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Fossil Taxa (fossil + taxa)
Selected AbstractsEXHAUSTION OF MORPHOLOGIC CHARACTER STATES AMONG FOSSIL TAXAEVOLUTION, Issue 2 2000Peter J. Wagner Abstract., Frequencies of new character state derivations are analyzed for 56 fossil taxa. The hypothesis that new character states are added continuously throughout clade history can be rejected for 48 of theses clades. Two alternative explanations are considered: finite states and ordered states. The former hypothesizes a limited number of states available to each character and is tested using rarefaction equations. The latter hypothesizes that there are limited possible descendant morphologies for any state, even if the character has infinite potential states. This is tested using power functions. The finite states hypothesis explains states: steps relationships significantly better than does the ordered states hypothesis in 14 cases; the converse is true for 14 other cases. Under either hypothesis, trilobite clades show appreciably more homoplasy after the same numbers of steps than do molluscs, echinoderms, or vertebrates. The prevalence of the exhaustion pattern among different taxonomic groups implies that worker biases are not to blame and instead implicates biological explanations such as intrinsic constraints or persistent selective trends. Regardless of the source of increased homoplasy, clades appear to exhaust their available character spaces. Nearly all examined taxa show significant increases in proportions of incompatible character pairs (i.e., those necessarily implying homoplasy) as progressively younger taxa are added to character matrices. Thus, a deterioration of hierarchical structure accompanies character state exhaustion. Exhaustion has several implications: (1) the basic premise of cladistic analyses (i.e., that maximum congruence reflects homology rather than homoplasy) becomes increasingly less sound as clades age; (2) sampling high proportions of taxa probably is needed for congruence to discern homoplasy from homology; (3) stratigraphic data might be necessary to discern congruent homoplasy from congruent homology; and (4) in many cases, character states appear to have evolved in ordered patterns. [source] A new dimension in combining data?ACTA ZOOLOGICA, Issue 1 2010The use of morphology, phylogenomic data in metazoan systematics Abstract Giribet, G. 2010. A new dimension in combining data? The use of morphology and phylogenomic data in metazoan systematics. ,Acta Zoologica (Stockholm) 91: 11,19 Animal phylogenies have been traditionally inferred by using the character state information derived from the observation of a diverse array of morphological and anatomical features, but the incorporation of molecular data into the toolkit of phylogenetic characters has shifted drastically the way researchers infer phylogenies. A main reason for this is the ease at which molecular data can be obtained, compared to, e.g., traditional histological and microscopical techniques. Researchers now routinely use genomic data for reconstructing relationships among animal phyla (using whole genomes or Expressed Sequence Tags) but the amount of morphological data available to study the same phylogenetic patterns has not grown accordingly. Given the disparity between the amounts of molecular and morphological data, some authors have questioned entire morphological programs. In this review I discuss issues related to the combinability of genomic and morphological data, the informativeness of each set of characters, and conclude with a discussion of how morphology could be made scalable by utilizing new techniques that allow for non-intrusive examination of large amounts of preserved museum specimens. Morphology should therefore remains a strong field in evolutionary and comparative biology, as it continues to provide information for inferring phylogenetic patterns, is an important complement for the patterns derived from the molecular data, and it is the common nexus that allows studying fossil taxa with large data sets of molecular data. [source] Osteoderm morphology in recent and fossil euphractine xenarthransACTA ZOOLOGICA, Issue 4 2009C. M. Krmpotic Abstract The presence of osteoderms within the integument, forming a carapace, is one of the most distinctive features of armadillos with the external morphology of these elements forming the basis of most systematic schemes. This is especially true for fossil taxa, where these elements are most frequent in the palaeontological record. A detailed study of osteoderms from the cephalic shield and different regions of the dorsal armour of Chaetophractus villosus (Euphractinae, Xenarthra) was made and compared to those of the extant genus Dasypus (Dasypodinae, Xenarthra), and the extinct genus ,Eutatus. Three distinct histological zones were recognized: outer and inner zones are thin, formed by regular compact bone, the middle zone is thicker, with large cavities that contain mainly adipose tissue, hair follicles, and sweat and sebaceous glands. The internal structure of ,Eutatus (also a member of Euphractinae) osteoderms is close to that of C. villosus, consistent with the notion that these taxa are phylogenetically closely related. In contrast, Dasypus shows marked differences. Dasypus shows hair follicles associated with both gland types (sweat and sebaceous) and connected to foramina on the external surface. Although not observed in adult C. villosus, it has been documented during embryonic development, only to atrophy later in ontogeny. Furthermore, the presence of red bone marrow is rare in C. villosus, but widespread in Dasypus novemcinctus osteoderms. These results suggest an early split of both subfamilies and support the hypothesis that the Euphractinae are more derived than the Dasypodinae. [source] Cenozoic environmental change in South America as indicated by mammalian body size distributions (cenograms)DIVERSITY AND DISTRIBUTIONS, Issue 6 2001Darin A. Croft Abstract. A cenogram is a rank-ordered body size distribution of non-predatory terrestrial mammal species within a community. Studies of cenograms for modern faunas have shown that certain quantifiable attributes of cenograms are correlated with environmental variables such as rainfall and vegetation structure. Based on these correlations, cenograms of fossil communities have been used to infer palaeoenvironments and palaeoenvironmental variables. The present study uses cenogram statistics to interpret palaeoenvironmental conditions for eight Cenozoic South American mammal faunas, ranging from Eocene to Pleistocene in age. Body sizes for fossil taxa were taken either from the literature or were estimated using regressions of body size on molar length (or femoral bicondylar width) for modern mammals. Cenogram statistics are calculated for the eight fossil faunas and compared to similar statistics calculated for 16 modern South American mammal faunas, allowing palaeoenvironmental interpretations to be made. The palaeoenvironmental interpretations based on cenogram analyses sometimes support and sometimes contradict interpretations based on herbivore craniodental morphology (e.g. levels of hypsodonty). Simulations of expected errors in body size estimates for fossil taxa suggest that the discrepancies do not result primarily from erroneous body size estimates. It is possible that some of the incongruity in interpretations results from certain non-analogue attributes of South American faunas during much of the Cenozoic (e.g. the relatively depauperate mammalian predator diversity prior to the Great American Biotic Interchange). [source] EXHAUSTION OF MORPHOLOGIC CHARACTER STATES AMONG FOSSIL TAXAEVOLUTION, Issue 2 2000Peter J. Wagner Abstract., Frequencies of new character state derivations are analyzed for 56 fossil taxa. The hypothesis that new character states are added continuously throughout clade history can be rejected for 48 of theses clades. Two alternative explanations are considered: finite states and ordered states. The former hypothesizes a limited number of states available to each character and is tested using rarefaction equations. The latter hypothesizes that there are limited possible descendant morphologies for any state, even if the character has infinite potential states. This is tested using power functions. The finite states hypothesis explains states: steps relationships significantly better than does the ordered states hypothesis in 14 cases; the converse is true for 14 other cases. Under either hypothesis, trilobite clades show appreciably more homoplasy after the same numbers of steps than do molluscs, echinoderms, or vertebrates. The prevalence of the exhaustion pattern among different taxonomic groups implies that worker biases are not to blame and instead implicates biological explanations such as intrinsic constraints or persistent selective trends. Regardless of the source of increased homoplasy, clades appear to exhaust their available character spaces. Nearly all examined taxa show significant increases in proportions of incompatible character pairs (i.e., those necessarily implying homoplasy) as progressively younger taxa are added to character matrices. Thus, a deterioration of hierarchical structure accompanies character state exhaustion. Exhaustion has several implications: (1) the basic premise of cladistic analyses (i.e., that maximum congruence reflects homology rather than homoplasy) becomes increasingly less sound as clades age; (2) sampling high proportions of taxa probably is needed for congruence to discern homoplasy from homology; (3) stratigraphic data might be necessary to discern congruent homoplasy from congruent homology; and (4) in many cases, character states appear to have evolved in ordered patterns. [source] Evolution of M1 crown size and cusp proportions in the genus HomoJOURNAL OF ANATOMY, Issue 5 2009Rolf Quam Abstract Previous research into tooth crown dimensions and cusp proportions has proved to be a useful way to identify taxonomic differences in Pliocene and Pleistocene fossil hominins. The present study has identified changes in both M1 crown size and cusp proportions