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While the monophyly of winged insects (Pterygota) is well supported, phylogenetic relationships among the most basal extant pterygote lineages are problematic. Ephemeroptera (mayflies) and Odonata (dragonflies) represent the two most basal extant lineages of winged insects, and determining their relationship with regard to Neoptera (remaining winged insects) is a critical step toward understanding insect diversification. A recent molecular analysis concluded that Paleoptera (Odonata + Ephemeroptera) is monophyletic. However, we demonstrate that this result is supported only under a narrow range of alignment parameters. We have further tested the monophyly of Paleoptera using additional sequence data from 18SrDNA, 28S rDNA, and Histone 3 for a broader selection of taxa and a wider range of analytical methodologies. Our results suggest that the current suite of molecular data ambiguously resolve the three basal winged insect lineages and do not provide independent confirmation of Odonata + Neoptera as supported via morphological data.

The earliest branching event in winged insects, one of the core problems regarding early insect evolution, was addressed using characters of the head. The head is arguably one of the most complex body regions in insects and the phylogenetic information content of its features has been demonstrated. In contrast, the wings and other body parts related to the flight apparatus and sperm transmission are not useful in the context of this problem, as the outgroups (silverfish and bristletails) are wingless and transmit spermatophores externally. Therefore, they show profound differences in the organization of the postcephalic body, and assessment of homology and subsequent phylogenetic analysis of features of these body regions is extremely difficult. The core of this study is the investigation of head structures of representatives of the major clades of dragonflies. A detailed description of the head of Lestes virens is presented and was used as a starting point for the compilation of a character set and a character state matrix for the entire Dicondylia (winged insects + silverfish), with a main focus on the placement of dragonflies and consequently the basal branching event within winged insects. Our results indicate a sister-group relationship between a clade Palaeoptera (dragonflies + mayflies) and the megadiverse monophyletic lineage Neoptera. We show that despite considerable structural similarity between the odonate and neopteran mandible, the muscle equipment in dragonflies is more plesiomorphic with respect to Dicondylia than previously known. Odonata and Ephemeroptera also share presumably derived features of the antenna, maxilla, and labial musculature. Parsimony analyses of the head data unambiguously support a clade Palaeoptera. � The Willi Hennig Society 2012.

The structure of insect wing articulation is considered as reliable source of high level characters for phylogenetic analyses. However, the correct identification of homologous structures among the main groups of Pterygota is a hotly debated issue. Therefore, the reconstruction of the wing bases in Paleozoic extinct relatives is of great interest, but at the same time it should be treated with extreme caution due to distortions caused by taphonomic effects. The present study is focused on the wing base in Dunbaria (Spilapteridae). The articulation in Dunbaria quinquefasciata is mainly formed by a prominent upright axillary plate while the humeral plate is markedly reduced. Due to unique preservation of surface relief of the axillary plate, its composition shows a detailed pattern of three fused axillary sclerites and presumable position of the sclerite 3Ax. The obtained structures were compared among Spilapteridae and to other palaeodictyopterans Ostrava nigra (Homoiopteridae) and Namuroningxia elegans (Namuroningxiidae). The comparative study uncovered two patterns of 3Ax in Dunbaria and Namuroningxia, which correspond to their different suprafamilial classification. In contrast to previous studies these new results reveal the homologous structural elements in the wing base between Paleozoic Palaeodictyoptera and their extant relatives of Ephemeroptera, Odonata and Neoptera.

Phylogenetic relationships of basal insects remain a matter of discussion. In particular, the relationships among Ephemeroptera, Odonata and Neoptera are the focus of debate. In this study, we used a next-generation sequencing approach to reconstruct new mitochondrial genomes (mitogenomes) from 18 species of basal insects, including six representatives of Ephemeroptera and 11 of Odonata, plus one species belonging to Zygentoma. We then compared the structures of the newly sequenced mitogenomes. A tRNA gene cluster of IMQM was found in three ephemeropteran species, which may serve as a potential synapomorphy for the family Heptageniidae. Combined with published insect mitogenome sequences, we constructed a data matrix with all 37 mitochondrial genes of 85 taxa, which had a sampling concentrating on the palaeopteran lineages. Phylogenetic analyses were performed based on various data coding schemes, using maximum likelihood and Bayesian inferences under different models of sequence evolution. Our results generally recovered Zygentoma as a monophyletic group, which formed a sister group to Pterygota. This confirmed the relatively primitive position of Zygentoma to Ephemeroptera, Odonata and Neoptera. Analyses using site-heterogeneous CAT-GTR model strongly supported the Palaeoptera clade, with the monophyletic Ephemeroptera being sister to the monophyletic Odonata. In addition, a sister group relationship between Palaeoptera and Neoptera was supported by the current mitogenomic data.

Topographic anatomy of ascending (AN) and descending (DN) neurons of the supraesophageal and thoracic ganglia in the nervous system of winged insects (Pterygota), representatives of the infraclasses Palaeoptera (Odonata, Aeschna grandis, dragonfly) and Neoptera (Blattoptera, Periplaneta americana, cockroach), was studied. These insects differ in ecological niches, lifestyles, sets of behavioral complexes, levels of locomotor system development, evolutionary age and systematic position. Cell bodies and processes of ANs and DNs were stained with nickel chloride (NiCl2), and their topography was studied on total preparations of the supraesophageal and thoracic ganglia. Unlike cockroaches, the dragonfly protocerebrum was found to contain DNs sending their processes to ocelli. Dragonfly DN processes exhibit a specific branching pattern in thoracic ganglia, with collaterals coming off both ipsi- and contralaterally. In cockroaches, collaterals of DN processes come off ipsilaterally. The AN cell bodies in dragonfly meso- and metathoracic ganglia lie both ipsi- and contralaterally relative to the ascending process, whereas in cockroaches most of the AN cell bodies in the same ganglia are located contralaterally. Substantial differences in the distrubution of DNs and ANs in insects with different manners of locomotion appear to reflect different degrees of control the supraesophageal ganglion exerts over the activity of segmental centers. This does not seem to be related to the evolutionary age of insects or their systematic position. Probably, different degrees of control over locomotion depend on the way of food acquisition: catching prey in the air in “paleopterous” dragonflies versus maneuverable walking or running over a solid substrate in “neopterous” cockroaches.

