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Well-sampled dinosaur communities from the Jurassic through the early Late Cretaceous show greater taxonomic diversity among larger (>50 kg) theropod taxa than communities of the Campano-Maastrichtian, particularly to those of eastern/central Asia and Laramidia. The large carnivore guilds in Asiamerican assemblages are monopolized by tyranno-saurids, with adult medium-sized (50-500 kg) predators rare or absent. In contrast, various clades of theropods are found to occupy these body sizes in earlier faunas, including early tyrannosauroids. Assemblages with 'missing middle-sized' predators are not found to have correspondingly sparser diversity of potential prey species recorded in these same faunas. The 'missing middle-sized' niches in the theropod guilds of Late Cretaceous Laramidia and Asia may have been assimilated by juvenile and subadults of tyrannosaurid species, functionally distinct from their adult ecomorphologies. It is speculated that if tyrannosaurids assimilated the niches previously occupied by mid-sized theropod predators, we would expect the evolution of distinct transitions in morphology and possibly the delay of the achievement of somatic maturity in species of this taxon. Key words: dinosaurs, ontogeny, theropod, paleoecology, Mesozoic, Tyrannosauridae. Les communautes de dinosaures bien echantillonnees du Jurassique jusqu'a debut du Cretace tardif presentent une plus grande diversite taxonomique au sein des taxons de grands theropodes (>50 kg) que les communautes du Campano-Maastrichtien, en particulier celles de l'Asie orientale/centrale et de la Laramidie. Les tyrannosaurides monopolisent les guildes de grands carnivores dans les assemblages asiamericains, dans lesquels les predateurs adultes de taille moyenne (50-500 kg) sont rares ou absents. En revanche, divers clades de theropodes presentent ces tailles de corps dans les assemblages plus vieux, dont certains des premiers tyrannosauro'ides. Les assemblages dont les predateurs de taille moyenne sont absents ne presentent pas une diversite moindre correspondante d'especes de proies potentielles. Les niches dont sont absentes les tailles moyennes dans les guildes de theropodes du Cretace tardif de la Laramidie et de l'Asie pourraient avoir ete assimilees par des individus juveniles et subadultes d'especes de tyrannosaurides qui sont fonctionnellement differents de leurs ecomorphologies adultes. Il est postule que, si des tyrannosaurides ont assimile les niches auparavant occupees par des predateurs theropodes de taille moyenne, une evolution caracterisee par des transitions distinctes sur le plan de la morphologie et, possiblement, une maturite somatique plus tardive chez les especes de ce taxon seraient attendues. [Traduit par la Redaction] Mots-cles: dinosaures, ontogenese, theropode, paleoecologie, Mesozo'ique, tyrannosaurides., Introduction Dale Russell's(1970) review of the Tyrannosauridae of the Late Cretaceous Western Canada represents one of the most significant contributions to the study of the tyrant dinosaur in the mid-20th [...]

Mid-altitude, mid-latitude mountains are complex environments owing to their Pleistocene glacial heritage, the importance of geomorphic processes on the steep slopes, and the climatic conditions that are often close to periglacial. These factors, along with the fragmentation of the alpine habitats, enhance the topographic and floristic diversity of these environments in northeastern North America. Through case studies, this synthesis underlines the interactions between the geosphere (glacial, paraglacial, and periglacial processes), the atmosphere (climatic fluctuations), and the biosphere (vegetation establishment and evolution to the present day) that explain the low elevation of the northeastern North American alpine environment and that testify to its complexity. Vegetation established earlier in the southern ranges, following the same general trend as the Laurentian Ice Sheet recession. However, local factors such as ice retreat, response to global-scale climate changes, and paraglacial processes acted in synergy to increase the resilience and to influence the occurrence of alpine landscapes. The establishment of the latter environment can therefore be considered to be azonal. Finally, our findings highlight the lack of a conceptual framework, systemic studies, and multi-proxy reconstructions of alpine environments located at the limit of bioclimatic zones controlled by the equilibrium between biostatic and rhexistatic regimes. Les montagnes d'altitude et de latitude moyennes constituent des environnements complexes en raison de leur heritage glaciaire Pleistocene, de l'importance des processus geomorphologiques sur les pentes abruptes et des conditions climatiques qui s'approchent souvent de conditions periglaciaires. Jumeles a une fragmentation des habitats alpins, ces facteurs rehaussent la diversite topographique et floristique de ces environnements dans le nord-est de l'Amerique du Nord. Par des etudes de cas, la presente synthese souligne les interactions entre la geosphere (processus glaciaires, paraglaciaires et periglaciaires), l'atmosphere (fluctuations climatiques) et la biosphere (etablissement de la vegetation et son evolution jusqu'a maintenant) qui expliquent l'elevation peu elevee de l'environnement alpin dans le nord-est de l'Amerique du Nord et qui temoignent de sa complexite. La vegetation s'est etablie plus tot dans les etendues au sud, suivant la meme tendance generale que le retrait de l'Inlandsis laurentidien. Toutefois, des facteurs locaux, tels que le retrait glaciaire, la reaction aux changements climatiques a l'echelle mondiale et les processus paraglaciaires ont agi en synergie pour avoir une influence sur la presence des divers paysages alpins et pour augmenter leur resilience. L'etablissement de ce dernier environnement peut donc etre considere comme etant azonal. Finalement, nos resultats mettent en evidence le manque de cadre conceptuel, d'etudes systemiques et de reconstructions multi-proxy des environnements alpins situes a la limite des zones bioclimatiques controlees par l'equilibre entre les regimes biostatiques et rhexistatiques. [Traduit par la Redaction], Introduction The diverse and combined influences of many orogenies--some in the recent past on a geological timescale--with the many subsequent erosion agents, which depend on climatic variations at local and [...]

Author(s): Pavel Flegontov [sup.1] [sup.2] [sup.3] , N. Ezgi Altinisik [sup.1] , Piya Changmai [sup.1] , Nadin Rohland [sup.4] , Swapan Mallick [sup.4] [sup.5] [sup.6] , Nicole Adamski [sup.4] [sup.5] [...], Much of the American Arctic was first settled 5,000 years ago, by groups of people known as Palaeo-Eskimos. They were subsequently joined and largely displaced around 1,000 years ago by ancestors of the present-day Inuit and Yup'ik.sup.1-3. The genetic relationship between Palaeo-Eskimos and Native American, Inuit, Yup'ik and Aleut populations remains uncertain.sup.4-6. Here we present genomic data for 48 ancient individuals from Chukotka, East Siberia, the Aleutian Islands, Alaska, and the Canadian Arctic. We co-analyse these data with data from present-day Alaskan Iñupiat and West Siberian populations and published genomes. Using methods based on rare-allele and haplotype sharing, as well as established techniques.sup.4,7-9, we show that Palaeo-Eskimo-related ancestry is ubiquitous among people who speak Na-Dene and Eskimo-Aleut languages. We develop a comprehensive model for the Holocene peopling events of Chukotka and North America, and show that Na-Dene-speaking peoples, people of the Aleutian Islands, and Yup'ik and Inuit across the Arctic region all share ancestry from a single Palaeo-Eskimo-related Siberian source. DNA analysis of ancient individuals and modern populations suggests that the population history of North America can be explained by the admixture of two ancestral lineages--Palaeo-Eskimos and First Peoples.