within the genus Homo, with M1 overall crown size reduction apparently occurring in two main stages. The first stage (a reduction of ca. 17%) is associated with the emergence of Homo ergaster and Homo erectus sensu stricto. The second stage (a reduction of ca. 10%) occurs in Homo sapiens, but the reduced modern human M1 tooth crown size was only attained in Upper Paleolithic times. The absolute sizes of the individual cusps are highly positively correlated with overall crown size and dental reduction produces a reduction in the absolute size of each of the cusps. Most of the individual cusps scale isometrically with crown size, but the paracone shows a negative allometric relationship, indicating that the reduction in paracone size is less than in the other M1 cusps. Thus, the phylogenetically oldest cusp in the upper molars also seems to be the most stable cusp (at least in the M1). The most striking change in M1 cusp proportions is a change in the relative size of the areas of the paracone and metacone. The combination of a small relative paracone and a large relative metacone generally characterizes specimens attributed to early Homo, and the presence of this character state in Australopithecus and Paranthropus suggests it may represent the primitive condition for the later part of the hominin clade. In contrast, nearly all later Homo taxa, with the exception of Homo antecessor, show the opposite condition (i.e. a relatively large paracone and a relatively small metacone). This change in the relationship between the relative sizes of the paracone and metacone is related to an isometric reduction of the absolute size of the metacone. This metacone reduction occurs in the context of relative stability in the paracone as crown size decreases. Among later Homo taxa, both Homo heidelbergensis and Homo neanderthalensis show a further reduction of the metacone and an enlargement of the hypocone. Fossil and contemporary H. sapiens samples show a trend toward increasing the relative size of the protocone and decreasing the relative size of the hypocone. In Europe, modern human M1 cusp proportions are essentially reached during the Upper Paleolithic. Although some variation was documented among the fossil taxa, we suggest that the relative size of the M1 paracone and metacone areas may be useful for differentiating the earliest members of our genus from subsequent Homo species. [source] Appositional enamel growth in molars of South African fossil hominidsJOURNAL OF ANATOMY, Issue 1 2006Rodrigo S. Lacruz Abstract Enamel is formed incrementally by the secretory activity of ameloblast cells. Variable stages of secretion result in the formation of structures known as cross striations along enamel prisms, for which experimental data demonstrate a correspondence with daily periods of secretion. Patterns of variation in this daily growth are important to understanding mechanisms of tooth formation and the development of enamel thickness. Transmitted light microscopy (TLM) of histological ground sections and scanning electron microscopy (SEM) of bulk specimens or their surface replicas are the usual methods for investigating cross striations. However, these methods pose some constraints on the study of these features in Plio-Pleistocene hominid enamel, the specimens of which may only rarely be sectioned for TLM or examined on only their most superficial surfaces for SEM. The recent development of portable confocal scanning optical microscopy (PCSOM) resolves some of the restrictions on fractured enamel surfaces, allowing the visualization of cross striations by direct examination. This technology has been applied here to the study of Australopithecus africanus and Paranthropus robustus hominid molars from the Plio-Pleistocene of South Africa. We hypothesize that these taxa have increased enamel appositional rates compared with modern humans, because despite having thicker enamelled molars (particularly P. robustus), the enamel crowns of these fossil taxa take an equivalent or reduced amount of time to form. Cross striations were measured in cuspal, lateral and cervical regions of the enamel crowns, and, within each region, the inner, middle and outer zones. Values obtained for A. africanus outer zones of the enamel crown are, in general, lower than those for P. robustus, indicating faster forming enamel in the latter, while both taxa show higher rates of enamel growth than modern humans and the African great apes. This demonstrates a relatively high degree of variability in the mechanisms underlying the development of enamel across taxa. [source] Perspectives on hyperphalangy: patterns and processesJOURNAL OF ANATOMY, Issue 3 2004Tim J. Fedak Abstract Hyperphalangy is a digit morphology in which increased numbers of phalanges are arranged linearly within a digit beyond the plesiomorphic condition. We analyse patterns and processes of hyperphalangy by considering previous definitions and occurrences of hyperphalangy among terrestrial and secondarily aquatic extant and fossil taxa (cetaceans, ichthyosaurs, plesiosaurs and mosasaurs), and