Few animals have evolved to survive the unforgiving Antarctic like penguins. Species such as the emperor penguin have overlapping layers of insulating plumage, densely packed veins to recirculate body heat, and enough belly to withstand cold winds reaching minus 80 degrees Fahrenheit.
With all these cold-weather adaptations, it’s hard to imagine penguins living anywhere else. But ancient penguin fossils have been found along the equator, and many of these prehistoric seabirds predate the formation of the Antarctic ice sheets. “They experienced some of the hottest times 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. — Basically, they developed in the absence of ice. ”
To determine how penguins moved from mild tropical waters to the polar seas, Dr. Ksepka and colleagues recently analyzed the genomes of all living penguins, including chicks like the foot-tall blue penguin, rarities like the yellow-eyed penguin found endangered, and show stoppers such as the yellow-crested rockhopper penguin. However, the genetics of modern penguins had little to tell researchers. Most modern bloodlines date back only a couple of million years, obscuring much of the 60-million-year odyssey of penguin evolution.
Dr Ksepka said more than three-quarters of all penguin species are “extinct”. He added: “You have to look at the fossil record, otherwise you will only get a piece of history.”
To complement modern data, the researchers studied the fossils of a motley crew of ancient seafarers. Some prehistoric penguins plied the tropical waters of Peru using spear-like beaks to harpoon fish. Others had long legs, and the largest of them could reach seven feet in height. Some even had patches of rusty red feathers.
Comparing the genomes of modern penguins with fossil penguins allowed the team to reconstruct penguin evolution. In their findings, published Tuesday in Nature Communications, the researchers identified the genes that helped penguins go from wading through warm waters to perfecting polar diving. Some of these genes contributed to the ability of penguins to accumulate fat, while others turned their shriveled wings into streamlined flippers. Some have even boosted the penguins’ immune systems or helped them cope with lack of oxygen during deep dives.
The researchers also identified genes that helped penguins fine-tune their eyes to see through the icy depths. While most birds have four colored cones in their eyes, penguins have one of them inactive, hindering their ability to see green and red. Instead, their eyes adjusted to the surrounding blue of the ocean.
Some of the missing genes have puzzled researchers. While modern penguins eat krill, the team found evidence that their ancestors did not have genes that would have helped break down crustacean shells. This may be evidence that ancient penguins speared larger prey such as fish and squid. Penguins keep a limited sky. Their taste buds can only pick up salty and sour tastes, which is “pretty good if you’re eating fish,” Dr. Ksepka said. “That’s probably why they’re so happy with sardines.”
When these changes happened in the ancient penguins, they stuck. Genetic analysis has shown that penguins generally have the slowest rate of evolution of any group of birds. Because they look so whimsical, this icy rate of change is amazing. But it shows just how successful the penguin’s chubby but streamlined body is—it has only changed in slow increments over millions of years. But emperor penguins, which breed during the harsh Antarctic winter, have the highest rate of evolution of any penguin, leading researchers to conclude that cooler temperatures are somehow speeding up penguin evolution.
Juliana Vianna, an ecologist at the Pontifical Catholic University of Chile, says the idea is consistent with the southward march of penguins during periods of global cooling. “Their evolutionary history is largely tied to historical climate change and glaciation,” said Dr. Vianna, who recently led a similar study but was not involved in the new study.
Understanding how penguins have changed in the past can provide insight into how these cold weather specialists might fare in a hotter future. “Warming temperatures will affect penguin biogeographic ranges, the species they rely on for food and the species that in turn prey on them,” said Daniel Thomas, a paleontologist at Massey University in New Zealand and author of the new study.
Although the study is a comprehensive look at the penguin family, one seabird is still missing – the last flying penguin, Dr. Ksepka said. The small, puffin-like bird likely lived in ancient New Zealand, but its fossils have proven elusive. “That would be the number one thing I would ask for if I had a genie,” he said.
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