Sediment disturbance by Ediacaran bulldozers and the roots of the Cambrian explosion

Se han documentado fósiles de rastros de excavadoras de sedimentos en los estratos ediacaranos terminales del Grupo Nama en Namibia, donde se encuentran en el miembro Spitskop de la Formación Urusis (subgrupo Schwarzrand). Consisten en fósiles de trazas unilobadas a bilobadas horizontales a subhorizontales que describen garabatos, círculos y, más raramente, espirales y meandros abiertos, y que muestran una estructura interna indicativa de relleno activo. Su presencia sugiere que la explotación del ecoespacio infaunal poco profundo por parte de bilateros relativamente grandes ya estaba en marcha en los albores del Fanerozoico. El excavado eficiente sugiere que el desarrollo de la espina dorsal está muy probablemente relacionado con el aumento del tamaño del cuerpo de los metazoos. Estos fósiles en trazas son los primeros representantes claros hasta ahora registrados del arrastre de sedimentos, actividad que puede haber tenido un impacto negativo en las comunidades de alimentación en suspensión y/o de osmotrofos, así como en las esteras, lo que representa los primeros ejemplos de ingeniería de ecosistemas y amensalismo de grupos tróficos. La aparición de bulldozers de sedimentos puede haber promovido el establecimiento de gradientes en la distribución horizontal y vertical de material orgánico en relación con entornos espacialmente heterogéneos en el fondo marino en un momento crítico de la evolución de la Tierra.Trace fossils of sediment bulldozers are documented from terminal Ediacaran strata of the Nama Group in Namibia, where they occur in the Spitskop Member of the Urusis Formation (Schwarzrand Subgroup). They consist of unilobate to bilobate horizontal to subhorizontal trace fossils describing scribbles, circles and, more rarely, open spirals and meanders, and displaying an internal structure indicative of active fill. Their presence suggests that exploitation of the shallow infaunal ecospace by relatively large bilaterians was already well underway at the dawn of the Phanerozoic. Efficient burrowing suggests coelom development most likely linked to metazoan body-size increase. These trace fossils are the earliest clear representatives so far recorded of sediment bulldozing, an activity that may have had a negative impact on suspension-feeding and/or osmotroph communities, as well as on matgrounds, representing early examples of ecosystem engineering and trophic-group amensalism. The occurrence of sediment bulldozers may have promoted the establishment of gradients in horizontal and vertical distribution of organic material in connection with spatially heterogeneous environments on the sea floor at a critical time in Earth evolution.• Natural Sciences and Engineering Research Council (NSERC) Discovery. Grants 311726-05/13 y 311727-05/15, para Louis Alberto Buatois y Maria Gabriela Mángano • Palaeontological Scientific Trust (Sudáfrica). Ayuda a John Almond • Ministerio de Ciencia e Innovación y Fondo Europeo de Desarrollo Regional (FEDER). Subvención CGL-2012-37237, para Sören JensenpeerReviewe

Aggregation and Representation in the European Parliament Party Groups

While members of the European Parliament are elected in national constituencies, their votes are determined by the aggregation of MEPs in multinational party groups. The uncoordinated aggregation of national party programmes in multinational EP party groups challenges theories of representation based on national parties and parliaments. This article provides a theoretical means of understanding representation by linking the aggregation of dozens of national party programmes in different EP party groups to the aggregation of groups to produce the parliamentary majority needed to enact policies. Drawing on an original data source of national party programmes, the EU Profiler, the article shows that the EP majorities created by aggregating MEP votes in party groups are best explained by cartel theories. These give priority to strengthening the EP’s collective capacity to enact policies rather than voting in accord with the programmes they were nationally elected to represent

What determines demand for European Union referendums?

Notwithstanding elite opposition to referendums as inconsistent with theories of representative democracy, the 27-nation European Election Study finds that 63 per cent of EU citizens want a vote on EU treaties. One explanation is that the majority want more popular participation in politics; another is that referendums are demanded by those negative about the performance of their governors at national and EU levels; a third is that demand is higher where referendums are part of the national context. Multi-level statistical analysis shows greater support for the hypotheses that citizens dissatisfied with government performance are more likely to want referendums to check their governors and that national context matters. However, dissatisfied EU citizens are a minority; most who endorse EU referendums are actually pro-EU. This lowers the risk of defeat if the EU consulted its citizens in a pan-European referendum