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While the terrestrial environment of Antarctica is on the brink of extinction, the marine ecosystem tells a different story. The cold seas surrounding the continent have become a haven for biodiversity, analogous to the polar oceans of the Holocene era. Rich in krill, these waters support a myriad of species, creating a submerged paradise. However, this balance was achieved only recently, after a significant loss of biodiversity, most notably the collapse of the productive Antarctic kelp forests following the Continental Crisis. This ecological disaster wiped out several marine groups, including the aquashifts, which are now absent from Antarctic waters. Yet, amidst this upheaval, a group of egg-bearing aquatic birds known as reefsurfers has thrived, evolving rapidly in the wake of the crisis and often significantly altering their body plans to adapt to the new environment.
One of the most remarkable species to emerge is the chimney searipper (Cetaciornis ungulatum), the largest eggpoucher to ever evolve in Antarctica, with a body length of 5 meters and a weight of 1.5 tons. This makes it one of the heaviest birds ever to have evolved, alongside with some species of ducktails. As the apex predator of the Antarctic seas, the chimney searipper primarily feeds on fish and marine birds, making it an ecological analogue to the leopard seal, capable of moving swiftly in the water but also crawling on the ground and ice to rest. Its robust wing-flippers, equipped with large keratinized appendages, allow it to maintain a firm grip on slippery icy surfaces or steep rocky coasts. While its hind limbs serve as powerful paddles for swimming, they are nearly useless on land due to their extreme distal positioning and rotation, causing the feet to lean on their internal lateral parts, similar to but opposite of the foot posture of ground sloths.
The chimney searipper is a specialized reefsurfer hunter, stalking its prey along the coast while remaining mostly submerged, with only its distinctive chimney-like nose protruding above the water, functioning like a snorkel. This unique feature not only aids in its stealthy approach but also gives the species its vernacular name. Its hunting adaptations are further enhanced by its "toothed" tongue and long bony extensions on its beak, which are used to firmly grasp prey. These bony teeth, however, are not meant for shredding, as the tongue teeth do, but for ensuring that prey cannot escape.
Reproduction and chick-rearing for this species occur on land. Females give birth directly to live young, expelling a soft eggshell as a waste in the process, since the embryo hatches inside the mother womb. The young remain hidden on the ice or ground for about a week, during which they are fed by their mothers through regurgitated, partially digested food. After the first week, the chicks begin to follow their mothers into the water, becoming fully independent after six months, though they start to separate from their mothers around three-months old.
On land, chimney searippers are social creatures, often interacting with neighbors and other species not seen as ordinary prey. However, their calm behaviour on land sharply contrasts with their ferocity in the water, where they become deadly predators to other reefsurfers, including fully aquatic species that give birth in the water, like the reverse reefsurfer (Criophagornis antarcticus) and the long-necked reefsurfer (Elasmornis piscivorus), derived from the carnage reefsurfer.
These two species are abundant in Antarctic waters, each with distinct feeding strategies and lifestyles. The long-necked reefsurfer, true to its name, uses its elongated neck to catch fish, relying on its strong hind limbs for propulsion and high maneuverability. In contrast, the reverse reefsurfer has a more derived body plan, with an elongated body, long front flippers, and vertebrae adapted for vertical movement. Its nearly immobile but robust back legs, still equipped with a large flat claw used for propulsion and a vestigial one, function similarly to a dolphin's fluke, providing powerful bursts of speed.
The reverse reefsurfer is a bottom feeder, searching for prey such as crustaceans, fish, and submerged birds in the ocean floor's mud, often employing ram feeding by keeping its mouth open while swimming forward.
Although being common prey of chimney searippers, these two species can defend from this predator if on large groups by pecking the predator near the highly sensible and vascularized cloaca; that's why searippers prefer to feed on the young of these reefsurfers instead of fully grown individuals, which can be nearly as big as it, but not as heavy.
Despite the diverse evolutionary paths taken by reefsurfers, some species have retained a penguin-like appearance, such as the dwarf reefsurfer (Maritimornis pinguimimus). Inhabiting the last remnants of kelp forests in the Pacific Rim, this small species, roughly the size of a Gentoo penguin, primarily uses its feet for propulsion and lives in large colonies of up to 300 individuals. These colonies breed on small, isolated rocky islands, reducing the risk of predation by terrestrial predators, although some carnivores like the antarctic ottofox and the banchisaraptor can easily access to these areas. Dwarf reefsurfers feed mainly on small crustaceans found in the kelp forests, a habitat that was once widespread across Antarctica but is now restricted to a few islands in the Sanctuary Peninsula due to the rapid cooling after the Continental Crisis.
While the survival of dwarf reefsurfers may be at risk if the ice continues to expand, other species of the genus Maritimornis have already adapted to life in the coldest areas of the continent.
In contrast to the bleak outlook for most terrestrial species, the future of reefsurfers seems secure, regardless of what the climate might bring. These birds, with their remarkable adaptability and resilience, are likely to continue thriving in Antarctica's cold seas for many more millennia and, why not, millions of years.
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