Penguins are perhaps best known as flightless birds whose feathers help them “fly” through Antarctic waters. But penguins lost their ability to fly and instead became streamlined swimmers about 60 million years ago, long before the Antarctic ice sheet formed – and researchers have now uncovered how that happened.
A new study of penguin fossils and the genomes of current and recently extinct penguins identified an array of genetic adaptations made by birds to live an aquatic lifestyle; From vision that is sensitive to blue tones under water, to genes related to blood oxygenation, and even to changes in bone density. Together, the findings suggest that penguins as a group adapted to survive some of the severe environmental changes that unfolded over millions of years.
The oldest penguin fossils date back 62 million years, said study co-author Daniel Kesepka, a paleontologist at the Bruce Museum in Greenwich, Connecticut. By that time, penguins were already flightless, although they looked very different from modern penguins. They had longer legs and beaks, and their wings were still more feathered than those of the flipper, Kesepka told Live Science.
“These early ones are probably evolving from a puffin-like animal that can still fly in the air,” Kesepka said. (This flying ancestor has not yet been discovered in the fossil record, so it is not known exactly when penguins lost their airborne abilities.)
Over time, evolution created “an inspiring troupe of interesting penguin characters,” Kesepka said, ranging from penguins with long spear-like bills to red-winged penguins to birds that are one or two larger than today’s largest penguin species. feet tall, the emperor, who measures approximately 3 feet 7 inches (1.1 m) tall.
In the study, researchers evaluated fossil evidence from the genomes of all living penguins, as well as partial genomes for those that went extinct in the past few hundred years. The findings suggest that penguins originated near New Zealand some 60 million years ago, spread to South America and Antarctica, and then returned to New Zealand. Kesepka said that most species alive today diverged from each other over the past 2 million years. During that period, Earth went through cycles of glacial and interglacial periods in which polar ice expanded and retreated. Moving ice pushed penguins north, perhaps cutting off some populations from each other and enabling them to take their own evolutionary paths for about 100,000 years. By the time the ice retreated, individual penguins had evolved into different species.
“It doesn’t affect all species equally, but it’s almost as if someone is turning the crank to create more penguin species,” Kesepka said.
Despite all the changes, penguins have the slowest growth rate of change of all birds, researchers reported July 19 in the journal nature communication (opens in new tab), It was surprising and remains unclear, Kesepka said. Larger animals and animals that reproduce relatively slowly, as do penguins, tend to have slower growth rates, he said. However, some birds that are larger than penguins develop more quickly than penguins. Other types of birds that reproduce at the same rate as penguins also tend to evolve more quickly, so more work is needed to understand why penguins are so slow to evolve, Kesepka said.
While the evolution of penguins may have been comparatively slow, it has provided them with many adaptations for life in and around the ocean. They share a suite of genes with other flightless birds that probably shortened their wings, and they also have unique genes that turn many of the muscles in the feathers of penguin ancestors into tendons, which are part of penguin wings. harden and make them look like flippers. The researchers also found mutations in genes associated with calcium storage, which may contribute to the dense bones that help penguins dive.
Evolution has also produced many other changes, such as genes associated with fat storage and temperature regulation. An interesting finding was that penguins lost several genes early in their evolution that were associated with digesting the exoskeleton of crustaceans. This suggests that early penguins had a diet centered around prey such as fish and squid, Kesepka said. But the expansion of ice sheets created an Antarctic ecosystem that was rich in krill, which are tiny crustaceans. Fortunately, the researchers found, the penguins had one gene left — the CHIA gene — that enabled them to still digest crustaceans.
“If that last one had come off, they might have been hard to digest. [krill]Kasepka said.
Kesepka warned that about 75% of all penguin species are extinct, and that climate change could be further extinguished. This is especially true for species with distinct lifestyles, such as the emperor penguin (Aptenodytes forsteri) that breed entirely on sea ice. If sea ice melts, Kesepka said, emperor penguin Mayu The struggle to find a breeding site, At the other end of the spectrum, little penguins living in the rocky Galapagos Islands live so far from other lands that they have nowhere to run if their equatorial habitat gets too hot.
“We certainly think that these animals are vulnerable to environmental change, and in many cases they are already considered endangered,” Kesepka said. “In other cases they may become more vulnerable over the next few decades.”
Originally published on Live Science.