Few animals have evolved to survive merciless Antarctica as well as penguins. Species like the Emperor Penguin have overlapping layers of plumage that insulates them from the cold, densely distributed veins to recycle body heat, and a paunch sufficient to withstand a cold approaching minus 62 degrees Celsius.
With all these adaptations to withstand the cold, it’s hard to imagine penguins living anywhere else. But ancient penguin fossils have been found around the equator, and many of these prehistoric seabirds predate the formation of the Antarctic ice caps.
“Penguins lived in some of the hottest periods in Earth’s history, when the temperature at the equator was 5 degrees higher than it is today,” commented paleontologist Daniel Ksepka of the Bruce Museum in Greenwich, Connecticut. “Basically, they developed in a context that didn’t have ice.”
To determine how penguins made the transition from warm tropical waters to polar seas, Ksepka and his colleagues recently analyzed the genomes of all living penguins, including tiny species such as the blue penguin, which measures 30 centimeters, rarities like the penguin. endangered yellow-eyed penguin, and showy birds such as the rockhopper penguin. But what they were able to discover from the genetic data of modern penguins was limited. Most modern lineages date to just two or three million years ago, obscuring most of the 60 million years of the penguins’ evolutionary odyssey.
Ksepka said that more than three-quarters of all penguin species are extinct today. According to him, “you have to study the fossil record, otherwise you only see a fragment of history.”
To complement the modern data, the scientists examined fossils from a wide variety of ancient seabirds. Some prehistoric penguins lived in the tropical waters off Peru and harpooned fish with their spear-shaped beaks. Others had long legs; the largest of the penguins may have surpassed 2.1 meters in height. Some even had rust-red patches of feathers.
Comparing the genomes of modern penguins with fossil penguins allowed researchers to reconstruct the evolution of penguins. In their findings, published Tuesday in Nature Communications, they identified genes that helped penguins make the transition from swimming in warm, shallow water to perfecting diving in polar waters.
Some of these genes benefited their ability to store fat, while others converted their wrinkled wings into streamlined fins. Some even strengthened the penguins’ immune systems or helped them tolerate low oxygen levels during deep dives.
The researchers also identified genes that helped adapt the penguins’ eyes to be able to see better in icy, deep water. While most birds have four eye cones, one of them is inactive in penguins, impairing their ability to see green and red. Instead, his eyes adapted to adjust to the blue of the ocean.
Some genes that were not present puzzled researchers. While modern penguins devour krill, scientists have found evidence that their ancestors lacked genes that would have helped them decompose crustacean shells. This could be evidence that ancient penguins fed on larger prey such as fish and squid. Penguins retain a limited taste. Your taste receptors can only pick up on salty and sour flavors — “very good if you’re eating fish,” Ksepka said. “Must be why they like sardines so much.”
When these changes occurred with ancient penguins, they stuck. Genetic analyzes have revealed that penguins generally have the lowest evolutionary rate of any group of birds. Because its appearance is so bizarre, this very slow rate of transformation seems surprising. But he reveals just how successful the chubby but streamlined body plan of penguins is — over millions of years it has only changed in very slow increments.
But emperor penguins, which breed during the harsh Antarctic winter, have the highest evolutionary rate of any penguin, a fact that leads researchers to deduce that lower temperatures somehow accelerate the evolution of penguins.
Ecologist Juliana Vianna, from the Pontifical Catholic University of Chile, says this idea is consistent with the hypothesis that the penguins’ southward march occurred during phases of global cooling. “Their evolutionary history is closely associated with climate change and historical glaciation,” said Vianna, who recently led similar research but was not involved in the new study.
Understanding how penguins have changed in the past could provide clues to predicting how these cold-weather experts might fare in a warmer future. “Rising temperatures will impact biogeographical areas inhabited by penguins, the species they feed on and the species that in turn hunt them,” said Daniel Thomas, a paleontologist at Massey University in New Zealand and one of the authors. of the new study.
The survey covered the entire penguin family, but, according to Ksepka, one seabird was left out: the last flying penguin. This small, puffin-like bird probably lived in New Zealand in the past, but no fossils could be obtained. “If I had a genie in the lamp, this would be the first thing I would ask for,” Ksepka said.
Translation by Clara Allain