Reefsurfers
The new penguins

It has been almost 20 million years since the END, the major mass extinction that struck the antarctic biota. Although the local fauna has recovered well, the event has left significant scars on the local and possibly global ecosystems. Many animal and plant groups have yet to return to Antarctica, including penguins, the symbol of the icy continent. With the exception of the bellydruggers, semi-burrowing penguins that survived the disaster, marine penguins have not yet made their reappearance on the territory, suggesting that the group may be extinct not only locally but perhaps globally as well. Unfortunately, there can be no certainty, but there are many clues that point to this scenario, including the emergence of a group of penguin-like aquatic birds, called reefsurfers.
Although they resemble large sturdy-beaked penguins, these seabirds are not at all related to penguins. They are, in fact, eggpouchers, a group of ovoviviparous cuckoos that have adapted to an aquatic lifestyle. Currently, there are at least four species in the icy continent, with the common reefsurfer (Magnathalassornis meridionalis) being the most widespread and prominent, reaching the size of an adult person.

Despite being a recently evolved group, reefsurfers already exhibit remarkable adaptations for marine life, such as hydrodynamic structure and the distal positioning of their hind limbs, which serve as their primary means of propulsion. This method of movement is much more similar to that of a cormorant or Hesperornis (a Mesozoic aquatic bird) than that of a penguin (which uses its wings for propulsion instead).
The diet of modern reefsurfers is still relatively unspecialized, but it is starting to show its first divergences. One group shows tendencies toward a piscivorous diet (like the common reefsurfer), while another group is slowly specializing toward durophagy and herbivory (with shorter and sturdier beaks).
Despite their ovoviviparity, all reefsurfer species must return to land to give birth to their offspring, similar to seals (which also mysteriously disappeared after the END, along with cetaceans). After hauling their large bodies onto a safe beach (often an island area), the females give birth to a highly precocious chick that has already hatched from the egg. The hatching occurs inside the mother's body, which then separately expels the shell and the offspring.

Due to the distal positioning of their limbs, reefsurfers are unable to walk and instead shuffle on land in a manner similar to a grebe, occasionally using their relatively smaller but robust wings for assistance. Despite their significant size compared to the average penguin, reefsurfers are often preyed upon by carnivorous aquashifts.