recent studies that elucidate the factors involved in terrestrial autopod joint induction. Extreme hyperphalangy, defined as exceeding a threshold condition of 4/6/6/6/6, is shown only to be found among secondarily aquatic vertebrates with a flipper limb morphology. Based on this definition, hyperphalangy occurs exclusively in digits II and III among extant cetaceans. Previous reports of cetacean embryos having more phalanges than adults is clarified and shown to be based on cartilaginous elements not ossified phalanges. Developmental prerequisites for hyperphalangy include lack of cell death in interdigital mesoderm (producing a flipper limb) and maintenance of a secondary apical ectodermal ridge (AER), which initiates digit elongation and extra joint patterning. Factors of the limb-patterning pathways located in the interdigital mesoderm, including bone morphogenetic proteins (BMPs), BMP antagonists, fibroblast growth factors (FGFs), growth/differentiation factor-5 (GDF-5), Wnt-14 and ck-erg, are implicated in maintenance of the flipper limb, secondary AER formation, digit elongation and additional joint induction leading to hyperphalangy. [source] Floristic turnover in Iceland from 15 to 6 Ma , extracting biogeographical signals from fossil floral assemblagesJOURNAL OF BIOGEOGRAPHY, Issue 9 2007Friđgeir Grímsson Abstract Aim, This study aims to document the floristic changes that occurred in Iceland between 15 and 6 Ma and to establish the dispersal mechanisms for the plant taxa encountered. Using changing patterns of dispersal, two factors controlling floristic changes are tested. Possible factors are (1) climate change, and (2) the changing biogeography of Iceland over the time interval studied; that is, the presence or absence of a Miocene North Atlantic Land Bridge. Location, The North Atlantic. Methods, Species lists of fossil plants from Iceland in the time period 15 to 6 Ma were compiled using published data and new data. Closest living analogues were used to establish dispersal properties for the fossil taxa. Dispersal mechanisms of fossil plants were then used to reconstruct how Iceland was colonized during various periods. Results, Miocene floras of Iceland (15,6 Ma) show relatively high floristic turnover from the oldest floras towards the youngest; and few taxa from the oldest floras persist in the younger floras. The frequencies of the various dispersal mechanisms seen in the 15-Ma floras are quite different from those recorded in the 6-Ma floras, and there is a gradual change in the prevailing mode of dispersal from short-distance anemochory and dyschory to long-distance anemochory. Two mechanisms can be used to explain changing floral composition: (1) climate change, and (2) the interaction between the dispersal mechanisms of plants and the increasing isolation of proto-Iceland during the Miocene. Main conclusions, Dispersal mechanisms can be used to extract palaeogeographic signals from fossil floras. The composition of floras and dispersal mechanisms indicate that Iceland was connected both to Greenland and to Europe in the early Middle Miocene, allowing transcontinental migration. The change in prevalence of dispersal modes from 15 to 6 Ma appears to reflect the break-up of a land bridge and the increasing isolation of Iceland after 12 Ma. Concurrent gradual cooling and isolation caused changes in species composition. Specifically, the widening of the North Atlantic Ocean prevented taxa with limited dispersal capability from colonizing Iceland, while climate cooling led to the extinction of thermophilous taxa. [source] Panbiogeography of Nothofagus (Nothofagaceae): analysis of the main species massingsJOURNAL OF BIOGEOGRAPHY, Issue 6 2006Michael Heads Abstract Aim, The aim of this paper is to analyse the biogeography of Nothofagus and its subgenera in the light of molecular phylogenies and revisions of fossil taxa. Location, Cooler parts of the South Pacific: Australia, Tasmania, New Zealand, montane New Guinea and New Caledonia, and southern South America. Methods, Panbiogeographical analysis is used. This involves comparative study of the geographic distributions of the Nothofagus taxa and other organisms in the region, and correlation of the main patterns with historical geology. Results, The four subgenera of Nothofagus have their main massings of extant species in the same localities as the main massings of all (fossil plus extant) species. These main massings are vicariant, with subgen. Lophozonia most diverse in southern South America (north of Chiloé I.), subgen. Fuscospora in New Zealand, subgen. Nothofagus in southern South America (south of Valdivia), and subgen. Brassospora in New Guinea and New Caledonia. The main massings of subgen. Brassospora and of the clade subgen. Brassospora/subgen. Nothofagus (New Guinea,New Caledonia,southern South America) conform to standard biogeographical patterns. Main conclusions, The vicariant main massings of the four subgenera are compatible with largely allopatric differentiation and no substantial dispersal since at least the Upper Cretaceous (Upper