Few animals have evolved to survive the irreconcilable Antarctic as penguins. Species such as the emperor penguin have overlapping layers with insulating plumage, tightly packed veins to recycle body heat and just enough belly to cope with wind freezes approaching minus 80 degrees Fahrenheit.
With all these cold weather adaptations, it is difficult to imagine penguins living anywhere else. But fossils of ancient penguins have appeared along the equator, and many of these prehistoric seabirds are before the formation of the Antarctic ice sheet. “They lived through some of the warmest 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. “They initially evolved in an ice-free context.”
To find out how penguins moved from warm, tropical waters to polar oceans, Dr. Ksepka and his colleagues recently analyzed the genomes of all living penguins, including pipsqueaks like the foot-tall blue penguin, rarities like the endangered yellow-eyed penguin, and showstoppers like the yellow-tufted steinhoppepingvinen. However, the genetics of modern penguins could tell scientists only so much. Most modern ancestry dates back only a few million years, obscuring most of the 60 million-year-old odyssey of penguin evolution.
Dr. Ksepka said that more than three quarters of all penguin species “are now extinct.” He added: “You have to look at the fossil record, otherwise you only get a fragment of history.”
To supplement the modern data, the researchers examined fossils from a motley crew of ancient sailors. Some prehistoric penguins swept tropical waters off Peru, using spear-like beaks to harpoon fish. Others had long legs, and the largest may have pushed itself seven feet high. Some even had stains with rusty red feathers.
Comparing the genomes of modern penguins with fossil penguins allowed the team to reconstruct the penguin evolution. In their findings, published Tuesday in Nature Communications, the researchers found genes that helped penguins go from wading through warm water to perfecting the polar cliff. Some of these genes helped the penguins’ ability to pack on fat, while others molded their shrunken wings into streamlined flippers. Some even strengthened penguins’ immune systems or helped them tolerate low oxygen during deep dives.
The researchers also identified genes that helped fine-tune penguin eyes to look through icy depths. While most birds have four color cones in their eyes, one of these is inactive in penguins, which hinders their ability to see green and red. Instead, their eyes have adapted to the blue surroundings of the ocean.
Some missing genes were confusing for the researchers. While modern penguins devour krill, the team found evidence that their ancestors lacked genes that would have helped break down crustacean shells. This may be evidence that ancient penguins spit on larger prey, such as fish and squid. Penguins retain a limited palate. Their taste receptors can only pick up salty and sour tastes, which is “pretty good if you eat fish,” said Dr. Ksepka. “That’s probably why they’re quite happy with sardines.”
When these changes occurred in old penguins, they became stuck. The genetic analyzes revealed that penguins generally have the lowest evolutionary rate of any group of birds. Because they look so bizarre, this glacier change seems surprising. But it reveals how successful the penguin’s full but streamlined body plan is – over millions of years it has only changed in slow motion. But emperor penguins, which nest during the bitter Antarctic winter, have the highest rate of evolution of any penguin, leading researchers to conclude that colder temperatures somehow accelerate the penguin’s evolution.
Juliana Vianna, an ecologist at the Papal Catholic University of Chile, says that this idea is in line with the southern march of penguins that occurs during global cooling attacks. “Their evolutionary history is pretty much associated with historical climate change and glaciers,” said Dr. Vianna, who recently led similar research but was not involved in the new study.
Understanding how penguins have changed in the past can provide clues to how these cold-weather specialists can cope in a warmer future. “Warming temperatures will affect the biogeographic areas of penguins, the species they depend on as food and the species that in turn hunt them,” said Daniel Thomas, paleontologist at Massey University in New Zealand and author of the new study.
While the research is a comprehensive look at the penguin family, said Dr. Ksepka, there is still a seabird missing – the last flying penguin. The small, puffin-like bird probably lived in old New Zealand, but the fossils have proven to be elusive. “That would be the No. 1 thing I would ask for if I had a genius,” he said.