Penguins are like the bird version of whales and seals, evolving to be at home in the water despite coming from land animals. They evolved to colonize the oceans even sooner and can dive deeper and hold their breath for longer. Sometimes they even swim faster than many marine mammals. They first appeared after the extinction of the non-avian dinosaurs, quickly diversifying.
They dominate the southern hemisphere while being one of the only land animals found in Antarctica. No other land animals live here throughout the winter, and penguins may have a good claim of being the occupant of one of the harshest environments by any multiple cell organism.
About 61 million years ago, a bird lived on the South Island of New Zealand. It stood upright, measured about a meter tall, with wings short for its large body and a long, narrow bill. It couldn’t fly, but it used those short wings to propel itself into the coastal waters of the Paleocene Epoch. The scientists who described this creature named it Waimanu manneringi. Also, it’s the oldest fossil of a penguin.
Paleontologists can tell from the shape of its skeleton that Waimanu was already a flightless waterbird, like modern penguins. But they don’t know what came before it and what the transition from flying bird to early penguin looked like. The fossils could describe that have yet to be discovered. But experimental work on modern birds that can both dive and fly gives us clues about what it took for penguins to go from the sky to the sea. Why penguins gave up on flying is as interesting as how it might’ve happened.
How did penguins get to Antarctica?
Waimanu lived 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 Era. So, Waimanu managed something its non-avian dinosaur ancestors never had in taking to the water: it became fully aquatic. Waimanu was only the first member of a diverse and sometimes strange group of diving birds.
Evolution of Penguins
Penguins evolved from flying ancestors who were actual giants for millions of years. Some of them were even dressed a little more casually. The thing to know about modern penguins is that they’re specialized in underwater life.
While they still have to molt and breed on land, they’ve evolved many features that make them dynamic marine predators. For example, they’ve got unique scale-like feathers that help keep them warm and dry in cold ocean waters. They’ve also got rete mirabile systems in their limbs and head.
These neighboring blood vessels transfer heat between the arteries, where the blood from the heart is warmer. The vein’s blood is colder. This exchange helps keep the penguin’s core temperature by buffering the much cooler blood returning to the heart.
- Their wing joints are stiffer than flying birds, which helps them produce thrust on the downstroke and the wing’s upstroke.
- The muscles that raise the wing on the upstroke are much bigger than in other birds.
So the place they attach to the penguin’s shoulder blade is much bigger than in other birds. This powerful double-stroke allows penguins to move easily through water, denser than air. Their bones are also denser than flying birds. After all, penguins aren’t trying to stay up in the air. They’re fighting against the buoyancy of seawater. Those dense bones are part of what gives penguins such a great fossil record! They evolved from a flying ancestor.
- The closest living relatives of the penguins are the Procellariiformes, including albatrosses, petrels, and storm petrels. They could fly!
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, the flight is energetically expensive, but it helps you do long travel distances and avoid predators. It’s hard to be good at both in terms of anatomy and biomechanics.
One theory is that they were closely related to prehistoric birds known as Protopteryx, which went extinct around 20 million years ago. These birds show remarkable similarities with penguins. They live in the northern hemisphere and are sometimes referred to as the northern penguins. If these birds were closely related, penguins’ closest relatives must be cormorants and pelicans.
However, some recent studies have shown that the rib cage and shoulders of the flattop turrets differ significantly from penguins. Their similar traits may be due to convergent evolution. This DNA evidence has them more closely aligned with the albatross and petrels.
Penguins wings evolution
In a paper published in 2013, researchers compared energy use in two species of living birds to figure out why. They studied thick-billed murres, which are wing-propelled divers, and pelagic cormorants, which are foot-propelled divers. Both of these species also fly. So the researchers could calculate the energy costs for that, too. They found that the more specialized wings become for diving, the worse they are for flying.
- They need a large body size and shorter, flatter wings with dense, enlarged bones for wing-propelled diving. All of these things maximize the length and efficiency of every dive.
But these features are also the exact opposite of what they need for efficient flight. So, there’s a pretty straightforward trade-off in anatomy here. 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. After the extinction at the end of the Cretaceous, diving predators like small mosasaurs and plesiosaurs were gone. So their ecological niches were suddenly open.
The larger marine reptiles and sharks that had made the seas so treacherous for diving birds were gone, too. So, with a new potential food source and fewer predators, those penguin ancestors that were better divers might have had an advantage. They are being able to get more food while using less energy. Once they started down the path toward “underwater flight,” there was no stopping them.
Penguins at Antarctica
Penguins probably evolved in New Zealand in the early Paleocene Epoch, around 61 million years ago, with Waimanu and its relatives. They made it to Antarctica by the late Paleocene, between 59 million and 56 million years ago. They arrived in South America by the middle Eocene Epoch, around 42 million years ago. By the late Eocene, between 37 million and 34 million years ago, there were at least two genera of penguins in Australia.
The largest living penguin is the emperor penguin, which stands a little over a meter tall and can weigh up to 40 kilograms. It would’ve looked small next to some of its Paleocene relatives from New Zealand. Crossville was over 1.5 meters tall and weighed nearly twice as much as an emperor penguin, between 70 and 80 kg.
Kumimanu was even bigger. It stood about 1.7 meters tall and tipped the scales at over 100 kilograms. Both of these species show up not long after penguins first evolved. It tells paleontologists that not flying meant they could go all-in on becoming more efficient divers. Several groups independently developed large body sizes as a result.
Antarctica in the Late Eocene was home to at least two more giant penguin species. Anthropornis was about the size of Kumimanu, close to 2 meters tall, and about 100 kg. But one species in the genus Palaeeudyptes was the penguin heavyweight champ. It stood over 2 meters tall and weighed about 115 kg. Finally, another of these Late Eocene giant penguins wasn’t the dapper bird. We call it Inkayacu, and it lives in Peru. It was found with fossilized feathers that contained preserved melanosomes, cells making and storing pigment.
Instead of making its feathers black and white, they looked like those of other modern birds that are gray and reddish-brown! The giant penguins were victorious for millions of years. But they’d mostly disappeared by about 23 million years ago and were gone 18 million years ago. The cause might have been the rise of marine mammals, especially new-toothed whales, in the Oligocene Epoch.
Like seals and sea lions, toothed whales and pinnipeds might have competed with the giant penguins for food. Social pinnipeds might’ve competed with the penguins for safe breeding places, too. But the jury is still out because testing hypotheses about competition in the fossil record is complex.
Penguins live on all southern continents, from Antarctica to the Galapagos Islands. They reached about 4 million years ago, where cold ocean currents keep the waters cooler. It looks like the history of penguins may have been tightly linked to the rise and fall of the other organisms around them.
The extinction of the marine reptiles at the end of the Cretaceous left many empty niches they could dive into. They spread throughout the southern continents until some were lost to new marine mammals. The penguins still around today are the descendants of that ancient lineage that went from the sky to the sea.
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Grabski, Valerie. “Little Penguin – Penguin Project.” The Penguin Sentinels/University of Washington.
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