Nearly half a billion years before the first conga line, marine creatures resembling today’s horseshoe crabs did their own version of the social dance. Newly described fossils capture clusters of these animals sashaying across the ocean floor in lines, perhaps to migrate as a group or gather for mating. The fossils confirm that animals started to coordinate their movements early in Earth’s evolutionary history, researchers announced today in the journal Scientific Reports.

By about 520 million years ago, early life-forms had evolved sophisticated sensory organs, such as antennae and eyes, along with brains that could process all the incoming data. These developments let animals sense each other and act in unison.

The newly described fossils, which date back