Another giant bird has been torn from its grave: the ancient Rēkohu/Chatham Island penguin. Just how big was it?

Standing at just over a metre tall, Kupoupou stilwelli was a big bird. It was as large as the giant Otago parrot, or as tall as a metre ruler.

Sixty million years ago, long before any giant turtles, crocodiles or mysterious proto-marsupials grew in the belly of St Bathans, eons before Haast eagles and moa stalked the land, and even before the continent of Zealandia had finished running away from Australia, the penguin walked (well, it swam).

That infamous meteor had hit Mexico only four million years earlier, and in the dinosaurs’ absence, mammals and birds were making a break for it evolution-wise. This, the Paleocene era, was populated by abominably large mammals and the “terror birds”.

It’s possible that on our own Rēkohu/the Chatham Islands the original penguin shook its wing at the skies and leapt into a southern ocean, starting an evolutionary history that would, one day, result in the Steve Irwin-starring film Happy Feet.

“We think it’s likely that the ancestors of penguins diverged from the lineage leading to their closest living relatives – such as albatross and petrels – during the Late Cretaceous period, and then many different species sprang up after the dinosaurs were wiped out,” said Paul Scofield, senior curator of natural history at the Canterbury Museum.

Was Kupoupou a terror bird? Although it couldn’t run as fast as the beaked apex predators of South America, it sure could swim with the best of them. Although it’s no bigger than an Emperor penguin – it’s not even bigger than a King penguin – it was pretty special for being among the first birds to take the plunge. Its name, Kupoupou, means “diving bird” in te reo Moriori.

Flinders University PhD candidate Jacob Blokland studied fossils collected from New Zealand’s forgotten islands and discovered a feathery “missing link”.

Kupoupou is the oldest known penguin with proportions like our modern feathery kings. Blokland said the penguin “had proportionally shorter legs than some other early fossil penguins. In this respect, it was more like the penguins of today, meaning it would have waddled on land.”

“These birds lived in a time right after the dinosaurs and many other life forms went extinct, in relatively empty oceans,” he said. “Penguins in these seas would have had very few competitors and that likely allowed them to be so successful back then.”

He went on to explain that there was a possibility Kupoupou was the terror bird of the Southern Seas. “I don’t know if penguins were the ‘apex predators’ but they were definitely some of the top predators back in this time that we know about.”

These slippery figures swam in New Zealand’s waters while they were tropical, and before whales or great white sharks turn up in the fossil record (although there were some ugly mugs hanging out in the depths). Despite having it pretty good, it wasn’t the baddest lad in town: around the same time Kupoupou lived, we also see ancient penguin fossils along the South Island coast including the truly monstrous Crossvallia waiparensis. Blokland said it wasn’t currently clear how Kupoupou fit into the big picture.

“I would say that these penguins likely coexisted, overlapped in habitat somewhat, and were closely related, but exactly how closely related each species was to each other is still a subject of ongoing research.”

So, did our big water boys swim the 800 kilometres from Rēkohu to the South Island, or even further south where today’s penguins frolic in rocks and rapidly melting ice?

“It could be that the evolution of structures and physiological adaptations to foraging in cold water enabled these birds to swim further, and eventually make it to Antarctica and other regions of the Southern Hemisphere,” said Blokland.

Head of Paleontology at the University of Canterbury, Catherine Reid, agreed it was possible Kupoupou swam a Hell of a long way. “Chatham Rise has, in the past, been exposed land area and then drowned through the start of the Paleocene, so in the time of Kupoupou there would have been a shallow undersea ridge, and perhaps a few remaining islands,” she said. A place for the penguins to roost for an evening before continuing their journey.

She also pointed out that the discovery’s age means our humble micro-continent could have invented penguins. “The latest finding by Jacob suggests that penguin evolution may have begun in the New Zealand region and these new fossils are certainly amongst the oldest in the group.”

Blokland’s discovery is based on five partial skeletons. Two more skeletons were discovered belonging to a different, bigger species that lived on Rēkohu, but there’s not enough material for it to get a name yet.

But when it does, don’t forget Kupoupou.