Campanian), by which time the fossil record shows that the four subgenera had evolved. The New Guinea,New Caledonia distribution of subgenus Brassospora is equivalent to its total main massing through geological time and is explained by different respective relationships of different component terranes of the two countries. Global vicariance at family level suggests that Nothofagaceae/Nothofagus evolved largely as the South Pacific/Antarctic vicariant in the breakup of a world-wide Fagales ancestor. [source] Skull shape and feeding strategy in Sphenodon and other Rhynchocephalia (Diapsida: Lepidosauria),JOURNAL OF MORPHOLOGY, Issue 8 2008Marc E.H. Jones Abstract The Rhynchocephalia are a group of small diapsid reptiles that were globally distributed during the early Mesozoic. By contrast, the only extant representatives, Sphenodon punctatus and S. guntheri (Tuatara), are restricted to New Zealand off-shore islands. The Rhynchocephalia are widely considered to be morphologically uniform but research over the past 30 years has revealed unexpected phenotypic and taxonomic diversity. Phylogenetically "basal taxa" generally possess relatively simple conical or columnar teeth whereas more derived taxa possessed stouter flanged teeth and sophisticated shearing mechanisms: orthal in some (e.g., Clevosaurus hudsoni) and propalinal in others (e.g., S. punctatus). This variation in feeding apparatus suggests a wide range of feeding niches were exploited by rhynchocephalians. The relationship of skull shape to skull length, phylogenetic grouping, habit, and characters relating to the feeding apparatus are explored here with geometric morphometric analysis on two-dimensional landmarks. Principle components analysis demonstrates that there are significant differences between phylogenetic groups. In particular, Sphenodon differs significantly from all well known fossil taxa including the most phylogenetically basal forms. Therefore, it is not justifiable to use Sphenodon as a solitary outgroup when studying skull shape and feeding strategy in squamates; rhynchocephalian fossil taxa also need to be considered. There are also significant differences between the skull shapes of aquatic taxa and those of terrestrial taxa. Of the observed variation in skull shape, most variation is subsumed by variation in dentary tooth base shape, the type of jaw movement employed (e.g., orthal vs. propalinal) and the number of palatal tooth rows. By comparison, the presence or absence of flanges, dentary tooth number and palatal tooth row orientation subsume much less. Skull length was also found to be a poor descriptor of overall skull shape. Compared to basal rhynchocephalians members of more derived terrestrial radiations possess an enlarged postorbital area, a high parietal, and a jaw joint positioned ventral to the tooth row. Modification of these features is closely associated with increased biting performance and thus access to novel food items. Some of these same trends are apparent during Sphenodon ontogeny where skull growth is allometric and there is evidence for ontogenetic variation in diet. J. Morphol., 2008. © 2008 Wiley-Liss, Inc. [source] Estimating ancestral distributions of lineages with uncertain sister groups: a statistical approach to Dispersal,Vicariance Analysis and a case using Aesculus L. (Sapindaceae) including fossilsJOURNAL OF SYSTEMATICS EVOLUTION, Issue 5 2009A.J. HARRIS Abstract, We propose a simple statistical approach for using Dispersal,Vicariance Analysis (DIVA) software to infer biogeographic histories without fully bifurcating trees. In this approach, ancestral ranges are first optimized for a sample of Bayesian trees. The probability P of an ancestral range r at a node is then calculated as where Y is a node, and F(rY) is the frequency of range r among all the optimal solutions resulting from DIVA optimization at node Y, t is one of n topologies optimized, and Pt is the probability of topology t. Node Y is a hypothesized ancestor shared by a specific crown lineage and the sister of that lineage "x", where x may vary due to phylogenetic uncertainty (polytomies and nodes with posterior probability <100%). Using this method, the ancestral distribution at Y can be estimated to provide inference of the geographic origins of the specific crown group of interest. This approach takes into account phylogenetic uncertainty as well as uncertainty from DIVA optimization. It is an extension of the previously described method called Bayes-DIVA, which pairs Bayesian phylogenetic analysis with biogeographic analysis using DIVA. Further, we show that the probability P of an ancestral range at Y calculated using this method does not equate to pp*F(rY) on the Bayesian consensus tree when both variables are <100%, where pp is the posterior probability and F(rY) is the frequency of range r for the node containing the specific crown group. We tested our DIVA-Bayes approach using Aesculus L., which has major lineages unresolved as a polytomy. We inferred the most probable geographic origins of the five traditional sections of Aesculus and of Aesculus