Can you name the five most significant evolutionary changes that made beetles the most successful and diversified of all insects? Hint : check Fig. 1 for the five modifications marked on the evolutionary tree of insect orders. Fig. 1. The most strongly supported clades of the insect orders show dramatic changes in the number of species (estimates based on Gullan and Cranston 2005), suggesting that the changes at the numbered nodes represent major improvements in fitness. Odonata and Ephemeroptera (together known as Palaeoptera) are 3 times as speciose as the more primitive, wingless orders; orthopteroid orders (Pliconeoptera) together are 4 times as speciose as Palaeoptera; hemipteroid orders (here named Clavoptera) are 4 times as speciose as Pliconeoptera; neuropteroid orders (except Coleoptera) are 6 times as speciose as Clavoptera, and Coleoptera alone are almost as speciose as all the other neuropteroid orders put together, and some taxonomists claim that there are more than 10 times as many beetles as other neuropteroids. For morphological and anatomical changes at the numbered nodes, see text. Photograph by Nicholas Aflitto. The first change, of course, is the evolution of wings (node 1 in Fig. 1) that created the paleopterous orders, represented in the modern fauna by Ephemeroptera and Odonata, and the second (node 2) was the ability of Neoptera to fold those wings over the back, preventing them from being damaged when evading predators. The majority of Coleoptera have taken this process one step farther: they can fold their wings in half (node 5) and hide them under the …

The phylogenetic relationships of the winged insect lineages – mayflies (Ephemeroptera), damselflies and dragonflies (Odonata), and all other winged insects (Neoptera) – are still controversial with three hypotheses supported by different datasets: Palaeoptera, Metapterygota and Chiastomyaria. Here, we reanalyze available phylogenomic data with a focus on detecting confounding and alternative signal. In this context, we provide a framework to quantitatively evaluate and assess incongruent molecular phylogenetic signal inherent in phylogenomic datasets. Despite overall support for the Palaeoptera hypothesis, we also found considerable signal for Chiastomyaria, which is not easily detectable by standardized tree inference approaches. Analyses of the accumulation of signal across gene partitions showed that signal accumulates gradually. However, even in case signal only slightly supported one over the other hypothesis, topologies inferred from large datasets switch from statistically strongly supported Palaeoptera to strongly supported Chiastomyaria. From a morphological point of view, Palaeoptera currently appears to be the best-supported hypothesis; however, recent analyses were restricted to head characters. Phylogenetic approaches covering all organ systems including analyses of potential functional or developmental convergence are still pending so that the Palaeoptera problem has to be considered an open question in insect systematics.

The phylogenetic relationships of the winged insect lineages - mayflies (Ephemeroptera), damselflies and dragonflies (Odonata), and all other winged insects (Neoptera) - are still controversial with three hypotheses supported by different datasets: Palaeoptera, Metapterygota and Chiastomyaria. Here, we reanalyze available phylogenomic data with a focus on detecting confounding and alternative signal. In this context, we provide a framework to quantitatively evaluate and assess incongruent molecular phylogenetic signal inherent in phylogenomic datasets. Despite overall support for the Palaeoptera hypothesis, we also found considerable signal for Chiastomyaria, which is not easily detectable by standardized tree inference approaches. Analyses of the accumulation of signal across gene partitions showed that signal accumulates gradually. However, even in case signal only slightly supported one over the other hypothesis, topologies inferred from large datasets switch from statistically strongly supported Palaeoptera to strongly supported Chiastomyaria. From a morphological point of view, Palaeoptera currently appears to be the best-supported hypothesis; however, recent analyses were restricted to head characters. Phylogenetic approaches covering all organ systems including analyses of potential functional or developmental convergence are still pending so that the Palaeoptera problem has to be considered an open question in insect systematics.

Phylogenetic relationships among the basal orders of winged insects remain unclear, in particular the relationship of the Ephemeroptera (mayflies) and the Odonata (dragonflies and damselflies) with the Neoptera. Insect evolution is thought to have followed rapid divergence in the distant past and phylogenetic reconstruction may therefore be susceptible to problems of taxon sampling, choice of outgroup, marker selection, and tree reconstruction method. Here we newly sequenced three mitochondrial genomes representing the two most diverse families of the Ephemeroptera, one of which is a basal lineage of the order. We then used an additional 90 insect mitochondrial genomes to reconstruct their phylogeny using Bayesian and maximum likelihood approaches. Bayesian analysis supported a basal Odonata hypothesis, with Ephemeroptera as sister group to the remaining insects. This was only supported when using an optimized data matrix from which rogue taxa and terminals affected by long-branch attraction were removed. None of our analyses supported a basal Ephemeroptera hypothesis or Ephemeroptera + Odonata as monophyletic clade sister to other insects (i.e., the Palaeoptera hypothesis). Our newly sequenced mitochondrial genomes ofBaetis rutilocylindratus,Cloeon dipterum, andHabrophlebiodes zijinensishad a complete set of protein coding genes and a conserved orientation except for two inverted tRNAs inH. zijinensis.Increased mayfly sampling, removal of problematic taxa, and a Bayesian phylogenetic framework were needed to infer phylogenetic relationships within the three ancient insect lineages of Odonata, Ephemeroptera, and Neoptera. Pruning of rogue taxa improved the number of supported nodes in all phylogenetic trees. Our results add to previous evidence for the Odonata hypothesis and indicate that the phylogenetic resolution of the basal insects can be resolved with more data and sampling effort.

The holotype is redescribed of the giant pterygote insect Bojophlebia prokopi Kukalova-Peck, 1985 from the Pennsylvanian of the Czech Republic. Multiple errors in the original description are documented and corrected. Bojophlebia prokopi has neither any visible traces of a costal brace nor an anal brace, but it does show triadic branchings of MA, MP, CuA, and even, as rare a plesiomorphy, of CuP. It is therefore rejected as a fossil stem mayfly and attributed as sister group of all other Hydropalaeoptera. The first cladistic analysis of fossil palaeopterous insects, including different palaeodictyopterid groups, is presented. A revised phylogeny of Hydropalaeoptera and the stem line of Ephemeroptera are suggested. Palaeodictyopterida is recognized as sister group of Neoptera; thus Palaeoptera s.l. is rejected as a paraphyletic taxon. Four new higher taxa – Paranotalia, Euhydropalaeoptera, Neopterygota and Litophlebioidea superfam. nov. – are introduced, as well as the new family Lithoneuridae.http://zooba...

The order in which the 3 groups of winged insects (the Pterygota) diverged from their common ancestor has important implications for understanding the origin of insect flight. But despite this importance, the split between the Odonata (dragonflies and damselflies), Ephemeroptera (mayflies), and Neoptera (the other winged orders) remains very much unresolved. Indeed, previous studies have obtained strong apparent support for each of the 3 possible branching patterns. Here, we present a systematic reinvestigation of the basal pterygote split. Our results suggest that outgroup choice and limited taxon sampling have been major sources of systematic error, even for data sets with a large number of characters (e.g., in phylogenomic data sets). In particular, a data set of 113 taxa provides consistent support for the Palaeoptera hypothesis (the grouping of Odonata with Ephemeroptera), whereas results from data sets with fewer taxa give inconsistent results and are highly sensitive to minor changes in data and methods. We also focus on recent methods that exploit temporal information using fossil calibrations, combined with additional assumptions about the evolutionary process, and so reduce the influence of outgroup choice. These methods are shown to provide more consistent results, for example, supporting Palaeoptera, even for data sets that previously supported other hypotheses. Together, these results have implications for understanding insect origins and for resolving other problematic splits in the tree of life. (Bayesian phylogenetics; BEAST; Chiastomyaria; Metapterygota; Pterygota.)

