More than 50 million years ago, a 340-pound penguin waddled the beaches of New Zealand.

Fossils of the massive seabirds were discovered on a New Zealand beach, according to a study published on Feb. 8 in the Journal of Paleontology. Estimated to have weighed 340 pounds, the penguin, with the scientific name of Kumimanu fordycei, would have been roughly the size of an adult silverback gorilla.

“According to our analyses. K. Fordycei is the biggest penguin currently known,” Daniel Ksepka, an author of the study and a paleontologist and curator of the Bruce Museum in Greenwich, Connecticut, told Live Science in an e-mail. In comparison, the largest living penguin species, the emperor penguin, is typically about 4 feet tall and weighs around 77 pounds.

A team of researchers, led by Alan Tennyson, a paleontologist from the Museum of New Zealand Te Papa Tongarewa, discovered the fossils of the Kumimanu fordycei alongside eight other specimens inside the beach boulders of North Otago on New Zealand’s South Island between 2016 and 2017. Per The New York Times, the force of the tide cracked open several of the 57-million-year-old boulders to reveal the fossils within. The boulders dated to somewhere between 59.5 million years ago and 55.5 million years ago.

Alongside the Kumimanu fordycei were five remains belonging to a second new species named Petradyptes stonehousei, a fossil from the known giant penguin Kumimanu biceae, and two small humeri from an as yet unnamed penguin species.

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With the use of a 3D scanner, scientists were able to compare the fossils with those of other prehistoric birds. They estimate the Kumimanu fordycei to have weighed around 340 pounds. With only fragments of a skeleton, they were not able to accurately pinpoint the length of the behemoth, but Ksepka estimates it to have been around 5-feet-2. The Petradyptes was estimated to have weighed around 110 pounds. The Kumimanu got its name from a mash-up of the Maori words for “monster” and “bird,” and Petradyptes means “rock diver.”

Asked why the penguin would have grown to such a massive size, Ksepka replied, “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 100 pound size barrier allowed the earliest penguins to spread from New Zealand to other parts of the world.”

Per The New York Times, the Kumimanu and Petradyptes are among the earliest penguin fossils found. They provide a tantalizing look at the evolution of the penguin. Both of the skeletons possess flippers comparative to ones on auks or puffins, seabirds that fly and dive, allowing scientists a glimpse into how the penguin lost the ability to fly in favor of swimming. It may even lead to answers about the ecology of the Paleogene Era.

Co-author of the study Daniel Thomas of the University of Auckland told Phys.org, “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. 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.”

One thing is for sure, the titanic Kumimanu would have made for a fantastical sight on a New Zealand beach.