Long before the British were famous for queuing, trilobites were showing the way. This collective action is demonstrated in a series of stunning fossil finds of linear trilobite clusters in the upper Tremadocian Fezouata Shale, Morocco (figure 1). Trilobites are a group of extinct marine arthropods with a distinct three-lobed body, and some had amazing eye design.
The research team were clear that the lines of these creatures were not moved into this position by the water or sediment flowing around them. Rather, their conga line was a deliberate shared action which has been magnificently preserved.
Whatever the reason for these fossilized trilobite line-ups, one thing is clear—they must have formed rapidly. One commentator asked the obvious, “So you might be wondering how these chains of trilobites were preserved as if in a snapshot of daily life?” Those who believe that the earth is billions of years old may not be happy with the answer.
These fossilized lines are overwhelmingly dominated by the trilobite species Ampyx priscus, which have no eyes. It is believed that the spear-like snout to the front and the long rear-pointing spines acted as mechanoreceptors and/or allowed for chemical communication. Ampyx priscus was probably using “its long projecting spines to maintain a single-row formation by physical contacts”1 or possibly picking up on chemical cues (e.g. pheromones), with those in the line.
The trilobite line was compared with modern-day marine crustaceans, which also demonstrate similar collective behaviour. The spiny lobster Palinurus ornatus living in the Bahamas region performs mass single-file migrations “either in possible response to storm-induced environmental disturbances, or for reaching spawning grounds.”1
The researchers proposed that the trilobites’ behaviour was for similar purposes. Moving in this linear fashion reduces the hydrodynamic drag, saving energy. It may also have been to dissuade possible predators, by presenting as too large to deal with readily.
Whatever the reason for these fossilized trilobite line-ups, one thing is clear—they must have formed rapidly. The researchers came to the same conclusion. None of the trilobite fossils were broken up or dislocated, and very few showed any signs of enrollment—curling up into a defensive ball when feeling threatened. They wrote:
“These linear clusters most likely represent in situ clusters which retain most of the original position of individuals at the time of their death … . The amount of sediment deposited during a storm event was probably sufficient to entomb trilobites … . in situ but not powerful enough to take them away. This process is usually invoked to explain the exceptional and in situ preservation … . [and] The extreme rarity of enrolled specimens in linear clusters would support the hypothesis of a very sudden death either induced by water poisoning or by rapid deposition of sediment which hindered enrollment in most specimens.”
The rather obvious conclusion is that they were buried exceptionally quickly, not over millions of years.