A short introduction to trilobites

Many people interested in palaeontology and collecting fossils have either found fragments of trilobites in the field or marvelled at fossil examples of these animals displayed in museums around the world. Although they are essential components of palaeontological collections, thereby acting as index fossils for the Palaeozoic epochs (from the Cambrian to the Permian), data regarding their systematic and taxonomic categorisation, biology, and ecology are largely unknown among amateur fossil collectors. In this short contribution, I will provide an overview of the main characteristics of trilobites, which are of great importance if you wish to gain an understanding of these fascinating organisms, which became extinct 220mya.

Fig. 1 (top): Crude systematics of the Trilobita (superclass). In general, ten main orders can be distinguished, from which six important orders can be identified (Agnostida, Redlichiida, Ptychopariida, Phacopida, Nectaspida and Lichida), while the remaining orders, referred to as Corynexochida, Asaphida, Harpida, and Proetida (not shown above), play only a minor role, due to their similarity to members of the Redlichiida and Ptychopariida.

The systematics of trilobites

The heyday of the trilobites was during the Cambrian (570 to 505mya). Due to increased competition for food resources (for example, graptolites and brachiopods), they were subject to a successive displacement from their original habitats. This process was also accelerated by the appearance of predators, such as large cephalopods, eurypterids (which looked like gigantic crayfishes) and fishes. The evolution of better predators and competition for food finally resulted in the extinction of the trilobites during the Permian (220mya) and evolutionary innovations, such as the ability to roll up and the development of masticatory organs and long spines (see below), could only slow their decline.

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