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1.
2.
The small subunit of nuclear ribosomal RNA (SSU nrRNA), whose sedimentation is mostly 18S in eukaryotes, is considered a relatively conservative marker for resolving phylogenetic relationship at the order level or higher. Length variation in SSU nrDNA is common, and can be rather large in some groups. In studies of Hexapoda phylogeny, the SSU nrDNA has been repeatedly used as a marker. Sternorrhyncha has been rarely included. The lengths of SSU nrDNAs of sternorrhynchids, the basal group of Hemiptera identified in the previous study are 0.3-0.6 kb longer than the usual ones in Hexapoda (1.8-1.9 kb). To use the entire SSU nrDNA sequences or the length-variable parts could cause alignment trouble and therefore affect phylogenetic results, as shown in this study of Euhemiptera phylogeny. Two problems are particularly noticeable. One is that two hyper-variable regions flanking a short length-conservative region could become overlapped in the alignment. This will destroy the positional homology over a larger range. The other is that, when a base pair in a stem of the secondary structure is located near the length-variable regions (LVRs), the simultaneous positional homology of these two bases in the pair is always lost in the alignment results. In this study, the secondary structure model of Hexapoda SSU nrRNA was slightly adjusted and the LVR distributions in it were finely positioned. The noise caused by the hyper LVRs was eliminated and the simultaneous homology for the paired bases was recovered based on the secondary structure model. These corrections improved the quality of the data matrix and hence improved the resolving behavior of the algorithm used. This study provided more convincing evidence for resolving the Euhemiptera suborders phylogeny as (Archaeorrhyncha+(Clypeorrhyncha+(Coleorrhyncha+Heteroptera))). This result provided a more solid background for outgroup determination according to the phylogenetic studies inside each suborder. The problems caused by LVRs have seldom been well addressed. As phylogenetic reconstruction depends more on the data matrix itself than on the algorithm, and length variation of SSU/LSU rRNA exists more or less in any group, it is necessary to closely investigate the effect of rRNA length variation on alignment and phylogenetic reconstruction in more groups.  相似文献   

3.
Classically, Hemiptera is comprised of two suborders: Homoptera and Heteroptera. Homoptera includes Cicadomorpha, Fulgoromorpha and Sternorrhyncha. However, according to previous molecular phylogenetic studies based on 18S rDNA, Fulgoromorpha has a closer relationship to Heteroptera than to other hemipterans, leaving Homoptera as paraphyletic. Therefore, the position of Fulgoromorpha is important for studying phylogenetic structure of Hemiptera. We inferred the evolutionary affiliations of twenty-five superfamilies of Hemiptera using mitochondrial protein-coding genes and rRNAs. We sequenced three mitogenomes, from Pyrops candelaria, Lycorma delicatula and Ricania marginalis, representing two additional families in Fulgoromorpha. Pyrops and Lycorma are representatives of an additional major family Fulgoridae in Fulgoromorpha, whereas Ricania is a second representative of the highly derived clade Ricaniidae. The organization and size of these mitogenomes are similar to those of the sequenced fulgoroid species. Our consensus phylogeny of Hemiptera largely supported the relationships (((Fulgoromorpha,Sternorrhyncha),Cicadomorpha),Heteroptera), and thus supported the classic phylogeny of Hemiptera. Selection of optimal evolutionary models (exclusion and inclusion of two rRNA genes or of third codon positions of protein-coding genes) demonstrated that rapidly evolving and saturated sites should be removed from the analyses.  相似文献   

