Name: 当企鹅从天上飞向大海（When Penguins Went From The Sky To The Sea）
Uploaded: 2021-05-01T13:12:53.000Z
Duration: 11 min 39 s
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About 61 million years ago, on the shore of what's now the South Island of New Zealand,

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It stood upright, measured about a meter tall, with wings that were pretty short for its

And it couldn't fly, but it used those short wings to propel itself into the coastal waters

The scientists who described this creature named it Waimanu manneringi

And it's the oldest fossil that we've ever found of a penguin.

From the shape of its skeleton, paleontologists can tell that Waimanu was already a flightless

But they don't know what came before it -- what the transition from flying bird to

The fossils that could describe that for us have yet to be discovered.

But experimental work on modern birds that can both dive and fly is giving us clues about

what it took for penguins to go from the sky to the sea.

And the world those first penguins lived in?

Because why penguins gave up on flying is just as interesting as how it might've happened.

Waimanu lived just a few million years after the extinction that took out the non-avian

dinosaurs and all the predatory marine reptiles that had ruled the oceans of the Mesozoic

So, in taking to the water, Waimanu managed something its non-avian dinosaur ancestors

And Waimanu was only the first member of what would become a very diverse and sometimes

Today, we think of penguins as small-ish, waddling, tuxedo-birbs.

But they evolved from a flying ancestor, were actual giants for millions of years, and some

of them were even dressed a little more casually.

The thing to know about modern penguins is that they're really specialized for underwater

While they still have to molt and breed on land, they've evolved a ton of features

For example, they've got unique scale-like feathers that help keep them warm and dry

And they've also got structures called rete mirabile systems in their limbs and their

Incidentally, I saw this pronounced as "ree-tea" and "reet" so for this episode we're going with "ree-tea"

These networks of neighboring blood vessels transfer heat between the arteries, where

the blood coming from the heart is warmer, and the veins, where blood is colder.

This exchange helps keep the penguin's core temperature up by buffering the much cooler

Their wing joints are also stiffer than those of flying birds, which helps them produce

thrust on both the downstroke - like most birds do - and on the upstroke of the wing.

And the muscles that raise the wing on the upstroke are much bigger than in other birds

- so the place they attach on the penguin's shoulder blade is  also much bigger than in other

This powerful double-stroke allows penguins to move easily through water, which is denser

Their bones are also denser than you find in flying birds.

After all, penguins aren't trying to stay up in the air; they're fighting against

Those dense bones are part of what gives penguins such a great fossil record!

Now, we haven't yet found enough fossils to completely fill out the penguin family

But we know they evolved from a flying ancestor.

The closest living relatives of the penguins are the Procellariiformes which includes albatrosses,

And based on studies that use a combination of genetics, skeletal similarities, and LOTS

of statistics, it seems that the split between the two groups probably happened in the Late

Cretaceous Period, sometime between about 71 million and 66 million years ago.

So why would a bird trade the ability to fly for a lifestyle of full-time diving?

After all, flight is energetically expensive, but it helps you do things like travel long

Well, one answer is that it's hard to be really good at both, in terms of anatomy and

And in a paper published in 2013, researchers compared energy use in two species of living

They studied thick-billed murres, which are wing-propelled divers, and pelagic cormorants,

Now, both of these species also fly, so the researchers could calculate the energy costs

And they found that the more specialized wings become for diving, the worse they were for

For wing-propelled diving, you need  a large body size

and shorter, flatter wings with dense, enlarged bones,

because all of these things maximize the length and efficiency

But these features are also the exact opposite of what you need for efficient flight.

So, there's a pretty straightforward trade-off in anatomy here.

And it might be that the ecological conditions in which penguins evolved probably made it

easier for some birds to give up flight in favor of diving.

In the aftermath of the extinction at the end of the Cretaceous, diving predators like

small mosasaurs and plesiosaurs were gone, so their ecological niches were suddenly open.

And the larger marine reptiles and sharks that had made the seas so treacherous for

So, with a new potential source of food and fewer predators, those penguin ancestors that

were better divers might have had an advantage, being able get more food while using less

And once they started down the path toward “underwater flight,” there was no stopping

They spread quickly, by geological standards, to most of the places that we find them today.

We don't know what those first penguins looked like, because we haven't found any

fossils that show this transition directly.

But what we can say is that they were probably around 1 kilogram.

Because, that's the biggest that living birds get that can do both wing-propelled

And it's also the size of the smallest living penguin.

From there, true penguins probably evolved in what's now New Zealand in the early Paleocene

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当企鹅从天上飞向大海（When Penguins Went From The Sky To The Sea）

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