Chordates are animals with nifty features like notochords that stiffen their back, serial sets of body muscles, gill slits, and a head. In other words critters like you, me, your dog, that fish, and just about every sea squirt anyone’s ever met. This fossil gives us a glimpse at what our ancestors were like 600,000,000 years ago, back when animals looked significantly more like gelatinous sleeping bags than they do these days.