Standing 5ft 8in (1.7 metres) in its flippers, the giant bird weighed in at nearly 17 stone (100kg), says German ornithologist Gerald Mayr.

Dubbed “an ancient bird in an oversized tuxedo”, it’s scientific name is Kumimanu, Maori for Monster Bird. 

Its fossilised remains were found on New Zealand’s South island and have been dated to about 59 to 56 million years ago.

It thrived in the Late Paleocene about six million years after non-avian dinosaurs became extinct. 

It is one of the oldest penguins ever found and the second largest, beaten only by a fossil from Antarctica which was about 6ft tall and lived 40 million years ago.

Kumimanu’s giant size probably developed because it was flightless and allowed it to dive deeper than smaller modern relatives.

But Dr Mayr, from the Senckenberg Research Institute in Frankfurt, told Nature Communications, it was probably wiped out by the rise of large marine predators such as whales.

The bones were found in the Otago region and show that penguins became giants early in their evolution. 

Dr Mayr, who studied the fossils with New Zealand colleagues, said: “We examined the wing and leg bones of this penguin and quickly realised that we were looking at a previously unknown species. 

“The size of the bones indicates that this species stood over 1.7 meters tall and weighed more than 100 kilograms.

“Age datings reveal that the bird lived during the Late Paleocene, i.e., about 59 to 56 million years ago.

“The fossils are therefore among the oldest known penguin remains, and it is remarkable that even these early forms reached such an enormous size.”  

But Dr Mayr said Kumimanu probably flourished for only a relatively short period. 

He said: “Giant penguins developed shortly after the mass extinction near the end of the Cretaceous, approx. 66 million years ago. 

“It is possible that the disappearance of large marine reptiles enabled the penguins to explore new ecological niches. 

However, with the subsequent appearance of other large marine predators such as seals and toothed whales, the penguins faced new competition and predation – which may have led to their extinction.”