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| Kumimanu adapted from Nobu Tamura |
Around 57 million years ago, an enormous penguin swam through the seas of what is now Aotearoa New Zealand. Known from fossils described in 2023 as Kumimanu fordycei, this ancient marine lovely had an estimated body mass of around 150 kilograms.
That is a great deal of penguin.
The researchers’ calculations placed it among the strongest contenders for the heaviest penguin ever discovered. Its fossils come from rocks dated to between 59.5 and 55.5 million years ago, during the late Palaeocene—a time when life was exploring new possibilities following the extinction of the non-avian dinosaurs.
A GIANT HIDING INSIDE A BOULDER
The story begins with fossil-bearing boulders on the coast of North Otago, on New Zealand’s South Island.
Palaeontologist Alan Tennyson of the Museum of New Zealand Te Papa Tongarewa collected the penguin fossils studied by the team in 2016 and 2017. Locked inside the rock were clues to an ancient community of seabirds, including one exceptionally large individual.
Researchers created three-dimensional digital models of the bones to help study their anatomy. Among the remains was a remarkable humerus—the upper wing bone—that offered a way to investigate the bird’s size.
For those of us who love fossils, there is something especially pleasing about this part of the story. A boulder on a beach can hold the remains of an animal that once breathed, hunted and moved through a world we will never see.
The rock keeps its secrets until patient eyes and careful preparation bring them into view.
HOW DO YOU WEIGH A FOSSIL PENGUIN?
There are practical difficulties with asking a bird that has been dead for millions of years to step onto a scale.
Instead, palaeontologists look for relationships between the dimensions of bones and body mass in living animals. Those relationships can then help them estimate the mass of extinct relatives.
For this giant penguin, calculations using the length and width of the humerus produced estimates of approximately 148 and 160 kilograms. These are estimates with uncertainty, rather than a precise reading of the animal’s weight. Even so, both point to an exceptionally hefty bird.
Its height is less certain. We do not have a complete skeleton, and a heavy penguin is not necessarily the tallest penguin.
For comparison, large emperor penguins—the biggest penguins alive today—can weigh around 45 kilograms. Our fossil heavyweight could have outweighed three of those substantial birds combined.
WINGS FOR WATER
Penguins descend from flying birds, but their ancestors gradually became specialists in moving through water.
Once flight was lost, staying light enough to become airborne was no longer a requirement. Larger bodies became possible, and there were potential advantages to growing big.
A bulky, warm-blooded animal loses heat more slowly relative to its volume than a smaller one. For a bird spending time submerged, retaining warmth could make a considerable difference. Researchers have suggested that this may have helped drive the early evolution of giant penguins.
Greater size also raises intriguing questions about diving and feeding. Could these birds reach food that smaller penguins could not? Their bones invite us to investigate, although we cannot yet reconstruct their daily lives in detail.
AN ANCIENT PENGUIN WITH A DIFFERENT FLIPPER
The specimen described as Kumimanu fordycei was discovered in 2017, encased in a hard concretion. Fossil preparator Al Mannering carefully freed its bones from the rock.
The remains include a humerus, a vertebra and portions of other wing, shoulder-region and leg bones. They are now held at Te Papa in Wellington.
Those wing bones reveal an animal with some ancestral features, including flipper bones that were less flattened than those of living penguins. This was an early member of the penguin evolutionary story, with a combination of features different from the birds we know today.
The name fordycei honours New Zealand palaeontologist R. Ewan Fordyce and his contributions to understanding ancient life.
A LITTLE SCIENTIFIC NAME DETECTIVE WORK
There is a further twist to our giant’s story.
In a 2025 study, Gerald Mayr and colleagues questioned whether Kumimanu fordycei should be recognised as a separate species from the previously named Kumimanu biceae. They argued that the differences in size and bone shape could fall within the variation expected within one species.
They therefore considered K. fordycei likely to be a junior synonym of K. biceae. In everyday language, that means the newer name may refer to the same species as the older name.
This is part of the fascination of palaeontology. Finding a fossil begins a conversation. Further specimens, comparisons and analyses can change how we interpret it.
Whether these remains represent a separate species or an especially large individual of an already named one, the bones still belonged to an extraordinary penguin.
A BEACH WORTH VISITING—FROM A SAFE DISTANCE IN TIME
I have a soft spot for fossils that overturn our everyday expectations.
We know penguins as charismatic seabirds: diving, calling, tending their young and bustling about on shore. Then the fossil record introduces a relative with enough heft to make us reconsider the whole picture.
Somewhere along an ancient New Zealand coast, a very large bird once emerged from the sea. Millions of years later, pieces of its skeleton emerged from stone.
A beach boulder, a patient preparator and a remarkable wing bone have given us a glimpse of that encounter.
And what a lovely great penguin it was.
