Fossils of the largest penguin discovered in New Zealand | Polarjournal
The reconstruction of the two newly described penguin species illustrates the size of the giant penguin Kumimanu fordycei versus the much smaller Petradyptes stonehousei. Image: Simone Giovanardi

One of two species of prehistoric penguins newly discovered in New Zealand is the largest penguin species known to date and dwarfs those living today. An international team of researchers analyzed the fossils and estimated the average weight at 155 kilograms – more than three times that of the emperor penguin. This new discovery, published in the Journal of Paleontology, provides important insights into the evolution of penguins.

The fossils come from boulders sea-washed in North Otago on the South Island of New Zealand. Alan Tennyson of the Museum of New Zealand Te Papa Tongarewa, main author of the study, collected them in 2016 and 2017. Their age is estimated at 55.5 to 59.5 million years, which means they lived about five to ten million years after the extinction of the dinosaurs. Even for fossil penguins, they are very old, as described by Dr. Daniel Thomas, lecturer in zoology and ecology at Massey University in Auckland, New Zealand, and co-author of the study.

In total, the international team found fossil bones from nine new penguin specimens. Dr. Thomas and Dr. Simone Giovanardi, a zoologist at Massey University and also a co-author of the study, made 3D replicas of the fossils, which helped learn more about the penguins’ evolutionary history.

Reconstructions of the newly described fossil penguins (left, Kumimanu fordycei, center, Petradyptes stonehousei) show the size differences from the largest penguin living today (right, Emperor penguin Aptenodytes forsteri). The recovered bones of each species are shown in white. Image: Simone Giovanardi

The largest specimen found is the newly discovered giant penguin species Kumimanu fordycei, named after Professor Emeritus R. Ewan Fordyce of the University of Otago. Using the humerus (the top bone of the wing) – the largest ever found – the team estimated the penguin weighed between 148 and 159.7 kilograms. For comparison, the largest and heaviest penguin alive today, the emperor penguin, weighs between 22 and 45 kilograms.

According to Dr. Thomas, the size of Kumimanu fordycei and the fact that the giant penguin appeared so early in the history of penguins provides important insights into their evolution. “In finding this fossil, we’re learning a lot more about the early diversity of these animals. We have found what is essentially a new ceiling for penguin body size, establishing that they got really big really early on, and that maybe evolutionary rates for body size were rapid,” Dr. Thomas said in a Massey University news release.

He goes on to explain that the discovery of this fossil provides a solid basis for speculation that the rapid evolution toward large bodies in Paleocene penguins may be due to the advantages that larger bodies offer in heat storage.

“When we start thinking of these finds not as isolated bones but as parts of a whole living animal then a picture begins to form,” Dr. Thomas 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.”

Emperor penguins already have an impressive size but against their extinct relative Kumimanu fordycei they would seem tiny. Photo: Michael Wenger

Dr. Daniel Ksepka of the Bruce Museum in Greenwich, Connecticut, lead author of the study, adds: “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 100lb size barrier allowed the earliest penguins to spread from New Zealand to other parts of the world.”

The second new penguin species described by the study is Petradyptes stonehousei, named after famed polar explorer Dr. Bernard Stonehouse. It is slightly larger than the emperor penguin.

Both newly described species show that penguins became very large very early in their evolutionary history. They refined their flipper apparatus millions of years later. Both species had retained primitive features such as slimmer flipper bones and muscle attachment points similar to those of flying birds.

This fossil evidence supports the hypothesis that the origins of penguins are to be found in the Zealandia region.

Julia Hager, PolarJournal

Link to the study: Daniel T. Ksepka et al. ‘Largest-known fossil penguin provides insight into the early evolution of sphenisciform body size and flipper anatomy.’ Journal of Paleontology (2023). DOI: 10.1017/jpa.2022.88

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