Absolute axial growth and trunk segmentation in the early Cambrian trilobite <i>Oryctocarella duyunensis</i>

Abstract A short stratigraphic interval near Bulin in western Hunan (China) yields multiple specimens of the ~514-Myr-old oryctocarine trilobite Oryctocarella duyunensis . Size data obtained from these indicate that, meraspid degree 1 onward, degrees represent successive instars. Meraspid growth persisted until a terminal stage was reached, providing first example determinate trilobites and, notably, an early Cambrian species. The sample contains three varieties such stages, recognized as holaspids, with 9, 10, or 11 thoracic segments, respectively. During phase, rates were not constant this pattern seen assemblage differs modestly that reported same species two other localities, attesting to microevolutionary variation developmental patterns among collections.