Cladistics and the land plants: A response to Robinson

The reconstruction of phylogenetic relationships should be based not on belief but on an explicit and logical analysis of all available characters. Hennigian phylogenetic systematics (cladistics) provides a framework for evaluating putative homologies characterizing particular hierarchical levels, determining relationships of taxa sharing congruent patterns of homologies, and constructing a classification based on this information. Fossils can and should be included in the analysis if enough of the relevant characters are preserved; this is not currently possible for early land plants because of the fragmentary fossil record. To avoid circularity, adaptive and functional considerations should be addressed only after a phylogenetic hypothesis based on patterns on patterns of shared homologies is available.     

Nachtrag zu ‘Hepaticae Bomeenses (Oxford University Expedition to Sarawak, 1932)’

Abstract

Recent empirical advances in bryophyte systematics have been made in the discovery and detailed study of new characters. However, theoretical considerations have not kept pace. Proper attention has not been paid to how these new characters can be used to discover relationships among groups and produce classifications. Recent cladistic studies of the relationships of the major groups of bryophytes have demonstrated the feasibility and usefulness of an approach to phylogenetic systematics derived from the works of Hennig. A Hennigian approach attempts to find the particular hierarchical level at which a given character is a homology (i.e. a synapomorphy or shared, derived character), relationships are established by searching for congruent patterns of homologies, and the resulting hierarchical scheme is used as the basis for a classification. Such an approach provides a rigorous and explicit logic for investigating phylogeny and recognizing natural, historically discrete taxa. The theoretical advantages of a Hennigian approach are discussed and illustrated by examining the congruence of new characters data with preliminary cladograms of the major bryophyte groups.     

MORPHOMETRICS AND CLADISTICS: MEASURING PHYLOGENY IN THE SEA URCHIN ECHINOCARDIUM

A phylogenetic approach to the study of evolutionary patterns is based on taxic homologies (synapomorphies). In contrast, the recognition of evolutionary processes (namely heterochronies) involves analysis of the entire morphology. Recent developments in geometric morphometry permit analysis of morphological similarities grounded in operational homologies. Such morphometric techniques are explored (1) at the level of evolutionary processes, and (2) as a complement in exploration of phylogenetic relationships. To examplify this, we perform a two-part study of the ontogeny and phylogeny of the spatangoid sea urchin Echinocardium. First, a phylogenetic analysis of ten Recent species in the genus is performed on 18 informative characters of the test. Second, morphological divergences among the species are analyzed using procrustean (superimposition) methods based on 49 homologous points. An additive distance tree is built from a matrix of morphometric distances among adult specimens. This tree is fully congruent with the phyletic results. Ontogenetic processes are explored by inserting ontogenetic series into the analysis. A distance tree including the juvenile stages shows that the general evolutionary trend of the genus is peramorphic, but species-to-species comparisons attest that no general clinal trend exists. Our analysis emphasizes the importance of morphometric approaches in evolutionary studies (1) for the understanding of heterochronies; (2) to trace the morphological implications of phylogenetic patterns; and (3) to estimate the impact of homoplasies.     

Phylogeny and classification of the Catantopidae at the tribal level (Orthoptera, Acridoidea)

The grasshopper family Catantopidae is a well-known group, whose members include some of the most notorious agricultural pests. The existing classifications of the family are mostly utilitarian rather than being based on phylogenetic analysis and therefore unable to provide the stability desired for such an economically important group. In the present study, we present the first comprehensive phylogenetic analysis of the family based on morphology. By extensively sampling from the Chinese fauna, we included in the present analysis multiple representatives of each of the previously recognized tribes in the family. In total, we examined 94 genera represented by 240 species and evaluated 116 characters, including 84 for external morphology and 32 for male genitalia. The final matrix consists of 86 ingroup taxa and 88 characters. Our phylogenetic analyses resulted in a high resolution of the basal relationships of the family while showed considerable uncertainty about the relationships among some crown taxa. We further evaluated the usefulness of morphological characters in phylogeny reconstruction of the catantopids by examining character fit to the shortest trees found, and contrary to previous suggestions, our results suggest that genitalia characters are not as informative as external morphology in inferring higher-level relationship. We further suggest that earlier classification systems of grasshoppers in general and Catantopidae in particular most probably consist of many groups that are not natural due the heavy reliance on genitalia features and need to be revised in the light of future phylogenetic studies. Finally, we outlined a tentative classification scheme based on the results of our phylogenetic analysis.     