The relationships of the 3 major clades of winged insects—Ephemeroptera, Odonata, and Neoptera—are still unclear. Many morphologists favor a clade Metapterygota (Odonata+Neoptera), but Chiastomyaria (Ephemeroptera+ Neoptera) or Palaeoptera (Ephemeroptera+Odonata) has also been supported in some older and more recent studies. A possible explanation for the difficulties in resolving these relationships is concerted convergence—the convergent evolution of entire character complexes under the same or similar selective pressures. In this study, we analyze possible instances of this phenomenon in the context of head structures of Ephemeroptera, Odonata, and Neoptera. We apply a recently introduced formal approach to detect the occurrence of concerted convergence. We found that characters of the tentorium and mandibles in particular, but also some other head structures, have apparently not evolved independently, and thus can cause artifacts in tree reconstruction. Our subsequent analyses, which exclude character sets that may be affected by concerted convergence, corroborate the Palaeoptera concept. We show that the analysis of homoplasy and its influence on tree inference can be formally improved with important consequences for the identification of incompatibilities between data sets. Our results suggest that modified weighting (or exclusion of characters) in cases of formally identified correlated cliques of characters may improve morphology-based tree reconstruction. (Character clique; convergent evolution; Chiastomyaria; Ephemeroptera; homoplasy; Metapterygota; morphology; mouthparts; Odonata; phylogeny.)

This is the first reported primary sequence of a bioactive peptide isolated from three Ephemeroptera families. Peptides of the adipokinetic hormone (AKH) family from the corpora cardiaca of nymphs of Afronurus spp. (Family: Heptageniidae), Siphlonurus lacustris (Family: Siphlonuridae) and Ephemera danica (Family: Ephemeridae) were investigated functionally in homologous (hypertrehalosaemic activity demonstrated in E. danica nymphs) and heterologous (active in cockroach and locust) bioassays, and structurally by liquid-chromatography coupled with ion trap electrospray ionisation mass spectrometry. All species investigated synthesise the octapeptide code-named Anaim-AKH (pGlu-Val-Asn-Phe-Ser-Pro-Ser-Trp amide). Confirmation of this peptide being present in corpora cardiaca of E. danica nymphs was obtained via reverse phase-high pressure liquid chromatography. Phylogenetically, the presence of only one AKH peptide may constitute a basal condition; all other lower insect orders, e.g. Odonata, Blattodea, Orthoptera, amongst others, have more than one AKH analogue. We propose that Anaim-AKH is the ancestral peptide which may support the Palaeoptera hypothesis that mayflies (Ephemeroptera) and dragonflies (Odonata) form the Palaeoptera clade, the sister group of Neoptera. The structural data cannot, however, shed any light on the phylogenetic scenarios within Ephemeroptera itself. Finally, this study demonstrates the successful use of larvae as an alternative biological source to study neuropeptides in ephemeral, elusive or difficult to obtain adult insects.

Research over the last two decades has significantly increased our understanding of the evolutionary position of the insects among other arthropods, and the relationships among the insect Orders. Many of these insights have been established through increasingly sophisticated analyses of DNA sequence data from a limited number of genes. Recent results have established the relationships of the Holometabola, but relationships among the hemimetabolous orders have been more difficult to elucidate. As trong con- sensus on the relationships among the Palaeoptera (Ephemeroptera and Odonata) and their relationship to the Neoptera has not emerged with all three possible resolutions supported by different data sets.While polyneopteran relationships generally have resisted significant resolution, it is now clear that termites, Isoptera, are nested within the cockroaches, Blattodea. The newly discovered order Mantophasmatodea is difficult to place with the balance of studies favouring Grylloblattodea as sister-group.While some stu- dies have found the paraneopteran orders (Hemiptera, Thysanoptera, Phthiraptera and Psocoptera) monophyletic, evidence suggests that parasitic lice (Phthiraptera) have evolved from groups within the book and bark lice (Psocoptera), and may represent parallel evolutions of parasitism within two major louse groups. Within Holometabola, it is now clear that Hymenoptera are the sister to the other orders, that, in turn are divided into two clades, the Neuropteroidea (Coleoptera, Neuroptera and relatives) and the Mecopterida (Trichoptera, Lepidoptera, Diptera and their relatives). The enigmatic order Strep- siptera, the twisted wing insects, have now been placed firmly near Coleoptera, rejecting their close rela- tionship to Diptera that was proposed some 15 years ago primarily based on ribosomal DNA data. Phylogenomic-scale analyses are just beginning to be focused on the relationships of the insect orders, and this is where we expect to see resolution of palaeopteran and polyneopteran relationships. Future research will benefit from greater coordination between intra and inter-ordinal analyses. This will max- imise the opportunities for appropriate outgroup choice at the intraordinal level and provide the back- ground knowledge for the interordinal analyses to span the maximum phylogenetic scope within groups.

Taphonomic conditions of insects from the Late Carboniferous (Pennsylvanian) Konservat-Lagerstatte Hagen-Vorhalle (western Germany) are remarkably unique but have not been the focus of detailed work thus far. Their particular preservation is conspicuous and furthermore shows significant differences between “Palaeoptera” and Neoptera. The first are almost always completely preserved while the latter invariably lack an abdomen. Furthermore all Neoptera bear tiny bivalve prodissoconchs (~ 0.8–1.2 mm) or few dissoconchs (~ 1.3–1.4 mm) exclusively on the dorsal wing membrane. Taking into account geological, sedimentological, paleontological and paleo-oceanological data a novel taphonomic model is presented here. After a short period of drifting along the water/air contact layer “Palaeoptera” sank directly to the bottom whereas the soft-tissued abdomens of Neoptera began to decay under these oxic conditions. After loosing their abdomen the corpses sank to a pycnocline in a strongly stratified water body where a second period of drifting took place. At this stage the wings were settled by attaching bivalve larvae derived from a river. When the weight of the shells increased the insect/bivalve association broke through the pycnocline and sank to the bottom where they were finally embedded and fossilized.

This study determined the first complete mitochondrial genome of a damselfly, Euphaea formosa (Insecta: Odonata: Zygoptera), and reconstructed a phylogeny based on thirteen protein-coding genes of mitochondrial genomes in twenty-five representative hexapods to examine the relationships among the basal Pterygota. The damselfly's mitochondrial genome is a circular molecule of 15,700 bp long, and contains the entire set of thirty-seven genes typically found in insects. The gene arrangement, nucleotide composition, and codon usage pattern of the mitochondrial genome are similar across the three odonate species, suggesting a conserved genome evolution within the Odonata. The presence of the intergenic spacer s5 likely represents a synapomorphy for the dragonflies (Anisoptera). Maximum parsimony, maximum likelihood, and Bayesian analyses of both nucleotide and amino acid sequences cannot support the three existing phylogenetic hypotheses of the basal Pterygota (Palaeoptera, Metapterygota, and Chiastomyaria). In contrast, the phylogenetic results indicate an alternative hypothesis of a strongly supported basal Odonata and a sister relationship of the Ephemeroptera and Plecoptera. The unexpected sister Ephemeroptera + Plecoptera clade, which contradicts with the widely accepted hypothesis of a monophyletic Neoptera, requires further analyses with additional mitochondrial genome sampling at the base of the Neoptera.

