Few animals have evolved to survive in relentless Antarctica like penguins. Species like the emperor penguin have superimposed layers of insulating plumage, well-packed veins to recycle body heat, and enough belly to withstand the cold of the wind approaching 80 degrees Fahrenheit.
With all these adaptations to cold weather, it’s hard to imagine penguins living anywhere else. But ancient penguin fossils have appeared along the equator, and many of these prehistoric seabirds predate the formation of Antarctic ice sheets. “They experienced some of the hottest moments in Earth’s history, when it was five degrees warmer at the equator,” said Daniel Ksepka, a paleontologist at the Bruce Museum in Greenwich, Connecticut. “They basically evolved in an ice-free context.”
To determine how penguins moved from tropical waters to polar seas, Dr. Ksepka and colleagues recently analyzed the genomes of all living penguins, including one-foot-tall blue penguins, rarities such as the endangered yellow-eyed penguin, and lids such as the jumping penguin. of yellow rocks. However, the genetics of modern penguins could only tell researchers. Most modern lineages date back only a couple of million years, obscuring most of the 60 million-year-old odyssey of penguin evolution.
Dr. Ksepka said more than three-quarters of all penguin species “are now extinct.” He added: “You have to look at the fossil record, or you’ll just get a snippet of the story.”
To complement modern data, researchers examined fossils of a varied crew of ancient sailors. Some prehistoric penguins sailed the tropical waters of Peru, using spear-shaped beaks to harpoon fish. Others wore long legs, and the largest could have pushed seven feet tall. Some even had rusty red feather spots.
Comparing the genomes of modern penguins with fossil penguins allowed the team to reconstruct the evolution of penguins. In their findings, published Tuesday in Nature Communications, researchers identified genes that helped penguins move from wading through warm water to perfecting polar diving. Some of these genes helped the penguins pack up with fat, while others modeled their wrinkled wings on aerodynamic fins. Some even strengthened the penguins ’immune system or helped them tolerate low oxygen levels during deep dives.
The researchers also identified genes that helped sharpen the penguins ’eyes to look through the icy depths. While most birds have four colored cones in their eyes, one of these is dormant in penguins, making it difficult for them to see green and red. Instead, his eyes have adapted to suit the ambient blue of the ocean.
Some missing genes were perplexing to researchers. While modern penguins swallow krill, the team found evidence that their ancestors had nothing that would have helped break the shells of crustaceans. This may be evidence that ancient penguins were throwing larger prey, such as fish and squid. Penguins maintain a restricted palate. Its taste receptors can only pick up salty, sour flavors, which is “pretty good if you eat fish,” Dr. Ksepka. “That’s probably why they’re so happy with the sardines.”
When these changes occurred in ancient penguins, they were trapped. Genetic analyzes revealed that penguins generally have the lowest evolutionary rate of any group of birds. Because they seem so weird, this glacial exchange rate seems amazing. But it reveals the success of the penguin’s thick but streamlined body plan: for millions of years, it has only changed in slow increments. But emperor penguins, which breed during the bitter Antarctic winter, have the highest evolutionary rate of any penguin, which leads researchers to deduce that colder temperatures somehow accelerate the evolution of penguins.
Juliana Vianna, an ecologist at the Pontifical Catholic University of Chile, says this idea is consistent with the penguins’ southward march that occurs during episodes of global cooling. “Its evolutionary history is virtually associated with historical climate change and glaciation,” said Dr. Vianna, who recently led similar research but did not participate in the new study.
Understanding how penguins changed in the past can provide clues as to how these cold weather specialists might come out in a warmer future. “Warming temperatures will affect the biogeographic ranges of penguins, the species they depend on for food and the species that in turn hunt them,” said Daniel Thomas, a paleontologist at Massey University in New Zealand. and author of the new study.
Although the research is a comprehensive view of the penguin family, Dr. Ksepka said, a seabird is still missing: the last flying penguin. The small, fragile-like bird probably lived in ancient New Zealand, but its fossils have proved difficult to make. “That would be the number 1 I would ask if I had a genius,” he said.