More than half a billion years ago, during the Cambrian Period, Earth was reigned by primitive arthropods, distant ancestors of today's crustaceans, insects, and spiders. Among the oldest species of arthropods were a group called the Radiodonta. These creatures were so fierce that they were named after their scariest feature — their radiating teeth.
Radiodontas were the most ferocious predators of their time and prowled the oceans in search of prey, which they snatched up with large, spiny limbs called raptorial appendages. Placed at the front of their heads, these grasping limbs were used to pull prey into the radiodontas' circular mouths, which were filled with tooth-like serrations.
The fiercest of them all was Anomalocaris (pictured above and in the video below), an apex predator and one of the largest creatures of the Cambrian, reaching lengths of more than 3.2 feet.
If its size doesn't strike you as particularly impressive, you should note that before the Cambrian Period, which lasted between 543 million and 493 million years ago, most life forms were aquatic plants and primitive multicell organisms.
And, as it turns out, baby radiodontas were equally terrifying. A new study published on June 1 in the National Science Review uncovered that radiodontas didn't have to wait until they reached adulthood to become skilled, voracious predators.