基于表型性状的芍药不同品种群亲缘关系分析

芍药品种变异丰富,表型性状的研究对各品种进行科学分类及亲缘关系的研究具有重要意义。本研究以芍药DUS测试指南(2012版)为依据,以不同品种群的47个芍药品种为研究对象,选取了株高、分枝能力、茎秆颜色等33个表型性状(二元性状9个,数量多态性状3个,定性多态性状21个)进行了R型聚类分析、主成分分析和Q型聚类分析。结果表明:基于33个表型性状的聚类结果可以较好地区分芍药不同品种群的品种,其中国内品种与大多数国外品种亲缘关系较远;杂种芍药品种群的品种由于多亲本参与,起源复杂,聚类结果比较分散;伊藤品种群与杂种芍药品种群存在较近亲缘关系。本研究与前人利用形态和分子标记进行品种分类的结果基本一致,能够较准确反映品种间、品种群间的亲缘关系。     

Phylogenetic interpretation of ontogenetic change: sorting out the actual and artefactual in an empirical case study of centrarchid fishes

Hypothesized relationships between ontogenetic and phylogenetic change in morphological characters were empirically tested in centrarchid fishes by comparing observed patterns of character development with patterns of character evolution as inferred from a representative phylogenetic hypothesis. This phylogeny was based on 56–61 morphological characters that were polarized by outgroup comparison. Through these comparisons, evolutionary changes in character ontogeny were categorized in one of eight classes (terminal addition, terminal deletion, terminal substitution, non-terminal addition, non-terminal deletion, non-terminal substitution, ontogenetic reversal and substitution). The relative frequencies of each of these classes provided an empirical basis from which assumptions underlying hypothesized relationships between ontogeny and phylogeny were tested. In order to test hypothesized relationships between ontogeny and phylogeny that involve assumptions about the relative frequencies of terminal change (e.g. the use of ontogeny as a homology criterion), two additional phylogenies were generated in which terminal addition and terminal deletion were maximized and minimized for all characters. Character state change interpreted from these phylogenies thus represents the maxima and minima of the frequency range of terminal addition and terminal deletion for the 8.7 × 10³⁶ trees possible for centrarchids. It was found for these data that terminal change accounts for c. 75% of the character state change. This suggests either that early ontogeny is conserved in evolution or that interpretation and classification of evolutionary changes in ontogeny is biased in part by the way that characters are recognized, delimited and coded. It was found that ontogenetic interpretation is influenced by two levels of homology decision: an initial decision involving delimitation of the character (the ontogenetic sequence), and the subsequent recognition of homologous components of developmental sequences. Recognition of phylogenetic homology among individual components of developmental sequences is necessary for interpretation of evolutionary changes in ontogeny as either terminal or non-terminal. If development is the primary criterion applied in recognizing individual homologies among parts of ontogenetic sequences, the only possible interpretation of phylogenetic differences is that of terminal change. If homologies of the components cannot be ascertained, recognition of the homology of the developmental sequence as a whole will result in the interpretation of evolutionary differences as substitutions. Particularly when the objective of a study is to discover how ontogeny has evolved, criteria in addition to ontogeny must be used to recognize homology. Interpretation is also dependent upon delimitation within an ontogenetic sequence. This is in part a function of the way that an investigator ‘sees’ and codes characters. Binary and multistate characters influence interpretation differently and predictably. The use of ontogeny for determining phylogenetic polarity as previously proposed rests on the assumptions that ancestral ontogenies are conserved and that character evolution occurs predominantly through terminal addition. It was found for these data that terminal addition may comprise a maximum of 51.9% of the total character state change. It is concluded that the ontogenetic criterion is not a reliable indicator of phylogenetic polarity. Process and pattern data are collected simultaneously by those engaged in comparative morphological studies of development. The set of alternative explanatory processes is limited in the process of observing development. These form necessary starting points for the research of developmental biologists. Separating ‘empirical’ results from interpretational influences requires awareness of potential biases in the course of character selection, coding and interpretation. Consideration of the interpretational problems involved in identifying and classifying phylogenetic changes in ontogeny leads to a re-evaluation of the purpose, usefulness and information conveyed by the current classification system. It is recommended that alternative classification schemes be pursued.     

