When these changes occurred in ancient penguins, they stuck. The genetic analyses revealed that penguins generally have the lowest evolutionary rate of any group of birds. Because they look so bizarre, this glacial rate of change seems surprising. But it reveals how successful the penguin’s plump yet streamlined body plan is — over millions of years, it has changed only in slow increments. But emperor penguins, which breed during the bitter Antarctic winter, have the highest evolutionary rate of any penguin, leading the researchers to deduce that colder temperatures somehow speed penguin evolution.
Juliana Vianna, an ecologist at the Pontifical Catholic University of Chile, says this idea is consistent with the southward march of penguins occurring during bouts of global cooling. “Their evolutionary history is pretty much associated with historical climate change and glaciation,” said Dr. Vianna, who recently led similar research but was not involved in the new study.
Understanding how penguins changed in the past may offer clues to how these cold-weather specialists could fare in a hotter future. “Warming temperatures will impact the biogeographic ranges of penguins, the species they rely on as food and the species that, in turn, hunt them,” said Daniel Thomas, a paleontologist from Massey University in New Zealand and an author of the new study.
While the research is a comprehensive look at the penguin family, Dr. Ksepka said, there’s still one seabird missing — the last flying penguin. The small, puffinlike bird probably lived in ancient New Zealand, but its fossils have proved elusive. “That would be the No. 1 thing I’d ask for if I had a genie,” he said.