Tangshanaspis Zhou and Zhang, 1978 (Family Missisquoiidae), has been reported widely from western North America and has been assigned invariably to a single species, T. depressa (Stitt, 1971b). The base of the T. depressa Subzone as defined in Oklahoma is an important biostratigraphic datum for inter-regional correlation of uppermost Cambrian strata. Study of previously undescribed material in collections from Oklahoma shows that T. depressa is, in fact, a composite of cranidia and pygidia that belong to two stratigraphically segregated species in the Signal Mountain Formation. Tangshanaspis silveri n. sp. includes the pygidial morph originally attributed to T. depressa. Revision of the species from Oklahoma allows definition of a new biostratigraphic unit, the Tangshanaspis Zone, which is divided into a lower T. silveri Fauna and an overlying T. depressa Fauna; in addition to the eponymous species, the T. depressa Fauna includes pygidia that represent two additional species of Tangshanaspis that are placed in open nomenclature. Correlation with other areas suggests that the 'Missisquoia' mackenziensis Fauna of northern Canada may be equivalent to the T. silveri Fauna of Oklahoma, rather than a pre-Tangshanaspis interval that is unrepresented elsewhere in Laurentian North America. Tangshanaspis Zhou et Zhang, 1978 (famille des Missisquoiides) a ete signale en plusieurs localites de l'ouest de l'Amerique du Nord et a invariablement ete affecte a une seule espece, T. depressa (Stitt, 1971b). La base de la souszone a T. depressa definie en Oklahoma constitue une importante reference biostratigraphique pour la correlation interregionale des strates du sommet du Cambrien. L'etude de materiel non decrit auparavant de collections provenant de l'Oklahoma demontre que T. depressa est en fait un composite de cranidiums et de pygidiums appartenant a deux especes separees stratigraphiquement dans la Formation de Signal Mountain. Tangshanaspis silveri n. sp. comprend la forme pygidiale affectee initialement a T. depressa.La reevaluation des especes de l'Oklahoma permet la definition d'une nouvelle unite biostratigraphique, la zone a Tangshanaspis, qui est subdivisee en une faune inferieure a T. silveri et une faune sus-jacente a T. depressa. Outre l'espece eponyme, la faune a T. depressa comprend des pygidiums representant deux autres especes de Tangshanaspis qui sont placees en nomenclature ouverte. La correlation avec d'autres regions suggere que la faune a <> mackenziensis du nord du Canada pourrait etre equivalente a la faune a T. silveri de l'Oklahoma, plutot que de representer un intervalle pre-Tangshanaspis present nulle part ailleurs en Amerique du Nord laurentienne. [Traduit par la Redaction], Introduction Forty years ago, Stitt (1971b) described what at the time was the oldest North American species thought to belong to Missisquoia Shaw, 1951, M. depressa. This species appeared in [...]

The management of water resources in arid and semiarid areas has long been a challenge, from ancient Mesopotamia to the modern southwestern United States. As our understanding of the hydrological and climatological cycles has improved, and our ability to manipulate the hydrologic cycle has increased, so too have the challenges associated with managing a limited natural resource for a growing population. Modern civilization has made remarkable progress in water management in the past few centuries. Burgeoning cities now survive in desert regions, relying on a mix of simple and complex technologies and management systems to bring adequate water and remove wastewater. These systems have permitted agricultural production and urban concentrations to expand in regions previously thought to have inadequate moisture. However, evidence is also mounting that our current management and use of water is unsustainable. Physical, economic, and ecological limits constrain the development of new supplies and additional water withdrawals, even in regions not previously thought vulnerable to water constraints. New kinds of limits are forcing water managers and policy makers to rethink previous assumptions about population, technology, regional planning, and forms of development. In addition, new threats, especially the challenges posed by climatic changes, are now apparent. Sustainably managing and using water in arid and semiarid regions such as the southwestern United States will require new thinking about water in an interdisciplinary and integrated way. The good news is that a wide range of options suggest a roadmap for sustainable water management and use in the coming decades. climate change | soft path | freshwater | sustainability | water management doi/ 10.1073/pnas.1005473107

A key feature of anticipated 21st century droughts in Southwest North America is the concurrence of elevated temperatures and increased aridity. Instrumental records and paleoclimatic evidence for past prolonged drought in the Southwest that coincide with elevated temperatures can be assessed to provide insights on temperature-drought relations and to develop worst-case scenarios for the future. In particular, during the medieval period, ~AD 900-1300, the Northern Hemisphere experienced temperatures warmer than all but the most recent decades. Paleoclimatic and model data indicate increased temperatures in western North America of approximately 1[degrees]C over the long-term mean. This was a period of extensive and persistent aridity over western North America. Paleoclimatic evidence suggests drought in the mid-12th century far exceeded the severity, duration, and extent of subsequent droughts. The driest decade of this drought was anomalously warm, though not as warm as the late 20th and early 21st centuries. The convergence of prolonged warming and arid conditions suggests the mid-12th century may serve as a conservative analogue for severe droughts that might occur in the future. The severity, extent, and persistence of the 12th century drought that occurred under natural climate variability, have important implications for water resource management. The causes of past and future drought will not be identical but warm droughts, inferred from paleoclimatic records, demonstrate the plausibility of extensive, severe droughts, provide a long-term perspective on the ongoing drought conditions in the Southwest, and suggest the need for regional sustainability planning for the future. climate change | water resources | paleoclimatology | medieval period doi/ 10.1073/pnas.0911197107

