Evolutionary morphology of the circulatory system in Peracarida (Malacostraca; Crustacea)

We demonstrate that by formulating guidelines for evolutionary morphology the transparency, reproducibility, and intersubject testability of evolutionary hypotheses based on morphological data can be enhanced. The five main steps in our concept of evolutionary morphology are (i) taxon sampling, (ii) structural analysis, (iii) character conceptualization, (iv) phylogenetic analysis, and (v) evolutionary interpretation. We illustrate this concept on the example of the morphology of the circulatory organs in peracarid Malacostraca. The analysis is based on recently published accounts in which detailed structural analyses were carried out, and on the older literature. Detailed conceptualizations of 22 characters of the circulatory system are given for 28 terminals. In a further step these characters are included in a recently revised matrix, resulting in 110 characters. The resulting parsimony analysis yielded a single most parsimonious tree with a length of 309 steps. The most significant results are that Peracarida is monophyletic, Amphipoda is the sister taxon to the Mancoida sensu stricto, the relict cave‐dwelling taxa Thermosbaenacea, Spelaeogriphacea, and Mictocarididae form a monophylum and Tanaidacea is the sister group to a monophylum comprising Cumacea and Isopoda. The evolutionary analysis shows that the ground pattern features of the circulatory organs in Peracarida are a tubular heart extending through the whole thorax, a posterior aorta with lateral arteries, and a ventral vessel system. Important features within the Peracarida are the backward shift of the anterior border of the heart, the reduction of the ventral vessel system, and two patterns of cardiac arteries, one common to the amphipod and tanaidacean terminals, and one to the cumacean and isopod terminals. © The Willi Hennig Society 2009.     

The Tetraconata concept: hexapod-crustacean relationships and the phylogeny of Crustacea

A growing body of evidence indicates that Crustacea and Hexapoda are sister groups, rather than Hexapoda and Myriapoda. Some recent molecular data even suggest that Mandibulata is not monophyletic, with Myriapoda and Chelicerata instead being sister groups. Here, arguments for homology of the mandible throughout mandibulate arthropods and for a monophyletic Mandibulata will be presented, as well as arguments supporting the taxon Tetraconata (i.e. Crustacea + Hexapoda). The latter include molecular data (nuclear and mitochondrial ribosomal RNAs and protein coding genes), and morphological characters such as ommatidial structure, the presence of neuroblasts and a very similar axonogenesis of pioneer neurons. However, crustaceans are insufficiently sampled for the molecular data, and studies of neurogenesis are lacking for many crustacean taxa. Remipedia, Cephalocarida and Maxillopoda are particularly problematic. This is important for the entire problem, because monophyly of the Crustacea has not yet been proven beyond doubt and several molecular analyses suggest a paraphyletic Crustacea. Here, arguments for the monophyly of the Crustacea are reviewed and two alternatives for the relationships between the five higher taxa Remipedia, Cephalocarida, Maxillopoda, Branchiopoda and Malacostraca are discussed: the Entomostraca concept sensu Walossek with Malacostraca as sister group to Cephalocarida, Maxillopoda and Branchiopoda, and the Thoracopoda concept sensu Hessler with Cephalocarida, Branchiopoda and Malacostraca forming a monophylum.     

The ovary structure and oogenesis in the basal crustaceans and hexapods. Possible phylogenetic significance

Recent large-scale phylogenetic analyses of exclusively molecular or combined molecular and morphological characters support a close relationship between Crustacea and Hexapoda. The growing consensus on this phylogenetic link is reflected in uniting both taxa under the name Pancrustacea or Tetraconata. Several recent molecular phylogenies have also indicated that the monophyletic hexapods should be nested within paraphyletic crustaceans. However, it is still contentious exactly which crustacean taxon is the sister group to Hexapoda. Among the favored candidates are Branchiopoda, Malacostraca, Remipedia and Xenocarida (Remipedia + Cephalocarida). In this context, we review morphological and ultrastructural features of the ovary architecture and oogenesis in these crustacean groups in search of traits potentially suitable for phylogenetic considerations. We have identified a suite of morphological characters which may prove useful in further comparative studies.     

