Parade Of Trilobites: Killed And Fossilized While Walking In Tandem – New Research

Eddie Gonzales Jr. – MessageToEagle.com – A team of researchers, among them Jean Vannier from the Laboratory of Geology of Lyon have described queues of a trilobite called Ampyx priscus, found in the Tremadocian Fezouata Shale Lagerstätte near Morocco.

In their paper, researchers report the unusual finding of a parade of trilobites—a group of the ancient arthropods—apparently killed and fossilized while walking in tandem, like an invertebrate conga line. They’re 480 million years old, from the Lower Ordovician, and were found in Morocco.

Did group behavior arise recently or is it primeval?

The study showed that the trilobites had probably been buried in their positions – all oriented in the same direction, in orderly lines, maintaining close contact with each other through their long spines—during storms.

How individuals interact and why they co-operate to constitute group-level patterns has been extensively studied in extant animals through a variety mechanistic, functional and theoretical approaches. Although collective and social behavior evolved through natural selection over millions of years, its origin and early history have remained largely unknown.

Image credit: Vannier et al., Scientific Reports, 2019

By comparing this observation with the behavior of living animals such as North American spiny lobsters, the scientists deduced that these Ampyx processions may illustrate a similar kind of collective behaviour—adopted in response to cyclic environmental disturbances like storms or to chemical signals associated with reproduction.

Ampyx shows that collective behavior in arthropods has a very deep ancestry back to the Lower Palaeozoic. This behavior was necessarily associated with a communication system between individuals involving motion and mechanical sensors, chemical signals.

The study also shows that “alignments of trilobites do not result from passive transportation and accumulation by currents but from a collective behavior. Ampyx priscus was probably migrating in groups and used its long projecting spines to maintain a single-row formation by physical contacts possibly associated with mechano-receptors and/or chemical communication. This group behavior may have been a response to environmental stress due to periodic storms shown by sedimentological evidence or was associated with reproduction. This record of linear clustering in early euarthropods suggests that intraspecific group-level patterns comparable to those of modern animals already existed 480 million years ago in the early stages of the Great Ordovician Biodiversification Event,” researchers write in the paper.

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Written by Eddie Gonzales Jr. – MessageToEagle.com Staff