The beasters by RisingMagpie on DeviantArt (original) (raw)

80 million years After-Present

Antarctic Chronicles - "Let it big": the famelic beasters

With such an abundance of large herbivores, the trample steppe is, without exaggeration, a paradise for predators, especially for the beasters, are a group of robust sheardogs adapted to persistence hunting. Their ability to pursue prey for hours has made them the top predators of this biome, displacing ambush hunters like barkdowners, which have adapted to smaller sizes to hide under the few shrubs and tall grass of the trample steppe. While abundant, the group has maintained a low level of biodiversity because of their high trophic level, with only two widespread species found.

The most charismatic of the two species is undoubtedly the smoky beaster (Magnagnathus horribilis) due to its size and frightening appearance. To our knowledge, Antarctica has never seen a predatory land mammal as large as this creature: male smoky beasters, which are on average 20% larger than females, typically weigh between 180-300 kg (400-660 lbs), with a height of 1.4 meters, just 20 cm shorter than the famous short-faced bear. This height is achieved thanks to their long and robust legs, allowing these animals to gallop like a horse.
Among the predators of Antarctica, smoky beasters have the highest hunting success rate, approximately 60-70%. Their efficiency can be attributed to their highly cooperative hunting behavior and high stamina. While not as fast as their prey (they rarely exceed 35 km/h), smoky beasters can maintain their top speed for an extended period. Stalking and running intermittently can last up to 2 days, often ending with the prey collapsing from exhaustion without the ability to defend itself from the beaster pack.

As mentioned, smoky beasters are highly social animals that form family groups consisting of a breeding pair and their young. Females do not go into estrus annually but only after all their offspring leave the pack, usually at around 3 years of age. Because of this, smoky beaster packs are usually small, with a maximum of 7 individuals in the largest packs.
Smoky beasters primarily prey on large herbivores like stottmice, rostrids, and the largest species of hoofpoles. They are also the only Antarctic predators that habitually hunt tramplerats. This giant and seemingly invulnerable rodent can make up to 20% of a beaster's diet. In order to hunt them, the adult female and their offspring isolate the young tramplerats from the herd, while the male beasters proceed to inflict severe wounds on the hips, the only defenseless parts of a tramplerat. When the tramplerat falls to the ground due to its injuries, one of the two adult beasters usually proceeds to bite the herbivore's muzzle to block respiration. Prey is rarely eaten while still alive due to their top rank in the Antarctic trophic level, with no animals capable of stealing their kill: smoky beasters prefer to take their time in order to safely kill their prey, without the risk of injuring themselves during the hunt.

While smoky beasters are found almost exclusively in the trample steppe and the southern part of the coldvanna, the other beaster species, the tarsisnatcher (Anterolutra rostriphaga), has a cosmopolitan distribution in Antarctica. This beaster is a medium to large predator, weighing between 30 and 80 kg, depending on sex and latitude, with a specialized diet that mainly consists of large ground birds, such as rostrids, which can make up as much as 80% of its diet, with the remain composed of stottmice and young thagomicers. Their hunting technique involves fatally injuring the legs of rostrids, the most reachable part of these birds but also their most dangerous weapon. To withstand the power of a rostrid's kick, tarsisnatchers possess a robust skull and vertebrae, which can be as thick as those of smoky beasters. Due to the hollow bones of birds, the legs of rostrids can be more easily broken than those of mammals of the same size. After one of the rostrid's legs is fatally damaged, these birds become completely harmless and unable to defend themselves.
Unlike smoky beasters, tarsisnatchers immediately start consuming their not-yet-dead prey to feed as quickly as possible before another predator can steal their food, including their larger relatives: it's believed that 10-30% of tarsisnatchers succesful hunts are cleptoparasitized by smoky beasters.

Tarsisnatchers form larger social groups compared to smoky beasters, typically consisting of a dominant male and female and their followers, which can include their young or unrelated individuals from other packs. Although not as large as the packs of painted wolves or spotted hyenas, these packs can reach up to 15 individuals. Each individual cooperates in the hunt and possesses different roles depending on age and sex. Young individuals create panic inside rostrid herds without assisting physically in the hunt, while the strongest adult males are the first to target the legs of their prey. Because of this behavior, males have a higher mortality rate compared to females, up to 40% higher on average: possibly because of this risky role in the hunt, tarsisnatchers present a strong sexual dimorphism, with males being almost twice the size of a female, with also thicker skulls. The two sexes have also a slightly different color pattern: males possess a brown-greyish pattern and white stripes, while female are lighter and possess larger white patches and pointy ears.