Fang from the Abyss — Megalodon Teeth Found at 5,100m by E/V Nautilus

At 5,100 meters below the surface, in absolute darkness, ROV Hercules' lights caught a black triangle.

Serrated edges. A mineral crust built over millions of years from seawater. This was a tooth of Otodus (Megaselachus) megalodon — the Megalodon, extinct for approximately 3.5 million years.

Shark skeletons disappear. Teeth remain.

Shark skeletons are primarily cartilage, which decomposes after death on the seafloor. However, sharks continuously shed and replace teeth throughout their lives in a conveyor-belt fashion, leaving thousands of teeth behind. Those teeth settle into seafloor sediment and fossilize, waiting for explorers to find them.

Scientists can examine a tooth's shape and size to determine the species. Even partial teeth can be measured using formulas to estimate the original dimensions and the shark's full body length.

It's not just Megalodon

Deep-sea explorers encounter teeth from many prehistoric shark species, not just Megalodon. Each tooth's morphology helps identify the species. By comparing fossilized teeth with those of living species, scientists can infer the life histories and behaviors of extinct ones.

"Megalodon teeth have the same serration pattern as great white sharks, suggesting comparable predation methods."

2025: Into the Deep-Sea Abyssal Plain of the Cook Islands

During the 2025 NA176 expedition, E/V Nautilus surveyed the deep sea of the Cook Islands. For three weeks, the Corps of Exploration investigated depths greater than 5,100 meters (17,000 feet), with much of the work concentrated on the abyssal plain.

The stable conditions of the abyssal plain make it well-suited for preserving shark teeth. Normally, fossilized Megalodon teeth are most commonly found near shorelines where fossil beds are exposed by wave action or rivers. Most discoveries happen in locations easily accessible from land, while the deep sea remains largely unexplored.

2022: The First In Situ Deep-Sea Recovery

"Deep-sea fossils are typically collected by dragging nets on the bottom of the seafloor, without precise sampling location data."

During the 2022 NA141 expedition, ROV Hercules inadvertently sampled a fossilized Megalodon tooth at a depth of over 3,090 meters (10,000 feet) in the Johnston Unit of the Pacific Remote Islands Marine National Monument. Scientists later confirmed the tooth belonged to a Megalodon after analysis at the University of Rhode Island's Marine Geological Samples Laboratory.

This represents the first formally reported in situ observation and sampling of a fossil Megalodon tooth in the deep sea. In situ collection preserves stratigraphic context — which layer the tooth was in, and at what orientation — information that is critical for understanding fossil formation processes.

In 2024, OET's Media and Outreach Coordinator Jamie Zaccaria connected with Dr. Nicolas Straube and Jürgen Pollerspöck, who co-authored the paper documenting this landmark 2022 discovery.

Ferromanganese Crusts Keep Geological Time

The black coating on deep-sea teeth is ferromanganese crust — iron-manganese oxides that precipitate from seawater at an extraordinarily slow rate, coating objects on the deep ocean floor.

"These mineral deposits form at an average rate of 2.5 mm per million years."

By measuring the crust's thickness, scientists can estimate how long the tooth has rested on the seafloor since it sank.

深海のキャスパー — 世界を魅了した半透明タコ、発見から10年の軌跡