Three lithospheric cross sections provide a continental-scale synthesis of more than two decades of coordinated multidisciplinary research during the Canadian Lithoprobe project. The sections are based on seismic reflection and refraction data combined with a broad range of geological, geochemical, geochronological, and geophysical data. The dataset is derived from remnants of nearly every kind of tectonic regime, and the geologic history of the entrained rocks spans the Present to the Mesoarchean. The longest of the three cross sections is located within a 6000 km long Trans-Canada corridor traversing the North American continent at 45°N-55°N. From west to east, the profile crosses the Juan de Fuca ridge and active Cascadia subduction zone, the Cordilleran, Albertan, and Trans-Hudson orogens, the Superior Province, the Midcontinent rift, the Grenville and Appalachian orogens, and the Atlantic passive margin. The two northern cross sections include (i) a 2000 km long corridor in northwestern Canada (54°N-63°N) crossing the Cordilleran, Wopmay, and Slave orogens; and (ii) a 1600 km long corridor in northeastern Canada (52°N-61°N) crossing the New Quebec and Torngat orogens, the Nain craton, and the Makkovik and Grenville orogens. The unprecedented scale of the cross sections illuminates the assembly of the North American continent. Relationships between orogens are emphasized; plate collisions and accretions have sequentially stacked orogen upon orogen such that the older crust forms basement to the next younger. The large-scale perspective of these regional sections highlights the subhorizontal Moho that is indicative of either structural or thermal re-equilibration (or both), as few crustal roots beneath orogens are preserved. In contrast, heterogeneities in the lithospheric mantle suggest that, in certain situations, relict subducted or delaminated lithosphere can remain intact beneath and eventually within cratonic lithospheric mantle. Trois sections transversales lithographiques fournissent une synthase a l'eechelle continentale de plus de deux decennies de recherches multidisciplinaires coordonneees dans le cadre du projet canadien Lithoprobe. Les sections sont basees sur des donneees de sismique reflexion et refraction combineees a une vaste gamme de donnees geologiques, geochimiques, geeochronologiques et geophysiques. L'ensemble des donnees provient de lambeaux de presque tous les genres de regimes tectoniques et l'historique geologique des roches entrances couvre une peeriode allant du Present au Mesoarcheen. La plus longue des trois sections transversales est situeee le long d'un corridor transcanadien d'une longueur de 6000 km traversant le continent nord-americain a une latitude de 45-55 °N. D'ouest en est, le profile traverse la crete de Juan de Fuca et la zone de subduction active Cascadia, les orogenes de la Cordillere, de l'Alberta et trans-hudsonien, la province du Superieur, le rift mi-continental, les orogenes de Grenville et des Appalaches ainsi que la bordure passive de l'Atlantique. Les deux sections transversales au nord comprennent : (i) un corridor d'une longueur de 2000 km dans le nord-ouest du Canada (54-63 °N) traversant les orogenes de la Cordillere, de Wopmay et des Esclaves et (ii) un corridor d'une longueur de 1600 km dans le nord-est du Canada (52-61 °N) traversant les orogenes du Nouveau-Quebec et de Torngat, le craton de Nain et les orogenes Makkovik et de Grenville. L'eechelle sans precedent des sections transversals jette de la lumiere sur l'assemblage du continent nord-americain. Les relations entre les orogenes sont soulignees; des collisions entre des plaques et des accretions ont empile orogene sur orogene de maniere sequentielle de sorte que l'ancienne crcrate forme le socle de l'orogene qui suit. La perspective a grande eechelle de ces sections regionales souligne le Moho subhorizontal, indiquant un reequilibrage structural ou thermique (ou les deux) puisque peu de racines de la crcrate sont preeserveees sous les orogenes. Par ailleurs, les heterogeneeites dans le manteau lithospheerique suggerent que, dans certaines situations, une lithosphere relique subduite ou de delamination puisse demeurer intacte sous, et eventuellement dans, le manteau lithospherique cratonique. [Traduit par la Redaction], Introduction The North American continent is a geological mosaic representing 4 billion years of lithospheric growth, destruction, and reorganization. To determine the current structure of the Canadian continental lithosphere and [...]

The late Pleistocene witnessed the extinction of 35 genera of North American mammals. The last appearance dates of 16 of these genera securely fall between 12,000 and 10,000 radiocarbon years ago ([approximately equal to] 13,800-11,400 calendar years B.P.), although whether the absence of fossil occurrences for the remaining 19 genera from this time interval is the result of sampling error or temporally staggered extinctions is unclear. Analysis of the chronology of extinctions suggests that sampling error can explain the absence of terminal Pleistocene last appearance dates for the remaining 19 genera. The extinction chronology of North American Pleistocene mammals therefore can be characterized as a synchronous event that took place 12,000-10,000 radiocarbon years B.P. Results favor an extinction mechanism that is capable of wiping out up to 35 genera across a continent in a geologic instant. climate change | extraterrestrial impact | overkill | Quaternary extinctions | radiocarbon dates doi/10.1073/pnas.0908153106

Although the North American megafaunal extinctions and the formation of novel plant communities are well-known features of the last deglaciation, the causal relationships between these phenomena are unclear. Using the dung fungus Sporormiella and other paleoecological proxies from Appleman Lake, Indiana, and several New York sites, we established that the megafaunal decline closely, preceded enhanced fire regimes and the development of plant communities that have no modern analogs. The loss of keystone megaherbivores may thus have altered ecosystem structure and function by the release of palatable hardwoods from herbivory pressure and by fuel accumulation. Megafaunal populations collapsed from 14,800 to 13,700 years ago, well before the final extinctions and during the Bolling-Allerod warm period. Human impacts remain plausible, but the decline predates Younger Dryas cooling and the extraterrestrial impact event proposed to have occurred 12,900 years ago. 10.1126/science.1179504

Platycrinites is traditionally one of the more recognizable crinoids, a camerate crinoid with very few if any fixed brachials or interradials and a helically twisted column. Accordingly, many taxa have been assigned to this genus. With a better understanding of the Platycrinitidae, these characters actually unite the family Platycrinitidae rather than the genus. Further, use of different genus-diagnostic characters in Western Europe versus North America has resulted in a confused systematics for this important late Paleozoic family. Here, we objectively define genera within the Platycrinitidae and assign all species to either newly defined or newly named genera. A phylogenetic hypothesis, incorporating both parsimony-based character analysis and stratigraphic ranges, of the genera within the Platycrinitidae is presented. With consideration of the type species, Platycrinites laevis Miller, 1821, Platycrinites sensu stricto is distinguished from Platycrinites sensu lato, which is used for species that cannot be assigned with confidence to any objectively defined genus. New genera are Artaocrinus n. gen., Collicrinus n. gen., Elegantocrinus n. gen., and Laticrinus n. gen.; and Exsulacrinus Bowsher and Strimple, 1986 is designated a junior synonym of Platycrinites s.s. Collicrinus shumardi n. gen. and sp., Laticrinus oweni n. gen. and sp., and Laticrinus wachsmuthi n. gen. and sp. are described; and Platycrinitesformosus approximatus (Miller and Gurley, 1896a) is designated a junior synonym of Platycrinites formosus (Miller and Gurley, 1895a), which is reassigned here to Collicrinus n. gen. Platycrinites s.s. now includes 14 species and species-level taxa, and 76 species are assigned to Platycrinites s.l. Ten species are designated nomina dubia, as are taxa based solely on columnals or pluricolumnals. Two species are designated nomina nuda, and two are transferred to genera outside of the Platycrinitidae. In addition, twenty-seven species and four opennomenclature taxa are each reassigned to a different genus.

We present results from an early Eocene (ca. 50-56 Ma ago) regional modeling sensitivity experiment that examines the role of atmospheric C[O.sub.2] in determining the regional climate of western North America. This is the first paleoclimate modeling study to investigate the possible role of increased C[O.sub.2] in influencing the early Eocene climate on a regional scale. We take a regional modeling approach with the goal of using higher spatial resolution to elucidate the role of specific climate forcing mechanisms (here, C[O.sub.2]) upon a region with relatively dense paleoclimate proxy data coverage. The spatial resolution of global climate models does not permit the close comparison of model results to proxy climate data in a way that helps to distinguish between regional and global climate forcings, which is a goal of this study. While our results suggest that C[O.sub.2] was most likely at least as high as 2240 ppm, this high concentration does not yield a regional climate that matches regional proxy data in all aspects. Therefore, in combination with high atmospheric C[O.sub.2], other forcing factors must have played significant roles in defining the nature of early Eocene climate.

