Here’s what you’ll learn when you read this story:

• A new study details a whale necropolis stretching over 750 miles of seafloor in the southeastern Indian Ocean.
• Across 33 dives, a team of scientists discovered 476 whale fossils, five carcasses, and the deepest whale fall ever discovered.
• Among the fossils is a plethora of information about beaked whales, which are regarded as the least understood large mammals on Earth due to their isolation.

Whales come in all shapes and sizes, but one group among them remains the most mysterious: beaked whales. Although the family Ziphiidae contains 24 separate species, this group of whales is widely considered the “least understood group of large mammals on Earth.” This is mostly because they keep to themselves, hanging out in the deep ocean where they spend a majority of their lives diving for food like squid, crustaceans, and benthic fish.

Now, a new study in the journal Nature details the discovery of a lot of beaked whales—well, a lot of dead ones, that is. Led by researchers at the Chinese Academy of Sciences, this study describes the largest “whale graveyard” ever discovered on Earth. It’s located in the southeast Indian Ocean in an area known as the Diamantina Fracture Zone, roughly 700 miles west of Perth, Australia. Filled with various ridges and trenches, this zone formed as the Australian and Antarctic continents separated around 50 to 60 million years ago.

From February 8 until March 17, 2023, researchers aboard the R/V Tan Suo Yi Hao explored the Dordrecht Deep, one of the deepest trenches in the zone (which bottoms out at roughly 7,079 meters, or 23,225 feet). There, near the bottommost part of the trench, scientists spotted a whale fossil partially buried in the sediment. The team conducted 32 more dives, identifying 476 whale fossils, five whale carcasses, and the deepest “whale fall” ever discovered at 6,700 meters, or 22,000 feet, deep (the previous record holder in the North Atlantic was at only 13,200 feet). Extrapolating from those numbers, each square kilometer of this vast whale necropolis could therefore hold roughly seven to eight whale carcasses and a staggering 760 whale fossils.

“Whale falls are biodiversity oases at seabeds, yet their record from the oceans has remained sparse and fragmentary,” the authors wrote. “These findings reshape the understanding of the limits and biogeography of whale-fall ecosystems and establish some deep sea floors as a fossil archive for tracing cetacean evolution over geological time.”

While the largest carcass discovered belonged to the Antarctic minke whale (Balaenoptera bonaerensis), the rest were members of the Ziphiidae family of beaked whales. That isn’t all—the oldest fossil in the necropolis, at roughly 5.3 million years old, belonged to an extinct ancestor of the beaked whale in the genus Pterocetus. The authors also found a new species in that same genus and gave it the name Pterocetus diamantinae.

So… why so many dead whales in this specific area? Lead author Xiaotong Peng and his colleagues have a few ideas. One could be that the area serves as an ideal deep-water foraging ground for beaked whales, but its extreme depth might lure these whales to descend deeper than their maximum dive depth of 3,000 meters, or around 9,800 feet. This could lead to fatal exhaustion and decompression sickness, causing the corpses to pile up along the ocean floor. Another possibility could be Diamantina Zone’s V-shaped geography, which naturally funnels sinking carcasses from a wider area to concentrate at this location.

Whatever the reason, the world’s largest whale necropolis—essentially a fossil deposit in the making—is a boon for understanding the most enigmatic large mammal on the planet.

“As beaked whales are known primarily from rare strandings, their abundance, distribution and ecology remain poorly understood overall,” the authors wrote. “The Diamantina Zone necropolis constitutes a deep-sea fossil megasite: one that offers a window into the evolutionary history, paleoecology and population dynamics of beaked whales from the Pliocene to the present day.”