© The Norwegian Academy of Science and Letters • Zoologica Scripta, 34, 1, January 2005, pp57–69 57 Pohl, H., Beutel, R. G. & Kinzelbach, R. (2005). Protoxenidae fam. nov. (Insecta, Strepsi- ptera) from Baltic amber — a ‘missing link’ in strepsipteran phylogeny. — Zoologica Scripta, 34, 57– 69. A male specimen of a new strepsipteran genus and species (Protoxenos janzeni gen. et sp. nov.) and family (Protoxenidae fam. nov.) found in Baltic amber is described and illustrated. It shows features which are apparently more plesiomorphic than in hitherto known strepsipterans, such as laterally inserted eight-segmented antennae, very robust mandibles with a broad base, a prominent galea, a comparatively short, transverse metapostnotum, hindwings that are feebly extended in a rostrocaudal direction, and equally sclerotized abdominal tergites and sternites. Based on a cladistic analysis of 46 characters of males of 11 genera and three outgroup taxa, P. janzeni is the sister group of all other known strepsipterans, and Mengea the sister group of Strepsiptera s.s. Eoxenos is the sister group of the remaining extant strepsipterans and Menge- nillidae is therefore paraphyletic. Newly established groundplan features of Strepsiptera will facilitate the clarification of the systematic position of the Order in future studies. Hans Pohl & Ragnar Kinzelbach, Institut für Biodiversitätsforschung, Allgemeine und Spezielle Zoologie, Universitätsplatz 2, D-18055 Rostock, Germany. E-mail: hans.pohl@biologie.uni-rostock.de Rolf G. Beutel, Institut für Spezielle Zoologie und Evolutionsbiologie, FSU Jena, Germany Blackwell Publishing, Ltd. Protoxenidae fam. nov. (Insecta, Strepsiptera) from Baltic amber — a ‘missing link’ in strepsipteran phylogeny HANS POHL, ROLF G. BEUTEL & RAGNAR KINZELBACH Accepted: 15 March 2004 Introduction The discovery of the single known specimen of Protoxenos janzeni gen. et sp. nov. at a fossil fair in Hamburg is a high- light in the history of strepsipteran studies. The group is poorly represented in the fossil record. The creation of Protoxenidae fam. nov. helps reduce the ‘morphological gap’ between the twisted winged parasites and the other endop- terygote insects. The numerous autapomorphies of the endopterygote Strepsiptera remain the primary cause of the difficulties involved with the Order’s systematic placement. Despite intensive efforts, its phylogenetic position is still controversial. World-wide, there are c. 600 extant described strepsipteran species, traditionally classified within nine or 10 families (Kinzelbach 1978, 1990; Pohl 2002). The second instar larvae of all species and the neotenic females of the Stylopidia are endoparasites of various higher taxa of insects including the Zygentoma, Blattaria, Mantodea, Orthoptera, Hemiptera, Hymenoptera and Diptera. In correlation with their parasitic life-style, they have evolved an extremely modified morpho- logy and unusual life histories. Conspicuous characters of the males include reduced forewings, which resemble halteres and function in a similar manner, fan-shaped hindwings, and ‘raspberry’ compound eyes. Females are always wingless. They are free living in Mengenillidae and partly leave the lar- val exuviae. Stylopid females extrude from their host’s body wall only with the anterior part of their body; they remain enclosed in the exuviae and form a functional unit with them within the host. Kinzelbach (1971a,b, 1978, 1990) and Kathirithamby (1989) have provided comprehensive reviews of the biology, morphology and systematics of the Strepsiptera. Nearly all records of fossil Strepsiptera are of free-living males found in Baltic or Dominican amber, which were likely trapped on the sticky surface of fresh resin (Table 1). There are a few exceptions: one primary larva of Stichotrema eocaenicum ( Haupt, 1950) (Myrmecolacidae) found in Eocene brown coal of the Geiseltal near Halle an der Saale (Kinzelbach & Lutz 1985), a stylopized Camponotus sp. ( Hymenoptera: Formicidae) with two male puparia of Myrmecolacidae, found in Middle Eocene Messel oil slate ( Lutz 1990), and one female of a purported species of Myrmecolacidae parasitizing a prionomyrmecine ant, found in Baltic amber (Pohl & Kinzelbach 2001). Most of the fossils found so far are closely related (or nearly identical ) to representatives of extant genera or species, in particular those extracted from Dominican amber ( Kathiri- thamby & Grimaldi 1993; Kinzelbach & Pohl 1994; Pohl & Kinzelbach 1995). Even though Eocene brown coal (45 –50 million years old), Baltic (39 –50 Myo) and Dominican amber