4.
Hemipterans are characterized by the absence of the peritrophic membrane, an anatomical structure that envelopes the food bolus in the majority of insects. However, the microvillar membranes of many hemipteran midgut cells are not in direct contact with the food bolus, due to the existence of the so-called perimicrovillar membrane (PMM), which covers the microvilli extending into the gut lumen with dead ends. alpha-Glucosidase is a biochemical marker for PMM in the seed sucker bug Dysdercus peruvianus (Heteroptera: Pyrrhocoridae). In this article, we report that adults of the major hemipteran infra-orders (Sternorrhyncha, Auchenorrhyncha, and Heteroptera) have PMM and a major membrane bound alpha-glucosidase, which has properties similar to those of the D. peruvianus enzyme. A polyclonal antibody raised against the enzyme of D. peruvianus recognized the enzymes present in PMM from the above-mentioned hemipteran groups. The same antibody was also able of recognizing perimicrovillar alpha-glucosidase from thrips. No PMM nor membrane-bound alpha-glucosidase were found in Psocoptera and Phthiraptera midguts. This suggests that PMM and PMM-bound-alpha-glucosidase are widespread among insects of the order Hemiptera and of the sister order Thysanoptera. The data support the hypothesis that PMM may have originated in the Condylognatha (Paraneopteran taxon including Hemiptera and Thysanoptera) ancestral stock and are associated with plant sap feeding.  相似文献   

5.
Phylogenetic relationships among three paraneopteran clades (Psocodea, Hemiptera and Thysanoptera) were analysed based on the morphology of forewing base structure. Monophyly of Paraneoptera was supported by nine autapomorphies, monophyly of Condylognatha (= Thysanoptera + Hemiptera) by two autapo‐ morphies, monophyly of Thysanoptera by five autapomorphies and monophyly of Hemiptera by one autapomorphy. Thus, (Psocodea + (Thysanoptera + Hemiptera)) were proposed to be the phylogenetic relationships within Paraneoptera. A homoplastic similarity of the third axillary sclerite was observed between Thysanoptera and Heteroptera, and a possible evolutionary factor providing this homoplasy was discussed. The present analysis also suggested a monophyletic Auchenorrhyncha, and reduction of the proximal median plate was considered as an autapomorphy of this clade.  相似文献   

6.
The present paper describes the sensory structures on the apical segment of the labium in fifteen fulgoromorphan families (Hemiptera: Fulgoromorpha), using the scanning electron microscope. Thirteen morphologically distinct types of sensilla are identified: five types of multiporous sensilla, four types of uniporous sensilla and four types of nonporous sensilla. Three subapical sensory organ types are also recognized, formed from one to several sensilla, each characteristic of a family group. Sensilla chaetica (mechanoreceptive sensilla) fall into three categories dependent on length and are numerous and evenly distributed on the surface of the labium except where they occur on specialized sensory fields. The planthopper morphological ground plan is represented by two apical pair of sensory fields (dorsal and ventral) on which 11 dorsal pairs of sensilla (10 peg-like pairs + 1 specialized pair dome or cupola-like) and 2 ventral pairs of sensilla basiconica occur. Two main patterns (cixiid and issid) together with more specialized ones (derbid, lophopid, flatid and fulgorid) are reported. Disparity and diversity of the sensory structures are analyzed from a taxonomic and functional perspective. A gustatory function is provided for several chemoreceptive labial sensilla, as in the antennal flagellum sensilla in some other Hemiptera. This represents a more recently evolved function for the planthopper labium. Finally, further lines of study are suggested for future work on the phylogeny of the group based on the studied characters.  相似文献   

7.
Molecular phylogeny of the homoptera: a paraphyletic taxon   总被引:11,自引:0,他引:11  
Homoptera and Heteroptera comprise a large insect assemblage, the Hemiptera. Many of the plant sap-sucking Homoptera possess unusual and complex life histories and depend on maternally inherited, intracellular bacteria to supplement their nutritionally deficient diets. Presumably in connection with their diet and lifestyles, the morphology of many Homoptera has become greatly reduced, leading to major controversies regarding the phylogenetic affiliations of homopteran superfamilies. The most fundamental question concerns whether the Homoptera as a whole are monophyletic. Recent studies based on morphology have argued that the Homoptera Sternorrhyncha (Aphidoidea, Coccoidea, Psylloidea, Aleyrodoidea) is a sister group to a group comprising the Homoptera Auchenorrhyncha (Fulgoroidea, Cicadoidea, Cercopoidea, Cicadelloidea) and the Heteroptera, making the Homoptera paraphyletic. We sequenced the 5 580-680 base pairs of small-subunit (18S) ribosomal DNA from a selection of Homoptera, Hemiptera, and their putative outgroups, the Thysanoptera and Psocoptera, to apply molecular characters to the problem of Homoptera phylogeny. Parsimony, distance, maximum-likelihood, and bootstrap methods were used to construct trees from sequence data and assess support for the topologies produced. Molecular data corroborate current views of relationships within the Sternorrhyncha and Auchenorrhyncha based on morphology and strongly support the hypothesis of homopteran paraphyly as stated above. In addition, it was found that Homoptera Sternorrhyncha have extra, GC-rich sequence concentrated in a variable region of the 18S rDNA, which indicates that some unique evolutionary processes are occurring in this lineage.Correspondence to: C.D. von Dohlen  相似文献   