Phylogeny and reclassification of the Caucasigenini radiation from the Caucasus region (Gastropoda,Hygromiidae)

The Caucasigenini is an endemic radiation of hygromiid land snails from the Caucasus region. A phylogenetic analysis of morphological characters of the genitalia and the shell showed that the morphological characters are insufficient for resolving the relationships within the Caucasigenini. Convergences of the few parsimony informative characters in other groups of the Hygromiidae demonstrate that these characters are not reliable indicators of phylogenetic relationships. Phylogenetic analyses of sequences of cox1, 16S rDNA, 5.8S rDNA, ITS2 and 28S rDNA revealed several well‐supported groups. The relationships among these groups could not be resolved. It is likely that these groups originated in a rapid radiation during the uplift of the Caucasus. Based on the molecular phylogeny, we propose a new classification of the species of the Caucasigenini and establish a new genus, Lazicana gen. n.     

Computerized Analysis of Crustacean Relationships

The strengths and weaknesses of phylogenetic analysis using computers are reviewed from the viewpoint of understanding crustacean evolution. Computerized methods require the explicit presentation of characters and character state homologies. New techniques allow investigators to design evolutionary models into a character data matrix, or to use evolutionary models that make minimal a priori assumptions. The computer analysis relieves the investigator from the highly repetitious testing of trees, allows the concentration on the character state data, and provides objective methods for comparing trees, primarily their length. These are regarded as the strengths of computerized methods. The weaknesses of these methods include the relatively inscrutable nature of the character data matrix compared with the overall ‘gestalt’ of resulting trees, the difficulties of defining discrete homologies within the Crustacea, especially for counts of segmentation, the lack of clear intermediate character states in some multistate segmental characters, and the inability to define evolutionary polarity. These difficulties may be overcome by analysing the data using the minimal assumption models of character evolution, and by a recognition that the trees are a result of the input data, and therefore the data should be criticized, rather than the trees themselves. A ‘consensus’ character data set, including most extant major groups of the Crustacea as well as several key fossils, was assembled and revised by the participants in the workshop. An artificial taxon, ‘ur-crustacean characters’, was introduced to root the tree. Three observations may be made from parsimony analyses using several weighting and tree rooting methods. (1) The currently accepted large scale phylogeny and classification of the Crustacea is not corroborated. (2) The number of supposed plesiomorphic traits possessed by a taxon is not a good index for early derivation in crustacean evolution. (3) The taxon Maxillopoda is not supported by the arrangement of any of the trees.     

A phylogenetic interpretation of the Brachycera (Diptera) based on the larval mandible and associated mouthpart structures

Abstract. Based on outgroup comparison, the various components of the larval mandible of the Brachycera and their homologies are described. The final instar larval mandible of the Brachycera ground plan is comprised of a distal pointed hook and an inverted 'U'-shaped basal sclerite. The phylogenetic implications of the larval mandibular homologies and associated mouthpart structures for the current cladistic hypotheses of the Nematocera (Wood & Borkent, 1989) and orthorrhaphous Brachycera (Woodley, 1989) are evaluated.
A cladistic analysis of larval mouthpart characters largely supports the hypotheses of Wood & Borkent and Woodley. The presence of a pharyngeal filter is tentatively proposed as a synapomorphy of the Diptera exclusive of the Tipulomorpha and Bibionomorpha. Evidence is presented supporting a sister-group relationship between the Psychodomorpha ( sensu Wood & Borkent, 1989) and the Brachycera. The placement of the Pantophthalmidae in the Stratiomyomorpha is supported by the apomorphic development of the mandibular-maxillary complex and pharyngeal filter with posterior grinding mill. Additional larval mouthpart characters are proposed supporting the concept of the Eremoneura (Empidoidea + Cyclorrhapha). The ground plan of the Empidoidea appears to be characterized by the apomorphic development of a four-component mandible, in which the basal sclerite is subdivided into two connecting sclerites and a ventral sclerite. Morphological evidence is presented supporting the mandibular origin of the mouthhooks of the Cyclorrhapha.     