Pterygota are traditionally divided in two lineages, the "Palaeoptera" and Neoptera. Despite several efforts neither morphology nor molecular systematics have resolved the phylogeny of the pterygote insects. Too few markers have yet been identified for adequately tracking mesozoic-aged divergences. We tested the Elongation factor-1alpha for its phylogenetic value in pterygote insect systematics. This highly conserved nuclear protein-coding gene has previously been reported to be useful in other groups for phylogenetic analyses at the intraordinal level as well as at the interordinal level. The analyses suggest that EF-1alpha DNA sequences as well as intron positions provide informative markers for pterygote phylogenetics.

In the search for the sister group of modern Ephemerida, we used the evolutionary groundplan method to identify synapomorphies in wing articulation. The evolutionary approach is necessary because post-groundplan wing adaptations have obscured the phylogenetically informative higher-level synapomorphies in modern Ephemerida, Odonata and Neoptera. Protowing-level sclerites are recognisable fragments of the first limb-derived pleuron, arranged in eight rows above the pathways delivering blood to the eight principal wing veins. Each row includes three sclerites (proxalare, axalare and fulcalare) which articulate with the basivenale (wing blood sinus). Over the course of the pterygote evolutionary history, many row-sclerites have assembled into clusters, plates, or processes, the composition of which can be most clearly recognised by comparison with ancestral Paleozoic fossils. The extant orders Ephemerida and Odonata (Palaeoptera: Hydropalaeoptera) share a derived anterior articular plate (AAP) composed of fo...

One of the most fascinating Bauplan transitions in the animal kingdom was the invention of insect wings, a change that also contributed to the success and enormous diversity of this animal group. However, the origin of insect flight and the relationships of basal winged insect orders are still controversial. Three hypotheses have been proposed to explain the phylogeny of winged insects: 1) the traditional Palaeoptera hypothesis (Ephemeroptera + Odonata, Neoptera), 2) the Metapterygota hypothesis (Ephemeroptera, Odonata + Neoptera), and 3) the Chiastomyaria hypothesis (Odonata, Ephemeroptera + Neoptera). Neither phylogenetic analyses of single genes nor even multiple marker systems (e.g., molecular markers + morphological characters) have yet been able to conclusively resolve basal pterygote divergences. A possible explanation for the lack of resolution is that the divergences took place in the mid-Devonian within a short period of time and attempts to solve this problem have been confounded by the major challenge of finding molecular markers to accurately track these short ancient internodes. Although phylogenomic data are available for Neoptera and some wingless (apterygote) orders, they are lacking for the crucial Odonata and Ephemeroptera orders. We adopt a multigene approach including data from two new expressed sequence tag projects-from the orders Ephemeroptera (Baetis sp.) and Odonata (Ischnura elegans)-to evaluate the potential of phylogenomic analyses in clarifying this unresolved issue. We analyzed two data sets that differed in represented taxa, genes, and overall sequence lengths: maxspe (15 taxa, 125 genes, and 31,643 amino acid positions) and maxgen (8 taxa, 150 genes, and 42,541 amino acid positions). Maximum likelihood and Bayesian inference analyses both place the Odonata at the base of the winged insects. Furthermore, statistical hypotheses testing rejected both the Palaeoptera and the Metapterygota hypotheses. The comprehensive molecular data set developed here provides conclusive support for odonates as the most basal winged insect order (Chiastomyaria hypothesis). Data quality assessment indicates that proteins involved in cellular processes and signaling harbor the most informative phylogenetic signal.

