323-1 Trilobite Behavior and Evolution Over the Precambrian-Cambrian Boundary in the White-Inyo Mountains and Death Valley (CA, NV)

Abstract:

Here we present evidence of suggested biotic interactions between the earliest Cambrian trilobites and worms from lower Cambrian strata of the White-Inyo Mountains and Death Valley area in western Nevada and eastern California. This research examines the differences and similarities between trilobites, their evolution and behavior over the Precambrian-Cambrian boundary between two depositional environments. The depositional environment of the lower Cambrian Campito Formation of the White-Inyo Mountains is considered to be relatively shallow, located distally on the continental slope of a passive margin, likely between fair weather wave base and storm wave base. Conversely, the depositional environment of the Wood Canyon Formation in the Death Valley area represents a more proximal environment to the shoreline. Both formations contain some of the first trilobite body fossils found in the United States. However, arthropod trace fossils occur in much older Precambrian strata at both locations. Therefore, it is commonly believed that trilobites evolved prior to their appearance in the fossil record from an unmineralized Precambrian ancestor.

This project examines not only the first trilobite body fossils, but also the first arthropod traces, to learn more about trilobite evolution and behavior prior to and during the Cambrian Explosion. Methods of investigation include analysis of early Cambrian trilobite body fossils and Precambrian-Cambrian arthropod trace fossils reposited at the Natural History Museum of Los Angeles County and the Denver Museum of Nature and Science, as well as thin section analysis of these specimens. This project is unique in that it is the first to integrate investigations of the paleontology and sedimentology of these formations on a microscopic scale.

Preliminary results from trace fossils show evidence of biotic interactions between Precambrian-Cambrian arthropods and worms. There appears to be a close and common relationship between arthropod traces and worm burrows at both depositional environments. This suggests that arthropods and worms have had a biotic relationship since before the mineralization of trilobites in the early Cambrian. Additionally, the presence of microscopic Planolites burrows associated with trilobite-bearing strata, further suggests a biotic relationship between trilobites and the trace makers. Though it is commonly accepted that trilobites preyed on worms during the Cambrian, it is unclear what the relationship is between Precambrian arthropods and worms. Further study is needed to confirm this relationship.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.