What can a prehistoric conga line teach us about collective social habits? According to a study published mid-October in Scientific Reports: quite a bit.
Single-file organization is a complex collective social behavior dating back at least 480 million years, as this study claims. Paleontologist Jean Vannier, the study's lead author, and his colleagues found fossilized marine animals called trilobites (and more specifically, Ampyx) lined up single-file in present-day Morocco. These blind animals formed into a string, with most individuals facing the same way.
These researchers' findings confirm that collective behavior "has a very ancient origin," according to their study's abstract.
Why Do Animals Line Up?
Researchers have tried for years to explain linear tendencies in early arthropod fossils, suggesting that they might have formed lines while seeking shelter in the seafloor or as a result of ocean current forces. Vannier, on the other hand, "thought it was important to re-explore this topic with new eyes," according to the New York Times.
Because most of the lined-up Ampyx creatures were sexually mature, Vannier and his research team think they might have been traveling to spawning grounds. The nature of their deaths, which implies they died suddenly, also suggests they might have marched single-file to escape dangerous storm conditions.
"These options are not mutually exclusive," the study states. "[They] may have alternatively responded to environmental stress and reproduction signals by adopting the same behavior."
How it Happened
Early life-forms had developed sophisticated sensory organs – such as antennae, eyes and brains that can process incoming data – by 520 million years ago, according to National Geographic. These animals were equipped to sense each other and act in unison, and Vannier claims that's exactly what they did.
The trilobites featured in Vannier's study are related to modern-day insects, crustaceans and spiders. In the Bahamas, spiny lobsters migrate in lines similar to those formed by the prehistoric trilobites. These lobsters depend on variations in the Earth's magnetic field to form their lines, and their ancestors' tendencies might tell us a bit about how and when those behaviors started.
"It shows that collective behavior is not a new evolutionary innovation that appeared a couple of million years ago," Vannier told National Geographic in an email. "Instead, it is much older, dating back to the first biodiversification events of animal life."
That said, in most fossils of trilobite clusters, the individuals point in random directions, according to National Geographic. That's why the Ampyx's single-file lines stand out. Vannier and his team suspect that they perhaps felt each other's spines to organize themselves as they migrated in a group.
"It is a very intriguing example of group behavior," Vannier told National Geographic.