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Dryad

Data from: Absolute axial growth and trunk segmentation in the early Cambrian trilobite Oryctocarella duyunensis

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Dec 15, 2020 version files 222.07 KB
Jul 29, 2021 version files 1.14 MB

Abstract

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