Early invasions of the North American shore occurred mainly via deposition of ballast rock, which effectively transported pieces of the intertidal zone across the Atlantic. From 1773-1861, >880 European ships entered Pictou Harbor, Nova Scotia, as a result of emigration and trade from Europe. The rockweed Fucus serratus (1868) and the snail Littorina littorea ([approximately equal to]1840) were found in Pictou during this same period. With shipping records (a proxy for propagule pressure) to guide sampling, we used F. serratus as a model to examine the introductions because of its relatively low genetic diversity and dispersal capability. Microsatellite markers and assignment tests revealed 2 introductions of the rockweed into Nova Scotia: 1 from Galway (Ireland) to Pictou and the other from Greenock (Scotland) to western Cape Breton Island. To examine whether a high-diversity, high-dispersing species might have similar pathways of introduction, we analyzed L. littorea, using cytochrome b haplotypes. Eight of the 9 Pictou hapiotypes were found in snails collected from Ireland and Scotland. Our results contribute to a broader understanding of marine communities, because these 2 conspicuous species are likely to be the tip of an 'invasion iceberg' to the NW Atlantic from Great Britain and Ireland in the 19th Century. Fucus serratus | Littorina littorea | propagule pressure

Although geneticists and archaeologists continue to make progress world-wide in documenting the time and place of the initial domestication of a growing number of plants and animals, far less is known regarding the critically important context of coalescence of various species into distinctive sets or complexes of domesticates in each of the world's 10 or more independent centers of agricultural origin. In this article, the initial emergence of a crop complex is described for one of the best-documented of these independent centers, eastern North America (ENA). Before 4000 B.P. there is no indication of a crop complex in ENA, only isolated evidence for single indigenous domesticate species. By 3800 B.P., however, at least 5 domesticated seed-bearing plants formed a coherent complex in the river valley corridors of ENA. Accelerator mass spectrometer radiocarbon dates and reanalysis of archaeobotanical assemblages from a short occupation of the Riverton Site in Illinois documents the contemporary cultivation at 3800 B.P. of domesticated bottle gourd (Lagenaria siceraria), marshelder (Iva annua var. macrocarpa), sunflower (Helianthus annuus var. macrocarpus), and 2 cultivated varieties of chenopod (Chenopodium berlandieri), as well as the possible cultivation of Cucurbita pepo squash and little barley (Hordeum pusillum). Rather than marking either an abrupt developmental break or a necessary response to population-packing or compressed resource catchments, the coalescence of an initial crop complex in ENA appears to reflect an integrated expansion and enhancement of preexisting hunting and gathering economies that took place within a context of stable long-term adaptation to resource-rich river valley settings. agriculture | archaeology | Chenopodium | domestication

The fossil assemblages of the Late Cretaceous of North America are dominated by large-bodied dinosaur species. Associated skeletons of small dinosaurs are exceedingly rare, and small ( Campanian | Dinosaur Park Formation | microraptorinae | theropoda

A charcoalified fossil flower, Potomacanthus lobatus gen. et sp. nov., is described from the Early Cretaceous (Early to Middle Albian) Puddledock locality, Virginia, USA. Internal floral structure was studied using nondestructive synchrotron-radiation x-ray tomographic microscopy (SRXTM). The flower is bisexual and trimerous. The perianth consists of two whorls of tepals. The androecium has two whorls of fertile stamens. Anthers open by two distally hinged valves. The gynoecium consists of a single carpel that is plicate in the style and ascidiate in the ovary and contains a single pendant ovule. The fossil flower shares many similarities with flowers of extant Lauraceae and is unlike flowers of other families of Laurales. However, the fossil flower also differs in detail from all extant or fossil Lauraceae, particularly in configuration of the androecium. The new taxon, together with previously described but more fragmentary material from the Puddledock locality, provides the earliest fossil record of plants more closely related to Lauraceae than to any other extant family. It reveals several derived morphological characters that are potential synapomorphies among extant representatives of the family Lauraceae and contributes to the growing evidence for an early diversification of Laurales before the end of the Early Cretaceous. Key words: androecium; Early Cretaceous; floral structure and reconstruction; fossil; Lauraceae; Laurales; Potomac Group; x-ray tomography.

Late Jurassic--Cretaceous are-related volcaniclastic rocks from the southern Guerrero and western Mixteca terranes of Mexico were analyzed by U-Pb detrital zircon geochronology (laser ablation-multicollector--inductively coupled plasma--mass spectroscopy) to place constraints on the depositional history and provenance of the rocks. Pre--Middle ,Jurassic basement rocks and sandstone from the Upper Cretaceous Mexcala Formation were also analyzed to define the origin and provenance of the prevolcanic substratum, and the time of accretion of Guerrero composite terrane sequences. Data from the Taxco-Taxco Viejo, Teloloapan, and Arcelia assemblages indicate that the youngest (129-141 Ma) zircon fraction in each sequence was derived from local volcanic sources, whereas older populations (ca. 247-317, 365-459, 530-617, 712-878, 947-964, 1112-1188, 1350-1420, 1842-1929, 2126-2439, and 2709-3438 Ma) show sediment influx from varied sources, most likely through grain recycling. The major zircon clusters in these sequences match the populations recorded in the nearby Acatlan Complex. In contrast, the Huetamo sample is dominated by Lower Cretaceous (ca. 126 Ma) zircons of local volcanic provenance, and the Zihuatanejo sample contains zircon clusters (ca. 259, ca. 579, and ca. 947-1162 Mat comparable to major populations recorded in the underlying Arteaga Complex. A sample from the Middle Triassic--Middle Jurassic Arteaga Complex at Tzitzio contains zircon clusters (ca. 202-247, ca. 424, ca. 600, ca. 971, and ca. 2877 Ma) consistent with an ultimate derivation from both North American and South American sources. The sample from the Las Ollas suite contains comparable zircon populations (ca. 376-475, ca. 575, ca. 988-1141, and ca. 2642-2724 Ma). and it is interpreted to be part of the prevolcanic basement. In contrast, the youngest zircon cluster (ca. 105 Ma) in the Mexcala Formation coincides with the major volcanic events in the Taxco-Taxco Viejo, Teloloapan, and Arcelia assemblages, whereas the older clusters (ca. 600, ca. 953, ca. 1215, ca. 1913, and ca. 2656-2859 Ma) broadly match the major populations recorded in rocks from the Acatlan Complex. These new data combined with available geochemical and isotopic data indicate that the Taxco-Taxco Viejo arc assemblage developed on continental crust. The Acatlan Complex is the most plausible candidate. The Teloloapan and Arcelia arc assemblages were developed on oceanic crust as offshore arcs facing the Acatlan Complex. The Zihuatanejo terrane assemblages were developed on the Arteaga Complex, and evidence no influence from the Acatlan Complex. This suggests that these assemblages were formed farther away or in a restricted basin. The Guerrero composite and Mixteca arc successions are coeval with the Alisitos arc of northern Mexico and in part with the Nevada and Klamath ranges of the southwestern United States, and with the arc series from the Greater and Lesser Antilles and northern South America. Data indicate that during late Mesozoic time, southwestern North America was a site of intensive volcanism in a complex arc-trench system similar to that of the east Pacific. Our data are consistent with a diachronic accretion of the Guerrero composite terrane sequences, beginning during late Cenomanian time with the amalgamation of the Teloloapan and probably the Arcelia assemblages, and finishing at the end of Cretaceous time with the accretion of the Zihuatanejo terrane assemblages. Keywords: U-Pb detrital zircon, Late Jurassic-Cretaceous arc successions, Guerrero terrane, Mixteca terrane, southern Mexico, southwestern North America, Caribbean region.

