Ancient penguins were huge. That’s what fossils of a newly described penguin species dubbed Kumimanu biceae suggest. Researchers estimate the bird weighed in at 101 kilograms, and—based on the length of a femur bone found near the eastern coast of New Zealand’s southern island—was about 1.77 meters tall, about the same as an average adult human. In contrast, today’s largest living penguin, the emperor penguin, is half as massive and shorter by half a meter. The new fossil isn’t the only known giant penguin—others were similar in size and the largest likely stood about 2 meters tall—but K. biceae is one of the oldest. The bird lived 55 million to 60 million years ago, just after the mass extinction that took out the dinosaurs, researchers report today in Nature Communications.
That means these penguins became sizable soon after they became flightless divers. Once their body size wasn’t constrained by a need to be aerodynamic, they could grow to substantial dimensions. When the dinosaurs disappeared, large marine reptiles vanished, too, and that may have left the seas open for K. biceae to inhabit. So, why aren’t modern penguins as humongous? The disappearance of gigantic penguins coincides with the rise of seals and toothed whales, the researchers say, so there may have been competition for food and safe places to breed and rear young. But, exactly how these mammals pushed out the gigantic birds is still a mystery.