Colour Patterns in Devonian Trilobites

ABSTRACT

Many living marine animals exhibit striking colour patterns on their external skeletons or on exposed flesh. Such colour patterns surely existed in fossil animals, but usually have faded, partially or more often completely, or have been modified by diagenesis. Some reported patterns may indeed have resulted from diagenesis alone and thus are not original. Here we assess colour patterns in trilobites in Devonian specimens from North America and in new material from Germany. Specimens of Eldredgeops crassituberculata (Stumm, 1953) from the Middle Devonian Silica Shale, Sylvania, Ohio show spots on the pleurae, a brown band on the axial ribs and shadowy brown patches on the glabella. We advance reasons why these are most likely original. Distinctive patterns in the pygidia of Scutellum geesense Rud. & E. Richter 1956, Calycoscutellum sp., Scabriscutellum scabrum (Goldfuss, 1842) and Thysanopeltella acanthopeltis Barrande 1852 from the Devonian of Germany are illustrated here. Several specimens from different localities show a medium brown band fading to whitish towards the margin of the pygidium. These patterns are most unlikely to be random or, as argued here, diagenetic. They represent, in our opinion, original colour bands. We speculate that these colour patterns may have functioned as camouflage in a shallow-water visual world determined by ever-changing patterns of light.

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