Glacial Lake Agassiz has been implicated as the trigger for numerous episodes of abrupt climate change at the close of the last ice age, yet the beginning age of the lake has never been determined. Here we report the first numerical age data on the Big Stone Moraine and the oldest beaches of glacial Lake Agassiz. Organic remains from lakes, bogs, and channels distal to, and inset to, the Big Stone Moraine require that glacial activity at this moraine ceased prior to 12,000 [sup.14]C yr B.P. (13,950 cal [calendar] yr). A site near New Effington, South Dakota (United States), implies full glacial recession north of the topographic divide prior to 11,810 [sup.14]C yr B.P. (13,670 cal yr), synchronous with the beginning of glacial Lake Agassiz. Lake Agassiz shorelines inset to the moraine yield optically stimulated luminescence (OSL) ages from 14,200-12,600 yr cal. Lower strandlines are younger, but the similarity of ages suggests that initial lake lowering was faster than OSL ages can currently resolve. Nevertheless, the OSL ages represent the first numerical age assignments for the Herman, Norcross, and Upham beach ridges, setting the stage for future numerical age assignments within the Lake Agassiz basin. These two dating methods yield strongly consistent results within stated uncertainties. The age of the Big Stone Moraine implies an interval of rapid retreat for the Des Moines lobe of the Laurentide Ice Sheet during the Bolling-Allerod warm interval. The overlapping ages for the uppermost beach levels and abandonment of the highest Lake Agassiz spillway indicate a rapidly evolving lake until at least 13,500 yr cal. Keywords: glacial lake, beach ridge, deglaciation, optically stimulated luminescence dating, OSL.

The Younger Dryas cold interval represents a time when much of the Northern Hemisphere cooled from [approximately equal to] 12.9 to 11.5 kiloyears B.P. The cause of this event, which has long been viewed as the canonical example of abrupt climate change, was initially attributed to the routing of freshwater to the St. Lawrence River with an attendant reduction in Atlantic meridional overturning circulation. However, this mechanism has recently been questioned because current proxies and dating techniques have been unable to confirm that eastward routing with an increase in freshwater flux occurred during the Younger Dryas. Here we use new geochemical proxies ([DELTA]Mg/Ca, U/Ca, and [sup.87]Sr/[sup.86]Sr) measured in planktonic foraminifera at the mouth of the St. Lawrence estuary as tracers of freshwater sources to further evaluate this question. Our proxies, combined with planktonic [[delta].sup.18][O.sub.seawater] and [[delta].sup.13]C, confirm that routing of runoff from western Canada to the St. Lawrence River occurred at the start of the Younger Dryas, with an attendant increase in freshwater flux of 0.06 [+ or -] 0.02 Sverdrup (1 Sverdrup = [10.sup.6] [m.sup.3]*[s.sup.-1]). This base discharge increase is sufficient to have reduced Atlantic meridional overturning circulation and caused the Younger Dryas cold interval. In addition, our data indicate subsequent fluctuations in the freshwater flux to the St. Lawrence River of [approximately equal to] 0.06-0.12 Sverdrup, thus explaining the variability in the overturning circulation and climate during the Younger Dryas. abrupt climate change | Atlantic meridional overturning circulation | paleoclimate

The abundance of birds recorded in the North American Breeding Bird Survey decreased by up to 18 percent between 1966 and 2005. The abundance of US and Canadian resident species [...]

Interpretation of soil organic C (SOC) dynamics depends heavily on analytical methods and management systems studied. Comparison of data from long-term corn (Zea mays)-plot soils in Eastern North America showed mean residence times (MRTs) of SOC determined by [sup.14]C dating were 176 times those measured with [sup.13]C abundance following a 30-yr replacement of [C.sub.3] by [C.sub.4] plants on the same soils. However, MRTs of the two methods were related ([r.sup.2] = 0.71). Field [sup.13]C MRTs of SOC were also related ([R.sup.2] = 0.55 to 0.85) to those measured by [sup.13]C[O.sub.2] evolution and curve fitting during laboratory incubation. The strong relations, but different MRTs, were interpreted to mean that the three methods sampled different parts of a SOC continuum. The SOC of all parts of this continuum must be affected by the same controls on SOC dynamics for this to occur. Methods for site selection, plant biomass, soil sampling and analysis were tested on agricultural, afforested-agriculture, and native forest sites to determine the controls on SOC dynamics. Soil-C changes after afforestation were -0.07 to 0.55 Mg C [ha.sup.-1][yr.sup.-1] on deciduous sites and -0.85 to 0.58 Mg C [ha.sup.-1] [yr.sup.-1] under conifers. Soil N changes under afforestation ranged from -0.1 to 0.025 Mg N [ha.sup.-1] [yr.sup.-1. Ecosystem N accumulation was -0.09 to 0.08 Mg N [ha.sup.-1] [yr.sup.-1]. Soil C and N sequestration but not plant biomass were related to soil Ca, Mg, and K contents. Comparative, independent assays of long-term plots provides information for concept testing and the confidence necessary for decision-makers determining C-cycle policies.

The suggestion by Jones et al. (2002) that a terminal Pleistocene-early Holocene California site contains evidence for a separate coastal migration into the New World is challenged. The authors ignore the fact that some 100 or more generations passed since the initial New World colonization event(s) and the occupation of their site (Cross Creek), during which time many cultural changes could be expected, including post-big-game-hunting coastal adaptations throughout the Americas. Moreover, the amount of food refuse is so minuscule that inferring the exact nature of the initial Cross Creek economy is doubtful at best. The recovered chipped stone artifacts have no diagnostic value for economic function or ecological correlation, and the grinding stones suggest more seed than sea exploitation. Lastly, what is known about the biological origins, variation, and microevolution of Native Americans does not support a direct coastal migration from Siberia to California. Se desafia in sugerencia hecha por Jones, et al. (2002), en el sentido de que un sitio de California del Pleistoceno terminal- Holoceno temprano contiene evidencia de una migracion costera diferente hacia el Nuevo Mundo. Los autores ignoran a las 100 o mas generaciones que pasaron desde el inicio de los eventos de la colonizacion del Nuevo Mundo y la ocupacion de su sitio (Cross Creek), durante cuyo tiempo se esperarian muchos cambios culturales, incluso adaptaciones costeras post-caza mayor por todas partes de las Americas. Ademas, la cantidad de desecho de la comida es tan minuscula, que se pone en duda la misma inferencia sobre la naturaleza de la economia inicial del Cross Creek. Los artefactos de piedra recuperados no tienen valor diagnostico por funcion economica o correlacion ecologica, y las piedras de molienda sugieren mas uso de semillas que explotacion del mar. Finalmente lo que es sabido acerca de los origenes biologicos, variacion, y micro evolucion de Americanos Nativos no apoya una migracion co stera directa de Siberia a California., Terry L. Jones et al. (2002:213) argue that the types of tools and fauna found at the Cross Creek site (CA-SLO-1797) in south-central California are 'profoundly different from the terminal [...]

