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Temkin I.,National Museum of Natural History
BMC Evolutionary Biology | Year: 2010

Background. The superfamily Pterioidea is a morphologically and ecologically diverse lineage of epifaunal marine bivalves distributed throughout the tropical and subtropical continental shelf regions. This group includes commercially important pearl culture species and model organisms used for medical studies of biomineralization. Recent morphological treatment of selected pterioideans and molecular phylogenetic analyses of higher-level relationships in Bivalvia have challenged the traditional view that pterioidean families are monophyletic. This issue is examined here in light of molecular data sets composed of DNA sequences for nuclear and mitochondrial loci, and a published character data set of anatomical and shell morphological characters. Results. The present study is the first comprehensive species-level analysis of the Pterioidea to produce a well-resolved, robust phylogenetic hypothesis for nearly all extant taxa. The data were analyzed for potential biases due to taxon and character sampling, and idiosyncracies of different molecular evolutionary processes. The congruence and contribution of different partitions were quantified, and the sensitivity of clade stability to alignment parameters was explored. Conclusions. Four primary conclusions were reached: (1) the results strongly supported the monophyly of the Pterioidea; (2) none of the previously defined families (except for the monotypic Pulvinitidae) were monophyletic; (3) the arrangement of the genera was novel and unanticipated, however strongly supported and robust to changes in alignment parameters; and (4) optimizing key morphological characters onto topologies derived from the analysis of molecular data revealed many instances of homoplasy and uncovered synapomorphies for major nodes. Additionally, a complete species-level sampling of the genus Pinctada provided further insights into the on-going controversy regarding the taxonomic identity of major pearl culture species. © 2010 Tmkin; licensee BioMed Central Ltd. Source

Labandeira C.C.,National Museum of Natural History | Labandeira C.C.,University of Maryland University College
Annals of the Missouri Botanical Garden | Year: 2010

A defining event for Mesozoic plant-pollinator interactions is the angiosperm radiation, which extended the reach of pollinating insects during the Early Cretaceous in a brief interval of geologic time. Recent evidence indicates that events beginning in the Early Permian and increasing during the Middle Jurassic provided repeated opportunities for insect feeding on pollen, pollination drops, and reproductive tissues of extinct gymnosperm lineages. Pollination was an associated development. Studies on the detailed mouthpart structure of several fluid-feeding insect lineages indicate targeting of certain tubular features of gymnosperm ovulate organs that previously were considered anomalous and difficult to interpret. One mouthpart type, the long-proboscid condition, consists of elongate, tubular (siphonate) proboscises that accessed surface fluids powered by a cibarial pump, often assisted with a distal proboscis sponging organ. These proboscises were received in ovulate organs through often intricate cupulate integumental tubes, interovular channels, salpinx tubuli, pappus tubules, prolonged micropyles, and a catchment funnel-pipe-micropyle device. These ovulate structures also are consistent with insect access to nutritive rewards, including pollination drops, nectarial secretions, and pollen. Other evidence for pollination includes the entomophilous structure and size of pollen found on insect and plant contact surfaces and in insect guts, nutritional levels of modern pollination drop fluids similar to angiosperm nectar for supporting metabolically high activity levels of aerially active insects, and plant-host outcrossing. While the long-proboscid pollination mode of fluid feeding targeted gymnosperm hosts that deployed unisexual reproductive organs at some distance from each other, either on the same or on different plants, another mode of pollination, that of mandibulate insects, consumed typically solid tissues in compact bisexual strobili, targeting pollen and perhaps pollination drops (adults), and associated sterile tissues (larvae). These two groups of pollinator associations were irretrievably altered as angiosperms diversified during a 35-million-year interval of the Early Cretaceous, evident in three patterns. First was the demise of most pollinator associations that evolved during the preceding 65 million years; second was the lateral transfer of some of these associations onto angiosperms that continue today as relicts; and third was emergence of new pollinator associations with angiosperms. © 2010 Missouri Botanical Press. Source

Fox D.L.,University of Minnesota | Honey J.G.,University of Colorado at Boulder | Martin R.A.,Murray State University | Pelaez-Campomanes P.,National Museum of Natural History
Bulletin of the Geological Society of America | Year: 2012

