An artist's impression of the giant penguin Kumimanu fordycei on a beach alongside a group of smaller Petradyptes stonehousei penguins

The penguin Kumimanu fordycei would have towered over other speciessuch as Petradyptes stonehousei more than 55 million years ago. Image © Dr Simone Giovanardi.

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The largest ever penguin species has been discovered in New Zealand

Two new species of giant penguin have been described from fossils found on a New Zealand beach.

One species, Kumimanu fordycei, weighed an estimated 150 kilogrammes and is currently thought to be one of the largest penguins ever.

Giant penguins once roamed the seas and beaches of New Zealand over 50 million years ago.

Weighing about the same as a giant panda, and heavier than even the largest bird alive today, Kumimanu fordycei would have been a graceful giant as it swam through the oceans.

Dr Daniel Field, a University of Cambridge researcher who co-authored the description of the species, says, 'Fossils provide us with evidence of the history of life, and sometimes that evidence is truly surprising.'

'Many early fossil penguins attained enormous sizes, easily dwarfing the largest penguins alive today. Our new species Kumimanu fordycei is the largest fossil penguin ever discovered.'

The paper, published in the Journal of Paleontology, also describes a second substantially sized species, Petradyptes stonehousei. Even though it is around 100 kilogrammes lighter than K. fordycei, it's still larger than any living penguin.

Together, these birds would have been an important part of marine ecosystems recovering from a mass extinction that wiped out almost 80% of all species.

Outlines of the body shape of Kumimanu fordycei, Petradyptes stonehousei and an emperor penguin with their skeletons highlighted

Fossil penguins are known mainly from arm and leg bones, with the known bones of Kumimanu fordycei (left), Petradyptes stonehousei (middle) and an emperor penguin (right) shown in white. Image © Dr Simone Giovanardi.

What are the largest penguins?

The largest living penguin is the emperor penguin, with the biggest individuals weighing around 45 kilogrammes and standing around 1.2 metres tall. But in the past penguins were much bigger.

The tallest ever penguin was probably Palaeeudyptes klekowskii, which was discovered on Seymour Island off the coast of Antarctica. It is thought to have been around two metres tall, and weighed around 116 kilogrammes. 

A fossil of an Anthropornis penguin found on the island may have been even taller, but this is likely to have been an exceptional individual. The majority of these penguins were only 1.7 metres tall and weighed around 80 kilogrammes.

While Palaeeudyptes klekowskii remains the tallest ever penguin, it is no longer the heaviest. At an estimated 150 kilogrammes, Kumimanu fordycei would have been around three times heavier than any living penguin.

While it's uncertain how tall the species was, the height of a closely related species, Kumimanu biceae, has been estimated at 1.77 metres.

These measurements, however, are all open for debate. Many fossil penguins are only known from preserved arm and leg bones, rather than complete skeletons. This means that scientists have to estimate how big they were based on the relationship between bone size and overall size in living species.

As a result, it's very possible that the estimated size of these penguins could change as new fossils are discovered.

'Kumimanu fordycei would have been an utterly astonishing sight on the beaches of New Zealand 57 million years ago, and the combination of its sheer size and the incomplete nature of its fossil remains makes it one of the most intriguing fossil birds ever found,' Dr Field says.

'Hopefully, future fossil discoveries will shed more light on the biology of this amazing early penguin.'

How did giant penguins evolve?

Zealandia, an area of the Earth's crust containing New Zealand and New Caledonia, was once a hotspot of penguin life. Many of the earliest known species have been found in this region, with scientists believing that this is where penguins first evolved.

The oldest fossil penguin remains are around 62 million years old, but they only appear around 30 million years after penguins are first thought to have evolved from their closest relatives, the petrels.

Like some modern species of petrels, the ancestors of penguins are thought to have been divers that swam on the surface using their feet and used their wings to help propel them underwater. Over time, the birds became more adapted for an aquatic lifestyle as their wings became flippers more adapted to gliding through the water.

Eventually, the birds lost the ability to fly altogether. This would have allowed early penguins to become much bigger, as they no longer had to support their own weight to take off.

Being large would have been helpful as it reduced the amount of energy needed to dive. But it also had a number of other advantages.

'A bigger penguin could capture larger prey, and more importantly it would have been better at conserving body temperature in cold waters,' says Dr Daniel Ksepka, a curator at the Bruce Museum. 'It is possible that breaking the 45-kilogramme size barrier allowed the earliest penguins to spread from New Zealand to other parts of the world.'

A group of adult and juvenile emperor penguins sit on ice

Emperor penguins are the largest living penguins, but evolved much later, and are much smaller, than their giant relatives. Image © vladsilver/Shutterstock

Why did giant penguins become extinct?

With a variety of large species found throughout the Paleogene Epoch (66-23 million years ago), giant penguins appear to have been thriving. They are known to have reached as far as Antarctica and Peru as they spread across the Earth.

Around 20 million years ago, however, they vanished from the fossil record. While it's not entirely certain what led to their demise, the arrival of new predators might be to blame.

'The disappearance of large penguins is around the same time that seals are spreading throughout the Southern Hemisphere,' Dr Ksepka says. 'We don't know exactly when the first seal arrives or the last giant penguin dies, but I think it is plausible that competition with pinnipeds wiped out the largest penguins.'

'This could have been due to a combination of direct predation pressure, competition for prey, and seals monopolising nesting sites.'

Smaller penguins, meanwhile, were less affected by these new arrivals and would give rise to the ancestors of modern species around 14 million years ago.