Claw-headed Sea Monster Babies Were Toothy Killing Machines

A fossil of a vicious clawed sea monster dating from around 500 million years ago has become the smallest complete example of a particularly deadly creature found to date.

The 360-degree mouth of the juvenile Lyrarapax unguispinus was bursting with serrated teeth and its head was crowned with two spiky claw-shaped appendages. Just like its parents, this baby beast was born to kill.

Half a billion years ago, the Earth was a very different place. Animal diversity was booming at an unprecedented rate, and the arthropod was king of the hill. A manifold of paired appendages sprouted from these creatures' segmented bodies, and the appendages of one—the ocean-dwelling L. unguispinus—were particularly deadly.

6_12_Trilobites and starfish fossils
Ancient trilobites and starfish left behind fossilized remains. Arthropods like trilobites and the Lyrarapax unguispinus analyzed in this study inhabited Earth’s oceans more than 500 million years ago. Getty Images

The tiny 0.7-inch fossil of L. unguispinus, scientists wrote in a study published this month in National Science Review, had miniature versions of the weapons you would expect to see on its fully grown relatives.

"Its adult-like morphology—especially the fully developed frontal appendages and [mouth]—indicates that L. unguispinus was a well-equipped predator at an early developmental stage," the researchers wrote.

The team thinks these spiky face-claws would grab hold of prey before the critter shoveled it into its dagger-filled mouth. "This likely resulted in crushing or slicing of prey before ingestion," the scientists reported. Similar claws, they wrote, appeared on creatures like Amplectobelua stephenensis.

Read more: Girl finds 475-million-year-old trilobite fossil on a walk

Had it survived long enough to grow up, the sea-faring spawn could have swelled to more than 3.2 feet long. The vicious creature was an apex predator in its day and sat at the top of the food chain. Its circle of teeth makes it a radiodontan—one of a group of arthropods marked by similar round rows of fangs.

More than 500 million years ago, our planet was in the midst of something called the Cambrian Explosion, where the diversity of life on Earth soared. The pressure on animals to adapt to a world bursting with fresh competition would have been huge during this period.

The researchers think this bloodthirsty rivalry may have driven the rapid evolution of L. unguispinus' fearsome features. They wrote: "Intense predation occurring on all scales during the early phase of animal evolution was undoubtedly a critical driver behind the morphological and ecological innovations arising throughout the Cambrian."

Related: Scorpion-tailed spider chimera found in amber is missing link between ancient arachnids and modern spiders

Nowadays, these sea monsters now linger only in the fossil record. That being said, their ancestors live on in the form of modern scorpions, crustaceans and spiders.