From flocks of birds to schools of fish, modern species across the animal kingdom enjoy each other’s company—so much so that they’ll engage in what’s known as collective behavior, coordinating their movements to act in unison.
Now, a team of scientists may have uncovered clues to when in our evolutionary timeline some of these gregarious group-ups first arose: single-file queues. As they report today in the journal Scientific Reports, conga lines were apparently a thing 480 million years ago—and the creatures that danced in them looked a heck of a lot like horseshoe crabs with pigtails.
These ancient animals are trilobites: marine arthropod predecessors of today’s insects, spiders, and crustaceans that emerged more than 500 million years ago, around the time life was undergoing a series of booms in biodiversity. The trilobite group was a diverse one, but so far, just one species, Ampyx priscus, had the cognitive wherewithal to line up in an orderly fashion.
At least, that’s what study author Jean Vannier, a paleontologist at the University of Lyon, argues in his team’s new paper. After unearthing a series of fossils from near Zagora, Morocco, the researchers were surprised to find several tidy queues of three to 22 Ampyx priscus specimens enshrined in rock, reports Michael Greshko for National Geographic.
Trilobites lacked both eyes and a sophisticated nervous system. But a series of long, spine-like appendages protruding from their bodies might have enabled the creatures to communicate through touch or chemical signals, perhaps enabling them to root out and join queues of their kin. In support of this, adjacent trilobites’ spines overlap in several line-ups.
Traveling around like this was probably a sensible strategy, the researchers argue. It can minimize the amount of drag followers experience from surrounding fluids like air or water, saving energy.
It’s unclear where the trilobites were headed, but the researchers have a couple theories. All the trilobites in the rock were sexually mature, suggesting they may have been filing toward breeding grounds. It’s also possible they may have been caught mid-retreat from a storm—ironically, one that could have stirred up the sediments that buried them en masse, reports Becky Ferreira for The New York Times.
Whatever the cause behind the arthropod’s collective demise, their camaraderie has stood the test of time, potentially pushing the origins of this behavior further back than ever before.
“People don’t tend to think where the origins of [group] behavior came from,” John Paterson, a paleontologist at Australia’s University of New England who reviewed the study, told Greshko. “That’s quite fascinating, that even things like behavior can be preserved in the fossil record.”