—In post-Cambrian time, five events—the end-Ordovician, end-Frasnian in the Late Devonian, end-Permian, end-Triassic, and end-Cretaceous—are commonly grouped as the ‘‘big five’’ global intervals of mass extinction. Plotted by magnitude, extinction intensities for all Phanerozoic substages show a continuous distribution, with the five traditionally recognized mass extinctions located in the uppe...

Abstract. Articulated holaspid specimens of Placoparia Hawle and Corda, 1847 Eoharpes Raymond, 1905 entombed inside cephalopod conchs under the remains large illaenid, asaphid, cyclopygid dalmanitid trilobites from Middle Ordovician Šárka Formation Prague Basin (Czech Republic) are described discussed. Two such samples were also found in overlying Dobrotivá Middle/Late age. Four articulated juv...

The Kings-Kaweah ophiolite belt of the southwestern Sierra Nevada Foothills was generated in two pulses of mid-oceanic-ridge basalt (MORB) magmatism. The first was in the Early Ordovician, which resulted in the generation of a complete abyssal crust and upper mantle section. The crustal section was rendered from convecting mantle whose Nd, Sr, and Pb isotopic systematics lie at the extreme end ...

Transposition in conservative fields reaches its full potential in case that is unexplainable for any well-established theory. There are a number of phenomena and findings in various areas of science that stays in disagreement with those theories. Number of them were analyzed and described in this paper. Additionally, reason for Z-Process and its consequences in the galaxy scale was given.

The Mongolepidida is an Order of putative early chondrichthyan fish, originally erected to unite taxa from the Lower Silurian of Mongolia. The present study reassesses mongolepid systematics through the examination of the developmental, histological and morphological characteristics of scale-based specimens from the Upper Ordovician Harding Sandstone (Colorado, USA) and the Upper Llandovery-Low...

BACKGROUND We examine the environmental, climatic and geographical controls on tropical ostracod distribution in the marine Ordovician of North America. METHODOLOGY/PRINCIPAL FINDINGS Analysis of the inter-regional distribution patterns of Ordovician Laurentian ostracods, focussing particularly on the diverse Late Ordovician Sandbian (ca 461 to 456 Ma) faunas, demonstrates strong endemicity a...

The colonization of the terrestrial environment by land plants transformed the planetary surface and its biota, and shifted the balance of Earth's biomass from the subsurface towards the surface. However there was a long delay between the formation of palaeosols (soils) on the land surface and the key stage of plant colonization. The record of palaeosols, and their colonization by fungi and lic...

The Siluro-Ordovician Southern Uplands terrane occupies a key position in the Caledonian Orogen, yet its genesis is controversial. Marginal basin, back-arc and forearc tectonic regimes, operative at the Laurentian margin of the Iapetus Ocean, have all been invoked. Fresh andesitic detritus within turbidite sandstones has, until now, been assumed to provide evidence for an Ordovician, supra-subd...

Bivalves and gastropods are the two largest classes of extant molluscs. Despite sharing a huge number of features, they do not share a key ecological one: gastropods are essentially epibenthic, while most bivalves are infaunal. However, this is not the ancestral bivalve condition; Cambrian forms were surface crawlers and only during the Ordovician a fundamental infaunalization process took plac...

U-Pb and Ar/Ar dates from the Talladega belt, southernmost Appalachians, provide insight into the timing and nature of pre-Alleghanian tectonism in this region. Low-grade metasedimentary rocks of the Talladega belt represent the outermost preserved portions of the southern Laurentian margin, thus recording the earliest orogenic events that affected the margin, in addition to later overprinting ...