Life cycle evolution in the trilobites and from the Cambrian Series 2 (Stage 4) of South China.

The evolution process can be reconstructed by tracking the changes in the dynamic characters of life cycles. A number of related trilobites from the Cambrian of South China provide additional information for the study of trilobite evolutionary patterns, which has been hampered by previous incomplete fossil record though. Here, and represent related Cambrian oryctocephalid trilobites from South China, are comprehensively discussed over the ontogeny, and the results show that, from via to , their exoskeletal morphology shows a directional evolution. Based on the direction of evolutionary changes in the development of and , we speculate that likely evolved from instead of evolved from , as was previously assumed. This inference is also supported by the phylogenetic tree. This research provides not only a better understanding of the mechanisms of evolution in trilobites, but also new insights for the relationship between developmental evolutionary changes and phylogeny in trilobites.