Interspecies and intraspecific variability in the trilobites Duyunaspis and Balangia from the Cambrian Series 2 (Stage 4) of Jianhe, South China

Abstract

Though morphological variation among trilobites has been studied for some time, it is difficult to identify differences between interspecific and intraspecific variations. In this study, the intergeneric, interspecific, and intraspecific variations of the Cambrian oryctocephalid trilobites Duyunaspis and Balangia from Jianhe, South China are analysed using geometric morphometrics. In addition to the number of thoracic segments and the relative size of the pygidium compared to the cephalon mentioned in previous studies, the results in this study suggest that the predominant variation of Duyunaspis and Balangia is the presence or absence of the glabellar furrow. The interspecific variations of Duyunaspis (D. duyunensis, D. paiwuensis and D. jianheensis) mainly lie in the types of facial suture, occipital ring and glabella. Although the differences of D. duyunensis or D. jianheensis from adjacent sections have been observed, these variations may be caused by ontogeny, and do not reach the magnitude of interspecific variations in Duyunaspis. This research provides a better quantitative understanding of the variability in oryctocephalid trilobites.