The name Myllokunmingia may not ring a bell, but it is worth knowing. This 520-million-year-old creature was the size of a guppy, with a tiny swordfish-like fin running high over its back. The fossils it has left behind preserve traces of a skull.

Humans have a skull, too. This and a number of other traits we share with Myllokunmingia reveal it to be one of the oldest, most primitive vertebrates yet found. It is, in other words, a hint of where we came from.

Myllokunmingia emerged during one of the most important phases in the history of life, an evolutionary boom known as the Cambrian explosion (named for the geological period when it took place). Over the course of about 20 million years, the oldest known fossils of most of the major groups of living animals appear, revealing a rapid diversification of life that led directly to humans.

“It’s rapid in geological terms, but it’s probably not rapid to anyone who’s not a geologist,” said Paul Smith, the director of the Oxford Museum of Natural History.