Fossils from New Zealand have revealed a giant penguin that was a big as a grown man. It measured nearly 1.77 meters long when swimming and weighed in at 101 kilograms. However on the ice things would look different. When standing, the ancient bird was maybe only 1.6 meters.

The newly found bird is about 18 centimeters longer than any other ancient penguin that has left a substantial portion of a skeleton, said Gerald Mayr of the Senckenberg Research Institute and Natural History Museum in Frankfurt, Germany. A potentially bigger rival is known only from a fragment of leg bone, making a size estimate difficult.

The biggest penguin today, the emperor in Antarctica, stand less than 1.2 meters tall.

Mayr and others describe the giant creature in a paper released Tuesday by the journal Nature Communications. They named it Kumimanu, which refers to Maori words for 'monster bird'. The fossils are 56 million to 60 million years old. That's nearly as old as the very earliest known penguin fossils, which were much smaller, said Daniel Ksepka, curator at the Bruce Museum of Greenwich, Connecticut. He has studied New Zealand fossil penguins but didn't participate in the new study.

Te Papa museum curator Alan Tennyson said the boulder containing the bones was founds on Otago beach in 2004. "The beach was a known site for bird fossils, but only very fragmentary pieces," he said.

Mr Tennyson said giant penguins were thought to be the norm during much of the history of the birds, between 60 million and 20 mullion years ago until marine mammals evolved. "At the time of the giant penguin there were no whales, or seals, but by the time 20 million years came around whales and seals were really diversifying, so I think maybe they ate the giant penguins or out-competed them."

Birds often evolve toward large sizes after they lose the ability to fly, Mayr said. In fact, the new paper concludes that big size appeared more than once within the penguin family tree. However researchers believe they died out when larger marine mammals like toothed whales and seals showed up and provided competition for safe breeding places and food. The newcomers may also have hunted the big penguins, he said.