Polychaete phylogeny based on morphological data – a comparison of current attempts

Annelid phylogeny is one of the largest unresolved problems within the Metazoa. This is due to the enormous age of this taxon and also strongly influenced by the current discussion on the position of the Arthropoda, which traditionally is hypothesized to be the annelid sister taxon. Within the framework of recent discussions on the position of the Annelida, the ground pattern of this taxon is either a clitellate-like, parapodia-less dwelling organism or an organisms that resembles errant polychaetes in having parapodia and gills and probably being a predator. To solve this problem different attempts have been made in the past, cladistic analysis, scenario based plausibility considerations and a successive search for sister taxa base on isolated characters. These attempts are presented and critically discussed. There is at least strong support for the Annelida as wells as for several of its taxa above the level of traditional families; the monophyly of the Polychaeta, however, remains questionable. The term taxon is used here in the sense of group of things that share certain characteristics. Biological taxa are not necessarily monophyletic, although many of them turned out to be. In terms of phylogenetic systematics taxa should be monophyletic.     

The position of Cetacea within mammalia: phylogenetic analysis of morphological data from extinct and extant taxa

Knowledge of the phylogenetic position of the order Cetacea (whales, dolphins, and porpoises) within Mammalia is of central importance to evolutionary biologists studying the transformations of biological form and function that accompanied the shift from fully terrestrial to fully aquatic life in this clade. Phylogenies based on molecular data and those based on morphological data both place cetaceans among ungulates but are incongruent in other respects. Morphologists argue that cetaceans are most closely related to mesonychians, an extinct group of terrestrial ungulates. They have disagreed, however, as to whether Perissodactyla (odd-toed ungulates) or Artiodactyla (even-toed ungulates) is the extant clade most closely related to Cetacea, and have long maintained that each of these orders is monophyletic. The great majority of molecule-based phylogenies show, by contrast, not only that artiodactyls are the closest extant relatives of Cetacea, but also that Artiodactyla is paraphyletic unless cetaceans are nested within it, often as the sister group of hippopotamids. We tested morphological evidence for several hypotheses concerning the sister taxon relationships of Cetacea in a maximum parsimony analysis of 123 morphological characters from 10 extant and 30 extinct taxa. We advocate treating certain multistate characters as ordered because such a procedure incorporates information about hierarchical morphological transformation. In all most-parsimonious trees, whether multistate characters are ordered or unordered, Artiodactyla is the extant sister taxon of Cetacea. With certain multistate characters ordered, the extinct clade Mesonychia (Mesonychidae + Hapalodectidae) is the sister taxon of Cetacea, and Artiodactyla is monophyletic. When all fossils are removed from the analysis, Artiodactyla is paraphyletic with Cetacea nested inside, indicating that inclusion of mesonychians and other extinct stem taxa in a phylogenetic analysis of the ungulate clade is integral to the recovery of artiodactyl monophyly. Phylogenies derived from molecular data alone may risk recovering inconsistent branches because of an inability to sample extinct clades, which by a conservative estimate, amount to 89% of the ingroup. Addition of data from recently described astragali attributed to cetaceans does not overturn artiodactyl monophyly.     

Phylogenetic relationships and limb loss in sub-Saharan African scincine lizards (Squamata: Scincidae)

Skinks are the largest family of lizards and are found worldwide in a diversity of habitats. One of the larger and more poorly studied groups of skinks includes members of the subfamily Scincinae distributed in sub-Saharan Africa. Sub-Saharan African scincines are one of the many groups of lizards that show limb reduction and loss, and the genus Scelotes offers an excellent opportunity to look at limb loss in a phylogenetic context. Phylogenetic relationships were reconstructed for a total of 52 taxa representing all subfamilies of skinks as well as other Autarchoglossan families using sequence from six gene regions including; 12S, 16S, and cytochrome b (mitochondrial), as well as alpha-Enolase, 18S, and C-mos (nuclear). The family Scincidae is recovered as monophyletic and is the sister taxon to a (Cordylidae+Xantusiidae) clade. Within skinks the subfamily Acontinae is monophyletic and sister group to all remaining skinks. There is no support for the monophyly of the subfamilies Lygosominae and Scincinae, but sub-Saharan African scincines+Feylinia form a well supported monophyletic group. The monophyly of Scelotes is confirmed, and support is found for two geographic groups within the genus. Reconstructions of ancestral states for limb and digital characters show limited support for the reversal or gain of both digits and limbs, but conservative interpretation of the results suggest that limb loss is common, occurring multiple times throughout evolutionary history, and is most likely not reversible.     

