While exploring a remote island off the coast of New Zealand in 1999, paleontologist Richard Köhler came upon something extraordinary. Embedded in the side of a cliff overlooking Waihere Bay on Pitt Island was, frozen in time, an entire mummified fish fossil. Buried in what used to be sediment, it looked more alive than most creatures that were around 55 million years ago. It was also unlike any fossil that had ever surfaced before in New Zealand.

Köhler kept notebooks documenting his findings. He had studied fossilized fish and sharks, but this fish was a rare three-dimensional fossil preserved in remarkable detail, from the rays of its fins to its individual scales. After dislodging it in several large chunks, he brought the fish back to the University of Otago’s Department of Geology in Dunedin, New Zealand, where it was prepared in painstaking detail by his late colleague Andrew Grebnaff before being put into storage. Then it was nearly forgotten.

Emeritus Professor Daphne Lee and late Professor Ewan Fordyce remembered being impressed by the find. Neither of them had ever unearthed a mummified fossil before. This was a fish with a muscular body, strong fins, and an armor of thick scales, and its upturned mouth could easily open into a cavernous trap to gulp down prey. While it had not yet been assigned to a species, its morphology echoed the tarpons that hunt in the open ocean today. Tarpons are powerful predators that also swallow their prey—usually smaller fish or crustaceans—whole. Many can grow to more than 8 feet in length and weigh over 300 pounds. They are widespread through the Atlantic and Indo-Pacific, but have long since vanished from the seas around New Zealand.

Lee and her research team began to draft a paper in 2023, but information on the discovery of the fossil and its surrounding geology were missing. Köhler had passed away several years earlier, and his notebooks, which were filled with meticulously documented discoveries, seemed to have been lost along with him. Then came an unexpected connection. Köhler’s son enrolled as a student at the University of Otago and, while sorting through his father’s belongings, discovered the field notebooks tucked away among his possessions. When he met Lee and learned of the research team’s work, he donated the notebooks to the university, filling in the crucial gaps in the fossil’s story.

Not only was the fish an uncommon sight because its mummified remains had survived since the Paleogene Age, but in New Zealand, it was also the first known predatory bony fish found in rocks of that age. It was named Ikawaihere koehleri in honor of the man who had risked climbing a sheer cliff to retrieve it. The fossil has since reshaped scientific understanding of the prehistoric marine fauna of the region and the evolution of modern tarpon.

“This new taxon is the most complete and informative fossil megalopid reported to date from the Southern Hemisphere,” the researchers said in their study, which was recently published in the New Zealand Journal of Geology and Geophysics, “and evidence that a large tarpon-like fish with a number of derived features had reached the eastern margin of Gondwana by relatively early in the Cenozoic.”

Tarpons belong to a broader group called elopomorphs, which includes all ray-finned fishes along with several types of eels and deep-dwelling species. Elopomorphs appeared during the Late Jurassic at a time when Earth’s only landmasses were the supercontinents Gondwana and Laurasia. The rarity of these fossils in locations that used to be part of Gondwana suggests they most likely originated in the waters of the Northern Hemisphere, closer to Laurasia—the oldest known specimen from a Gondwanan location was found in what is now Queensland, Australia. Tarpons are able to tolerate water with a low oxygen content because of swim bladders that became adapted to such conditions, and while they can survive in brackish water and even freshwater, where I. koehleri lived and hunted is unknown.

What’s especially intriguing about I. koehleri is that its tail fin is vaguely reminiscent of tetrapodomorph fish, which were precursors to early tetrapods that used their fins to push themselves along in an early form of walking during the middle of the Devonian period, almost 400 million years ago. It would be hundreds of millions of years before elopomorphs entered the scene. How the I. koehleri specimen was preserved is still a mystery. Its body lay relatively undisturbed after it died and there was no evidence of scavenging. Some traces of bacterial decomposition were found, leading Lee and her team to think that the fish had been temporarily exposed, but then it must have been buried or carried by the waves to colder waters before it could decay beyond recognition.

“Based on what we currently know of the elopomorph fossil record, it appears [they] did not become well-established in the southern oceans until sometime into the Cenozoic portion of its history,” said Lee. “The new taxon is a distinctive and dramatic new addition to the marine fossil record of Zealandia.”