Systematic Entomology (2012), 37, 215–222 DOI: 10.1111/j.1365-3113.2011.00608.x On the edge of parasitoidism: a new Lower Cretaceous woodwasp forming the putative sister group of Xiphydriidae + Euhymenoptera LARS KROGMANN 1 and A N D R ´ E NEL 2 1 Staatliches Museum f¨ ur Naturkunde, Entomologie, Rosenstein 1, Stuttgart, Germany and 2 CNRS UMR 7205, CP 50, Entomologie, Mus´ eum National d’Histoire Naturelle, Paris, France Abstract. The fossil woodwasp Cratoenigma articulata gen. et sp.n. (Insecta: Hymenoptera) is described from the Lower Cretaceous Crato formation of Brazil. This fossil cannot be placed in any existing superfamily, but its putative phylogenetic position within Hymenoptera is discussed in detail on the basis of relevant thoracic, abdominal and wing venation characters. These characters are critically evaluated and compared with those of extant and fossil Hymenoptera. The phylogenetic position of C. articulata sp.n. is investigated relative to extant Xyelidae, Tenthredinoidea s.l., Pamphilioidea, Cephidae, Siricoidea, Xiphydriidae, Orussidae and Apocrita, and also to Mesozoic Gigasiricidae, Myrmiciidae, Daohugoidae, Sepulcidae, Anaxyelidae, Paroryssidae and Ephialtitidae. Based on the presence of a synapomorphic transscutal articulation, a plesiomorphic unconcealed mesopostnotum and autapomorphic hindwing venation (cu-a distinctly basal to fork between M and Cu), C. articulata sp.n. most likely forms the sister group of Xiphydriidae + Euhymenoptera. This would place it well within Unicalcarida, i.e. the clade in which the transition from endophytic to parasitoid lifestyle evolved. Introduction The evolutionary history of Hymenoptera, which represents one of the largest radiations of hexapods, can be traced back to the Triassic, approximately 230 Ma (Grimaldi & Engel, 2005). Over the past decade several studies have greatly contributed to our knowledge of the early evolution of the order by largely resolving the phylogenetic relationships among the ‘symphy- tan’ families (e.g. Vilhelmsen, 2001; Schulmeister et al., 2002; Schulmeister, 2003a, b; Heraty et al ., 2011; Sharkey et al., 2011). Well-supported relationships revealed by these stud- ies are: (i) Xyelidae is the sister group of the remaining Hymenoptera; (ii) Tenthredinoidea s.l. (Blasticotomidae, Ten- thredinidae, Cimbicidae, Diprionidae, Argidae and Pergidae) are monophyletic, and the Blasticotomidae is the sister group of the remaining Tenthredinoidea (i.e. to Tenthredinoidea s.s.); Correspondence: Lars Krogmann, Staatliches Museum f¨ ur Natur- kunde, Entomologie, Rosenstein 1, 70191 Stuttgart, Germany. E-mail: lars.krogmann@smns-bw.de The authors contributed equally to this paper. (iii) Pamphilioidea (Pamphiliidae and Megalodontesidae) are monophyletic; (iv) Xiphydriidae is the sister group of Euhymenoptera (Orussidae + Apocrita); and (v) Unicalcarida (Cephidae, Siricoidea, Xiphydriidae and Euhymenoptera) are monophyletic. Unresolved questions concern the monophyly of Siricoidea (Anaxyelidae and Siricidae), and the phylogenetic position of Siricoidea and Cephidae relative to Xiphydriidae + Euhymenoptera. The early evolution of hymenopteran taxa is of general biological interest, as it was accompanied by a dramatic change in biology from phyto- and xylophagy (i.e. sawflies and woodwasps) to parasitoidism (Euhymenoptera) (see Vilhelmsen & Turrisi, 2011). Most phylogenetic stud- ies were exclusively based on extant taxa, even though there are numerous Mesozoic ‘families’ described (e.g. Rasnitsyn, 2002; Rasnitsyn & Zhang, 2010, and references therein) for which monophyly and phylogenetic relationships to extant taxa remain questionable (see review in Grimaldi & Engel, 2005). Here, we contribute to the knowledge of the early evolutionary history of Hymenoptera in describing a new, well- preserved fossil woodwasp from the Lower Cretaceous Crato formation of Brazil. This fossil cannot be placed in any existing  2011 The Authors Systematic Entomology  2011 The Royal Entomological Society 215