ummary 1. The evidence for Hennig‘S (1969) hierarchial classification of the higher hexapodan taxa (here termed “orders”) is reviewed and additional data are considered. 2. The monophyly of the Hexapoda and the sister group relationship between Entognatha and Insecta (Archaeognatha + Zygentoma + Pterygota) are accepted. MANTON'S theory of an independent origin of Diplura, Protura, Collemboia, Thysanura (s. lat.) and Pterygota is found to be based on an unwarranted importance attached to autapomorphies and on inadequate considerations of those ancestral stages considered by Manton to be “functionally impossible”. 3. The monophyly of Hennig'S taxon Dicondylia (Zygentoma + Pterygota) is accepted and substantiated by further evidence. 4. A taxon constituted by the recent palaeopteran orders, Ephemeroptera and Odonata, is not accepted as monophyletic, the latter order being considered the sister group of the Neoptera. 5. The phylogenetic interrelationships of the lower neopteran orders (Plecoptera + Pauro-metabola sensu HENNIG) are considered entirely unclarified. HENNIG'S classification as well as the theories on supraordinal relationships by, e. g., BLACKITH and BLACKITH (1968), GILES (1963), RICHARDS and DAVIES (1957), Ross (1965), RAHLE (1970), SHAROV (1968/71) and WILLE (1960) are shown to be very weakly founded, but construction of an alternative classification is not attempted. The monophyletic nature of the order Blattopteroidea (Man-todea + Blattariae + Isoptera) is considered firmly established. 6. The ground plan of the Phasmatodea is inadequately known. The current primary division of the order is questioned, and the Californian genus Timema is suggested to be the primitive sister-group of all other Phasmatodea together. 7. The monophyly of the taxon “Eumetabola” (Paraneoptera + Holometabola) is substantiated only by its possession of a “jugal bar” (HAMILTON 1972). SHAROV'S (1966) account of the phylogenetic significance of embryonic growth patterns in the major pterygote division is discarded. 8.HENNIG'S theory of the paraneopteran nature of the Zoraptera is preferred to theories of blattopteroid affinities of this order. Assumedly specific zorapteran-isopteran similarities are invalidated by those characters in the Zoraptera (corpotentorium, female subgenital plate) which show that this order could at most have been the sister-group of the Blatto-pteroidea as a whole. 9. The monophyly of the entities Psocodea (Psocoptera + Phthiraptera) and Condylognatha (Hemiptera + Thysanoptera) is accepted. It is likely that the Psocoptera is paraphyletic in terms of Phthiraptera. HENNIG'S subdivisions of the Hemiptera: Heteropteroidea (including Coleorrhyncha), Auchenorrhyncha and Sternorrhyncha are accepted. 10. MICKOLEIT'S (1973) findings concerning the ovipositor-structures provide the most weighty evidence for the monophyly of the Neuropteroidea (Megaloptera + Raphidioptera + Neuroptera) and for the relationship of this group to the Coleoptera. Following KINZEL-BACH (1971), the Strepsiptera is tentatively placed as the sister-group of the Coleoptera. 11. HENNIG'S suggestion of a sister-group relationship between the Hymenoptera and the Mecopteroidea probably provides the best working hypothesis of the position of the former group. 12. The Mecopteroidea and its two sub-groups Amphiesmenoptera (Trichoptera + Lepido-ptera) and Antliophora (Mecoptera + Siphonaptera + Diptera) are considered mono-phyletic entities. The arguments, mentioned by HENNIG, against the inclusion of the Siphonaptera in the Mecopteroidea are discarded, and evidence is provided for a sister-group relationship between this order and Mecoptera (including Neomecoptera). The Zeugloptera are true Lepidoptera. Zusammenfassung Die Stammesgeschichte der „Ordnungen” der Hexapoden. Eine kritische Beurteilung des heutigen Wissens 1. Die Grundlagen der hierarchischen Klassifikation der hoheren Taxa der Hexapoden (hier „Ordnungen” genannt) von HENNIG (1969) werden uberpruft und durch zusatzliche Daten beurteilt. 2. Die Monophylie der Hexapoda und die Schwestergruppen-Beziehungen zwischen Ento-gnatha und Insecta (Archaeognatha + Zygentoma + Pterygota) werden ubernommen. Es wird gezeigt, das die Theorie von MANTON uber einen eigenen Ursprung der Diplura, Protura, Collembola, Thysanura (s. lat.) und Pterygota begrundet ist auf einer nicht ge-rechtfertigten Betonung von Autapomorphien und auf unangemessenen Erwagungen iiber jene ancestralen Stufen, die MANTON als „funktionell unmoglich” bezeichnet. 3. Die Monophylie von HENNIGS Taxon Dicondylia (Zygentoma + Pterygota) wird ubernommen und durch weitere Befunde untermauert. 4. Nicht anerkannt als monophyletisch wird ein Taxon, welches aus den rezenten palaeopteren Ordnungen Ephemeroptera und Odonata gebildet wurde. Die Odonata werden als die Schwestergruppe der Neoptera erachtet. 5. Die stammesgeschichtlichen Beziehungen der Ordnungen der niederen Neoptera (Pleco-ptera + Paurometabola sensu HENNIG) werden als vollig ungeklart bezeichnet. Sowohl die Klassifikation durch HENNIG als auch die Theorien von Uberordnungsbeziehungen, vertre-ten durch BLACKITH und BLACKITH (1968), GILES (1963), RICHARDS und DAVIES (1957), Ross (1965), RAHLE (1970), SHAROV (1968/71) und WILLE (1960) sind sehr schwach begriindet; eine alternative Klassifikation wird aber nicht versucht. Die Monophylie der Ordnung Blattopteroidae (Mantodea + Blattariae + Isoptera) wird als wohl begrundet angesehen. 6. Der Grundplan der Phasmatodea ist ungenugend bekannt. Die derzeitige Gliederung der Ordnung wird in Frage gestellt und die kalifornische Gattung Timema als die primitive Schwestergruppen aller anderen Phasmatodea erachtet. 7. Die Monophylie des Taxons „Eumetabola” (Paraneoptera + Holometabola) grundet sich nur auf den Besitz eines „jugal bar” (HAMILTON 1972). SHAROVS (1966) Hinweis auf die phylogenetische Bedeutung des embryonalen Wachstumsmusters wird verworfen. 8. HENNIGS Theorie von der paraneopteren Natur der Zoraptera wird gegenuber den Theorien einer blattopteroiden Verwandtschaft dieser Ordnung der Vorzug gegeben. Hervor-gehobene besondere Ahnlichkeiten zwischen Zoraptera und Isoptera werden bedeutungslos, weil andere Eigenarten der Zoraptera (Corpotentorium, weibliche Subgenitalplatte) darauf hinweisen, das diese Ordnung hochstens als die Schwestergruppe der Blattopteroidea in ihrer Gesamtheit gelten kann. 9. Die Monophylie der Einheiten Psocodea (Pocoptera + Phthiraptera) und Condylognatha (Hemiptera + Thysanoptera) wird ubernommen. Es ist wahrscheinlidi, das die Psocoptera paraphyletisdi mit Rucksicht auf die Phthiraptera sind. HENNIGS Untergliederung der Hemiptera in Heteropteroidea (einsdilieslich Coleorrhyncha), Auchenorrhyndia und Sternor-rhyncha wird anerkannt. 10. MICKOLEITS (1973) Eeststellungen an den Ovipositor-Strukturen stellen die widitigsten Grundlagen fur eine Monophylie der Neuropteroidea (Megaloptera + Raphidioptera + Neuroptera) dar sowie fur Beziehungen dieser Gruppe zu den Coleoptera. Gemas KINZEL-BACH (1971) werden die Strepsiptera zOgernd als Schwestergruppe der Coleoptera be-zeichnet. 11. HENNIGS Annahme einer Schwestergruppenbeziehung zwischen Hymenoptera und den Mecopteroidea ist wahrscheinlidi die beste Arbeitshypothese Uber die Stellung der erst-genannten Gruppe. 12. Die Mecopteroidea und ihre zwei Untergruppen Amphiesmenoptera (Tridioptera + Lepido-ptera) und Antliophora (Mecoptera + Siphonaptera+Diptera) werden als monophyletisch eraditet. Die von HENNIG genannten Argumente gegen die Einbeziehung der Siphonaptera in die Mecopteroidea werden nicht ubernommen; es werden Hinweise darauf gemacht, dafi zwischen dieser Gruppe und Mecoptera (einschlieslich Neomecoptera) Sdiwestergruppen-beziehungen bestehen. Die Zeugloptera sind echte Lepidoptera.

The first complete mitochondrial genome of a mayfly, Parafronurus youi (Arthropoda: Insecta: Pterygota: Ephemeroptera: Heptageniidae), was sequenced using a long PCR-based approach. The genome is a circular molecule of 15,481 bp in length, and encodes the set of 38 genes. Among them, 37 genes are found in other conservative insect mitochondrial genomes, and the 38(th) unique gene is trnM-like (trnM2). The duplication-random loss model can be used to explain one of the translocations at least. The A+T content of the control region is 57%, the lowest proportion detected so far in Hexapoda. Based on the nucleotide dataset and the corresponding amino acid dataset of 12 protein-coding genes, Bayesian inference and maximum likelihood analyses yielded stable support for the relationship of the three basal clades of winged insects as Ephemeroptera+(Odonata+Neoptera).

The ability to fly is the decisive factor for the evolutionary success of winged insects (Pterygota). Despite this, very little is known about the ground-pattern and evolution of the functionally very important wing base. Here we use the Ephemeroptera, usually regarded as the most ancient flying insects, as a model for the analysis of the flight musculature and the sclerites of the wing base. Morphology and anatomy of the pterothorax of 13 species of Ephemeroptera and five species of Plecoptera were examined and a detailed description of Habroleptoides confusa (Ephemeroptera: Leptophlebiidae) is given. A new homology of the wing base sclerites in Ephemeroptera is proposed. The wing base of Ephemeroptera possesses three axillary sclerites that are homologous to the first axillary, the second axillary and the third axillary of Neoptera. For example, the third axillary possesses the axillary-pleural muscle that mostly is considered as a characteristic feature of the Neoptera. Many of the muscles and sclerites of the flight system of the Ephemeroptera and Neoptera can be readily homologised. In fact, there are indications that a foldable wing base may be a ground plan feature of pterygote insects and that the non-foldable wing base of the Ephemeroptera is a derived state.

