Anytime one thinks "flightless bird" and "aquatic bird" put together, one would immediately think of Sphenisciformes, the penguins.
But during the Late Cretaceous, there swam a different kind of flightless aquatic bird, one with a greater distribution than the penguins' cold southern waters. They were the hesperorns, the "western birds".
As you can see, they were lankier and more streamlined than their penguin upstarts, which raises the question.
In an alternate Earth where penguins never existed or have yet to exist, colonies of hesperorns can be found in coastlines all around the world. (Wouldn't nip the existence of the pinnipeds in the bud, but they would be confined to the shadows.) There are hesperorns in Antarctica, a continent buried under a mile of steep, slippery ice. With that in mind, would the Antarctic hesperorns keep their ancestral sleekness, or would they have to shorten their body designs to make them more penguin-like?