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".

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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?

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    $\begingroup$ A nice, simple and straightforward concept. An interesting twist on the possibilities of speculative evolution. Never heard of hesperorns before now, glad you helped me make their acquaintance. $\endgroup$ – a4android Jan 12 '17 at 3:32

Heat loss is proportional to surface area, heat generation is proportional to volume

Penguins are stout because

  • Fat is good insulation

  • The closer you are to a sphere, the less heat you lose to the (cold) enviornment

The bird you picture there looks like a cormorant. Cormorants work just fine, and live in all sorts of primarily tropical and subtropical environments.

However, if these birds (or cormorants) were to adapt to an Antarctic lifestyle, they would need fat layers for insulation and lower their surface are to volume ratio to reduce heat loss.

In short, they would look like penguins.

  • $\begingroup$ What you are saying is natural selection will favour the survival and adaptation of shorter, fatter hesperorns. The Antarctic hesperorn will develop into something closely resembling the penguins of Antarctica. $\endgroup$ – a4android Jan 12 '17 at 3:08
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    $\begingroup$ @a4android True. Is that not clear from my wording? $\endgroup$ – kingledion Jan 12 '17 at 3:17
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    $\begingroup$ It is, but I was filling in the in- between the lines bit about natural selection. Too often folks, this isn't a reflection on yourself, talk about evolution as if it was a deterministic process. When it's more like nature rolling the dice a squillion times and sometimes coming up with a result. Ignoring that, you gave a good clear answer. $\endgroup$ – a4android Jan 12 '17 at 3:29
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    $\begingroup$ @a4android To anybody that is even slightly scientifically literate it is clear that when such expressions are used, they are just that: expressions. When everybody knows what a linguistic shortcut means it is perfectly correct to use it as a substitute for a more technically correct if longer alternative. Anyways... The sun will be rising soon. Oh sorry, I should say the rotation of the earth around its axis will soon progressively cause more of the sun to become visible above the horizon from my specific point of view. $\endgroup$ – AngelPray Jan 12 '17 at 3:58
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    $\begingroup$ @AngelPray In defense of a4android, and as a person who also posts on the more scientifically minded Stack Exchange sites, not everyone on the internet is even slightly scientifically literate. Your sunrise example is amusing, though. $\endgroup$ – kingledion Jan 12 '17 at 4:02

Really expanding on kingledion's answer, evolutionary pressures will lead to what is known as "convergent evolution".

The issue is the environment requires some very specific adaptations to fill the niche of aquatic predator. Since the prey is underwater, a streamlined hydrodynamic shape is required to be fast enough to successfully hunt. Since the waters and surrounding air are cold, the creature needs some means to retain body heat. Penguins who had these traits passed them on to their offspring, while those who did not starved or froze to death, and had fewer or no offspring.

We can see this in multitudes of natural examples. Sharks, Tuna, Ichthyosaurs and Dolphins come from four very different evolutionary paths and are entirely different species, yet have all evolved similar shapes in order to be top marine predators in their environments. Wolves have similar looks to extinct Thylacine, or Marsupial Wolf. A browse through the biology section of the library will turn up numerous other examples.

Going the other way, there have been species of penguins that lived in New Zealand some 25 million years ago that were large and skinny instead. Since they lived in warmer climates, their need for insulating fat or a low surface to volume ratio was limited, while obviously being large bestowed some sort of competitive advantage, perhaps in fending off other predatory species or being able to hunt larger prey.

So depending on how specialized the evolutionary niche is, expect your species to converge towards an "ideal" solution regardless of the starting point in evolution, given enough time and how rigorous the conditions actually are.


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