Re‐evaluation of the conodont Iapetognathus and implications for the base of the Ordovician System GSSP

Terfelt, F, Bagnoli, G. & Stouge, S. 2011: Re‐evaluation of the conodont Iapetognathus and implications for the base of the Ordovician System GSSP. Lethaia, Vol. 45, pp. 227–237. In 2000, the International Union of Geological Sciences (IUGS) ratified the decision from the International Working Group on the Cambrian–Ordovician Boundary (COBWG) to place the Global boundary Stratotype Section and Point (GSSP) for the base of the Ordovician System in the Green Point section, Newfoundland, Canada, at a point coinciding with the first appearance of the conodont Iapetognathus fluctivagus. However, a restudy of the conodont successions from Green Point shows that this species is not present at the boundary interval, and as a consequence the section does not fulfil the biostratigraphical requirements of a GSSP. The GSSP horizon as now defined is based on a level part‐way through the range of I. preaengensis– a species with lower first appearance datum (FAD). The true FAD of I. fluctivagus is above the FAD of planktonic graptolites and well above the FAD of I. preaengensis. As a consequence of these problems, a restudy of the GSSP section and the other sections in the Cow Head Group is necessary. A redefinition of the GSSP horizon is suggested. The following four alternative horizons have potential as new horizons for the GSSP level: the FAD of Cordylodus intermedius; the FAD of Cordylodus andresi; the FAD of Eoconodontus notchpeakensis; and the FAD of the agnostoid Lotagnostus americanus. □Boundary, Cambrian, conodont, Global boundary Stratotype Section Point, Iapetognathus, Ordovician.     

Conodontophorid biodiversification during the Ordovician in South China

Wu, R., Stouge, S. & Wang, Z. 2012: Conodontophorid biodiversification during the Ordovician in South China. Lethaia, Vol. 45, pp. 432–442. Analysis of the Ordovician conodontophorid diversity pattern for South China using normalized and total diversity measures reveals that diversity peaks occurred in the mid‐Tremadocian, mid‐late Floian, early Dapingian and mid‐Darriwilian periods. The conodontophorids radiated during the Floian, maintaining relatively high diversity into the early part of the Middle Ordovician until a significant diversity decrease occurred in the late Dapingian. A relatively low diversity level prevailed in the Late Ordovician. Three diversification intervals based on origination, extinction and turnover rates have been identified i.e. (1) Tremadocian to mid‐late Floian, (2) early Dapingian and (3) late Dapingian to early Darriwilian. Diversity curves for conodontophorids, brachiopods, graptolites, acritarchs and trilobites from South China are comparable during the Early Ordovician, although differences are apparent in the Middle and Late Ordovician. In South China, conodontophorid diversity reacted primarily to sea‐level changes during the Early and Middle Ordovician, when the peak of this biodiversification generally coincided with a transgression. Climate changes – especially the global cooling that occurred during the Late Ordovician glaciation – and sea‐water chemistry were also important controlling factors. □Biodiversification, conodonts, Ordovician, South China.     

Structure of Intestine, Pancreas, and Spleen of the Australian Lungfish, Neoceratodus forsteri (Krefft)

The structure of the intestine and its adnexa in the Australian lungfish Neoceratodus forsteri (Krefft), is described from four adult specimens and compared with that of other lungfish. In all lungfish genera the intestine is thick and straight and contains a complicated spiral valve; a pyloric fold separates the foregut from the midgut. In Neoceratodus the coiling of the intestinal lumen begins in the prepyloric or gastric region, unlike in other vertebrates with a spiral valve, where it begins behind the pylorus. The spiral valve of Neoceratodus begins as a deep groove on the right side of the foregut, just behind the glottis. Such a prepyloric groove is present but poorly developed also in the lungfishes Protopterus and Lepidosiren and contains a prepyloric spleen in all genera. A separate postpyloric spleen is situated in the free margin of the spiral valve, i.e. in the axis of the intestine. The spleen has a heavily pigmented cortex containing large amounts of iron. The pancreas, buried in the spiral valve in front of the pylorus in Neoceratodus , contains numerous islets of Langerhans, similar to those of tetrapods. This is unexpected because the islets of Protopterus , described by Gabe in 1969, are more like the large, encapsulated "Brockmann bodies" of teleosts.     

THE ANATOMY OF MENASPIS ARMATA AND THE PHYLETIC AFFINITIES OF THE MENASPID BRADYODONTS

The two best preserved specimens of the Upper Permian fish Menaspis armata have been reinvestigated, resulting in new interpretations of a variety of anatomical features. The conclusion is reached that the menaspids cannot possibly be closely related to the chimaeriforms (myriacanthids, squalorajids, and chimaerids), nor to any of those better known bradyodonts (chondrenchelyids, helodontids or edestids) with which they were previously classified. Among the bradyodonts, their closest relatives are probably to be found within the cochliodontids. As far as other elasmobranchiomorphs are concerned, the menaspids may be somehow related to, though surely not direct descendants of, the rhenanids, and it is conceivable that both these groups are derived from the same ancestral forms among the early arthrodires or the arthrodire predecessors.     

Deconstructing crop processes and models via identities

This paper is part review and part opinion piece; it has three parts of increasing novelty and speculation in approach. The first presents an overview of how some of the major crop simulation models approach the issue of simulating the responses of crops to changing climatic and weather variables, mainly atmospheric CO₂ concentration and increased and/or varying temperatures. It illustrates an important principle in models of a single cause having alternative effects and vice versa. The second part suggests some features, mostly missing in current crop models, that need to be included in the future, focussing on extreme events such as high temperature or extreme drought. The final opinion part is speculative but novel. It describes an approach to deconstruct resource use efficiencies into their constituent identities or elements based on the Kaya‐Porter identity, each of which can be examined for responses to climate and climatic change. We give no promise that the final part is ‘correct’, but we hope it can be a stimulation to thought, hypothesis and experiment, and perhaps a new modelling approach.