This is only the second time the species has been recorded while alive. “I thought it was A.I.,” says fish biologist Kory Evans.

These sea monsters grew upwards of 40 feet (12 meters) long. About half that length was neck, a feature that allowed Styxosaurus to sneak up on schools of fish as it slowly cruised the shallow ...

The basking shark’s scientific name, Cetorhinus maximus, roughly translates to “great-nosed sea monster” in Greek. In reality, these placid sharks, found the world over, are totally harmless.

Xiphactinus was one of the largest bony fish of the Late Cretaceous and is considered one of the fiercest creatures in the sea. A powerful ... long (5-meter-long) monster through the surface ...

The short-necked plesiosaur likely had few enemies, but those that attacked were some of the fiercest monsters of the seas, including sharks with razor-sharp teeth and the giant mosasaur Tylosaurus.

Females likely migrated hundreds of miles to lay eggs on sandy beaches, much like sea turtles do today. Movement onshore, however, was difficult. An adult female Protostega may have weighed a ton ...

This story appears in the October 2017 issue of National Geographic magazine. How close can you really get to two monster squid fighting? Very close, it turns out. This month National Geographic ...

Podolsky co-directed Sea of Shadows, a National Geographic documentary about activists’ and undercover investigators’ work to help save the species. In this fight against extinction ...