Late Ordovician Mass Extinction: Earth, fire and ice

The Late Ordovician Mass Extinction was the earliest of the ‘big’ five extinction events and the earliest to affect the trajectory of metazoan life. Two phases have been identified near the start of the Hirnantian period and in the middle. It was a massive taxonomic extinction, a weak phylogenetic extinction and a relatively benign ecological extinction. A rapid cooling, triggering a major ice age that reduced the temperature of surface waters, prompted a drop in sea level of some 100 m and introduced toxic bottom waters onto the shelves. These symptoms of more fundamental planetary processes have been associated with a range of factors with an underlying driver identified as volcanicity. Volcanic eruptions, and other products, may have extended back in time to at least the Sandbian and early Katian, suggesting the extinctions were more protracted and influential than hitherto documented

The Irish Ordovician brachiopod fauna: A taxonomic renaissance

Despite its small areal extent, the island of Ireland exposes eight Caledonian tectonic terranes; six of them contain Ordovician brachiopod assemblages. These terranes record the early phases and destruction of the Iapetus Ocean through the occurrence of latitude-sensitive brachiopod faunas during the Middle Ordovician and early Late Ordovician; more cosmopolitan faunas characterized the later Ordovician

Big mice die young: early life body weight predicts longevity in genetically heterogeneous mice

Small body size has been associated with long life span in four stocks of mutant dwarf mice, and in two varieties of dietary restriction in rodents. In this study, small body size at ages 2–24 months was shown to be a significant predictor of life span in a genetically heterogeneous mouse population derived from four common inbred mouse strains. The association was strongest for weights measured early in adult life, and somewhat weaker, though still statistically significant, at later ages. The effect was seen both in males and females, and was replicated in an independent population of the same genetic background. Body size at ages 2–4 months was correlated with levels of serum leptin in both males and females, and with levels of IGF-I and thyroid hormone in females only. A genome scan showed the presence of polymorphic alleles on chromosomes 2, 6, 7 and 15 with significant effects on body weight at 2–4 months, at 10–12 months, or at both age ranges, showing that weight gain trajectory in this stock is under complex genetic control. Because it provides the earliest known predictor of life span, body weight may be usefully included in screens for induced mutations that alter aging. The evidence that weight in 2-month-old mice is a significant predictor of life span suggests that at least some of the lethal diseases of old age can be timed by factors that influence growth rate in juvenile rodents.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75162/1/j.1474-9728.2002.00006.x.pd

Late Ordovician and early Silurian virgianid and stricklandioid brachiopods from North Greenland: implications for a warm‐water faunal province

An unusually rich and diverse suite of virgianid brachiopods, hitherto poorly known, is systematically described here for the first time from the Ordovician–Silurian boundary interval (late Katian – Aeronian) of North Greenland. The Late Ordovician virgianids comprise typical taxa of the warm‐water Tcherskidium fauna (e.g. Tcherskidium tenuicostatum, Proconchidium schleyi, Holorhynchus giganteus and Deloprosopus dawesi sp. nov.). Among the early Silurian taxa, Virgiana hursti sp. nov. occurs as abundant shell beds, similar to other congeneric species in Laurentia, but has somewhat larger internal skeletal structures, albeit not as extravagantly developed as in the late Katian virgianids; Borealoides balderi gen. et sp. nov. shows extreme thickening of the shell wall and internal structures, approaching the extravagant calcification of Katian virgianids. The highly distinctive mid‐Aeronian stricklandioid brachiopod genus, Kulumbella, characterized by a shell with criss‐cross (divaricate) ribbing, also occurs in North Greenland, represented by K. heimdali sp. nov., which has the largest and most strongly biconvex shells for the genus. Palaeogeographically, the Late Ordovician virgianid fauna of Laurentia was highly distinct, confined to the low–mid tropical latitudes north of the palaeoequator. In comparison, the early Silurian (Rhuddanian) Virgiana and some related taxa in Laurentia spanned the tropics of both hemispheres, forming extensive shell beds in carbonate basins, although Borealis and Borealoides gen. nov. remained confined largely to the northern hemisphere, suggesting a certain level of provincialism extending into the earliest Silurian. A palaeoecological preference for warm‐water carbonate settings would explain the unusual abundance and richness of the virgianid faunas in North Greenland

Late Darriwilian (Middle Ordovician) conodonts from eastern and southeastern Ireland

