産卵管が保存された化石に基づくナギナタハバチ類の初期進化

概要

Six species of the Late Triassic primitive sawflies assigned to family Xyelidae, were newly described based on the well-pr eserved fossil assemblage fr om the Upper Triassic (Carnian) Momonoki Formation in Yamaguchi, southwest Japan. The sawfly fossils are usually preserved as separated wings, while two complete body fossils still keeping ovipositors were newly found. It is the first disc overy of intac t bodies for subfam ily Madygellinae. The madygellines are the important basal repr esentatives of xyelid sawflies appeared in Triassic, but their wings were the only thing we could find previously. Information from the intact body fossils is expected to be useful for updating the classific ation, and following com prehensive features were confirmed, i. e., xyelid-lik e antenna, str aight or weakly arcuated anterior margin and the straight positor margin of pr onotum, well developed ovipositor, the absence of the anterior branch of RS, straight RS, narrow c ostal spac e, weak or absence SC. In relation, they have the most primitive slender type of ovipositors. Taking sever al ovipositor-preserved Hymenoptera fossils as well as extant species into consideration, two evolutionar y tr ends of ovipositors, i. e., towar ds stout and towar ds hyper -slender, can be r ec ognized in the history of Hymenoptera. The stout type appeared in her bivorous sawflies diversified after Middle Jurassic. It can be interpreted as adaptation to newly em erging plants in mid-Mesozoic. On the other hand, the hyper-slender type appear ed in Middle Jur assic. It was associated with the functional change, i. e., it gave rise to parasitic wasps spawning eggs to larvae in Jurassic, and further, to venomous stingers of wor ker bees. The morphology of ovipositor s is an impor tant key to understand the early evolution of basal Hym enopter a, and the slender type of ovipositor show in Tr iassic Madygellinae is the origin of various forms and functions of the ovipositors of Symphyta diversified after Middle Jurassic.