This Ancient Fossil With a Brain and Guts

WE KNOW WHAT FOSSILS LOOK like. For example, typical dinosaur fossils are bones turned to stone and preserved from the passage of time, located, if we're particularly lucky, in large collections that can be reassembled to represent the beast they used to prop up in their entirety.

- Jackie Appel

Now, not all fossils are like that. Some are just impressions of small creatures or animals left in rocks, but most have something in common-it's just the hard stuff left behind. With the exception of those found in environments particularly adept at preservation, the soft tissues degrade over time and all we're left with is stony bone.

But not always. Sometimes we get lucky-like a team did recently, when they located a fossil of a 520-million-year-old worm larva that still had its brain and guts intact.