The order Zoraptera (angel insects) is one of the least known insect groups, containing only 32 extant species. The phylogenetic position of Zoraptera is poorly understood, but it is generally thought to be closely related to either Paraneoptera (hemipteroid orders: booklice, lice, thrips, and bugs), Dictyoptera (blattoid orders: cockroaches, termites, and mantis), or Embioptera (web spinners). We inferred the phylogenetic position of Zoraptera by analyzing nuclear 18S rDNA sequences, which we aligned according to a secondary structure model. Maximum likelihood and Bayesian analyses both supported a close relationship between Zoraptera and Dictyoptera with relatively high posterior probability. The 18S sequences of Zoraptera exhibited several unusual properties: (1) a dramatically increased substitution rate, which resulted in very long branches; (2) long insertions at helix E23; and (3) modifications of secondary structures at helices 12 and 18.

Polyneoptera is a name sometimes applied to an assemblage of 11 insect orders comprising the lower neopterous or “orthopteroid” insects. These orders include familiar insects such as Orthoptera (grasshoppers), Blattodea (roaches), Isoptera (termites) (Mantodea) praying mantises, Dermaptera (earwigs), Phasmatodea (stick insects), Plecoptera (stoneflies), as well as the more obscure, Embiidina (web-spinners), Zoraptera (angel insects) and Grylloblattodea (ice-crawlers). Many of these insect orders exhibit a high degree of morphological specialization, a condition that has led to multiple phylogenetic hypotheses and little consensus among investigators. We present a phylogenetic analysis of the polyneopteran orders representing a broad range of their phylogenetic diversity and including the recently described Mantophasmatodea. These analyses are based on complete 18S rDNA, 28S rDNA, Histone 3 DNA sequences, and a previously published morphology matrix coded at the ordinal level. Extensive analyses utilizing different alignment methodologies and parameter values across a majority of possible ranges were employed to test for sensitivity of the results to ribosomal alignment and to explore patterns across the theoretical alignment landscape. Multiple methodologies support the paraphyly of Polyneoptera, the monophyly of Dictyoptera, Orthopteroidea (sensu Kukalova-Peck; i.e. Orthoptera + Phasmatodea + Embiidina), and a group composed of Plecoptera + Dermaptera + Zoraptera. Sister taxon relationships between Embiidina + Phasmatodea in a group called “Eukinolabia”, and Dermaptera + Zoraptera (“Haplocercata”) are also supported by multiple analyses. This analysis also supports a sister taxon relationship between the newly described Mantophasmatodea, which are endemic to arid portions of southern Africa, and Grylloblattodea, a small order of cryophilic insects confined to the north-western Americas and north-eastern Asia, in a group termed “Xenonomia”. This placement, coupled with the morphological disparity of the two groups, validates the ordinal status of Mantophasmatodea. © The Willi Hennig Society 2005.

The nuclear small subunit rRNA (18S) has played a dominant role in the estimation of relationships among insect orders from molecular data. In previous studies, 18S sequences have been aligned by unadjusted automated approaches (computer alignments that are not manually readjusted), most recently with direct optimization (simultaneous alignment and tree building using a program called "POY"). Parsimony has been the principal optimality criterion. Given the problems associated with the alignment of rRNA, and the recent availability of the doublet model for the analysis of covarying sites using Bayesian MCMC analysis, a different approach is called for in the analysis of these data. In this paper, nucleotide sequence data from the 18S small subunit rRNA gene of insects are aligned manually with reference to secondary structure, and analyzed under Bayesian phylogenetic methods with both GTR+I+G and doublet models in MrBayes. A credible phylogeny of Insecta is recovered that is independent of the morphological data and (unlike many other analyses of 18S in insects) not contradictory to traditional ideas of insect ordinal relationships based on morphology. Hexapoda, including Collembola, are monophyletic. Paraneoptera are the sister taxon to a monophyletic Holometabola but weakly supported. Ephemeroptera are supported as the sister taxon of Neoptera, and this result is interpreted with respect to the evolution of direct sperm transfer and the evolution of flight. Many other relationships are well-supported but several taxa remain problematic, e.g., there is virtually no support for relationships among orthopteroid orders. A website is made available that provides aligned 18S data in formats that include structural symbols and Nexus formats.

Monophyly of the pterygote insects is generally accepted, but the relationships among the three basal branches (Odonata, Ephemeroptera and Neoptera) remain controversial. The traditional view, to separate the pterygote insects in Palaeoptera (Odonata + Ephemeroptera) and Neoptera, based on the ability or inability to fold the wings over the abdomen, has been questioned. Various authors have used different sets of morphological characters in support of all three possible arrangements of the basal pterygote branches. We sequenced 18S and 28S rDNA from 18 species of Odonata, 8 species of Ephemeroptera, 2 species of Neoptera, and 1 species of Archaeognatha in our study. The new sequences, in combination with sequences from GenBank, have been used in a parsimony jackknife analysis resulting in strong support for a monophyletic Palaeoptera. Morphological evidence and the phylogenetic implications for understanding the origin of insect flight are discussed.

The holotype specimen of the ‘protodonate’Erasipteroides valentini (Brauckmann in Brauckmann et al., 1985) and the paratype specimen K-13 of the giant ‘protodonate’Namurotypus sippeliBrauckmann and Zessin, 1989 from the Upper Carboniferous (Namurian B) of Hagen-Vorhalle (Germany) are redescribed, and a new specimen of Erasipteroides cf. valentini is described. The new evidence is used to refine the groundplan reconstruction of Odonatoptera and the reconstruction of odonatoid phylogeny. Prothoracic winglets for Erasipteroides and the absence of an archaedictyon are documented. Furthermore, a very long and sclerotized ovipositor with gonangulum is described from the female holotype specimen of Erasipteroides valentini, and it is proposed that it was not used for endophytic but for endosubstratic oviposition. The record of prothoracic winglets in early odonatoids, and their presence in fossil Palaeodictyoptera and ‘protorthopteres’, indicates that the groundplan of Pterygota indeed included three pairs of wings. A phylogenetic analysis suggests that the Palaeozoic giant Meganisoptera and “higher” odonatoids (incl. crowngroup Odonata) together form a monophyletic group which is here named Euodonatoptera. Erasipteroides and the other ‘Erasipteridae’ are shown to be more closely related to Euodonatoptera than to Eugeropteridae. The description of the male primary genital structures of Namurotypus sippeli is emended and a new interpretation is proposed, including new hypotheses concerning their function. The males of Namurotypus had a paired penis with a pair of lateral parameres, and a pair of leaf-like, but still segmented, gonopods. Segmented leg-like male gonopods are considered as a groundplan character of insects, while a paired penis is regarded as a putative synapomorphy of the palaeopterous insect orders Palaeodictyopteroida, Ephemeroptera, and Odonatoptera. It is proposed that Namurotypus did not mate by direct copulation but retained the archaic deposition of external spermatophores, just like the primarily wingless insects. The sigmoidal male cerci may have been placed behind the female head and used to drag the female over the spermatophore, which is remotely similar to the mating behaviour of some extant arachnids (e.g. Amblypygi). Three hypothetical scenarios regarding the evolution of secondary copulation in modern Odonata are proposed.