Phylogenetic analysis of phenotypic characters of Tunicata supports basal Appendicularia and monophyletic Ascidiacea

With approximately 3000 marine species, Tunicata represents the most disparate subtaxon of Chordata. Molecular phylogenetic studies support Tunicata as sister taxon to Craniota, rendering it pivotal to understanding craniate evolution. Although successively more molecular data have become available to resolve internal tunicate phylogenetic relationships, phenotypic data have not been utilized consistently. Herein these shortcomings are addressed by cladistically analyzing 117 phenotypic characters for 49 tunicate species comprising all higher tunicate taxa, and five craniate and cephalochordate outgroup species. In addition, a combined analysis of the phenotypic characters with 18S rDNA-sequence data is performed in 32 OTUs. The analysis of the combined data is congruent with published molecular analyses. Successively up-weighting phenotypic characters indicates that phenotypic data contribute disproportionally more to the resulting phylogenetic hypothesis. The strict consensus tree from the analysis of the phenotypic characters as well as the single most parsimonious tree found in the analysis of the combined dataset recover monophyletic Appendicularia as sister taxon to the remaining tunicate taxa. Thus, both datasets support the hypothesis that the last common ancestor of Tunicata was free-living and that ascidian sessility is a derived trait within Tunicata. “Thaliacea” is found to be paraphyletic with Pyrosomatida as sister taxon to monophyletic Ascidiacea and the relationship between Doliolida and Salpida is unresolved in the analysis of morphological characters; however, the analysis of the combined data reconstructs Thaliacea as monophyletic nested within paraphyletic “Ascidiacea”. Therefore, both datasets differ in the interpretation of the evolution of the complex holoplanktonic life history of thaliacean taxa. According to the phenotypic data, this evolution occurred in the plankton, whereas from the combined dataset a secondary transition into the plankton from a sessile ascidian is inferred. Besides these major differences, both analyses are in accord on many phylogenetic groupings, although both phylogenetic reconstructions invoke a high degree of homoplasy. In conclusion, this study represents the first serious attempt to utilize the potential phylogenetic information present in phenotypic characters to elucidate the inter-relationships of this diverse marine taxon in a consistent cladistic framework.     

28S rDNA evolution in the Eumalacostraca and the phylogenetic position of krill

The Malacostraca are an ancient and morphologically diverse class of Crustacea. The phylogenetic position of one order within this class, the Euphausiacea ("krill," subclass Eumalacostraca) was investigated using 28S rDNA sequences from representatives of several malacostracan orders. Phylogenies for these sequences were estimated by maximum-likelihood and maximum-parsimony analysis. The results of these analyses produced a new scheme for evolution within the Eumalacostraca. The new phylogenies suggested that Euphausiacea are most closely related to the Mysida and not the Decapoda, as is generally thought. Furthermore, the Mysida were found not to be closely related to the Lophogastrida, which are often considered their sister taxon. These hypotheses were tested against the hypotheses of monophyly for the Eucarida, Mysidacea, and Peracarida and found to be significantly better on the basis of the 28S rDNA data.     

Taxonomic Review of the Orders Mysida and Stygiomysida (Crustacea,Peracarida)

The order Mysida (2 families, 178 genera, 1132 species) contains species across a broad range of habitats, such as subterranean, fresh, brackish, coastal, and surface to deep-sea habitats. The Stygiomysida (2 families, 2 genera, 16 species), however, are found primarily in subterranean waters, but always in waters with a marine influence. The Mysida and Stygiomysida body is divided into three main regions: cephalon, thorax, and abdomen. They are shrimp-like in appearance, containing morphological features earlier referred to as defining a "caridoid facies". The shrimp-like morphology was to some extent diagnostic for the historic Decapod taxon Schizopoda, containing the Nebalia, Mysida, Lophogastrida, and Euphausiacea. In 1904 the concept of Schizopoda was abandoned, and the Mysidacea (Mysida and Lophogastrida) along with Cumacea, Amphipoda, Isopoda, and Tanaidacea were placed in a new taxon, the Peracarida. Later discoveries of groundwater mysids led to the establishment of Stygiomysida, but placement to either Lophogastrida or Mysida remained unclear. The presence of oostegites and absence of podobranchiae, coupled with non-statocyst bearing uropods have been used to classify the Stygiomysida as a primitive Mysida family, comparable to Petalophthalmidae. On the other hand, equally suggestive characters, but for a Lophogastrida affiliation, was suggested for the archaic foregut characters and again, non-statocyst bearing uropods. With the inclusion of DNA sequence data of ribosomal genes, sister group relationships between Stygiomysida, Lophogastrida, and Mictacea within the Peracarida are observed, which supports a classification of the Stygiomysida as a separate order removed from the Mysida.     