Does minimizing homoplasy really maximize homology? MaHo: A method for evaluating homology among most parsimonious trees

Parsimony analysis aims at finding the tree that best fits hypotheses of homology. However, parsimony does not directly maximize homology, but minimizes homoplasy. When a parsimony analysis results in more than a single most-parsimonious tree (MPT), it is shown that the number of homologous characters may vary significantly. We propose a method called MaHo to identify, among the MPTs, the tree(s) that has (have) the highest number of characters that are homologies. We apply this approach to the phylogenetic relationships of the Dombeyoideae (Malvaceae) of the Mascarene Islands. A parsimony analysis was performed, including 31 representatives of the Dombeyoideae. The search resulted in 29,336 MPTs. MaHo was used in order to improve the resolution of the consensus and to increase the number of unambiguous homologies. The consensus of the 7592 MPTs presenting the highest number of homologies was chosen. This resulted in unravelling five additional synapomorphies and in reducing the number of MPTs.     

Phylogenetic relationships of Microdontinae (Diptera: Syrphidae) based on molecular and morphological characters

The intrasubfamilial classification of Microdontinae Rondani (Diptera: Syrphidae) has been a challenge: until recently more than 300 out of more than 400 valid species names were classified in Microdon Meigen. We present phylogenetic analyses of molecular and morphological characters (both separate and combined) of Microdontinae. The morphological dataset contains 174 characters, scored for 189 taxa (9 outgroup), representing all 43 presently recognized genera and several subgenera and species groups. The molecular dataset, representing 90 ingroup species of 28 genera, comprises sequences of five partitions in total from the mitochondrial gene COI and the nuclear ribosomal genes 18S and 28S. We test the sister‐group relationship of Spheginobaccha with the other Microdontinae, attempt to elucidate phylogenetic relationships within the Microdontinae and discuss uncertainties in the classification of Microdontinae. Trees based on molecular characters alone are poorly resolved, but combined data are better resolved. Support for many deeper nodes is low, and placement of such nodes differs between parsimony and Bayesian analyses. However, Spheginobaccha is recovered as highly supported sister group in both. Both analyses agree on the early branching of Mixogaster, Schizoceratomyia, Afromicrodon and Paramicrodon. The taxonomical rank in relation to the other Syrphidae is discussed briefly. An additional analysis based on morphological characters only, including all 189 taxa, used implied weighting. A range of weighting strengths (k‐values) is applied, chosen such that values of character fit of the resulting trees are divided into regular intervals. Results of this analysis are used for discussing the phylogenetic relationships of genera unrepresented in the molecular dataset.     

Floral anatomy of Thomandersia (Lamiales), with particular reference to the nature of the retinaculum and extranuptial nectaries

Thomandersia is an isolated genus that is currently unplaced in Lamiales. In the past it has been classified in Acanthaceae or Pedaliaceae, on the basis of intuitive assessments of a limited number of morphological characters. Recent molecular sequenced-based phylogenies have suggested a relationship to Bignoniaceae, Schlegeliaceae or Verbenaceae. Here we present new observations of the floral anatomy of Thomandersia , with particular emphasis on the structure of the retinaculum, a character shared with Acanthaceae, and calyx nectaries, which may be shared with other families in Lamiales. The morphological and anatomical characters of Thomandersia are discussed in the context of recent phylogenetic hypotheses for Lamiales, with the aim of identifying potential primary and secondary homologies between Thomandersia and related families in Lamiales. We find that Thomandersia shares a range of characters with each of the families to which it might be sister-group, and that some of these primary homologies must therefore be homoplastic. In particular, if the topology based on molecular sequence data is correct, the retinacula of Thomandersia and Acanthaceae are homoplastic and represent an example of parallel morphological evolution.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 469–482.     