8.
Phylogenetic relationships among the Neotropical cichlid subfamily Geophaginae were examined using 136 morphological characters and a molecular dataset consisting of six mitochondrial and nuclear genes. Topologies produced by morphological and combined data under parsimony were contrasted, congruence among different partitions was analysed, and potential effects of character incongruence and patterns of geophagine evolution on phylogenetic resolution are discussed. Interaction of morphological and molecular characters in combined analysis produced better resolved and supported topologies than when either was analysed separately. Combined analyses recovered a strongly supported Geophaginae that was closely related to Cichlasomatinae. Within Geophaginae, two sister clades included all geophagine genera. Acarichthyini (Acarichthys+Guianacara) was sister to the ‘B clade’, which contained the ‘Geophagus clade’ (‘Geophagussteindachneri+Geophagus sensu stricto, and both sister to Gymnogeophagus) as sister to the ‘Mikrogeophagus clade’ (Mikrogeophagus+‘Geophagusbrasiliensis), and in turn, the Geophagus and Mikrogeophagus clades were sister to the crenicarine clade (Crenicara+Dicrossus) and Biotodoma. The second geophagine clade included the ‘Satanoperca clade’ (Satanoperca+Apistogramma and Taeniacara) as sister to the ‘Crenicichla clade’ (Crenicichla+Biotoecus). Several lineages were supported by unique morphological synapomorphies: the Geophaginae + Cichlasomatinae (5 synapomorphies), Geophaginae (1), Crenicichla clade (3), crenicarine clade (1), the sister relationship of Apistogramma and Taeniacara (4) and of Geophagus sensu stricto andGeophagussteindachneri (1), and the cichlasomine tribe Heroini (1). Incorporation of Crenicichla in Geophaginae reconciles formerly contradictory hypotheses based on morphological and molecular data, and makes the subfamily the most diverse and ecologically versatile clade of cichlids outside the African great lakes. Results of this study support the hypothesis that morphological differentiation of geophagine lineages occurred rapidly as part of an adaptive radiation.  相似文献   

9.
The phylogenetic placement of the moss bugs (Insecta: Hemiptera: Coleorrhyncha) has been highly controversial. Many apparent morphological apomorphies support the close relationship between Coleorrhyncha and Heteroptera (=true bugs). However, a recent phylogenomic study strongly supported a sister group relationship between Coleorrhyncha and Auchenorrhyncha (planthoppers, leafhoppers, treehoppers, spittlebugs, and cicadas). To test these two alternative hypotheses, we examined the fore‐ and hindwing base structure of the only known extant macropterous species of Coleorrhyncha using binocular and confocal laser scanning microscopes and analyzed the data selected from the wing base phylogenetically. When full morphological data including the wing base characters were analyzed, the sister group relationship between Coleorrhyncha + Heteroptera was supported, agreeing with previous consensus based on morphology. In contrast, when only wing base characters were analyzed separately, the clade Coleorrhyncha + Auchenorrhyncha was recovered, in agreement with the result from the phylogenomic study. The membranous condition of the proximal median plate in the forewing was identified as a potential synapomorphy of the latter grouping, and the absence of the tegula was excluded as a potential synapomorphy of Coleorrhyncha and Heteroptera.  相似文献   

