Life cycle evolution in the trilobites Balangia and Duyunaspis 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, Balangia and Duyunaspis represent related Cambrian oryctocephalid trilobites from South China, are comprehensively discussed over the ontogeny, and the results show that, from B. balangensis via D. duyunensis to D. jianheensis, their exoskeletal morphology shows a directional evolution. Based on the direction of evolutionary changes in the development of Balangia and Duyunaspis, we speculate that Duyunaspis likely evolved from Balangia instead of Balangia evolved from Duyunaspis, 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.

Automated summary

The evolution process can be reconstructed by tracking the changes in the dynamic characters of life cycles. Trilobite evolutionary patterns are studied using related trilobites from the Cambrian of South China, providing additional information due to previous incomplete fossil records. The study discusses the ontogeny of Balangia and Duyunaspis, revealing a directional evolution in their exoskeletal morphology. Based on the evolutionary changes observed, it is speculated that Duyunaspis evolved from Balangia instead of the previous assumption of Balangia evolving from Duyunaspis. The findings also support the inference made by the phylogenetic tree.