150-kg penguin that lived in New Zealand 55 million years ago is the new all-time heavyweight

Imagine a penguin waddling toward you. Adorable, right? Who doesn’t love penguins? Now imagine that penguin weighing more than 150 kilograms, looking you straight in the eye?

If you were to travel to New Zealand 55 million years ago, you might have exactly that experience. Fossil bones of penguins unearthed in 2016 and 2017 include two newly discovered penguin species, one of which is the largest known to science – more than three times the size of the largest living penguins.

The fossils were discovered in boulders that date to between 55.5 and 59.5 million years old on a beach in North Otago on New Zealand’s south island. That means the penguins were around within a few million years of the extinction of the non-avian dinosaurs 66 million years ago.

Emperor penguins, the tallest and heaviest of all modern penguins, can reach approximately 120-130 centimetres in height and typically weigh between 25 and 45 kg.

Kumimanu fordycei, the larger of the two newly discovered prehistoric penguin species, would have tipped the scales at 154 kg and been as tall as an average human.

Even Petradyptes stonehousei, the other species discovered in North Otago, would have dwarfed today’s biggest penguins with a mass of 50 kg.

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Palaeontologists, led by researchers from the University of Cambridge, used laser scans to create digital models of the fossil bones of Kumimanu and Petradyptes. These models allowed the team to compare the fossil species with other prehistoric birds, and flying diving birds like auks, and modern penguins.

They were able to estimate the dimensions of the birds by measuring hundreds of modern penguin bones and predicted the long-extinct penguins’ mass using the dimensions of the flipper bones.

“Fossils provide us with evidence of the history of life, and sometimes that evidence is truly surprising,” says Dr Daniel Field from Cambridge in a Science X article. “Many early fossil penguins attained enormous sizes, easily dwarfing the largest penguins alive today.” For comparison, Field adds that K. fordycei would have weighed more than basketball player Shaquille O’Neal at his peak!

Kumimanu knocks out the previous all-time penguin heavyweight champion, Palaeeudyptes klekowskii, which lived in Antarctica about 37 million years ago and weighed in at 116 kg.

Both new species show that penguins got very large very early in penguin evolution, millions of years before their flipper apparatus was fine-tuned. The team described their flippers as more primitive, with slender and exhibiting muscle attachment points that more closely resemble those of flying birds.

Dr Daniel Ksepka tells Science X: “Size conveys many advantages. A bigger penguin could capture larger prey, and more importantly it would have been better at conserving body temperature in cold waters. It is possible breaking the [45 kg] size barrier allowed the earliest penguins to spread from New Zealand to other parts of the world.”

The researchers also postulate that the penguins’ size may have allowed them to dive to greater depths than modern penguins.

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Dr Daniel Thomas from Massey University in Auckland, NZ says large, warm-blooded marine animals living today can dive to great depths. “This raises questions about whether Kumimanu fordycei had an ecology that penguins today don’t have, by being able to reach deeper waters and find food that isn’t accessible to living penguins,” Thomas says.

The findings are detailed in a paper published in the Journal of Paleontology.