10.
The newly sequenced complete mitochondrial genome of the brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is a circular molecule of 16,518 bp with a total A+T content of 76.4% and two extensive repeat regions in A+T rich region. Nucleotide composition and codon usage of H. halys are about average when compared with values observed in 19 other published hemipteran mitochondrial genomes. Phylogenetic analyses using these 20 hemipteran mitochondrial genomes support the currently accepted hypothesis that suborders Heteroptera and Auchenorrhyncha form a monophyletic group. The mitochondrial gene arrangements of the 20 genomes are also consistent with our results.  相似文献   

11.
Hemiptera is the largest order in Paraneoptera and the fifth largest in Insecta. Disputes about hemipteran phylogeny have concerned the monophyly of Auchenorrhyncha and relationships between the suborders Fulgoromorpha, Cicadomorpha, Coleorrhyncha and Heteroptera. In a phylogenomic study of Hemiptera, we add two new mitochondrial genomes of Peloridiidae (Coleorrhyncha) to those reported in GenBank, to complete the taxon sampling of all suborders. We used two types of data – amino acid sequences and nucleotides of various combinations between protein coding genes, tRNAs and rRNAs – to infer the phylogeny of Hemiptera. In total 27 taxa of Paraneoptera were sampled, 24 of them being hemipterans. Bayesian inference, maximum likelihood and maximum parsimony analyses were employed. The relationship of Cicadomorpha + Heteroptera is always stable in the results with different combinations between data types and phylogenetic methods, but our results challenge the monophyly of ‘Homoptera’ and Auchenorrhyncha. In evaluating the relative contribution of each gene, the phylograms generated by single genes CO1, ND1, ND2, ND4 and ND5, respectively, closely matched the tree yielded by the combined datasets. In light of the taxon‐sampling sensitivity of trees based on mitochondrial genomes, the results need to be tested with further data from nuclear genes.  相似文献   

12.
Numerous physiological processes in insects are tightly regulated by neuropeptides and their receptors. Although they form an ancient signaling system, there is still a great deal of variety in neuropeptides and their receptors among different species within the same order. Neuropeptides and their receptors have been documented in many hemipteran insects, but the differences among them have been poorly characterized. Commercial grapevines worldwide are plagued by the bug Daktulosphaira vitifoliae (Hemiptera: Sternorrhyncha). Here, 33 neuropeptide precursors and 48 putative neuropeptide G protein-coupled receptor (GPCR) genes were identified in D. vitifoliae. Their expression profiles at the probe and feeding stages reflected potential regulatory roles in probe behavior. By comparison, we found that the Releasing Hormone-Related Peptides (GnRHs) system of Sternorrhyncha was differentiated from those of the other 2 suborders in Hemiptera. Independent secondary losses of the adipokinetic hormone/corazonin-related peptide receptor (ACP) and corazonin (CRZ) occurred during the evolution of Sternorrhyncha. Additionally, we discovered that the neuropeptide signaling systems of Sternorrhyncha were very different from those of Heteroptera and Auchenorrhyncha, which was consistent with Sternorrhyncha's phylogenetic position at the base of the order. This research provides more knowledge on neuropeptide systems and sets the groundwork for the creation of novel D. vitifoliae management strategies that specifically target these signaling pathways.  相似文献   

13.
A morphological phylogenetic analysis of the tribe Tropiduchini (Hemiptera: Tropiduchidae) is provided for 21 genera among the 26 recognized, including the new genus Oechalinella Wang gen.n. , with a new species Oechalinella bifasciata Wang sp.n. Monophyly of the tribe is well supported by synapomorphies derived from the male genitalia. The strict consensus supports two subclades: ((Montrouzierana + Thymbra) + Thaumantia+) as sister to the clade (Leptovanua + (Vanua + Varma+) + Daradacella+). In the first subclade, the clade (Montrouzierana + Thymbra), distributed in New Caledonia and Papua New Guinea, is well supported by three synapomorphies based on the tegmina, while the Thaumantia+ group is characterized by the conformation of the anal tube and male gonostyli, and distributed from Malesia to Papuasia and in Central Africa. The second subclade is largely distributed from China to Malesia, Papuasia, Southwestern and the Northwestern Pacific islands. The position of the genus Leptovanua remains uncertain. The Varma+ clade is recovered in all analyses. Implied weighting analysis placed the Varma+ lineage as sister to all other genera forming a new group (Leptovanua+ + ((Montrouzierana + Thymbra) + Thaumantia+)). Fennah's definition of Tropiduchini is reviewed according to the phylogenetic results and an identification key to all genera is provided with a referenced synopsis of their distribution. Globally, Tropiduchini exhibits an inter‐tropical latitudinal distribution and a paradoxical bimodal longitudinal distribution pattern in continental Africa, South‐east Asia and the Pacific islands. Distribution data concern nearly 80% of insular taxa. The phylogenetical results suggest that: (i) the tribe originates from continental China; (ii) it evolved mainly from Papuasia by stepping‐stone colonization events, promoting subsequent insular speciation; and (iii) its evolution has mainly been directed by dispersion versus vicariance.  相似文献   

