemic South American mammals known for their bizarre appearance, including a barrel-shaped body, sometimes equipped with a short trunk like a tapir, and four enlarged canines similar to elephant tusks. These mammals were among the largest ever to exist in South America, with some species possibly exceeding six tons. Although astrapotheres like Antarctodon and Trigonostylops were already known from Antarctic fossils, this new species was significantly larger and more complete than previous finds, with an estimated weight of nearly one ton.

The creature is scientifically fascinating for several reasons, primarily due to its bizarre appearance, even for an astrapothere. Unlike its relatives, which had pairs of enlarged canines facing downward in the upper jaw and upward in the lower jaw, this newly discovered astrapothere appeared to have a large pair of tusks in the upper jaw oriented upwards like boars' tusks. The lower pair of tusks remains unknown due to the lack of complete mandibles, but the absence of teeth cavities suggests either a strong reduction or complete absence of lower canine tusks. No astrapothere was known to have this tusk orientation until now, hence its chosen generic name, Supradon, meaning "Teeth on top." The complete scientific name given to this astrapothere is Supradon postumus (Turnwell, 5449), with "postumus" meaning "late," referencing its geological dating. While other Antarctic astrapothere fossils were known from the early Cenozoic in the Paleocene and Eocene (about 60 to 37 million years ago), no species were known to have survived the formation of the Antarctic Circumpolar Current at the start of the Oligocene (34 million years ago). This current caused a rapid cooling event in Antarctica that formed the first Antarctic ice sheets. It was once believed that a massive extinction occurred after this event, with no large vertebrates surviving. However, the discovery of Supradon postumus, dated to the middle Oligocene at the end of the Rupelian age (29 million years ago), challenges this belief.

The now richer Antarctic fossil record reveals that although the post-Eocene cooling event was extremely impactful, it was not as catastrophic as once thought; it was more of a fossil gap.
S. postumus tells another story about Antarctica's climate and habitat where it lived. After the global cooling, the early asset of Antarctic forests, initially dominated by austral beeches (Nothofagus spp.), almost disappeared except in lowland areas. Few frost-tolerant and drought-adapted gymnosperms, like podocarps, were able to expand. Closed habitats reduced in number in favor of more shrubby open habitats, such as those where Supradon postumus lived. According to palynological data from the Fantiman Formation, "Grunt" lived in a semi-open lowland environment dominated by conifers like Podocarpus, Microcachrys, and Araucaria. Angiosperms included mostly Nothofagus shrubs, along with some species of the Proteaceae family and the Metrosideros and Freycinetia genera.

S. postumus teeth show higher wear compared to other astrapotheres, suggesting an intermediate feeding habit trending towards grazing, consistent with the expansion of grasses in Antarctica during the Oligocene. The sturdier limbs and hips also indicate a more terrestrial lifestyle compared to most astrapotheres, which are thought to have had a partial semiaquatic lifestyle similar to a hippo (at best) or a tapir (at worst). These adaptations align with the climatic conditions of its time and location. According to paleoclimatologists, the paleoclimate corresponding to the biota found in the Fantiman Formation was a cold, dry climate, with a mean annual temperature of 7-10°C and 600 mm of precipitation per year.

"Grunt" is a true survivor, managing to endure the incredibly rapid global cooling during the Eocene-Oligocene boundary and adapting to persist for nearly ten million years. However, this initial success was not meant to last forever. With the onset of the Miocene, ice expansion accelerated, covering almost every piece of land in Antarctica, ultimately dooming Supradon and its possible descendants to extinction.
Once again, the past offers an important lesson for the future: what has happened before can happen again, and there are very few ways to combat a threat when your enemy is not just a large predator but the entire global climate system.

*The BFG has reemerged as a pop culture icon at least 21 times since 1982, inspiring over 10 sequels and 92 novel variants, including films and videogames.

Insights: https://doi.org/10.1016/j.palaeo.2005.07.032