The Strategy of the Genes

Very different palaeogeographical reconstructions have been produced by a combination of palaeomagnetic and faunal data, which are re-evaluated on a global basis for the period from 500 to 400 Ma, and are presented with appropriate confidence (or lack of it) on six maps at 20 Ma intervals. The palaeomagnetic results are the most reliable for establishing the changing palaeolatitudes of Baltica, Laurentia and Siberia. However, global palaeomagnetic reliability dwindles over the 100 Ma, and more evidence for relative continental positioning can be gleaned from study of the distribution of the faunas in the later parts of the interval. The new maps were generated initially from palaeomagnetic data when available, but sometimes modified, and terranes were positioned in longitude to take account of key faunal data derived from the occurrences of selected trilobites, brachiopods and fish. Kinematic continuity over the long period is maintained. The many terranes without reliable palaeomagnetic data are placed according to the affinities of their contained fauna. The changing positions of the vast palaeocontinent of Gondwana (which has hitherto been poorly constrained) as it drifted over the South Pole during the interval have been revised and are now more confidently shown following analysis of both faunal and palaeomagnetic data in combination, as well as by the glacial and periglacial sediments in the latest Ordovician. In contrast, the peri-Gondwanan and other terranes of the Middle and Far East, Central Asia and Central America are poorly constrained.

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Earth geography from 500 to 400 million years ago: a faunal and palaeomagnetic review

The green lineage (Viridiplantae) comprises the green algae and their descendants the land plants, and is one of the major groups of oxygenic photosynthetic eukaryotes. Current hypotheses posit the early divergence of two discrete clades from an ancestral green flagellate. One clade, the Chlorophyta, comprises the early diverging prasinophytes, which gave rise to the core chlorophytes. The other clade, the Streptophyta, includes the charophyte green algae from which the land plants evolved. Multi-marker and genome scale phylogenetic studies have greatly improved our understanding of broad-scale relationships of the green lineage, yet many questions persist, including the branching orders of the prasinophyte lineages, the relationships among core chlorophyte clades (Chlorodendrophyceae, Ulvophyceae, Trebouxiophyceae and Chlorophyceae), and the relationships among the streptophytes. Current phylogenetic hypotheses provide an evolutionary framework for molecular evolutionary studies and comparative genomics. This review summarizes our current understanding of organelle genome evolution in the green algae, genomic insights into the ecology of oceanic picoplanktonic prasinophytes, molecular mechanisms underlying the evolution of complexity in volvocine green algae, and the evolution of genetic codes and the translational apparatus in green seaweeds. Finally, we discuss molecular evolution in the streptophyte lineage, emphasizing the genetic facilitation of land plant origins.

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Phylogeny and Molecular Evolution of the Green Algae

The apatite-group minerals of the general formula, M10(ZO4)6X2 (M = Ca, Sr, Pb, Na…, Z = P, As, Si, V…, and X = F, OH, Cl…), are remarkably tolerant to structural distortion and chemical substitution, and consequently are extremely diverse in composition (e.g., Kreidler and Hummel 1970; McConnell 1973; Roy et al. 1978; Elliott 1994). Of particular interest is that a number of important geological, environmental/paleoenvironmental, and technological applications of the apatite-group minerals are directly linked to their chemical compositions. It is therefore fundamentally important to understand the substitution mechanisms and other intrinsic and external factors that control the compositional variation in apatites.

The minerals of the apatite group are listed in Table 1⇓, and representative compositions of selected apatite-group minerals are given in Table 2⇓. Also, more than 100 compounds with the apatite structure have been synthesized (Table 3⇓). Phosphate apatites, particularly fluorapatite and hydroxylapatite, are by far the most common in nature and are often synonymous with “apatite(s)”. For example, fluorapatite is a ubiquitous accessory phase in igneous, metamorphic, and sedimentary rocks and a major constituent in phosphorites and certain carbonatites and anorthosites (McConnell 1973; Dymek and Owens 2001). Of particular importance in biological systems, hydroxylapatite and fluorapatite (and their carbonate-bearing varieties) are important mineral components of bones, teeth and fossils (McConnell 1973; Wright et al. 1984; Grandjean-Lecuyer et al. 1993; Elliott 1994; Wilson et al. 1999; Suetsugu et al. 2000; Ivanova et al. 2001).

View this table:

 Table 1. 
Summary of the apatite-group minerals



View this table:

 Table 2. 
Representative compositions and unit-cell parameters of selected apatite-group minerals.



View this table:

 Table 3. 
Formulas of selected synthetic compounds with the apatite structure.



Following Fleischer and Mandarino (1995), Table 1⇑ also includes melanocerite-(Ce), tritomite-(Ce), and tritomite-(Y), the compositions …

Compositions of the Apatite-Group Minerals: Substitution Mechanisms and Controlling Factors

Mass extinctions and sea-level changes

Rare earth elements in old biogenic apatites

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Decision on the Devonian-Carboniferous boundary stratotype

/pdf/magnetosusceptibility-event-and-cyclostratigraphy-msec-of-1tk7evu8jh.pdf

MagnetoSusceptibility Event and Cyclostratigraphy (MSEC) of the Eifelian-Givetian GSSP and associated boundary sequences in north Africa and Europe

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Definition of the Frasnian/Famennian Stage boundary

The terminal zone of the Frasnian standard conodont zonation, the linguiformis Zone has been subdivided into alower part defined by the total range of Palmatolepis linguiformis and an upper part defined by the absence of the nominal species together with the rare occurrences of Pa. ultima (= Pa. praetriangularis) and Ancyrognathus (= Ancyroides) ubiquitus . This subdivision has proved to be effective in sections on different continental blocks. Furthermore, the two subdivisions correlate exactly with subdivisions formally recognized herein of Montagne Noire Zone 13 (13b and 13c). The lower boundary of the linguiformis Zone lies closely below the base of the Upper Kellwasser event bed, the top of which coincides with the end-Frasnian extinction. Nonetheless, prominent gaps in the geographic distribution of Pa. linguiformis have led to some difficulty in the identification of the zone. These gaps have been partially closed by discoveries of the species in areas where it was unknown until now, notably the central Moroccan Meseta and especially the Frasnian/Famennian boundary-stratotype section at Coumiac Upper Quarry in the Montagne Noire, southern France. Nevertheless, anomalous areas of absence, such as the Anti-Atlas Mts. of southern Morocco and western Canada still exist. The trilobite Palpebralia brecciae is widespread in Europe, North Africa, and Australia, providing evidence for correlation of the lower part of the linguiformis Zone in sections where the nominal conodont species has not been found. Analysis of variation in the relative abundance of the principal conodont genera leads to the conclusion that no substantial difference exists in the conodont associations among representative sections in four of the continental blocks.

Chapter 7Subdivision of the terminal Frasnian linguiformis conodont Zone, revision of the correlative interval of Montagne Noire Zone 13, and discussion of stratigraphically significant associated trilobites

Raimund Feist

Papers

Rare earth elements in old biogenic apatites

Decision on the Devonian-Carboniferous boundary stratotype

MagnetoSusceptibility Event and Cyclostratigraphy (MSEC) of the Eifelian-Givetian GSSP and associated boundary sequences in north Africa and Europe

Definition of the Frasnian/Famennian Stage boundary

Chapter 7Subdivision of the terminal Frasnian linguiformis conodont Zone, revision of the correlative interval of Montagne Noire Zone 13, and discussion of stratigraphically significant associated trilobites