How the penguins beat the heat and went south

Few animals have evolved to survive in Antarctica as unforgiving as penguins. Species such as the emperor penguin have intertwined layers of insulating feathers, tightly packed veins to recycle body heat, and enough leeway to weather wind chills approaching minus 80 degrees Fahrenheit.

With all these adaptations to cold weather, it’s hard to imagine penguins living anywhere else. But fossils of ancient penguins appeared along the equator, and many of these prehistoric seabirds predate the formation of the Antarctic ice sheets. “They’ve experienced some of the hottest times in Earth’s history, when the temperature was five degrees higher at the equator,” said Daniel Ksepka, a paleontologist at the Bruce Museum in Greenwich, Connecticut. “It basically evolved in an ice-free context.”

To determine how penguins move from temperate tropical waters to polar seas, Dr. Ksepka and colleagues recently analyzed the genomes of all living penguins, including pipsqueaks such as the tall blue penguin, a rarity such as the endangered yellow penguin, and penguin appearances such as the yellow rock penguin. However, the genetics of modern penguins can tell researchers only so much. Most modern dynasties date back only two million years, obscuring most of the 60 million-year saga of penguin evolution.

Dr. Ksepka said that more than three-quarters of all penguin species are “now extinct”. “You have to look at the fossil record, otherwise you only get part of the story,” he added.

To complement the recent data, the researchers examined fossils from a diverse crew of ancient sailors. Some prehistoric penguins were drowning in the tropical waters off Peru, using spearlike bills for fish harpoons. Others wore long legs, the largest perhaps having pushed seven feet long. Some even had patches of rusty red feathers.

Comparing the genomes of modern penguins with those of fossil penguins has allowed the reconstruction of penguin evolution. In their findings, published Tuesday in Nature Communications, the researchers identify the genes that helped penguins transition from wading in warm waters to mastering polar descents. Some of these genes helped the penguins’ ability to clump with blubber, while others shaped their deflated wings into streamlined fins. Some have even boosted the penguins’ immune systems or helped them tolerate a lack of oxygen during deep dives.

The researchers also identified genes that helped adjust penguins’ eyes to see through icy depths. While most birds have four color cones in their eyes, one of them is inactive in penguins, hindering their ability to see green and red. Instead, their eyes had adapted to adapt to the blue color of the ocean.

Some of the missing genes have been baffling to researchers. As modern penguins devour krill, the team found evidence that their ancestors lacked genes that would have helped break down crustacean scales. This may be evidence that ancient penguins drove out larger prey, such as fish and squid. Penguins maintain a restrained palate. Taste receptors can only pick up on salty and sour flavors, which is “very good if you’re eating fish,” said Dr. Ksepka said. “Maybe that’s why they are so happy with sardines.”

When these changes occurred in ancient penguins, they remained stuck. Genetic analyzes revealed that penguins in general have the lowest evolutionary rate of any group of birds. Since it looks so strange, this rate of glacial change seems surprising. But it does reveal just how well a plump, streamlined penguin’s body plan works—over millions of years, it’s changed only in slow increments. But emperor penguins, which breed during the harsh Antarctic winter, have the highest evolutionary rate of any penguin, leading researchers to conclude that cold temperatures somehow speed up penguin evolution.

This idea is consistent with the southward march of penguins that occurs during bouts of global cooling, says Juliana Viana, an ecologist at the Pontifical Catholic University of Chile. Dr. said. Viana, who recently led similar research but was not involved in the new study.

Understanding how penguins have changed in the past may provide clues to how these cold-weather specialists will thrive in a hotter future. “Rising temperatures will affect the penguins’ biogeographical ranges, the species that depend on them for food, and the species that hunt them,” said Daniel Thomas, a paleontologist from Massey University in New Zealand and author of the new study.

While the research is a comprehensive look at the penguin family, Dr. There is still a missing seabird – another penguin, said Ksepka. This tiny puffin-like bird may have lived in ancient New Zealand, but its fossils have proven elusive. “That would be a number. The first thing I would have asked if I had a genie.”

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