Finding a fossil is no rare occurrence, but unearthing one with still part of its brain intact is a horse of a different color. That's what researchers in China discovered when they found a preserved brain in the fossil of one of the world's first known marine predators that lived 520 million years ago, as described in the journal Nature.

The fossils show an animal called Lyrarapax unguispinus that lived during the Cambrian Period, a pivotal juncture in the history of life on Earth when many major animal groups first appeared. It was a member of a group known as anomalocaridids - primitive relatives of arthropods, which include crustaceans, insects and spiders - that hunted prey with a pair of claw-like grasping appendages in front of the eyes.

The discovery revealed a brain that is surprisingly simple and less complex than those known from fossils of some of the animal's prey.

"Our discovery helps to clarify this debate," lead author Nicholas Strausfeld, director of the University of Arizona's Center for Insect Science, said in a statement. "It turns out the top predator of the Cambrian had a brain that was much less complex than that of some of its possible prey and that looked surprisingly similar to a modern group of rather modest worm-like animals."

The worm-like animals they are referring to are velvet worms that crawl along the ground in tropical and semitropical forests in the Southern Hemisphere. The researchers suggest that velvet worms may be very distant cousins of the anomalocaridids.

Velvet worms, also known as onychophorans, grow to a few inches in length, have two long feelers extending from the head and have numerous pairs of stubby, unjointed tubular legs that each end in a pair of small claws.

The Lyrarapax neuroanatomy resembles that of velvet worms in multiple ways, with a simple brain and a pair of ganglia - a cluster of nerve cells - placed in the front of the optic nerve and the base of the grasping appendages.

"And - surprise, surprise - that is what we also found in our fossil," Strausfeld added.

The fact that the brain of the earliest known predator appears much simpler than the previously unearthed brains of its contemporaries makes researchers wonder whether it's possible that predators drove the evolution of more complex brains.