Assessing similarity: on homology,characters and the need for a semantic approach to non‐evolutionary comparative homology

The problem of homology has been a consistent source of controversy at the heart of systematic biology, as has the step of morphological character analysis in phylogenetics. Based on a clear epistemic framework and a characterization of “characters” as diagnostic evidence units for the recognition of not directly identifiable entities, I discuss the ontological definition and empirical recognition criteria of phylogenetic, developmental and comparative homology, and how these three accounts of homology each contribute to an understanding of the overall phenomenon of homology. I argue that phylogenetic homologies are individuals or historical kinds that require comparative homology for identification. Developmental homologies are natural kinds that ultimately rest on phylogenetic homologies and also require comparative homology for identification. Comparative homologies on the other hand are anatomical structural kinds that are directly identifiable. I discuss pre‐Darwinian comparative homology concepts and their problem of invoking non‐material forces and involving the a priori assumption of a stable positional reference system. Based on Young's concept of comparative homology, I suggest a procedure for recognizing comparative homologues that lacks these problems and that utilizes a semantic framework. This formal conceptual framework provides the much needed semantic transparency and computer‐parsability for documenting, communicating and analysing similarity propositions. It provides an essential methodological framework for generalizing over individual organisms and identifying and demarcating anatomical structural kinds, and it provides the missing link to the logical chain of identifying phylogenetic homology. The approach substantially increases the analytical accessibility of comparative research and thus represents an important contribution to the theoretical and methodological foundation of morphology and comparative biology.     

Suprageneric systematics of flea beetles (Chrysomelidae: Alticinae) inferred from multilocus sequence data

Recent phylogenetic studies of flea beetles (Alticinae) based on morphological or molecular data have focused on the relationship and possible paraphyly with respect to the closely related Galerucinae, while the supra-generic classification mainly dates back to the 19th century. Here, phylogenetic analysis was performed on DNA sequences for two mitochondrial (rrnL and cox1) and two nuclear (SSU and LSU rRNA) genes from 158 genera and 165 species that cover most suprageneric groups of flea beetles proposed in the older literature. Various alignment strategies and tree search methods were used to test the stability of major clades. Besides confirmation of the placement of several alticine lineages within Galerucinae, a preliminary framework for classification of the main alticine clades was obtained. It is proposed to recognize 18 groups of genera based on well-supported nodes. These include the Altica, Amphimela, Aphthona, Blepharida, Chabria, Chaetocnema, Dibolia, Disonycha, Griva, Lactica, Longitarsus, Manobia, Monoplatus, Nisotra, Oedionychis, Pentamesa, Phygasia and Pseudodera groups. These groups provide a novel perspective to the existing classification. The analysis of 14 morphological characters used in the traditional classification of Alticinae and Galerucinae revealed high levels of homoplasy with respect to the DNA-based tree, but significant hierarchical structure in most of them. Even if not unique to any particular group of genera, these traits largely corroborate the groupings established with DNA sequences.     

Anchored hybrid enrichment challenges the traditional classification of flesh flies (Diptera: Sarcophagidae)

Sarcophagidae is one of the most species-rich families within the superfamily Oestroidea. This diversity is usually represented by three lineages: Miltogramminae, Paramacronychiinae and Sarcophaginae. Historically, the phylogenetic relationships among these lineages have been elusive, due to poorly supported hypotheses or small taxon sets, or both. This study provides a dramatic increase in molecular data, more balanced sampling of all three lineages from all biogeographical regions and a reassessment of morphological characters using scanning electron microscopy in the most comprehensive assessment of subfamily-level phylogeny in Sarcophagidae to date. This analysis of the largest molecular dataset ever produced for a phylogenetic analysis of a fly lineage, with 950 loci from anchored hybrid enrichment comprising 435 930 bp from 101 species, revealed Paramacronychiinae as sister to Miltogramminae, not to Sarcophaginae, as suggested by adult morphology. Maximum likelihood analysis produced a well-supported topology, with 91% of the nodes receiving strong bootstrap proportions (> 97%). In contrast to the molecular data, three out of nine morphological characters studied point to a sister-group relationship of (Sarcophaginae + Paramacronychiinae) and the remaining six characters are either silent on subfamily relationships or in need of further study. Re-examination of morphological structures provides new insights into the evolution of male genitalic traits within Sarcophagidae and highlights their convergence producing conflicting phylogenetic signal. Our phylogeny reconciles older and widely used systems of classification with tree-based thinking and sets up a classification of flesh flies that is more aligned with their evolutionary history.     