californica Nutt. and examined range subdivisions at parental nodes of these lineages. Additionally, we used the DIVA-Bayes data from Aesculus to quantify the effects on biogeographic inference of including two wildcard fossil taxa in phylogenetic analysis. Our analysis resolved the geographic ranges of the parental nodes of the lineages of Aesculus with moderate to high probabilities. The probabilities were greater than those estimated using the simple calculation of pp*F(ry) at a statistically significant level for two of the six lineages. We also found that adding fossil wildcard taxa in phylogenetic analysis generally increased P for ancestral ranges including the fossil's distribution area. The ,P was more dramatic for ranges that include the area of a wildcard fossil with a distribution area underrepresented among extant taxa. This indicates the importance of including fossils in biogeographic analysis. Exmination of range subdivision at the parental nodes revealed potential range evolution (extinction and dispersal events) along the stems of A. californica and sect. Parryana. [source] Discrimination of extant Pan species and subspecies using the enamel,dentine junction morphology of lower molarsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2009Matthew M. Skinner Abstract Previous research has demonstrated that species and subspecies of extant chimpanzees and bonobos can be distinguished on the basis of the shape of their molar crowns. Thus, there is potential for fossil taxa, particularly fossil hominins, to be distinguished at similar taxonomic levels using molar crown morphology. Unfortunately, due to occlusal attrition, the original crown morphology is often absent in fossil teeth, and this has limited the amount of shape information used to discriminate hominin molars. The enamel,dentine junction (EDJ) of molar teeth preserves considerable shape information, particularly in regard to the original shape of the crown, and remains present through the early stages of attrition. In this study, we investigate whether the shape of the EDJ of lower first and second molars can distinguish species and subspecies of extant Pan. Micro-computed tomography was employed to non-destructively image the EDJ, and geometric morphometric analytical methods were used to compare EDJ shape among samples of Pan paniscus (N = 17), Pan troglodytes troglodytes (N = 13), and Pan troglodytes verus (N = 18). Discriminant analysis indicates that EDJ morphology distinguishes among extant Pan species and subspecies with a high degree of reliability. The morphological differences in EDJ shape among the taxa are subtle and relate to the relative height and position of the dentine horns, the height of the dentine crown, and the shape of the crown base, but their existence supports the inclusion of EDJ shape (particularly those aspects of shape in the vertical dimension) in the systematic analysis of fossil hominin lower molars. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source] The tree of life and the rock of ages: Are we getting better at estimating phylogeny?BIOESSAYS, Issue 3 2002Matthew A. Wills In a recent paper,(1) palaeontologist Mike Benton claimed that our ability to reconstruct accurately the tree of Life may not have improved significantly over the last 100 years. This implies that the cladistic and molecular revolutions may have promulgated as much bad "black box" science as rigorous investigation. Benton's assessment was based on the extent to which cladograms (typically constructed with reference only to distributions of character states) convey the same narrative as the geochronological ages of fossil taxa (an independent data set). Fossil record quality varies greatly between major clades, and the palaeontological dating "yardstick" may be more appropriate for some groups than others. BioEssays 24:203,207, 2002. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/bies.10065. [source] Bird evolution in the Eocene: climate change in Europe and a Danish fossil faunaBIOLOGICAL REVIEWS, Issue 4 2006Bent E. K. Lindow ABSTRACT The pattern of the evolutionary radiation of modern birds (Neornithes) has been debated for more than 10 years. However, the early fossil record of birds from the Paleogene, in particular, the Lower Eocene, has only recently begun to be used in a phylogenetic context to address the dynamics of this major vertebrate radiation. The Cretaceous-Paleogene (K-P) extinction event dominates our understanding of early modern bird evolution, but climate change throughout the Eocene is known to have also played a major role. The Paleocene and Lower Eocene was a time of avian diversification as a result of favourable global climatic conditions. Deteriorations in climate beginning in the Middle Eocene appear to be responsible for the demise of previously widespread avian lineages like Lithornithiformes and Gastornithidae. Other groups, such as Galliformes display replacement of some lineages by others, probably related to adaptations to a drier climate. Finally, the combination of slowly deteriorating climatic