title: New fossil ephialtitids elucidating the origin and transformation of the propodeal-metasomal articulation in Apocrita (Hymenoptera).
abstract: BACKGROUND
  Apocrita has a special structure that its first abdominal segment has been incorporated into the thorax as the propodeum. The remaining abdomen, metasoma, is connected to this hybrid region via a narrow propodeal-metasomal articulation forming a "wasp waist", which serves an important function of providing maneuverability, flexibility and posture for oviposition. However, the origin and transformation of the propodeal-metasomal articulation are still vague. Ephialtitidae, as the basal group of Apocrita from the Early Jurassic to the Early Cretaceous, have shown various types of propodeal-metasomal articulations.
  
  
  RESULTS
  This study describes and illustrates two new genera with three new species, Acephialtitia colossa gen. et sp. nov., Proephialtitia acanthi gen. et sp. nov. and P. tenuata sp. nov., collected respectively from the Early Cretaceous Yixian Formation at Liutiaogou and the Middle Jurassic Jiulongshan Formation at Daohugou, both in Inner Mongolia, China. These genera are assigned to the Ephialtitidae based on their complete wing venation, e.g. 2r-rs, 2r-m, 3r-m and 2 m-cu always present in the forewings and Rs, M and Cu in the hind wings. These new fossil ephialtitids have well-preserved propodeal-metasomal articulations indicating metasoma is broadly attached to propodeum.
  
  
  CONCLUSIONS
  The broad articulation between the propodeum and metasoma in basal Ephialtitidae, likely passed on from a still more basal family Karatavitidae, suggests three separate pathways of the transformation of the "wasp waist" in three different derived lineages leading from Ephialtitidae to: (i) Kuafuidae and further to the remaining Apocrita, (ii) Stephanidae, and (iii) Evanioidea. In addition, the demise of ephialtitid wasps lagging behind the flourishing of angiosperms suggests that ephialtitid extinction might have been mainly driven by competition with numerous new taxa (eg. the abundant Cretaceous xylophilous Baissinae and Ichneumonoidea) appeared just before or/and soon after the J/K boundary.
authors.affiliation: College of Life Sciences, Capital Normal University, 105 Xisanhuanbeilu, Haidian District, Beijing, 100048, China. fenger4499@163.com.
authors.forename: Longfeng
authors.initials: L
authors.lastname: Li
authors.affiliation: College of Life Sciences, Capital Normal University, 105 Xisanhuanbeilu, Haidian District, Beijing, 100048, China. chungkun.shih@gmail.com.
authors.forename: Chungkun
authors.initials: C
authors.lastname: Shih
authors.affiliation: Paleontological Institute, Russian Academy of Sciences, 123, Profsoyuznayaul, Moscow, 117997, Russia. alex.rasnitsyn@gmail.com.|Department of Palaeontology, Natural History Museum, Cromwell Road, London, Sw7 5BD, UK. alex.rasnitsyn@gmail.com.
authors.forename: Alexandr P
authors.initials: AP
authors.lastname: Rasnitsyn
authors.affiliation: College of Life Sciences, Capital Normal University, 105 Xisanhuanbeilu, Haidian District, Beijing, 100048, China. rendong@mail.cnu.edu.cn.
authors.forename: Dong
authors.initials: D
authors.lastname: Ren
mesh_terms: D000005:Abdomen / Q000033:anatomy & histology; D000818:Animals; D002681:China; D005260:Female; D005580:Fossils; D006927:Hymenoptera / Q000033:anatomy & histology* / Q000145:classification*; D013909:Thorax / Q000033:anatomy & histology; D014921:Wings, Animal / Q000033:anatomy & histology