Relationships among the major lineages of Dictyoptera: the effect of outgroup selection on dictyopteran tree topology

Abstract Dictyoptera, comprising Blattaria, Isoptera, and Mantodea, are diverse in appearance and life history, and are strongly supported as monophyletic. We downloaded COII, 16S, 18S, and 28S sequences of 39 dictyopteran species from GenBank. Ribosomal RNA sequences were aligned manually with reference to secondary structure. We included morphological data (maximum of 175 characters) for 12 of these taxa and for an additional 15 dictyopteran taxa (for which we had only morphological data). We had two datasets, a 59‐taxon dataset with five outgroup taxa, from Phasmatodea (2 taxa), Mantophasmatodea (1 taxon), Embioptera (1 taxon), and Grylloblattodea (1 taxon), and a 62‐taxon dataset with three additional outgroup taxa from Plecoptera (1 taxon), Dermaptera (1 taxon) and Orthoptera (1 taxon). We analysed the combined molecular?morphological dataset using the doublet and MK models in Mr Bayes , and using a parsimony heuristic search in paup . Within the monophyletic Mantodea, Mantoida is recovered as sister to the rest of Mantodea, followed by Chaeteessa; the monophyly of most of the more derived families as defined currently is not supported. We recovered novel phylogenetic hypotheses about the taxa within Blattodea (following Hennig, containing Isoptera). Unique to our study, one Bayesian analysis places Polyphagoidea as sister to all other Dictyoptera; other analyses and/or the addition of certain orthopteran sequences, however, place Polyphagoidea more deeply within Dictyoptera. Isoptera falls within the cockroaches, sister to the genus Cryptocercus. Separate parsimony analyses of independent gene fragments suggest that gene selection is an important factor in tree reconstruction. When we varied the ingroup taxa and/or outgroup taxa, the internal dictyopteran relationships differed in the position of several taxa of interest, including Cryptocercus, Polyphaga, Periplaneta and Supella. This provides further evidence that the choice of both outgroup and ingroup taxa greatly affects tree topology.     

Higher Level Phylogeny of Curculionidae (Coleoptera: Curculionoidea) based mainly on Larval Characters, with Special Reference to Broad-Nosed Weevils

A cladistic analysis of Curculionidae was performed using 49 characters (41 from larvae, three from pupae, and five from adults). Illustrations of characters of immatures are provided. The analysis involved 19 terminal units and a hypothetical ancestor determined by the outgroup comparison method used to root the tree. One most parsimonious cladogram was obtained based on the complete data set and the following phylogenetic hypothesis is proposed: Ithycerinae, Microcerinae, and Brachycrinae sensu stricto are broad-nosed weevils placed sequentially at the base of the cladogram. The remaining weevil subfamilies form two major natural groups: one constituted by the sister taxa Rhynchophorinae—Platypodinae; the other with Erirhininae at the base, as sister taxon of the "Curculionidae sensu stricto " which show an unresolved trichotomy involving Curculioninae, Cossoninae—Scolytinae, and the clade including the Entiminae and allied subfamilies. This latter clade of broad-nosed weevils has Thecesterninae at the base; the next branch is Amycterinae, the sister taxon of the clade comprising two groups: one constituted by Aterpinae, Rhytirrhininae, and Gonipterinae; the other is Entiminae whose units form two main clades: one constituted by the sister tribes Pachyrhynchini—Ectemnorhinini, and the other by Alophini, Sitonini, and Entimini. When the analysis was done using only immature characters, results congruent with those based on the complete data set were obtained, except for the placement of Erirhininae. According to the results the hypothesis of monophyly of broad-nosed weevils is not accepted; the Entiminae are justified as monophyletic and their natural classification into tribes is proposed and the phylogenetic position and relationships of higher taxa of Curculionidae are discussed. This paper shows the importance of immature characters in recognition of natural groups and relationships in Curculionidae.     

