The earliest holometabolous insect from the Carboniferous: a crucial innovation with delayed success (Insecta Protomeropina Protomeropidae)

Insects dominate Earth by their diversity, and the most are Holometabola. Therefore, the holometabolous development characterised by a pupal stage between larvae and adult seems to be linked with the extensive radiation of insects. Holometaboly is suspected to appear in the carboniferous period, however until now fossils have not brought univocal evidence. The discovery in the Carboniferous (Early Langsettian, circa 310 mya, Bashkirian Stage) of France of the earliest Holometabola attributed to the Permian amphiesmenopteran or antliophoran family Protomeropidae brings the first irrefutable evidence that holometaboly existed in the Carboniferous. Given the climatic data of France at this period, this discovery contradicts the traditional scenarii of a relation between the acquisition of endopterygote pupal stage and climatic global cooling during Late Carboniferous and Early Permian. This example illustrates the hypothesis that a new, apparently more efficient, biological innovation is not always sufficient to guarantee the 'evolutionary success' of the concerned clade. Ecological opportunities have to be considered as well for this innovation success.