The fourth series of the Silurian System in Podolia

The Skala horizon of Podolia has been under discussion as a possible candidate for the stratotype of the fourth Silurian series (primary subdivision) in the international standard chronostratigraphical scale. After a brief survey of the history of investigation, the section through the basal boundary of the Skala horizon is fully documented. The lithostratigraphy, biostratigraphy, and correlation of the Skala horizon are then discussed.     

Biological externalities and evolution: a comment

Tullock's illuminating article in this Journal (1971) uses the economic theory of externality to anlyze the natural equilibira of biological systems where species interact. He demonstrates that the natural system does not attain a Pareto optimum—that it would be possible to increase both species (in a two-species model) by appropriate management. In this comment on his paper, his analysis is shown to result from implicit restrictions on further evolution which would be relevant to the external interaction. If evolution is allowed to proceed costlessly to internalize the externality, natural processes are shown to lead to optimality. Further, the directions of future evolution may be predicted from the analysis of biological externalities. The extension of Tullock's model to analyze further evolution is shown to be analogous to certain extensions of the standard model of economic externalities.     

Metamorphosis in a Silurian barnacle

Exceptionally preserved fossils from the Wenlock Series (Silurian) of Herefordshire, UK, provide unique evidence of metamorphosis from free-swimming cyprid larva to attached juvenile in a Palaeozoic barnacle. The larva had large brush-like anterior limbs. The juvenile shows the head transformed into a stalk and the development of the primordial condition of five mineralized plates within the carapace. The discovery of a cyprid larva indicates that crown group cirripedes had evolved by the Silurian.     

Indinavir resistance evolution: a comment

Dear Editor, I read the recent report on HIV with a great interest[2].Geng et al concluded that"Indinavir-resistance evolution was observed by single-genome amplification[2]"and"During the course of changing the regimen to incorporate Indinavir,the G73S mutation occurred and was combined with M46I/L90M[2]."I have some points for discussion on this work.First,focusing on the single-genome amplification,although it is acceptable the false positive can still be detected[3].     

Angiosperm classification and phylogeny: a rectifying comment

A commentary is given on the criticism of Dahlgren's recent classification of angiosperms by Corner ( Botanical Journal of the Linnean Society, 82: 81–87 (1981)). In his dissatisfaction with the current, (almost) generally accepted nomenclatural concepts he has chosen to use my classification as a target. It is agreed that nomenclature is not 'fair' to plant groups playing the most important role in building up the biosphere, and that nomenclatural constructions do not reflect the consideration given to various parts of the plant. Corner does not seem to be familiar with the fact that his so-called 'pseudons' are common to all current systems of classification, nor that the termination '-florae' has been used by Thorne (1968) and in a number of publications since. This suffix does not imply that the botanists using it neglect vegetative characters, nor characters from fruits and seeds. Other misunderstandings are also pointed out. In no case has it been satisfactorily demonstrated by Corner that my orders or superorders are unnatural entities (even though a number of them most likely are).     

Stromatoporoid-coral intergrowths in a Silurian biostrome

Four stromatoporoid species from a stromatoporoid biostrome in the middle Ludlow Hemse Beds, Gotland, Sweden, show intergrowths with syringoporid tabulate and rugose corals, and indicate close relationships between particular coral and stromatoporoid species. The stromatoporoid Clathrodictyon convictum always contains ?Syringopora and this tabulate is rarely found in the other stromatoporoids. C. convictum is also closely associated with Tryplasma flexuosum (rugosa) while Petrozium pelagicum (rugosa) occurs only in the stromatoporoids Plectostroma intermedium and Parallelostroma typicum. The microstructure of ?Syringopora within the stromatoporoids is composed of an inner lamellar layer and an outer radial layer of calcite crystals. Diagenetic alteration has affected the microstructure which differs from recently described Devonian forms having only a radial layer. This shows variability in the structure of the tabulates within stromatoporoids. Information is sparse on the range of such variation and assessment of the relative importance of taxonomic, palaeoenvironmental and diagenetic effects is not possible in the present sample. No evidence is found to prove the precise nature of the relationships; they were not parasitic but may have been mutually symbiotic, or (most probably) commensal. The results suggest that the corals selected the most suitable stromatoporoid species for their requirements. Stromatoporoid morphology may have had an important influence on the association, where corals are more abundantly associated with those stromatoporoid species which adopted a high profile. Overall the associations appear to have allowed the corals to explore higher energy habitats otherwise unavailable to their delicate branching structure.     

Brood care in a Silurian ostracod

An exceptionally preserved new ostracod crustacean from the Silurian of Herefordshire, England, preserves eggs and possible juveniles within its carapace, providing an unequivocal and unique view of parental brood care in the invertebrate fossil record. The female fossil is assigned to a new family and superfamily of myodocopids based on its soft-part anatomy. It demonstrates a remarkably conserved egg-brooding reproductive strategy within these ostracods over 425 Myr. The soft-tissue anatomy urges extreme caution in classifying 'straight-hinged' Palaeozoic ostracods based on the carapace alone and fundamentally questions the nature of the shell-based Palaeozoic ostracod record.     

Silurian brachiopods in a stromatoporoid bioherm

Ludlovian limestone at Ljugarn, Gotland. repreqents a shallow marine environment of stromatoporoid biohenns and flanking areas of mud and stromatoporoid debris. Brachiopods were restricted to surfaces of the debris deposits. Lissatrypa sulcata, a smooth atrypacean, dominated the brachiopod fauna, with individuals living beak downward in high density clusters, developing weaker pedicle attachment and a sulcus during ontogeny. Surrounding low density areas of Lissatrypa included small, pedicleattached, non-sulcate shells. Howellella, Spirigerina, and Morinorhynchus? lived in isolated clusters near low density Lissatrypa populations, and 10 other very rare brachiopod species may have been non-reproducing members of the community. Brachiopcd species diversity, and thus number of niches, was lower in the biohermal enviroment than in bathymetrically equivalent, level-bottom communities.