The 57 million-year-old fossil is both fearsome and comical: a long-beaked penguin that stood 5 feet 7 inches tall and weighed about 220 pounds.
“It was as tall as a medium-sized man,” said Gerald Mayr, a paleontologist at the Senckenberg Research Institute in Frankfurt, Germany, and lead author of a report in Nature Communications on Tuesday announcing the discovery.
By comparison, the tallest living species, the emperor penguin, reaches about four feet in height. Kumimanu biceae, as the fossil was named, would have towered above the emperor, and above just about all other known ancient penguins.
(In 2014, another team of researchers estimated that a 34-million-year-old species stood six feet tall, but they based that estimate only on two bone fragments.)
Kumimanu wasn’t just exceptionally big; it also ranks among the oldest penguin fossils yet found. Both its age and its size make Kumimanu important to understanding the astonishing transformation that turned a lineage of flying birds into flightless swimmers.
The 18 modern species of penguin, ranging from the coast of Antarctica to the Galápagos Islands at the Equator, are impressively adapted to aquatic life. Rigid, blade-shaped wings enable them to shoot through the water at up to 22 miles an hour. Record-setting human swimmers don’t even reach six m.p.h.
But their adaptations to water have also left them unable to fly. When penguins haul out to rest or rear their young, they can only waddle about on stumpy legs. “They’re so unbirdlike that many people would not know they are birds,” Dr. Mayr said.
While penguins may look profoundly different from other birds, their DNA points to a close kinship to such species as albatrosses and petrels. These birds all fly over water to hunt for prey, hinting that the ancestors of penguins may have, too.
Auks, which can dive over a hundred feet underwater, may be a living model of the first penguins.
Birds accumulate mutations in their DNA at a roughly clocklike rate, allowing scientists to estimate when their lineages branched apart. Studies suggest that penguins diverged around the time of the mass extinction that struck the planet about 66 million years ago.
A combination of massive volcanic eruptions and an asteroid impact are believed to have been responsible for the global catastrophe. Among the victims were giant marine reptiles and dinosaurs (with the exception of birds, which are feathered dinosaurs). The mass extinctions marked the end of the Mesozoic Era and the beginning of the Cenozoic, which continues today.
The first penguin fossils were uncovered in 1859, and since then more than 50 species have been identified. The oldest of these, found in New Zealand, date back about 60 million years. Known as Waimanu, the oldest known penguins lived just a few million years after the mass extinctions.
The new fossil penguin, Kumimanu, was discovered from bones packed in a rock on a New Zealand beach. Realizing that it was almost as old as Waimanu, Dr. Mayr and his colleagues eagerly studied Kumimanu for a better picture of early penguin evolution.
To see how it was related to other species, the scientists drew an evolutionary tree and found that Kumimanu and Waimanu belonged to its farthest branches. Their lineages have been extinct for tens of millions of years.
By contrast, all living penguins belong to a young branch of the tree. They share a common ancestor that lived only about 15 million years ago.
Kumimanu and Waimanu were already flightless, but they still held onto some primitive traits not found in living penguins.
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