Phylogenetic relationships of family groups in Pentatomoidea based on morphology and DNA sequences (Insecta: Heteroptera)

Phylogenetic relationships within the Pentatomoidea are investigated through the coding and analysis of character data derived from morphology and DNA sequences. In total, 135 terminal taxa were investigated, representing most of the major family groups; 84 ingroup taxa are coded for 57 characters in a morphological matrix. As many as 3500 bp of DNA data are adduced for each of 52 terminal taxa, including 44 ingroup taxa, comprising the 18S rRNA, 16S rRNA, 28S rRNA, and COI gene regions. Character data are analysed separately and in the form of a total evidence analysis. Major conclusions of the phylogenetic analysis include: the concept of Urostylididae is restricted to that of earlier authors; the Saileriolinae is raised to family rank and treated as the sister group of all Pentatomoidea exclusive of Urostylididae sensu stricto; a broadly conceived Cydnidae, as recognized by Dolling, 1981 , is not supported; the placement of Thaumastellidae within the Pentatomoidea is affirmed and the taxon is recognized at family rank rather than as a subfamily of Cydnidae, although its exact phylogenetic position within the Pentatomoidea remains equivocal; the Parastrachiinae is treated as also including Dismegistus Amyot & Serville and placed within a broadly conceived Corimelaenidae, the latter group being treated at family rank; the family‐group taxa Dinidoridae and Tessaratomidae probably represent a monophyletic group, but the recognition of monophyletic subgroups will benefit from additional representation in the sequence data set; and the Lestoniidae is treated as the sister group of the Acanthosomatidae. The Acanthosomatidae and Scutelleridae are consistently recovered as monophyletic. The monophyly of the Pentatomidae appears unequivocal, inclusive of the Aphylinae and Cyrtocorinae, on the basis of morphology, the latter two taxa not being represented in the molecular data set. © The Willi Hennig Society 2008.     

Monophyly, phylogenetic position and inter-familial relationships of the Alepocephaliformes (Teleostei) based on whole mitogenome sequences

Recent mitogenomic studies suggest a new position for the deep-sea fishes of the order Alepocephaliformes, placing them within the Otocephala in contrast to their traditional placement within the Euteleostei. However, these studies included only two alepocephaliform taxa and left several questions unsolved about their systematics. Here we use whole mitogenome sequences to reconstruct phylogenetic relationships for 11 alepocephaliform taxa, sampled from all five nominal families, and a large selection of non-alepocephaliform teleosts, to address the following three questions: (1) is the Alepocephaliformes monophyletic, (2) what is its phylogenetic position within the Teleostei and (3) what are the relationships among the alepocephaliform families? Our character sets, including unambiguously aligned, concatenated mitogenome sequences that we have divided into four (first and second codon positions, tRNA genes, and rRNA genes) or five partitions (same as before plus the transversions at third codon positions, using "RY" coding), were analyzed by the partitioned maximum likelihood and Bayesian methods. Our result strongly supported the monophyly of the Alepocephaliformes and its close relationship to the Clupeiformes and Ostariophysi. Altogether, these three groups comprise the Otocephala. Statistical comparison using likelihood-based SH test confidently rejected the monophyly of the Euteleostei when including the Alepocephaliformes. However, increasing the taxonomic sampling within the Alepocephaliformes did not resolve its position relative to the Clupeiformes and Ostariophysi. Within the Alepocephaliformes, our results strongly supported the monophyly of the platytroctid genera but not that of the remaining taxa. From one analysis to other, platytroctids were either the sister group of the remaining taxa or nested within the alepocephalids. Inferred relationships among alepocephaliform taxa were not congruent with any of the previously published phylogenetic hypotheses based on morphological characters.     

Germ band differentiation in the stomatopod Gonodactylaceus falcatus and the origin of the stereotyped cell division pattern in Malacostraca (Crustacea)

We analysed aspects of the embryonic development of the stomatopod crustacean Gonodactylaceus falcatus focusing on the cell division in the ectoderm of the germ band. As in many other malacostracan crustaceans, the growth zone in the caudal papilla is formed by 19 ectoteloblasts and 8 mesoteloblasts arranged in rings. These teloblasts give rise to the cellular material of the largest part of the post-naupliar germ band in a stereotyped cell division pattern. The regularly arranged cells of the genealogical units produced by the ectoteloblast divide twice in longitudinal direction. The intersegmental furrows form within the descendants of one genealogical unit in the ectoderm. Hence, embryos of G. falcatus share some features of the stereotyped cell division pattern with that in other malacostracan crustaceans, which is unique among arthropods. In contrast to the other malacostracan taxa studied so far, stomatopods show slightly oblique spindle direction and a tilted position of the cells within the genealogical units. The inclusion of data on Leptostraca suggests that aspects of stereotyped cell divisions in the germ band must be assumed for the ground pattern of Malacostraca. Moreover, Stomatopoda and Leptostraca share the lateral displacement of cells during the mediolateral divisions of the ectodermal genealogical units in the post-naupliar germ band. The Caridoida within the Eumalacostraca apomorphically evolved the strict longitudinal orientation of spindle axes and cell positions, reaching the highest degree of regularity in the Peracarida. The phylogenetic analysis of the distribution of developmental characters is the prerequisite for the analysis of the evolution of developmental patterns and mechanisms.     

