Surfing in the reef with reefsurfers

While most aquashifts are typically confined to the warmer coasts of Coldvanna during the summer months, there exists another group of aquatic vertebrates known as reefsurfers that have displayed remarkable adaptability to the frigid waters of the South Pole. Although not as swift as aquashifts, these birds possess exceptional maneuverability, akin to seals, enabling them to capture agile prey. In this competition-free environment, their biodiversity has flourished, resulting in the emergence of over 30 species endemic to Antarctica, each adapted to distinct habitats, diets, and climates. Among these, carnivorous species exhibit the highest diversity, while herbivorous species, although less varied, are more widespread.

Reefsurfers exhibit a size range spanning from a mere 4 kg to over 150 kg (9 to over 330 lbs), with the largest species being the carnage reefsurfer (Ichtyophaganax massiva). This species is characterized by long, robust legs, serving as its primary means of propulsion. Conversely, their wings have become vestigial and serve no significant purpose for the animal, even on land: in fact, the carnage reefsurfer represents the most highly derived bird within this group, having become an obligate aquatic creature that no longer relies on the land, not even for breeding purposes.
They are among the most viviparous-like of the reefsurfers, with an intriguing method of giving birth: after a two-month gestation period, carnage reefsurfers produce soft-shelled eggs that contain a well-developed and hyperprecocial chick. This chick eventually breaks the shell to take its first breath and swim to the surface. While this method may seem inefficient, it allows the young bird to take one final deep breath inside the egg before emerging and it reduces the effort required for chick expulsion, which, in turn, lowers mortality rates for females. This form of childbirth is not unique among tetrapods: large reptiles like mosasaurs are believed to exhibit a form of ovoviviparity rather than true viviparity. The boundary between these two reproductive strategies is somewhat arbitrary, as evolution operates in shades of grey, with each adaptation being both similar and distinct.

Despite their size, carnage reefsurfers are not equipped to prey on large prey due to their fragile toothed snouts. Their diet primarily consists of fish and mollusks but excludes other reefsurfers and aquashifts, which would be difficult to capture and consume. This is in contrast to toothless species with strong jaws, such as the icegrazer (Macrophyllodium glacialis).
Despite its name, the icegrazer is not an herbivorous species; the "grazer" attribute derives from its practice of gnawing on sea ice to create breathing holes. Despite being roughly human-sized, this aquatic bird is a specialized predator of other reefsurfers, including carnage reefsurfers. They are highly social creatures and often collaborate with a partner in hunting, both on land and water: while one individual force sunbathing reefsurfers to flee into the water, the other remains submerged to ambush them. Thanks to this strategy, icegrazers can capture prey several times their size; some subpopulations have even specialized further, targeting other aquatic vertebrates like young aquashifts.