conditions from the Middle Eocene onwards, appears to have slowed the evolutionary rate in Europe, as avian faunas did not differentiate markedly until the Oligocene. Taking biotic factors in tandem with the known Paleogene fossil record of Neornithes has recently begun to illuminate this evolutionary event. Well-preserved fossil taxa are required in combination with ever-improving phylogenetic hypotheses for the interrelationships of modern birds founded on morphological characters. One key avifauna of this age, synthesised for the first time herein, is the Lower Eocene Fur Formation of Denmark. The Fur birds represent some of the best preserved (often in three dimensions and with soft tissues) known fossil records for major clades of modern birds. Clear phylogenetic assessment of these fossils will prove critical for future calibration of the neornithine evolutionary timescale. Some early diverging clades were clearly present in the Paleocene as evidenced directly by new fossil material alongside the phylogenetically constrained Lower Eocene taxa. A later Oligocene radiation of clades other than Passeriformes is not supported by available fossil data. [source] Phylogeny of the sea spiders (Arthropoda, Pycnogonida) based on direct optimization of six loci and morphologyCLADISTICS, Issue 3 2007Claudia P. Arango Higher-level phylogenetics of Pycnogonida has been discussed for many decades but scarcely studied from a cladistic perspective. Traditional taxonomic classifications are yet to be tested and affinities among families and genera are not well understood. Pycnogonida includes more than 1300 species described, but no systematic revisions at any level are available. Previous attempts to propose a phylogeny of the sea spiders were limited in characters and taxon sampling, therefore not allowing a robust test of relationships among lineages. Herein, we present the first comprehensive phylogenetic analysis of the Pycnogonida based on a total evidence approach and Direct Optimization. Sixty-three pycnogonid species representing all families including fossil taxa were included. For most of the extant taxa more than 6 kb of nuclear and mitochondrial DNA and 78 morphological characters were scored. The most parsimonious hypotheses obtained in equally weighted total evidence analyses show the two most diverse families Ammotheidae and Callipallenidae to be non-monophyletic. Austrodecidae + Colossendeidae + Pycnogonidae are in the basal most clade, these are morphologically diverse groups of species mostly found in cold waters. The raising of the family Pallenopsidae is supported, while Eurycyde and Ascorhynchus are definitely separated from Ammotheidae. The four fossil taxa are grouped within living Pycnogonida, instead of being an early derived clade. This phylogeny represents a solid framework to work towards the understanding of pycnogonid systematics, providing a data set and a testable hypothesis that indicate those clades that need severe testing, especially some of the deep nodes of the pycnogonid tree and the relationships of ammotheid and callipallenid forms. The inclusion of more rare taxa and additional sources of evidence are necessary for a phylogenetic classification of the Pycnogonida. © The Willi Hennig Society 2006. [source] The phylogeny of the living and fossil Sphenisciformes (penguins)CLADISTICS, Issue 5 2006Daniel T. Ksepka We present the first phylogenetic analysis of the Sphenisciformes that extensively samples fossil taxa. Combined analysis of 181 morphological characters and sequence fragments from mitochondrial and nuclear genes (12S, 16S, COI, cytochrome b, RAG-1) yields a largely resolved tree. Two species of the New Zealand Waimanu form a trichotomy with all other penguins in our result. The much discussed giant penguins Anthropornis and Pachydyptes are placed in two clades near the base of the tree. Stratigraphic and phylogenetic evidence suggest that some lineages of penguins attained very large body size rapidly and early in the clade's evolutionary history. The only fossil taxa that fall inside the crown clade Spheniscidae are fossil species assigned to the genus Spheniscus. Thus, extant penguin diversity is more accurately viewed as the product of a successful radiation of derived taxa than as an assemblage of survivors belonging to numerous lineages. The success of the Spheniscidae may be due to novel feeding adaptations and a more derived flipper apparatus. We offer a biogeographical scenario for penguins that incorporates fossil distributions and paleogeographic reconstructions of the Southern continent's positions. Our results do not support an expansion of the Spheniscidae from a cooling Continental Antarctica, but instead suggest those species that currently breed in that area are the descendants of colonizers from the Subantarctic. Many important divergence events in the clade Spheniscidae can instead be explained by dispersal along the paths of major ocean currents and the emergence of new islands due to tectonic events. © The Willi Hennig Society 2006. [source] | ||||||||||||||||||||||