14.
Relationships within Chilopoda (centipedes) are assessed based on 222 morphological characters, complete 18S rRNA sequences for 70 chilopod terminals, the D3 region of 28S rRNA for 65 terminals, 16S rRNA sequences for 54 terminals and cytochrome c oxidase subunit I sequences for 45 terminals. Morphological and molecular data for seven orders of Diplopoda are used to root cladograms for Chilopoda. Analyses use direct character optimization for 15 gap and substitution models. The Pleurostigmophora and Epimorpha s.l. hypotheses are largely stable to parameter variation for the combined data; the latter clade is formalized as the new taxon Phylactometria. The combined data include parameter sets that support either the monophyly of Epimorpha s.str. (=Scolopendromorpha + Geophilomorpha) or Craterostigmus + Geophilomorpha; the former derives its support from morphology and the nuclear ribosomal genes. Monophyly of Lithobiomorpha and the sister group relationship between Lithobiidae and Henicopidae are stable for morphological and combined data, and are also resolved for the molecular data for 14 of 15 parameter sets. The fundamental split in Scolopendromorpha is between Cryptopidae and Scolopendridae sensu Attems. Blind scolopendromorphs unite as a clade in most molecular and combined analyses, including those that minimize incongruence between data partitions. Geophilomorpha divides into Placodesmata and Adesmata under nine of 15 explored parameter sets.  相似文献   

15.
External and internal head structures of Coleorrhyncha, a key-taxon within the Hemiptera, are described in detail and documented using modern techniques. The main focus is on Hackeriella veitchi, but two additional representatives of the Gondwanan relict group were also examined, and also head structures of Enicocephalidae, a member of a potentially basal heteropteran lineage. Features were compared to those documented in literature for the Sternorrhyncha, Auchenorrhyncha, and Heteroptera. Coleorrhyncha are characterized by highly modified head structures and correspondingly an entire series of autapomorphies, such as for instance a strongly flattened head capsule with fenestrations. However, they also display features that are likely plesiomorphic compared to members of other hemipteran groups. These include the almost complete tentorium and the lack of the gula. The sistergroup relationship between Coleorrhyncha and Heteroptera is well supported by cephalic features. Potential synapomorphies are the presence of a distinct mandibular sulcus, the reduced number of antennomeres, the absence of clasping organs in the labial groove, coiled accessory salivary ducts, the presence of a small cervical muscle M1a (M. pronotopostoccipitalis medialis), the presence of a second mandibular promotor M14 (M. zygomaticus mandibulae), the presence of M28 (M. verticopharyngalis), and M30 (M. frontobuccalis posterior).  相似文献   