Homologie und Taxonomie

Zusammenfassung Morphogenetische Untersuchungen ermöglichen eine zuverlässige Ermittlung der homologen Elemente in der Lobenlinie der Ammonoidea. Umgekehrt lehrt eine Analyse hypothetischer Vorstellungen, die man sich über die phylogenetischen Zusammenhänge gewisser Ammoneen-Gruppen gebildet hatte, daß sich daraus die Homologie-Beziehungen nicht herleiten lassen. Es besteht keine Konkordanz zwischen den morphologischen Tatbeständen und den stammesgeschichtlichen Konstruktionen, die sich in diesen Fällen als falsch erweisen. Daraus wird der Schluß gezogen, daß der Homologie-Begriff nur unvoreingenommen morphologisch definiert und interpretiert werden kann. Die auf morphologischer Grundlage ermittelten Homologien entscheiden über die Möglichkeit stammesgeschichtlicher Verknüpfungen, nicht aber umgekehrt phylogenetische Deutungen über die Homologie. Ebenso kann die stets unsichere Phylogenie nicht zur Grundlage der Systematik gemacht werden. Auch da liegen die logisch-methodischen Zusammenhänge umgekehrt: Die im System ausgedrückte Formverwandtschaft ist die Basis der Phylogenie und nicht die Phylogenie die der Morphologie. Die Theorie eines Phylogenetischen Systems der Organismen wird abgelehnt.

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Summary Morphogenetic investigations provide a firm basis for an exact identification of homologous elements in the suture line of ammonoids. On the other hand an analysis of current phylogenetic connections of certain ammonoid groups demonstrates that they give no clue for tracing homologies. There is no agreement between the morphological facts and the phylogenetic fictions, the latter in these cases being definitely wrong. Therefrom it is concluded that the concept of homology can only be defined and interpreted on a morphological basis. The established homologies are decisive for the admissibility of phylogenetic connections and not phylogenetic inferences for the recognition of homologies. In the same manner systematics cannot be based on the always unsafe phylogeny, but only on the actual facts of morphology. The concept of a phylogenetic classification of organisms is rejected.

     

Phylogeny in Echinocereus (Cactaceae) based on combined morphological and molecular evidence: taxonomic implications

Echinocereus is a morphologically diverse genus that includes 64 species grouped into eight taxonomic sections based on morphological traits. In previous molecular phylogenetic analyses, the relationships amongst Echinocereus species were not entirely revealed and useful characters to recognize clades were not provided. The inclusion of several sources of evidence in a phylogenetic analysis is likely to produce more supported hypotheses. Therefore, we performed a combined phylogenetic analysis with a set of 44 morphological characters and six chloroplast DNA sequences. Topologies from parsimony and Bayesian analyses were mostly congruent. However, the relationships of E. poselgeri were not consistent between analyses. A second Bayesian analysis using a long-branch extraction test resulted in a topology with the morphological position of E. poselgeri congruent with that in parsimony analysis. Parsimony and Bayesian analyses corroborated the monophyly of Echinocereus, which included eight monophyletic groups. The combined phylogeny integrated into different clades those taxa that were not determined in previous analyses and changed the relationships of some recognized clades. The clades did not recover the recent infrageneric classification. In the present study, a new sectional classification for Echinocereus is proposed based on the eight recovered clades, which is supported by a combination of morphological and molecular characters. An identification key for sections in the genus is included.     