Late Middle to Late Ordovician subtidal ramp carbonates of New Mexico, Texas, and Oklahoma contain abundant spiculitic chert (to 70% chert by volume) and phosphate (1-5 wt%), indicating that these rocks formed in an extensive upwelling zone. Upwelling began in the late Middle Ordovician (ca. 454 Ma) and persisted until the end of the Ordovician. Late Ordovician cherty carbonates also occur along the U.S. Cordilleran margin, inboard of organic-rich graptolitic shale and chert. The widespread occurrence of Late Ordovician cherty and phosphatic carbonates on southern and western Laurentia, in addition to phosphate-rich, cool-water carbonates over much of the North American Midcontinent, suggests vigorous thermohaline circulation related to prolonged (10-14 Ma) Gondwana glaciation. Keywords: Late Ordovician, glaciation, upwelling, chert, phosphate.

Many river systems in western North America retain a fluvial strath-terrace record of discontinuous downcutting into bedrock through the Quaternary. Their importance lies in their use to interpret climatic events in the headwaters and to determine long-term incision rates. Terrace formation has been ascribed to changes in sediment supply and/or water discharge produced by late Quaternary climatic fluctuations. We use a one-dimensional channel-evolution model to explore whether temporal variations in sediment and water discharge can generate terrace sequences. The model includes sediment transport, vertical bedrock erosion limited by alluvial cover, and lateral valley-wall erosion. We set limits on our modeling by using data collected from the terraced Wind River basin. Two types of experiments were performed: constant-period sinusoidal input histories and variable-period inputs scaled by the marine [[delta].sup.18]O record. Our simulations indicate that strath-terrace formation requires input variability that produces a changing ratio of vertical to lateral erosion rates. Straths are cut when the channel floor is protected from erosion by sediment and are abandoned--and terraces formed--when incision can resume following sediment-cover thinning. High sediment supply promotes wide valley floors that are abandoned as sediment supply decreases. In contrast, wide valleys are promoted by low effective water discharge and are abandoned as discharge increases. Widening of the valley floors that become terraces occurs over many thousands of years. The transition from valley widening to downcutting and terrace creation occurs in response to subtle input changes affecting local divergence of sediment-transport capacity. Formation of terraces lags by several thousand years the input changes that cause their formation. Our results suggest that use of terrace ages to set limits on the timing of a specific event must be done with the knowledge that the system can take thousands of years to respond to a perturbation. The incision rate calculated in the field from the lowest terrace in these systems will likely be higher than the rate calculated by using older terraces, because the most recent fluvial response in the field is commonly downcutting associated with declining sediment input since the Last Glacial Maximum. This apparent increase in incision rates is observed in many river systems and should not necessarily be interpreted as a response to an increase in rock-uplift rate. Keywords: fluvial features, landscape evolution, modeling, river terraces, sediment supply.

Few monitoring programs in North America track bird populations at a continental scale during the winter, a critical stage of the life cycle for many species. To date, only Christmas Bird Counts (CBC) have been used to index bird abundance in winter across North America. We evaluated another continentwide program, Project FeederWatch (PFW), which monitors many bird species more intensively than CBC. PFW is a survey in which volunteers use standardized methods to count birds visiting feeders every two weeks from November through April. We compared population indices and trends from PFW and CBC data for 43 species in 3 regions of Ontario, Canada, over a 21-year period from 1976-1997. Annual population indices from PFW were significantly positively correlated with similar indices from CBC for about 80% of species for which annual variation in counts was substantially greater than sampling error. Log-linear population trends from both surveys were also well correlated, though the absolute value of the trend estimates tended to be higher for PFW. The high consistency between surveys suggests that both may be suitable for detecting population changes for many bird species in winter, especially irruptive species that show large annual fluctuations, and species with marked population trends. However, some species did not correspond between surveys, despite being measured fairly precisely, highlighting the value of having two independent surveys to corroborate patterns. Christmas Bird Counts have the advantage that they sample more species, but Project FeederWatch has a more consistent protocol and continues through the winter, allowing analysis of changes in populations through the winter. Key words: bird surveys, Christmas Bird Count, irruptive species, monitoring, population trends, Project FeederWatch.

In ectotherms, lower mean temperatures and shorter growing seasons at higher latitudes would be expected to cause a reduction in the annual growth rate of an individual. If slower growth reduces fitness, then organisms at higher latitudes may evolve compensatory responses for these climatic effects. Two such forms of local adaptation with increasing latitude are possible: (1) the capacity for growth may shift to a lower range of temperatures (i.e., temperature adaptation) or (2) maximum growth rate may evolve inversely with length of the growing season (i.e., countergradient variation). A third alternative is a mixed strategy involving both of the above. We hypothesized that the form of local adaptation may be affected by constraints that vary within vs. among species. We used common-environment experiments to compare reaction norms for growth in response to temperature among local populations of two contiguous, closely related fish species, the Atlantic silverside, Menidia menidia (L.), and the tidewater silverside, M. peninsulae (Goode and Bean), which together have a range spanning much of the North American Atlantic coast. The common-environment experiments revealed countergradient variation: maximum growth rate increased with latitude both within and among species. However, growth reaction norms of the northern species were shifted to a lower range of temperatures than those of the southern species, indicating adaptation to temperature at the interspecific level. Hence, adaptation to temperature contributes to the interspecific variation, while countergradient variation contributes to both the intra- and interspecific differences. Key words: adaptation; Atlantic coast of North America; countergradient variation; genotype X environment interaction; growth rate; interspecific and intraspecific variation; latitudinal compensation; Menidia; reaction norm; seasonality; silversides; temperature, effects on growth.

