Evidence of one of the earliest known animal migrations – as well as the earliest example of politeness – has just been discovered in Poland’s Kowala Quarry, where researchers have found the fossilized remains of orderly queues of trilobites. Having remained neatly in single file for the past 365 million years, the well-mannered creepy crawlies may provide clues as to how these prehistoric creatures interacted.
Trilobites are ancient marine arthropods that died out during the Late Devonian Extinction. With no eyes or other photoreceptors, staying in touch with each other as they migrated across the ocean floor must have been quite a challenge, although the new discovery has finally provided some insight into how they achieved this.
Reporting their finding in the journal Palaeontology, the researchers describe 78 neat lines of trilobites, each containing up to 19 individuals. The spacing between the fossilized bodies is reminiscent of that sometimes seen in spiny lobsters as they migrate to their shallow breeding grounds each year in tidy single-file lines.
Though lobsters have eyes and can therefore see each other, visibility on the murky ocean floor can be pretty poor at times, so the snappers create urine trails that act as “scent paths”, allowing each lobster to detect the location of the one in front when they can’t see.
The study authors therefore propose that trilobites probably also stayed in formation using chemical signals – a phenomenon known as chemotaxis. They also hypothesize that the ancient creatures were probably migrating to the shallows to breed. As evidence for this, they describe the finding of several “trilobite nurseries”, made up of clusters of juveniles close to the lines of migrating adults.
Interestingly, the fact that these trilobites were found in perfect formation suggests that they all died at the exact same time. Though their cause of death is not entirely known, the researchers suggest that they may have either suffocated or been poisoned as storms disrupted the sediment on the ocean floor, causing oxygen levels to drop and carbon dioxide and hydrogen sulphide levels to rise. To the trilobites’ credit, they remained gracious and courteous until the bitter end, never stepping out of line despite coming face to face with their demise.