The Middle Ordovician (upper Darriwilian) marine deposits of the Bellewstown Limestone Member and Tramore Limestone Formation in eastern and southeastern Ireland, respectively, yield a diverse conodont assemblage of 21 taxa. The sedimentary rocks deposited on the Bellewstown Terrane represent an intra-Iapetus island arc setting. The Tramore Limestone was deposited in a back-arc setting at the eastern margin of the Leinster-Lakesman Terrane that is considered part of the peri-Gondwanan Ganderia Terrane. The conodont assemblage, including species of Baltoniodus, Eoplacognathus, Plectodina and Pygodus is assigned to the Pygodus serra Conodont Zone (upper Darriwilian, Middle Ordovician). The genera Drepanodus, Drepanoistodus, Gothodus, Panderodus, Periodon, Protopanderodus, Sagittodontus and Triangulodus and are also represented. The Darriwilian conodont assemblages from Bellewstown and Tramore in Ireland are characteristic of the 'eastern' Iapetus Ocean with a southern mid latitudinal position. The fauna resembles the San Rafael (Mendoza Province, Argentina) conodont fauna of the Cuyania Composite Terrane. Baltoniodus, Eoplacognathus and Sagittodontina are shared with faunas in Baltica, whereas Baltoniodus and Sagittodontina together with Yangtzeplacognathus occur in South China and Plectodina and Yangtzeplacognathus are recorded from Gondwana. An important factor influencing the distribution of conodont taxa is the siliciclastic-dominated sedimentation, interpreted to reflect cool to temperate water conditions. The Bellewstown and Tramore conodont fauna is in marked contrast to other deposits on island arcs and back-arc terranes within the Iapetus. These are interpreted to represent low latitudinal, warmer, oceanic water conditions with Laurentian faunal affinity. Some potential new species are introduced in open nomenclature

Insights into the morphology of Sphenothallus (Cnidaria): New features identified in an old genus, from the Carboniferous (Pennsylvanian, Bashkirian) of western Ireland

The recent discovery of well-preserved fragments of Sphenothallus in the Central Clare Group (Pennsylvanian) of western Ireland provides new insights into the morphology of this enigmatic, putative cnidarian. The specimens demonstrate a morphological plasticity, including features not previously described for Sphenothallus, such as the presence of flat sides and angular lateral margins, non-bilateral symmetry in sigmoidal cross-sections suggestive of growth torsion, and a new type of bifurcating branching (new term 'rail-track junction branching' introduced herein), not related to known budding. We propose that these structures were all growth-related features during life, and not post-mortem artefacts of collapse or compaction. The flat sides and growth torsion are compared with similar features in conulariids, supporting the previously proposed phylogenetic linkage between the two groups, which may be an example of atavism. However, the bifurcating 'railtrack junction branching' is unknown in conulariids or other similar organisms

Den østbaltiske Kunda Etage: Starten på ‘en store ordoviciske biodiversifikation’

Intet resumé

The Ordovician System: From overlapping unit stratotypes to Global Boundary Stratotype Sections and Points

For nearly a century the Ordovician System was hidden as Murchison and Sedgwick tussled over the overlapping ground between their Silurian and Cambrian systems. The Ordovician is, in fact, one of the longest of the geological periods, characterised by major magmatic and plate tectonic activity; the roles of microcontinents and volcanic archipelagos were significant in shaping the Ordovician planet and the evolution of its biotas, associated with an immense biodiversification, significant fluctuations in climate and sea levels, and the first Phanerozoic mass extinction of marine invertebrates. The period was unique in being thalassocratic; epicontinental seas had a wider reach than during any other geological period. The land areas were restricted to isolated microblocks of archipelagos of various sizes with low relief, with rivers traversing gentle gradients, carrying sparse terrigenous material seaward. It is an ancient world with few parallels elsewhere in the Phanerozoic, and little in common with Holocene ecosystems and environments. The Ordovician System was introduced by Charles Lapworth as a solution to the stratotypes of overlapping units loosely defined by Adam Sedgwick for the Cambrian and by Roderick Murchison for the Silurian. Following a period of intensive research into all the key regions of the globe, unit stratotypes in the type areas of England and Wales have been replaced by seven global stages and three series based on Global Boundary Stratotype Sections and Points, enhancing the definition of these chronostratigraphic units and facilitating global correlation. As a consequence, the biological and geological events during the period can be recognised, and the magnitude and significance of originations and extinctions understood. A global synthesis of successions in Europe (Geological Society, London, Special Publications, 532) and the rest of the world (Geological Society, London, Special Publications, 533) has emphasised the importance of a universal language for Ordovician chronostratigraphy and its dividends