The fine roots of trees are concentrated on lateral branches that arise from perennial roots. They are important in the acquisition of water and essential nutrients, and at the ecosystem level, they make a significant contribution to biogeochemical cycling. Fine roots have often been studied according to arbitrary size classes, e.g., all roots less than 1 or 2 mm in diameter. Because of the size class approach, the position of an individual root on the complex lateral branching system has often been ignored, and relationships between the form of the branching root system and its function are poorly understood. The fine roots of both gymnosperms and angiosperms, which formed ectomycorrhizae (EM) and arbuscular mycorrhizae (AM) fungal associations, were sampled in 1998 and 1999. Study sites were chosen to encompass a wide variety of environments in four regions of North America. Intact lateral branches were collected from each species and 18 561 individual roots were dissected by order, with distal roots numbered as first-order roots. This scheme is similar to the one commonly used to number the order of streams. Fine root diameter, length, specific root length (SRL; m/g), and nitrogen (N) concentration of nine North American tree species (Acer saccharum, Juniperus monosperma, Liriodendron tulipifera, Picea glauca, Pinus edulis, Pinus elliottii, Pinus resinosa, Populus balsamifera, and Quercus alba) were then compared and contrasted. Lateral roots 75% of the total number and length of individual roots sampled in all species except Liriodendron tulipifera. Both SRL and N concentration decreased with increasing root order in all nine species, and this pattern appears to be universal in all temperate and boreal trees. Nitrogen concentrations ranged from 8.5 to 30.9 g/kg and were highest in the first-order 'root tips.' On a mass basis, first-order roots are expensive to maintain per unit time (high tissue N concentration). Tissue N appears to be a key factor in understanding the C cost of maintaining first- and second-order roots, which dominate the display of absorbing root length. There were many significant differences among species in diameter, length, SRL, and N concentration. For example, two different species can have similar SRL but very different tissue N concentrations. Our findings run contrary to the common idea that all roots of a given size class function the same way and that a common size class for fine roots works well for all species. Interestingly, fine root lateral branches are apparently deciduous, with a distinct lateral branch scar. The position of an individual root on the branching root system appears to be important in understanding the function of fine roots. Key words: Acer saccharum; carbon; Juniperus monosperma; Liriodendron tulipifera; nitrogen; Picea glauca; Pinus edulis; Pinus elliottii; Pinus resinosa; Populus balsamifera; Quercus alba; roots.

Abstract: Corallimorpharia is currently considered an order of hexacorallian anthozoans. Being skeletonless, its members are sometimes referred to as sea anemones, but they are morphologically more similar to members of [...]

Cryptic invasions are a largely unrecognized type of biological invasion that lead to underestimation of the total numbers and impacts of invaders because of the difficulty in detecting them. The distribution and abundance of Phragmites australis in North America has increased dramatically over the past 150 years. This research tests the hypothesis that a non-native strain of Phragmites is responsible for the observed spread. Two noncoding chloroplast DNA regions were sequenced for samples collected worldwide, throughout the range of Phragmites. Modern North American populations were compared with historical ones from herbarium collections. Results indicate that an introduction has occurred, and the introduced type has displaced native types as well as expanded to regions previously not known to have Phragmites. Native types apparently have disappeared from New England and, while still present, may be threatened in other parts of North America.

It is surprising that after more than three decades into the plate tectonic revolution, we have so little direct observation of the mantle flow field that accompanies plate motion. The [...], Although motions at the surface of tectonic plates are well determined, the accompanying horizontal mantle flow is not. We have combined observations of surface deformation and upper mantle seismic anisotropy to estimate this flow field for western North America. We find that the mantle velocity is 5.5 ± 1.5 centimeters per year due east in a hot spot reference frame, nearly opposite to the direction of North American plate motion (west-southwest). The flow is only weakly coupled to the motion of the surface plate, producing a small drag force. This flow field is probably due to heterogeneity in mantle density associated with the former Farallon oceanic plate beneath North America.

Lythrum salicaria (purple loosestrife) is a nonindigenous invasive species characterized by prolific growth and abundance in marshy and riparian habitats across North America. Given its invasive success, we hypothesized this species may require less energy and/or use energy more efficiently for biomass construction than co-occurring noninvasive plant species. We measured leaf construction cost (CC), leaf mass per unit area (LMA), and leaf organic nitrogen and carbon content of L. salicaria and the five most abundant co-occurring species, Parthenocissus quinquefolia, Erigeron philadelphicus, Asclepias syriaca, Spiraea latifolia, and Solidago graminifolia, along dammed ponds in the Black Rock Forest, Cornwall, New York, USA. Lythrum salicaria, which was highly abundant (2.52 individuals/[m.sup.2]), exhibited significantly lower area-based leaf CC (44.47 [+ or -] 4.24 g glucose/[m.sup.2] leaf) than relatively less abundant species, suggesting energetics may influence its invasive success. Conversely, least abundant Solidago graminifolia (0.67 individuals/[m.sup.2]) exhibited the significantly highest leaf CC per unit leaf area (141.87 [+ or -] 39.21 g glucose/[m.sup.2] leaf). Overall, a negative correlation between species abundance and area-based leaf CC ([r.sup.2] = 0.73) indicated low energy requirements and/or high energy efficiency may influence relative abundance in the plant species studied. As it correlates with species abundance in this study, CC may be a useful tool for evaluating invasive potential. Key words: abundance; construction cost; energetics; invasive species; Lythraceae; Lythrum salicaria.

The article describes the formation of the North American crust as documented by Arizona's Cochise block, focusing on the rapid addition of evolved, juvenile metavolcanic arc rocks and the derivation of metasedimentary quartz-rich rocks. Documentation includes volcanic activity and delineation of suture zones and subduction complexes.

Issues relating to the effects of predation on forest grouse are presented. Predator control is considered as a means to increase densities of grouse in the forests of North America. It is found that the response of forest grouse to management of their habitat can be more easily predicted than for other species.

A fifty-year-old taxonomic issue in grasshopper systematics related to the subfamily Melanoplinae and inclusion of Bohemanella frigida in one of two tribes, the Nearctic-restricted Melanoplini and the Holarctically distributed Podismini, is discussed from the point of view of molecular phylogeography. B. frigida is now thought to belong to Podismini and to have come to North America from Eurasia over the Bering Land Bridge. Results of a molecular phylogenetic study put it in the Melanoplini, as it has been thought to be, from time to time. It would then have the name Melanoplus frigidus and have had a different direction of dispersal across the Bering Land Bridge, making it unique among orthopteran insects.

The (delta)(super 18)O values of river waters in Late Cretaceous and Paleogene basins of Alberta, Montana, Wyoming, and Colorado are calculated from the isotopic composition of unaltered aragonite mollusk fossils. The isotopic composition of these river waters has significant implications for the uplift and climate history of the mountains surrounding the basins. Our data show that the (delta)(super 18)O values of river water varied dramatically, ranging from -23% to -5% relative to Vienna standard mean ocean water, with an uncertainty of +/- 2%. Close stratigraphic association of river deposits with very different isotopic values indicates two different water sources: rainfall in the warm, low-elevation basins and snowfall in surrounding mountains. The (delta)(super 18)O difference between basinal and highland precipitation suggests that local relief was similar to today's, on the order of 2.5-3 km. Seasonal variation in shell (delta)(super 18)O values also indicates that there are times when large snow fields in the Maastrichtian and Paleocene mountains of Montana and Wyoming survived summer melting and were multiannual features.

The Pelona and Orocopia Schists are southern members of a eugeoclinal terrane that structurally underlies a large part of southwestern North America. Ion-microprobe U-Pb ages of >100 detrital zircons from three widely spaced samples of these two units indicate that deposition occurred after 70-80 Ma. Moreover, the distribution of zircon ages, including a significant peak centered ca. 1.7 Ga, implies a major contribution of detritus from the Mojave Desert and Transverse Ranges of southern California. Recrystallization of the schists at depths of 20-35 km occurred within 10-15 m.y. of deposition, which requires underthrusting at minimum rates of approximately 4-12 mm/yr for reasonable thrust dips. Considering that similar processes formed the more northern Rand Schist at somewhat earlier times, our results indicate a southward progression in timing of deformation for the schists' protoliths. This result is at odds with northward migration of deformation implied by the Baja British Columbia hypothesis. The age and provenance of the schist's protoliths are consistent with models that derive the schists from either the Franciscan Complex or Great Valley Group.