The Dermaptera are a small order of insects, marked by reduced forewings, hindwings with a unique and complicated folding pattern, and by pincer-like cerci. Hindwing characters of 25 extant dermapteran species are documented. The highly derived hindwing venation and articulation is accurately homologized with the other pterygote orders for the first time. The hindwing base of Dermaptera contains phylogenetically informative characters. They are compared with their homologues in fossil dermapteran ancestors, and in Plecoptera, Orthoptera (Caelifera), Dictyoptera (Mantodea, Blattodea, Isoptera), Fulgoromorpha and Megaloptera. A fully homologized character matrix of the pterygote wing complex is offered for the first time. The wing venation of the Coleoptera is re-interpreted and slightly modified. The all-pterygote character analysis suggests the following relationships: Pterygota: Palaeoptera + Neoptera; Neoptera: [Pleconeoptera + Orthoneoptera] + [Blattoneoptera + (Hemineoptera + Endoneoptera)]. Blattoneoptera share at least 15 wing apomorphies with the sistergroup Hemineoptera + Endoneoptera and none with the Orthoneoptera and Pleconeoptera; Blattoneoptera: (Grylloblattodea + (Dermaptera + Dictyoptera)); Dictyoptera: (Mantodea + (Blattodea + Isoptera). Dermaptera share 13 wing apomorphies with the sistergroup Dictyoptera. In order to document the intra-ordinal relationships of Dermaptera, 18 new characters of venation and articulation are added to an existing data set and analyzed cladistically. The following relationships are suggested (43 characters, tree length 72, CI 0.819 and RI 0.935). Dermaptera: Karschiellidae + ("Diplatyidae" + ("Pygidicranidae" + (Allostethus indicum + (Anisolabididae + ("Labiduridae" + [Forficulidae + (Chelisochidae + Spongiphoridae)]))))). The taxa in quotation marks are probably paraphyletic. Fossil Dermaptera and "Protelytroptera" show that wing-folding characters were already present in Permian ancestors. The evolution of the dermapteran wing-folding mechanism is discussed and the hindwing is presented as a working "origami" model, which will fold as in living earwigs. The functional role of the wing base in wing folding is examined. Characters in orders and other higher taxa are not independent and cannot be analyzed out of context with their groundplans. Higher systematics is dealing with diametrally different problems than species-level systematics. The necessity of using a different methodology for species-level and higher-level phylogenetics is discussed and recommendations are made.

Insecta is the most diversified animal group, which comprises more than a half of eukaryotic species. Its massive adaptive radiation is most frequently attributed to an origin of insect's wings and flapping flight. Due to lack of transitional forms in fossil record it is impossible to study directly these procedures but only in a theoretical approach only. In this thesis the origin of insect wings is considered in two ways - in evolutionary way, when the points of interest are selection pressures and evolutionary advantages for insects with proto-wings, and a morphological way, when objects of study are structures that preceded wings and developmental modules allowing this event. The present thesis contains review of relevant published hypothesis dealing with evolutionary and morphological origin of insect wings.

Many attempts to resolve the phylogenetic relationships of higher groups of insects have been made based on both morphological and molecular evidence; nonetheless, most of the interordinal relationships of insects remain unclear or are controversial. As a new approach, in this study we sequenced three nuclear genes encoding the catalytic subunit of DNA polymerase delta and the two largest subunits of RNA polymerase II from all insect orders. The predicted amino acid sequences (In total, approx. 3500 amino acid sites) of these proteins were subjected to phylogenetic analyses based on the maximum likelihood and Bayesian analysis methods with various models. The resulting trees strongly support the monophyly of Palaeoptera, Neoptera, Polyneoptera, and Holometabola, while within Polyneoptera, the groupings of Isoptera/“Blattaria”/Mantodea (Superorder Dictyoptera), Dictyoptera/Zoraptera, Dermaptera/Plecoptera, Mantophasmatodea/Grylloblattodea, and Embioptera/Phasmatodea are supported. Although Paraneoptera is not supported as a monophyletic group, the grouping of Phthiraptera/Psocoptera is robustly supported. The interordinal relationships within Holometabola are well resolved and strongly supported that the order Hymenoptera is the sister lineage to all other holometabolous insects. The other orders of Holometabola are separated into two large groups, and the interordinal relationships of each group are (((Siphonaptera, Mecoptera), Diptera), (Trichoptera, Lepidoptera)) and ((Coleoptera, Strepsiptera), (Neuroptera, Raphidioptera, Megaloptera)). The sister relationship between Strepsiptera and Diptera are significantly rejected by all the statistical tests (AU, KH and wSH), while the affinity between Hymenoptera and Mecopterida are significantly rejected only by AU and KH tests. Our results show that the use of amino acid sequences of these three nuclear genes is an effective approach for resolving the relationships of higher groups of insects.

The most primitive known wing articulation and wing folding in the Pterygota occurs in the extinct Palaeoptera the Diaphanopterodea. The oldest Diaphanopterodea Namurodiapha sippelorum n.gen., n.sp. (Namurodiaphidae n.fam.) is described from the early Late Carboniferous (Namurian B) of Hagen-Vorhalle, Ruhr area, West Germany. Unlike other Palaeoptera, the Diaphanopterodea show similar apomorphic venational features and parallel evolutionary trends in wing evolution, as in the unrelated Neoptera. This is explained (i) by convergence caused by the wing folding present in both Neoptera and Diaphanopterodea but absent in the rest of the Palaeoptera, and (ii) by a progressive diminution in size which affected the diaphanopterid and neopterous wing venation in a similar way. The wing articulation and the evolution of wing folding in the earliest known Palaeoptera and Neoptera are examined.

Phylogenies of major groups of insects based on both morphological and molecular data have sometimes been contentious, often lacking the data to distinguish between alternative views of relationships. This paucity of data is often due to real biological and historical causes, such as shortness of time spans between divergences for evolution to occur and long time spans after divergences for subsequent evolutionary changes to obscure the earlier ones. Another reason for difficulty in resolving some of the relationships using molecular data is the limited spectrum of genes so far developed for phylogeny estimation. For this latter issue, there is cause for current optimism owing to rapid increases in our knowledge of comparative genomics. At least some historical patterns of divergence may, however, continue to defy our attempts to completely reconstruct them with confidence, at least using current strategies.

We determined DNA sequences of SSU rRNA genes in twenty-nine polyneopteran insect species and aligned these with homologues from eight other insects. In a phylogenetic analysis we recovered the classic divisions of Palaeoptera and Neoptera, with the latter divided into monophyletic Paraneoptera and Polyneoptera. The polyneopterans divided into three lineages: one includes the Grylloblattodea, Dermaptera and Plecoptera, the second contains the Blattodea, and the third (Orthopteroidea sensu Hennig) contains the Embiidina, Phasmida, and Orthoptera, in that order. The monophyly of the Orthoptera is supported by the analyses, as is the separation between taxa from its suborders Caelifera and Ensifera. The Caelifera are not always supported as a monophyletic group; the basal Tridactyloidea are separated from the rest of the Caelifera in some analyses. Inside of Tridactyloidea, the Acridoidea, Pamphagoidea, Pneumoroidea and Trigonopterygoidea are always recovered as a monophyletic group. We also examined the basal orthopteran relationships, with the specific aim of assessing the antiquity of the Ensifera. Character state reconstructions indicated that the ancestral ensiferan sequence is very similar to the ancestral orthopteran sequence. However, likelihood ratio tests rejected the null hypothesis of a molecular clock and we conclude that a change in substitution rate has occurred within the Orthoptera and several of the other polyneopteran orders. Similar observations have been made in holometabolous insects, suggesting that variation in substitution rate is a general feature of insect nuclear rRNA evolution.

