Comrade Trilobites Marched in Tandem 480 Million Years Ago

Hang your head, Russia. The emergence of collective behavior has been a longstanding enigma in evolution, and now it turns out that ancestral arthropods would march to a common drum, though why they did so remains a mystery. Fossil trilobites found in Morocco who died in an orderly queue, for whatever reason, indicate that the ancient animals were capable of group behavior 480 million years ago.

The power of the masses goes back a long way. Almost 100 million years earlier, sessile Ediacarans named Ernietta had apparently developed a knack for collective eating. These tiny multicellular animals turn out to have lived in groups around 560 million years ago and engaged in “gregarious suspension feeding,” catching primordial plankton. In other words, they lived in groups, died and were fossilized in groups. But these Ediacarans at least weren’t motile.

Fast forward to the lower Ordovician around 480 million years ago and we find trilobites, zippy primitive arthropods with a lot of legs, apparently engaging in a social behavior that led them to die and be fossilized in lines, as divulged in Scientific Reports. 

In other words, group behaviors found in motile modern arthropods existed almost half a billion years ago, explain Jean Vannier and colleagues.

The march of the lobster