Walker Weyland’21 Explores the Direction of Early Trilobite Emigration and Origin
Arthropods first appear after the Ediacaran-Cambrian transition along with over 20 other phyla. Trilobites were among the most dominant clades of metazoans during the Cambrian but their origins remain obscured by gaps in the fossil record. The environment of the first trilobites and other Cambrian metazoans has been assumed to be shallow, near-shore ecosystems, where the first body and trace fossils of trilobitomorphs have been found. The enigmatic Ediacaran fauna that precedes them, however, seems to have first evolved in deeper, off-shore environments.
This study examines the morphometric change of early trilobite lineages to track the evolution of possible vestigial off-shore adaptations. Off-shore adaptations that are detectable in the fossil record were identified by looking at modern-day arthropod groups that have representatives in both near and off-shore settings. If trilobites evolved first in off-shore environments, like the Ediacaran-fauna, then the identified features should be selected against throughout the Cambrian. If trilobites first evolved in near-shore environments, then one would instead expect to see no appreciable pattern in the identified features across all of trilobita.