A phylogenetic hypothesis for Asilidae based on a total evidence analysis of morphological and DNA sequence data (Insecta: Diptera: Brachycera: Asiloidea)

An hypothesis of phylogenetic relationships of Asilidae and its constituent taxa is presented, combining morphological and DNA sequence data in a total evidence framework. It is based on 77 robber fly species, 11 Asiloidea outgroup species, 211 morphological characters of the adult fly, and approximately 7300 bp of nuclear DNA from five genes (18S and 28S rDNA, AATS, CAD, and EF-1α protein-encoding DNA). The equally weighted, simultaneous parsimony analysis under dynamic homology in POY resulted in a single most parsimonious cladogram with a cost of 27,582 (iterative pass optimization; 27,703 under regular direct optimization). Six of the 12 included subfamily taxa are recovered as monophyletic. Trigonomiminae, previously always considered as monophyletic based on morphology, is shown to be non-monophyletic. Two of the three Trigonomiminae genera, Holcocephala Jaennicke, 1867 and Rhipidocephala Hermann, 1926, group unexpectedly as the sister taxon to all other Asilidae. Laphriinae, previously seen in the latter position, is the sister group of the remaining Asilidae. Five other subfamily taxa, i.e. Brachyrhopalinae, Dasypogoninae, Stenopogoninae, Tillobromatinae, and Willistonininae, are also shown to be non-monophyletic. The phylogenetic relationships among the higher-level taxa are partly at odds with findings of a recently published morphological study based on more extensive taxon sampling. The total evidence hypothesis is considered as the most informative one, but the respective topologies from the total-evidence, morphology-only, and molecular-only analyses are compared and contrasted in order to discuss the signals from morphological versus molecular data, and to analyze whether the molecular data outcompete the fewer morphological characters. A clade Apioceridae+Mydidae is corroborated as the sister taxon to Asilidae.     

Global interrelationships of Plesiosauria (Reptilia,Sauropterygia) and the pivotal role of taxon sampling in determining the outcome of phylogenetic analyses

Previous attempts to resolve plesiosaurian phylogeny are reviewed and a new phylogenetic data set of 66 taxa (67% of ingroup taxa examined directly) and 178 characters (eight new) is presented. We recover two key novel results: a monophyletic Plesiosauridae comprising Plesiosaurus dolichodeirus, Hydrorion brachypterygius, Microcleidus homalospondylus, Occitanosaurus tournemirensis and Seeleyosaurus guilelmiimperatoris; and five plesiosaurian taxa recovered outside the split between Plesiosauroidea and Pliosauroidea. These taxa are Attenborosaurus conybeari, ‘Plesiosaurus’macrocephalus and a clade comprising Archaeonectrus rostratus, Macroplata tenuiceps and BMNH 49202. Based on this result, a new name, Neoplesiosauria, is erected for the clade comprising Plesiosauroidea and Pliosauroidea. Taxon subsamples of the new dataset are used to simulate previous investigations of global plesiosaurian relationships. Based on these simulations, most major differences between previous global phylogenetic hypotheses can be attributed to differences in taxon sampling. These include the position of Leptocleididae and Polycotylidae and the monophyly or paraphyly of Rhomaleosauridae. On this basis we favour the results recovered by our, larger analysis. Leptocleididae and Polycotylidae are sister taxa, forming a monophyletic clade within Plesiosauroidea, indicating that the large‐headed, short‐necked ‘pliosauromorph’ body plan evolved twice within Plesiosauria. Rhomaleosauridae forms the monophyletic sister taxon of Pliosauridae within Pliosauroidea. Problems are identified with previous phylogenetic definitions of plesiosaurian clades and new, stem‐based definitions are presented that should maintain their integrity over a range of phylogenetic hypotheses. New, rank‐free clade names Cryptoclidia and Leptocleidia are erected to replace the superfamilies Cryptoclidoidea and Leptocleidoidea. These were problematic as they were nested within the superfamily Plesiosauroidea. The incongruence length difference test indicates no significant difference in levels of homoplasy between cranial and postcranial characters.     