16.
Parasitoid wasps of the subfamily Telenominae (Hymenoptera: Platygastroidea, Platygastridae) develop as immatures within the eggs of other insects (Lepidoptera, Hemiptera, Diptera and Neuroptera). Rearing records indicate that individual species are restricted to attack hosts within only one of these four main groups. We conducted a phylogenetic analysis of the group using sequence data from multiple genes (18S, 28S, COI, EF‐1α) to assess the pattern of shifts among host groups and to test the monophyly of and relationships among genera and species‐groups. Telenominae sensu Masner—that is, including only the nominate tribe Telenomini—is not monophyletic. Representatives of the Psix group of genera (Psix Kozlov & Lê and Paratelenomus Dodd) form a monophyletic group that is sister to Gryon Haliday (Scelioninae: Gryonini) and are excluded from the subfamily. The remaining telenomines are monophyletic. The genus Phanuromyia Dodd and the crassiclava group of Telenomus Haliday, both recorded as parasitoids of planthopper eggs (Hemiptera: Auchenorrhyncha, Fulgoroidea), form a monophyletic group that is sister to all other telenomines exclusive of the Psix group. Twenty‐nine species of the crassiclava and aradi groups of Telenomus are transferred to Phanuromyia as new combinations. Basal elements of the remaining species are all in groups reared from the eggs of true bugs (Heteroptera), primarily the stink bugs (Pentatomoidea) and seed bugs (Lygaeoidea). A shift to parasitism of lepidopteran eggs evolved within a single clade, occurring either one or two times. From this clade a small group of species, the Telenomus tabanivorus group, subsequently shifted to parasitism of egg masses of true flies (Tabanidae and Stratiomyiidae). Aholcus Kieffer and Platytelenomus Dodd both belong to the clade of lepidopteran parasitoids and are considered as junior synonyms of Telenomus (new synonymy for Aholcus). The monophyletic status of the two core genera, Telenomus and Trissolcus could not be resolved using these data. The phylogenetic pattern of host shifts suggests comparisons among taxa that may be fruitful in elucidating mechanisms by which parasitoids locate their hosts, the proximate factors that determine the host range, and the changes in these factors that influence host changes.  相似文献   

17.
Phylogeny of the flyingfish family Exocoetidae (Teleostei, Beloniformes)   总被引:2,自引:0,他引:2  
The phylogeny of the flyingfish family Exocoetidae is studied cladistically, using 41 morphological characters encompassing early life history, and external and internal features. The monophyly of the family is supported by 10 synapomorphies. Within the family,Oxyporhamphus is the sister group to all other genera, the monophyly of the latter being defined by 10 synapomorphies.Fodiator is the sister group of genera characterized by the presence of chin barbels in juveniles.Parexocoetus is the sister group ofExocoetus, Cypselurus, Prognichthys andHirundichthys, the latter being defined by four synapomorphies. In the latter group,Exocoetus is the sister group of the other three genera. The phylogeny of the Exocoetidae is characterized by the stepwise upgrading of gliding capability, with sequential modifications of the caudal, pectoral and pelvic fins. The subfamily Oxyporhamphinae is resurrected.  相似文献   

18.
Scale insects (Hemiptera: Sternorrhyncha: Coccoidea) are a speciose and morphologically specialized group of plant-feeding bugs in which evolutionary relationships and thus higher classification are controversial. Sequences derived from nuclear small-subunit ribosomal DNA were used to generate a preliminary molecular phylogeny for the Coccoidea based on 39 species representing 14 putative families. Monophyly of the archaeococcoids (comprising Ortheziidae, Margarodidae sensu lato, and Phenacoleachia) was equivocal, whereas monophyly of the neococcoids was supported. Putoidae, represented by Puto yuccae, was found to be outside the remainder of the neococcoid clade. These data are consistent with a single origin (in the ancestor of the neococcoid clade) of a chromosome system involving paternal genome elimination in males. Pseudococcidae (mealybugs) appear to be sister to the rest of the neococcoids and there are indications that Coccidae (soft scales) and Kerriidae (lac scales) are sister taxa. The Eriococcidae (felt scales) was not recovered as a monophyletic group and the eriococcid genus Eriococcus sensu lato was polyphyletic.  相似文献   