There are two main competing hypotheses concerning the basal pterygote dichotomy. The first was proposed by Martynov (1925) and has been since widely supported (Rohdendorf, 1962; Boudreaux, 1979; Kristensen, 1981; Arnett, 1985; Carpenter, 1992; CSIRO, 1992). Currently, it is being most vigorously championed by Kukalova-Peck (1978–1992). This hypothesis infers that the main pterygote dichotomy separates Palaeoptera and Neoptera. The alternative hypothesis is mine (Rasnitsyn, 1976, 1980; Rohdendorf and Rasnitsyn, 1980). It claims that the basic pterygote dichotomy divides the Subclass Scarabaeona (= Pterygota) into Infraclasses Scarabaeones and Gryllones [the reasons for employing these names for higher taxa are explained in Rohdendorf (1977) and Rasnitsyn (1982, 1996)].

The objective of this paper is to show that the relationships between arthropodan higher taxa are most reliably revealed by ‘basal’ arthropodan structures, such as head and body segmentation, and leg-derived appendages (mouthparts, legs, genitalia, wings, and their articulations). For reliable assessment, the character transformations should be compared throughout all arthropodan groups, extinct and extant. Phylogeny of the higher taxa (Subphyla, Classes, Orders, and Superfamilies) has been mainly approached in two different ways. In this paper I loosely term these approaches the ‘restrictive’ and ‘historical’, respectively.

Phylogeny is evolutionary interrelationship expressed in terms of recency of common ancestry. The elaboration of the theoretical framework of phylogenetic systematics ("cladistics") by the Hennig school [(e.g. 34, 35); for an introduction to later developments see (5)] has led to an upsurge of interest in reconstruction of phylogenies and has proved particularly stimu­ lating for inquiries into concepts of interrelationships of higher categories. This review is devoted to a treatment of the phylogeny of extant orders of insects and their closest relatives. Palaeozoic hexapods are reviewed by Wootton in this volume. The "ordinal" level has been fixed largely by convention within each major group in the Animal Kingdom. The orders recognized here are presented in Figure 1. These taxa are obviously not equivalent by any criteria, but at least it can be argued that they are all monophyletic entities. A comprehensive treatise on the phylogeny of higher hexapod categories, including lengthy discussions of previous hypotheses, was published in 1969 by Hennig (35). Hennig's views were subsequently critically assessed by Kristensen (43) with reference to a substantial amount of additional evi­ dence. These two works provide extensive bibliographies and are referred to repeatedly throughout this review. Emphasis is laid on a presentation of current views, and particular consideration is given to the numerous new proposals made in a thought-provoking, recent book by Boudreaux (15).

Insects are generally considered to be rare in the Upper Carboniferous Coal Measures. However, recent work in the Westphalian D of SW England suggests that many have been overlooked in the past. This is because wings, which are the most characteristic insect fossils, may be mistaken for detached ‘fern’ pinnules, which are much more common. The resemblance may be functional convergence rather than leaf-mimicry. The earliest members of the class Insecta in the strict sense occur in the Upper Carboniferous. Eleven major divisions or orders are represented in the Coal Measures of which only four are still living. Primitively wingless insects (Archaeognatha) are present, relatives of familiar living insects such as the silverfish. There are numerous winged insects, some of which could fold their wings (Neoptera) and others which could not (Palaeoptera). Palaeopterous insects were more diverse than today. They include three extinct orders (Palaeodictyoptera, Megasecoptera, Diaphanopterodea) which were probably plant suckers like present clay bugs. Other extinct palaeopterous insects (order Protodonata) were probably aerial predators like modern dragonflies, and included some of the largest insects of all time (‘giant dragonflies’). By far the most common neopterous insects were cockroaches (Blattodea) which outnumber all other insects in the Upper Carboniferous. This abundance is perhaps less surprising when one considers the general picture of the coal forests as warm, humid, and rich in organic matter. Another important neopterous group was the extinct order Protorthoptera, which is probably related only in part to extant Orthoptera (grasshoppers, crickets and locusts). There is no evidence at this time of higher insects such as flies, fleas, beetles, moths and butterflies, ants, bees and wasps.

The oldest known odonatoid wings are described from the Namurian of Argentina: Eugeropteron lunatum Riek n.g. et sp. and Geropteron arcuatum Riek n.g. and sp. (Meganisoptera: Meganeurina: Eugeropteridae n. fam.). The wings are generalized and support a reinterpretation of the venation of living Odonata as being fully homologous to that of other pterygotes and closely related to Ephemeropteroidea, but different from Neoptera. Therefore, Paleoptera is a valid phylogenetic unit, and Odonatoidea and Ephemeropteroidea are sister groups.

The most primitive known pterygote terga, wing articulation, wings, and upper leg segments with exites, occur in gigantic Upper Carboniferous Paleodictyoptera, Homoiopteridae. Fossil features are used as clues for reinterpreting some structures connected with flight in modern Pterygota. Brief comparisons with Paleozoic Diaphanopterodea, Permothemistida, Ephemeroptera, Protodonata, and with living Ephemeroptera, Odonata, and Neoptera are given. The wing articulation of all Pterygota is derived from a common ancestral ground plan based upon features present in fossils. The ancestral wings were articulated by a closely packed band of multiple sclerites which were hinged to eight lateral tergal lobes, and aligned with eight pairs of wing veins. The axillaria of Neoptera and axillary plates of Paleoptera are composite sclerites, which originated by fusion of several sclerites of the original band. Articular patterns of Paleoptera and Neoptera evolved differently and show (i) the presence or absence of a gap at the cubital level, (ii) the presence or absence of a turning–pivoting composite third axillary sclerite (3Ax), and (iii) a different composition of all composite sclerites. Gliding and wing folding adaptations within the articular band are discussed. A new fossil-based interpretation of veinal stems, veinal sectors, and of their fluting near the wing base is offered. An underlying symmetry of thoracic tergal sulci, articular sclerites, and wing venation seems to point to a nearly symmetrical, nonflying pro-wing engaged in up-and-down movement. Evidence of articulation in Paleozoic nymphal wings and evolution of metamorphic instars are examined. Pitfalls of paleoentomological work are discussed. Criteria for major divisions of Pterygota are reassessed. It is hypothesized that the wing originated from the first segment (epicoxa) of the euarthropodan upper leg and its exite. An epicoxal podomere became incorporated into the body wall and broke up into an articular ring of dorsal and ventral sclerites, and an epicoxal exite flattened and became a pro-wing. The pro-wing originally operated on a row of pivots from the epicoxa and subcoxa (pleuron) and became mobilized by epicoxal leg musculature.