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Venom delivery systems occur in a wide range of extant and fossil vertebrates and are primarily based on oral adaptations.
Teeth range from unmodified (Komodo dragons) to highly specialized fangs similar to hypodermic needles (protero- and solenoglyphous
snakes). Developmental biologists have documented evidence for an infolding pathway of fang evolution, where the groove folds
over to create the more derived condition. However, the oldest known members of venomous clades retain the same condition
as their extant relatives, resulting in no fossil evidence for the transition. Based on a comparison of previously known specimens
with newly discovered teeth from North Carolina, we describe a new species of the Late Triassic archosauriform Uatchitodon and provide detailed analyses that provide evidence for both venom conduction and document a complete structural series from
shallow grooves to fully enclosed tubular canals. While known only from teeth, Uatchitodon is highly diagnostic in possessing compound serrations and for having two venom canals on each tooth in the dentition. Further,
although not a snake, Uatchitodon sheds light on the evolutionary trajectory of venom delivery systems in amniotes and provide solid evidence for venom conduction
in archosaur-line diapsids. 相似文献
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Lorenz M Nagel HD Granke O Kraft P 《Environmental pollution (Barking, Essex : 1987)》2008,155(3):426-435
Intensive forest monitoring by means of harmonised methods has been conducted in Europe for more than a decade. Risks of atmospheric nitrogen and sulphur deposition are assessed by means of calculations of critical loads and their exceedances. In the present study throughfall and bulk deposition of nitrate (N-NO(3)), ammonium (N-NH(4)) and sulphate (S-SO(4)) show marked spatial patterns and temporal trends. In the period of observation (1999-2004), sulphate deposition on intensive monitoring plots decreased by about one quarter. This is in line with the reduction of S deposition by 70% since 1981 in Europe as a result of successful air pollution control politics under the Convention on Long-range Transboundary Air Pollution (CLRTAP). However, sulphate and especially nitrate and ammonium deposition were found to still exceed critical loads at many forest sites, indicating a continued need for further implementation of air pollution abatement strategies. 相似文献
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Workforce engagement: What it is,what drives it,and why it matters for organizational performance 下载免费PDF全文
Based on a review of the history of the employee engagement construct and its measurement, we define workforce engagement as the aggregate of the work engagement experiences of individual employees in an organization. In contrast to most research on employee engagement, we study companies rather than individuals and the companies represent a diverse set of industries. We hypothesize and demonstrate on a sample of (up to) 102 publicly traded companies that workforce engagement significantly predicts organizational financial (adjusting for industry: Return on Assets, Net Margin but not Tobin's q) and customer metrics (the American Customer Satisfaction Index and the Harris Reputation Quotient) 1 and 2 years after the workforce engagement data were collected. In addition, using a split‐sample approach to avoid method bias, we hypothesize and show that (a) company organizational practices (the strongest correlate), supervisory support, and work attributes are significant correlates of workforce engagement and (b) that workforce engagement mediates the relationship between these correlates of engagement and the organizational performance metrics. Implications of the findings for research and practice are discussed. 相似文献
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Gregor Heinz-Detlef Nagel Hans-Dieter Posch Maximilian 《Water, Air, & Soil Pollution: Focus》2001,1(1-2):5-19
Critical Loads and levels have played a centralrole in the successful development of effect-based emissionreduction strategies for Europe in the fields of acidification,eutrophication and ground-level ozone. The aim of theInternational Programme on Mapping Critical Loads and Levelsled by Germany, with participation of 24 countries, is todetermine critical loads and levels for forest, crops, naturalvegetation, soils, water and materials. The exceedances ofcritical loads and critical levels are used to quantify the riskfor environmental damage by air pollution and tosupport the development of optimised abatement strategies. 相似文献