The first Chinese protolindeniid fossil (Odonata: Petalurida: Protolindeniidae) highlighting the evolution of wing hinge structures of Odonata

Homologizing the wing hinge structures of Odonata is challenging due to the coalescence of articular plates and the relictual nature of wing pteralia in extant species. Fossil evidence is crucial for tracing the evolutionary history of wing hinges in pterygote. A new protolindeniid genus and species, Sinoprotolindenia zhengi Wei, Ren, Nel & Wang Y. gen. et sp. nov., from the Lower Cretaceous Yixian Formation in northeastern China, provides exceptional preservation of wing pteralia of basal hinge line. The new species, sister to Petaluridae, provides new insights into the evolution of tergal wing hinge structures in Odonata. The study reveals that the SDP (semi-detached scutal plate) is a composite plate: mSDP originates from the specialized lateral margin of the prescutum, while dSDP and pSDP derive from 2 free pteralia. The scutellar process of Odonata derives from the fusion of 1 pterala to scutellum, homologous to the proxalare of A in Meganisoptera. These findings confirm that the ground plan of the tergal wing hinge in Odonata comprises 4 pteralia (dSDP, pSDP, pterala 1, and pterala 2). Most pteralia (excluding pterala 1) exhibit derived fusion with terga among Anisoptera, Anisozygoptera, Zygoptera, but Sinoprotolindenia + Petaluridae and Gomphidae still retain some ancestral conditions.