Revisiting the Raractocetus Fossils from Mesozoic and Cenozoic Amber Deposits (Coleoptera: Lymexylidae)

Simple Summary Lymexylidae is a small beetle family, with some members exhibiting strongly reduced elytra and largely exposed functional hind wings. Previously, four species from Kachin (Myanmar), Baltic, and Rovno ambers were assigned to the extant lymexylid genus Raractocetus. Our new examination suggests that these fossils are morphologically separated from the extant Raractocetus, primarily in the hind wing venation, and should be removed from Raractocetus. The fossils once assigned to Raractocetus Kurosawa from the Mesozoic and Cenozoic amber deposits differ from extant Raractocetus in the longer elytra, the more strongly projecting metacoxae, and the hind wing with vein 2A forked. Thus, these fossils should be removed from Raractocetus. Cretoquadratus engeli Chen from Kachin amber appears to be conspecific with R. fossilis Yamamoto. As a result, R. fossilis and R. extinctus Yamamoto from Kachin amber, R. balticus Yamamoto from Baltic amber, and R. sverlilo Nazarenko, Perkovsky & Yamamoto from Rovno amber are transferred to Cretoquadratus Chen, as C. fossilis (Yamamoto) comb. nov., C. extinctus (Yamamoto) comb. nov., C. balticus (Yamamoto) comb. nov., and C. sverlilo (Nazarenko, Perkovsky & Yamamoto) comb. nov., and C. engeli syn. nov. is suggested to be a junior synonym of C. fossilis.

Automated summary

A new examination suggests that the four fossils previously assigned to the lymexylid genus Raractocetus are morphologically separated from extant Raractocetus and should be removed from the genus. Additionally, fossils assigned to Raractocetus Kurosawa from amber deposits in different eras also differ from extant Raractocetus and should be removed from the genus. Furthermore, it was found that Cretoquadratus engeli Chen and R. fossilis Yamamoto are conspecific.