Fossiliferous strata in the Meade Basin (southwest Kansas) preserve numerous superposed mammalian faunas and calcareous paleosols that range in age from the Clarendonian North American Land Mammal Age (NALMA; 12.0-9.0 Ma, early late Miocene) to the early Irvingtonian NALMA (ca. 2.5-ca. 1.0 Ma, early Pleistocene). Faunas from these sections document the evolution of the small mammal community of the modern grassland ecosystem of the region, and the stable isotope composition of paleosol carbonates provides a means by which the environmental context of the evolution of the modern ecosystem may be documented. We used the stable carbon isotope composition (δ13C relative to Vienna Peedee belemnite [VPDB]) of 194 pedogenic carbonates from 19 measured sections to reconstruct the history of C4 grass abundance in the Meade Basin. Paleosol carbonate δ13C values reflect the proportion of C3 (trees, shrubs, cool- climate grasses) and C4 (warm-climate grasses) plants that grew in an ancient soil and provide a means with which to reconstruct past mammalian habitats. Paleosol carbonate δ13C values record a three-phase increase in the abundance of C4 biomass during the Neogene in the Meade Basin. Late Miocene sections have mean δ13C values of -7.6‰ ± 0.90‰ (Clarendonian) and -6.5‰ ± 0.31‰ (Hemphillian NALMA, 9.0-4.9 Ma), consistent with 17% and 26% C4 biomass, respectively. Miocene δ13C values from Meade are statistically identical to published δ13C values for Miocene paleosol carbonates elsewhere in the southern Great Plains, supporting the widespread presence of ~20% C4 biomass on average in the region throughout the Miocene. The abundance of C4 biomass increased between the end of the Hemphillian section and the beginning of the early Blancan NALMA (5.0-3.0 Ma). Early and middle Blancan (3.0-2.5 Ma) carbonates have statistically identical δ13C values (-4.9‰ ± 0.90‰ and -5.0‰ ± 1.10‰, respectively), suggesting a stable ecosystem during the early Pliocene, although high δ13C variability in densely sampled intervals suggests a high degree of landscape-scale variation in C4 abundance. The final phase, geochronologically controlled by two well- characterized ashes (Huckleberry Ridge, 2.10 Ma; Cerro Toledo B, 1.47-1.23 Ma) and magnetostratigraphy, is a trend to higher δ13C values from the late Blancan to early Irvingtonian (ca. 2.5-ca 1.0 Ma) from -4‰ at the base of the section to ~1‰ at the top, corresponding to an increase from almost 50% to 65% C4 biomass. The abundance of C4 biomass first reaches modern levels for the region (78% ± 10.9%) around the level of the Cerro Toledo B ash, indicating that a modern-like grassland ecosystem first appeared in the region ca. 1.3 Ma, although δ13C values do not remain consistently high through the rest of the section. © 2012 Geological Society of America. Source

Erwin D.H.,National Museum of Natural History | Erwin D.H.,Santa Fe Institute
Developmental Biology | Year: 2011

I present a new compilation of the distribution of the temporal distribution of new morphologies of marine invertebrates associated with the Ediacaran-Cambrian (578-510 Ma) diversification of Metazoa. Combining this data with previous work on the hierarchical structure of gene regulatory networks, I argue that the distribution of morphologies may be, in part, a record of the time-asymmetric generation of variation. Evolution has been implicitly viewed as a uniformitarian process where the rates may vary but the underlying processes, including the types of variation, are essentially invariant through time. Recent studies demonstrate that this uniformitarian assumption is false, suggesting that the types of variation may vary through time. © 2010. Source

Erwin D.H.,National Museum of Natural History
Paleobiology | Year: 2015

The extent of morphologic innovation during the Ediacaran-Cambrian diversification of animals was unique in the history of metazoan life. This episode was also associated with extensive changes in the redox state of the oceans, in the structure of benthic and pelagic marine ecosystems, in the nature of marine sediments, and in the complexity of developmental interactions in Eumetazoa. But did the phylogenetic and morphologic breadth of this episode simply reflect the unusual outcome of recurrent evolutionary processes, or was it the unique result of circumstances, whether in the physical environment, in developmental mechanisms, or in ecological interactions? To better characterize the uniqueness of the events, I distinguish among these components on the basis of the extent of sensitivity to initial conditions and unpredictability, which generates a matrix of possibilities from fully contingent to fully deterministic. Discriminating between these differences is important for informing debates over determinism versus the contingency in the history of life, for understanding the nature of evolutionary theory, and for interpreting historically unique events. © 2015 The Paleontological Society. All rights reserved. Source

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