Epizootiology and pathology of Entomophaga maimaiga (a fungus) infections in forest lepidoptera are discussed. DNA analysis shows that the fungal strain of E. maimaiga in North America now is significantly different from North American members of the same species complex, the lepidoptera-specific Entomophaga aulicae species complex. The pathogen was purposely introduced for biological control of L. dispar (gypsy moth) in 1910-11. The strain seen now may be from a more recent accidental introduction. So far isolates of the introduced pathogen have little heterogeneity in North America. Nonsuseptible lepidopteran larvae have been found. E. maimaiga cannot penetrate the cuticle or cannot survive inside the hemocoel. Range and density are discussed.

To test the hypothesis that island species exhibit lower genetic variability than mainland relatives, genetic data from three species of vireos endemic to Puerto Rico and Jamaica were compared with the White-eyed Vireo (Vireo griseus), a closely related species that breeds in North America. Variability was examined using random amplified polymorphic DNA (RAPD) markers. The White-eyed Vireo had a significantly higher proportion of polymorphic bands (67% of 115 total bands) than the Puerto Rican Vireo (V. latimeri; 38% of 95 bands), Jamaican Vireo (V. modestus; 34% of 107 bands), or Blue Mountain Vireo of Jamaica (V. osburni; 32% of 111 bands). The mean genetic distance among conspecific individuals (Jaccard's index) was significantly higher in the White-eyed Vireo (0.293) than in any of the three endemic species (Puerto Rican Vireo, 0.115; Jamaican Vireo, 0.115; Blue Mountain Vireo, 0.106); mean genetic distance values did not differ among the three endemic species. Population substructuring assessed by analysis of molecular variance (mathematical expression not reproducible in ASCII) and Wright's F(sub st) values revealed that the two common endemic species (Puerto Rican and Jamaican vireos) had greater among-population genetic variation than did three populations of the White-eyed Vireo. Genetic substructuring was moderate to substantial among two Puerto Rican Vireo populations ((mathematical expression not reproducible in ASCII) = 0.103, F(sub ST) = 0.141) and weak to moderate among two Jamaican Vireo populations ((mathematical expression not reproducible in ASCII) = 0.048, F(sub ST) = 0.117). The migratory White-eyed Vireo had the lowest values for both statistics ((mathematical expression not reproducible in ASCII) = 0.015, F(sub ST) = 0.109). Low among-individual, within-species genetic variation was related to island endemism but was not influenced by differences among endemics in habitat specificity or local abundance.

Arisaema dracontium (green dragon) is a perennial herb that is widely distributed in eastern North America. However, in Canada, at the northern edge of its distribution, the species is designated as 'vulnerable' with respect to conservation status. In natural populations, seedlings are uncommon; the present study was undertaken in order to characterize seed and seedling properties in green dragon. Seeds were sampled from five sites, ranging from Ontario at the northern limit of the distribution range, to Louisiana in the south. Seed germinability ranged from 25 to 55%, depending upon source. Experiments indicated that neither the hard seed coat nor a water-soluble exudate from the seed was responsible for inducing or maintaining dormancy. Patterns of seed germination appear to reflect general climatic conditions at the sites where seeds had originated. Cold stratification at 3 [degrees] C produced significantly greater relative germinability in all seed collections except the most southerly one, from Baton Rouge. These seeds also had a slower overall speed of germination. In contrast, germination of seeds from the most northerly site was promoted by cold stratification and occurred over a relatively brief period. Germination in alternating light and dark conditions decreased the speed of germination compared to germination in the dark, however exposure to light changed the phenology of germination by promoting development of adventitious roots and primary leaves in these seedlings. Key words: Araceae; Arisaema dracontium; cold stratification; dormancy; population variation; seed germination.

Long-lived perennials are a species-rich, ecologically important component of the North American deserts, yet we know little about their genetic structure, information important for their conservation. Agave victoriae-reginae is an endemic of the Chihuahuan Desert of northern Mexico that is endangered by collection for the ornamental trade. We examined levels and patterns of variation at ten polymorphic allozyme loci in ten populations representing the range of the species. Levels of genetic variation (mean [H.sub.e] = 0.335) and differentiation (mean [F.sub.ST] = 0.236) were high. Phenetic clustering suggested the existence of at least three distinct groups of populations. If this pattern of variation is representative of other long-lived desert perennials, it may explain the species richness of this group and will pose a real challenge to gene conservation efforts. Key words: Agave; Agavaceae; allozymes; conservation genetics; perennial; population genetics.

The biotype 4 strain of Trichoderma atroviride (T. atroviride) was the prominent cause of the green mold epidemic episodes which plagued the mushroom-growing region of North America during the 1950s. Through the use of randomly amplified polymorphic DNA (RAPD)-PCR, it was established that T. atroviride biotype 4 caused 90% of the green mold epidemic episodes during the period mentioned. However, results nullified the existence of preepidemic isolates in the region, possibly due to the fact that majority of the isolates have been isolated from compost and wooden surfaces.

Using all available biostratigraphic information and our own extensive magnetostratigraphic database, we have attempted to assess the synchronicity of depositional cycles recorded in the Paleogene epicontinental deposits on both sides of the North Atlantic as stage two of a four-stage global assessment of the eustatic sea-level model. Our conclusion is that the depositional histories of the U.S. Gulf of Mexico-Atlantic coastal plain and the North Sea basin show many similarities, on a variety of time scales, over the interval 60-46 Ma. Considering the tectonic imprint of the northeast Atlantic opening on the North Sea basin sea-level record for part of this time, it must give some weight to the claim that eustasy is the dominant mechanism controlling deposition on passive continental margins.

Morphologically similar flowering plants are seen in eastern Asia and eastern North America. The plants have fascinated botanists and biogeographers. Fossil and geologic evidence indicate multiple origins of the pattern in the Tertiary. The North Atlantic and Bering land bridges would be involved. Morphological stasis must have taken place in some of the disjunct groups in the north temperate zone.

New data contradict the mosasaur. bite hypothesis for the origin of holes seen in Placenticeras ammonites from the Late Cretaceous Pierre Shale and Bearpaw Formation of the western interior of North America. Observations of a limpet-infested Placenticeras ammonite and of several Placenticeras specimens with radular scratch marks reveal that the limpets dwelled on floating ammonites, and their homing activity produced circular depressions. When altered during diagenesis, the depressions mimic tooth punctures. Crushing experiments on fresh Nautilus shells using a mosasaur robot show that mosasaur bites could not have produced holes resembling those in the fossils. Furthermore, sectioning of 'bitten' ammonites reveals that sepia are sometimes intact under the holes, an observation irreconcilable with penetration by a tooth. We present an alternative interpretation that the alleged 'bite marks' in Placenticeras ammonites are really limpet home scars that were altered after burial. While predation of mosasaurs on ammonites remains a possibility, it would have to be demonstrated by other criteria. Our findings do not support mosasaur-ammonoid coevolution in the Late Cretaceous.