An investigation into the cladistic relationships and monophyly of therocephalian therapsids (Amniota: Synapsida)

A comprehensive phylogenetic investigation was performed to elucidate the cladistic relationships and possible monophyly of therocephalian therapsids (Amniota: Synapsida). The phylogenetic positions of 30 therapsid taxa were examined under maximum parsimony, including 23 therocephalian genera. The analysis incorporated 110 cranial and postcranial characters in order to assess the interrelationships of basal therocephalians and eutherocephalians and their relationships to Cynodontia, representing the most complete review of therocephalian phylogeny to date. The analysis supports the hypothesis that Therocephalia represents the monophyletic sister taxon to Cynodontia, with as many as 15 morphological synapomorphies, in contrast with other recent analyses of lesser taxon sampling. The results also support the hypothesis that Scylacosauridae is more closely related to Eutherocephalia than to the basal therocephalian family Lycosuchidae, supporting a ‘Scylacosauria’ clade. The taxa suggested here to be neotenic forms (e.g. Ictidosuchoides and Ictidosuchops) are positioned near the base of a monophyletic Baurioidea. Neotenic development of the therocephalian feeding apparatus and evolutionary parallelism with cynodonts are suggested to have been important trends in the early evolution of baurioid therocephalians into the Late Permian and Early Triassic.     

PHYLOGENETIC RELATIONSHIPS IN SEED PLANTS

Abstract— The phylogenetic relationships of nineteen extant and fossil seed plants are considered. Analysis of 31 characters produced ten topologically similar and equally parsimonious cladograms. A strict consensus tree derived from these cladograms places Lyginopteris as the sister taxon to the other seed plants included. Within this clade all the taxa considered, except medullosans and cycads, form a single monophyletic group defined by the presence of flattened seeds and saccate pollen ("platy-sperms"). Relationships between medullosans, cycads, and "platysperms" were not resolved, but within the "platysperm" clade conifers and cordaites ( Cordaixylon, Mesoxylon ) + Ginkgo form a monophyletic group ("coniferophytes"). The "higher platysperms" (glossopterids, Caytonia , corystosperms, Bennettitales, Pentoxylon , Gnetales, and angiosperms) are also monophyletic, but their relationship to "coniferophytes," peltasperms, and Callistophyton is unresolved. Pentoxylon is placed as sister taxon to the Bennettitales, and together they form the sister group to a clade in which Gnetales and angiosperm are sister taxa. The Bennettitales + Pentoxylon + Gnetales + angiosperms ("anthophytes") form a monophyletic sister group to the corystosperms. This analysis is compared with current classifications of seed plants. It does not support a close relationship between Bennettitales and cycads, it provides no evidence for seed plant polyphyly, and it strongly suggests that the current concept of seed ferns has little value in a phylogenetic context.     

PHYLOGENETIC ANALYSES OF THE BRYOPSIDALES (ULVOPHYCEAE,CHLOROPHYTA) BASED ON RUBISCO LARGE SUBUNIT GENE SEQUENCES1

Current taxonomy of the Bryopsidales recognizes eight families; most of which are further categorized into two suborders, the Bryopsidineae and Halimedineae. This concept was supported by early molecular phylogenetic analyses based on rRNA sequence data, but subsequent cladistic analyses of morphological characters inferred monophyly in only the Halimedineae. These conflicting results prompted the current analysis of 32 taxa from this diverse group of green algae based on plastid‐encoded RUBISCO large subunit (rbcL) gene sequences. Results of these analyses suggested that the Halimedineae and Bryopsidineae are distinct monophyletic lineages. The families Bryopsidaceae, Caulerpaceae, Codiaceae, Derbesiaceae, and Halimediaceae were inferred as monophyletic, however the Udoteaceae was inferred as non‐monophyletic. The phylogenetic position of two taxa with uncertain subordinal affinity, Dichotomosiphon tuberosus Lawson and Pseudocodium floridanum Dawes & Mathieson, were also inferred. Pseudocodium was consistently placed within the halimedinean clade suggesting its inclusion into this suborder, however familial affinity was not resolved. D. tuberosus was the inferred sister taxon of the Halimedineae based on analyses of rbcL sequence data and thus a possible member of this suborder.