The major groups of animals we see around us today -- from sponges to arthropods to chordates -- all showed up in this little window of time in the Cambrian.
Most of the main groups of the animal kingdom—arthropods, brachiopods, coelenterates, echinoderms, molluscs and even chordates, the branch from which vertebrates went on to develop—are found in the fossil beds of the Cambrian.
It's called a Pikaia and it's a little wormlike creature but it's thought that this is a chordate, and that is the branch of life that we're in, so it could that this is our earliest known ancestor.
Simple as it was, this was one of the earliest chordates -- part of the family that would give rise to the vertebrates and includes us, making us cousins over 500 million years removed.