A report published this week by Daniel Ksepka, of North Carolina State University, has revealed previously unknown fossilised species Kairuku Grebneffi and Kairuku Waitaki, that were discovered in the Waitaki 20 years ago.
The revelation has caused excitement in the international science community.
More remarkable is the penguins are believed to have stood 1.3m tall – 30cm taller than their nearest modern-day descendant, the emperor penguin, of Antarctica.
It weighed at least 60kg, which is 50 per cent heavier than the emperor.
Otago University geology professor Ewan Fordyce first came across the fossilised bones in a cliff in the Waihao Valley near Waimate in 1977 while on a field trip looking for whale and dolphin fossils.
He was a PhD student at the time.
"It was the broken end of a leg bone and I thought, `that looks different'.
"Then I realised the species was bigger than expected. We knew this was something big.
"We've had a succession of other finds since then," he said.
The latest was last December with discoveries in the Duntroon area.
The well-preserved fossils allowed scientists to rebuild the bird and form a "clear description".
"I thought we really should bring in one of the leading people [so in 2009] I invited Dr Ksepka to come over here and work with me on the material."
Dr Ksepka was able to help in rebuilding the fossils.
Students at the university had also helped with the project for their theses.
Dr Fordyce said the Waitaki Valley was ideal for excavating fossils as the limestone geology of the area aided preservation.
Remains of large penguins had been found in other areas of New Zealand and overseas but were not as complete as the fossils found in the Waitaki Valley.
It was "very, very satisfying" to have been part of the discovery, he said.
"It tells us that penguins were different in the past.
"Why were they bigger and why did they disappear? As far as why they disappeared we really don't know.
"It could have been, for example, climate change. It could have been the appearance of some new predator. There are a variety of options.
"Those questions that we can't easily answer, they're the thing that drives our research."
He said the large size of the seabird would have meant it could swim further and dive deeper than modern penguin species.
At least four individual Kairuku penguins are known. The fossils recovered from the Waitaki Valley are now displayed in the Geology Museum.
Remains of "giant" penguins were first recovered from New Zealand as long ago as the 1840s, but there were no reasonably complete specimens.
Dr Fordyce said the finds were very exciting for penguin biologists and provided a significant boost to what was known internationally about the history of penguins.
Finding such specimens offered the "chance of a lifetime" to better understand extinct penguins that lived before the earliest fossils of modern species more than 15 million years ago.
"For the first time we have been able to publish really clear evidence about the body size and proportions of these older penguins."
The diversity of species and the penguin's unique physique had made the reconstruction difficult.
"Kairuku was an elegant bird by penguin standards, with a slender body and long flippers, but short, thick legs and feet," Dr Ksepka said.
The researchers rebuilt size and proportions from two main fossils, using the skeleton of an existing king penguin as a model.
Dr Ksepka hoped that the rebuilding of Kairuku would give other palaentologists more information about other fossils found in that area, as well as add to the knowledge about giant penguin species.
- © Fairfax NZ News