Genomic relations among two non-mangrove and nine mangrove species of Indian Rhizophoraceae

Random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers were used to study the genomic relationship among 11 members of Indian Rhizophoraceae represented by nine true mangroves and two non-mangrove species. The AFLP and RAPD bands were scored and analyzed for genetic similarities and cluster analysis was done which separated the 11 species studied into two main groups, the true mangroves and the non-mangroves. The polymorphism observed for these markers showed a high degree of genetic diversity among the constituent taxa of the family. The phylogenetic relationship inferred from molecular marker systems supported the traditional taxonomic classification of the family Rhizophoraceae based on morphological characters at the levels of tribe, phylogeny and delimitation of genera and species, except the intra-generic classification of the genus Bruguiera and the placement of Rhizophora in the family Rhizophoraceae.     

Oral Region Homologies in Paleozoic Crinoids and Other Plesiomorphic Pentaradial Echinoderms

The phylogenetic relationships between major groups of plesiomorphic pentaradial echinoderms, the Paleozoic crinoids, blastozoans, and edrioasteroids, are poorly understood because of a lack of widely recognized homologies. Here, we present newly recognized oral region homologies, based on the Universal Elemental Homology model for skeletal plates, in a wide range of fossil taxa. The oral region of echinoderms is mainly composed of the axial, or ambulacral, skeleton, which apparently evolved more slowly than the extraxial skeleton that forms the majority of the body. Recent phylogenetic hypotheses have focused on characters of the extraxial skeleton, which may have evolved too rapidly to preserve obvious homologies across all these groups. The axial skeleton conserved homologous suites of characters shared between various edrioasteroids and specific blastozoans, and between other blastozoans and crinoids. Although individual plates can be inferred as homologous, no directly overlapping suites of characters are shared between edrioasteroids and crinoids. Six different systems of mouth (peristome) plate organization (Peristomial Border Systems) are defined. These include four different systems based on the arrangement of the interradially-positioned oral plates and their peristomial cover plates, where PBS A1 occurs only in plesiomorphic edrioasteroids, PBS A2 occurs in plesiomorphic edrioasteroids and blastozoans, and PBS A3 and PBS A4 occur in blastozoans and crinoids. The other two systems have radially-positioned uniserial oral frame plates in construction of the mouth frame. PBS B1 has both orals and uniserial oral frame plates and occurs in edrioasterid and possibly edrioblastoid edrioasteroids, whereas PBS B2 has exclusively uniserial oral frame plates and is found in isorophid edrioasteroids and imbricate and gogiid blastozoans. These different types of mouth frame construction offer potential synapomorphies to aid in parsimony-based phylogenetics for exploring branching order among stem groups on the echinoderm tree of life.     

Exoskeleton and Systematics: A Historical Problem in the Classification of Glyptodonts

The glyptodonts (Mammalia: Cingulata) are characterized by an exoskeleton comprising most notably an armored tail and an immobile dorsal carapace formed by a large number of osteoderms. In 1889, Florentino Ameghino published the first phylogenetic scenario for the glyptodonts, based on the sequential application of two transformation series related to the morphology of the tail armor and carapace osteoderms. From the early to mid 1900s, several authors used Ameghino’s transformation series subordinated to a model of evolution in which derived glyptodont groups had arisen independently from separate pre-middle Miocene ancestors. This approach, in which the morphological states of Ameghino’s series were considered analogous rather than homologous, provided different phylogenetic scenarios and the paraphyletic classification still in use. Two recent cladistic analyses based on cranial and postcranial (including caudal tube) characters support the monophyly of glyptodonts and suggest novel intra-clade relationships. However, neither analysis included the classic osteoderm characters used by earlier authors. Therefore, we propose new osteoderm and carapace characters and evaluate their performance in a new cladistic analysis. We found that: a) some osteoderm characters used by earlier authors to support ancestor-descendent hypotheses are in fact fully homoplastic autapomorphies (e.g., multiplication of the number of rows of peripheral figures); b) characters previously believed to have originated independently in several groups (e.g., presence of caudal tube) are synapomorphies at a wider hierarchical level; c) some ancestor–descendant pre-cladistic hypotheses are incompatible with the topology and synapomorphy distribution obtained; and d) there is no reason to favor exoskeletal characters in glyptodont systematics.