This illustration provided by Gerald Mayr shows the size of an ancient giant penguin Kumimanu biceae. Picture: Gerald Mayr/Senckenberg Research Institute via AP

Wellington - A penguin fossil the size of a human has been discovered in New Zealand, the country's national museum Te Papa said Wednesday, changing the way scientists think about the bird's evolution.

The fossil was discovered in a rock estimated to be between 55 and 60 million years old on a South Island beach in 2004 by Alan Tennyson, curator of vertebrates at Te Papa.

However, extraction of the bones, which form an incomplete skeleton, from within the rock had to wait until 2015 when the technology become available.

Based on the size of the bones, scientists estimate the penguin would have stood at 1.65 metres tall - the same height as an average human - and weighed 100 kilos. Today's largest penguin, the emperor, stands at 1.1 metres tall and weighs 23 kilos.

Tennyson told Radio NZ that the fossil was of huge global significance as it comes from a period just after the demise of the dinosaurs and shows that giant penguins were among the first penguins to have evolved. "That wasn't really known before now," Tennyson said.

"There's probably a relationship here, so the large animals like dinosaurs, non-avian dinosaurs and marine predators, all died out at that asteroid impact about 66 millions years ago," he said.

"That probably opened up empty niches which allowed other things to grow large and fill them like this penguin."

Tennyson called the penguin Kumimanu biceae - "Kumimanu" means "monster bird" in Maori and "biceae" honours his mother Bice Tennyson.

A paper on the project, which involved scientists from New Zealand and Germany, has been published in the online journal Nature Communications.