19.
Mammalodon colliveri is an unusual toothed archaic mysticete (Cetacea) from the Upper Oligocene Jan Juc Formation of south‐east Australia. The morphology of the holotype skull and postcrania are described in detail. Superimposed on the generally plesiomorphic archaeocete‐like morphology of Mammalodon are subtle mysticete synapomorphies. Derived features of Mammalodon include a short and bluntly rounded rostrum, reduced premaxillae, and anterodorsally directed orbits. Within Mysticeti, this suite of features is unique. The aberrant rostral morphology of Mammalodon suggests specialization for suction feeding. Janjucetus hunderi is placed in an expanded family Mammalodontidae. Phylogenetic analysis corroborates the monophyly of Basilosauridae, Neoceti, Odontoceti, and Mysticeti, and yields a novel hypothesis of toothed mysticete relationships: a basal clade of undescribed toothed mysticetes from South Carolina, a Llanocetidae + Mammalodontidae clade, and monophyletic Aetiocetidae are posited as successive sister taxa to edentulous baleen whales (Chaeomysticeti). Toothed archaic mysticetes clearly employed diverse prey capture strategies, with exaptations for filter feeding evolving sequentially in stem group Mysticeti. A stratigraphically calibrated phylogeny implies that the initial diversification of Mysticeti occurred during the Late Eocene. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 158 , 367–476.  相似文献   

20.
A cladistic investigation of the phylogenetic relationships among the three extant anteater genera and the three undoubted extinct myrmecophagid genera is performed based upon osteological characteristics of the skull and postcranial skeleton. One hundred seven discrete morphological characters are analyzed using the computer program PAUP. Characters are polarized via comparison to the successive xenarthran outgroups Tardigrada (represented by the living sloth Bradypus) and Cingulata (represented by the recent armadillos Dasypus and Euphractus). The analysis results in a single most-parsimonious tree (TL = 190, CI = 0.699, RI = 0.713). The tree corroborates the monophyly of the subfamilies Cyclopinae and Myrmecophaginae, the former including the extant Cyclopes and the Pliocene genus Palaeomyrmidon. Within the Myrmecophaginae the Miocene genus Protamandua is the sister taxon to a clade including the remaining three genera. The recent Tamandua is in turn the sister taxon to the extant Myrmecophaga plus the Pliocene genus Neotamandua. Contrary to the suggestions of recent authors, weak support is provided for the taxonomic distinctiveness of the latter genus from the recent Myrmecophaga. The monophyly of the Myrmecophagidae is supported by 15 unequivocal synapomorphies. The monophyly of the Cyclopinae and Myrmecophaginae is supported by 3 and 13 unambiguous synapomorphies, respectively. The enigmatic Eocene genus Eurotamandua, from the Messel fauna of Germany, is coded for the 107 morphological characters above and included in two subsequent PAUP analyses. The palaeanodont Metacheiromys is also added to these two analyses as a nonxenarthran outgroup to test for the possibility that Eurotamandua lies outside the Xenarthra. In the first analysis, Eurotamandua is constrained a priori to membership in the Vermilingua. The single most-parsimonious tree (TL = 224, CI = 0.618) that results places Eurotamandua as the sister group to the remaining anteater genera, contra Storch and Habersetzer's (1991) assignment of Eurotamandua to the vermilinguan subfamily Myrmecophaginae. Eurotamandua shares six unequivocal synapomorphies with other anteaters, including the absence of teeth and the presence of a lateral tuberosity on the fifth metatarsal. The remaining vermilinguans are united by 11 unequivocal synapomorphies, plus an additional 10 ambiguous synapomorphies. In the second analysis, the position of Eurotamandua is unconstrained. The resulting single most-parsimonious tree (TL = 219, CI = 0.632) places Eurotamandua outside Vermilingua as the sister group to the Pilosa (Vermilingua plus Bradypus). The monophyly of this node is supported by four unambiguous synapomorphies in the unconstrained analysis. Further manipulation of this second analysis shows that placement of Eurotamandua as the sister group to the Xenarthra or to the Palaeanodonta adds three steps to the shortest tree but is more parsimonious than its placement as a sister group to the Vermilingua is the previous analysis. The addition of pangolins to the analysis does little to alter the major phylogenetic conclusions of the study. The allocation of Eurotamandua to the Xenarthra, but as a sister group to the Pilosa, is a novel arrangement which leaves open the biogeographic question of how a xenarthran reached Western Europe during the Eocene.  相似文献   

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