Study of fossil and recent brachiopods,using a skyscan 1172 X-ray microtomograph

Fossil and recent brachiopods were studied with the aid of a Skyscan 1172 microtomograph. The capabilities of this method at different stages of studying, X-ray scanning and producing slices and 3D models are described. The method enables the study of punctuation, microornamentation, and inner structures of the brachiopod shells and soft tissues. The contrast of shell structures of fossil brachiopods is discussed; it depends on differences in the mineral composition of the shell and surrounding matter. This method allows studying the inner structure of the holotypes of brachiopod species without damaging their shells. The data on the efficiency of the method are provided.     

The origin of the spiriferidine brachiopods

Wright, Anthony D. 197901 15: The origin of the spiriferidine brachiopods. Lethaia . Vol. 12. pp. 29–33. Oslo. ISSN 0024–1164.
In recent years doubts have been expressed as to whether the strophic spiriferidines should continue to be grouped with the non-strophic spiriferids in the order Spiriferida or not. The solution to this problem will only be found by establishing the origin of the spiriferidines. A characteristic feature of the spiriferidines is their well developed micro-ornament; this is shared also by the orthid Platystrophiinae, and together with the striking similarity in overall morphology (well recognized in the early nineteenth century) it suggests that here, in the Platystrophia plexus, is the ancestral stock of the strophic spirebearers.
The Platystrophünae share with the non-strophic Rhynchonellida the potential to develop a spire. It is here considered that the former gave rise to the spiriferidines and the latter to the non-strophic spire-bearers. These quite separate developments justify the separation of the spire-bearers into the two orders Spiriferida and Atrypida.     

Ultrastructure of the loop of terebratulide brachiopods

The folded and twisted calcareous ribbon, forming both the ascending and descending lamellae of the loop of Waltonia inconspicua (Sowerby), is a two-layered structure consisting of a wedge of regularly stacked secondary layer fibres that overlie a thin layer of non-fibrous calcite (herein termed brachiotest). On one surface, that facing into the mantle cavity, secondary fibrous mosaic predominates, but smooth, finely banded brachiotest occurs as a narrow marginal lip upon which secondary layer fibres proliferate and progressively overlap. This growing edge of the ribbon is secreted by long, folded epithelial cells with digitate extensions to their apical plasmalemmas, which are distinguishable from the cuboidal epithelium-secreting fibres and their membranous sheaths. The other surface, facing the body cavity and the brachial coelom, consists entirely of roughened brachiotest exhibiting prominent banding that is aligned parallel to the growing loop edge. This surface is overlain by microfilamentar epithelium acting as a holdfast for the connective tissue frame of the lophophore. The other edge of the ribbon consists of truncated sections of both secondary-layer fibres and brachiotest which bear signs of resorption consistent with the degenerated state of the associated epithelium. Growth of the Waltonia loop is controlled by these localized processes of secretion and resorption of the fibrous and brachiotest layers and is typical of all terebratulides so far studied. The brachiotest is not homologous with the non-fibrous primary shell secreted at the valve margin. □ Brachiopoda, Articulata, Terebratulida, ultrastructure, lophophore, loop.     

'Flapping valves' in brachiopods

M. J. S. Rudwick and others postulate 'rhythmic-flow' feeding for the Permian richtho-feniacean bi-achiopods, whereas R. E. Grant claims that they fed by normal ciliary action. Suspension-feeding has two components, current generation and food capture; normal brachiopod lophophores do both, but this is neither universal nor compulsory among animals. Opening and closing the richthofeniid shell generated a 'tidal-flow' current precisely analogous to respiratory currents in mammals; this is neither inefficient nor 'self-defeating', as Grant claims. Grant's analysis fails because he chose the wrong mechanical analogy (a pump). Morphological features of richthofeniids are better explained on a tidal-flow hypothesis than on a ciliary-flow model, and all the data adduced by Grant in rejecting the former is compatible with it or favorable to it. It explains morphological features that are bizarre mysteries on the ciliaiy-current model, and is therefore superior even though it implies that these Permian brachiopods were radically innovative.     

Commissural asymmetry in brachiopods

Consistent asymmetric folding of the commissure is a characteristic feature of a small but significant number of brachiopod species. The feature may be obligate or facultative and is almost entirely confined to rhynchonellids, most of which are Mesozoic. The detailed nature of the asymmetry is very variable, but does not extend to internal hard parts such as crura. Taken as a whole, asymmetric brachiopod species show no preference for any particular environment or geographic region, and in no circumstances seem to have been markedly more or less successful than symmetric species. We are thus led to suggest that asymmetry was a genetically based condition which cropped up periodically in brachiopod evolution, and which possibly was selected neither particularly for nor against.     

Origin and dispersal of the earliest brachiopods

Brachiopods first appeared at the very beginning of the Phanerozoic together with the first skeletal organisms. Most brachiopod taxa that arose in the first half of the Cambrian had a short temporal range and became completely extinct by the middle of the Middle Cambrian. Rigid articulation of the valves of brachiopods was provided by various structures, which also appeared in the Early Cambrian. This fact points to the importance of this feature for the formation of the whole group and at the same time testifies to the high variability of rigid articulation at the early stages of brachiopod evolution. This is a typical manifestation of archaic diversity in this animal phylum, which appeared very early in the Phanerozoic. Another important property of the archaic diversity of the early brachiopods was the large number of centers of diversification. As for the majority of groups, climatic zonality was the main factor determining the distribution of brachiopods at the beginning of the Phanerozoic. The main ecological types of brachiopods also appeared in the Early Cambrian.     

Allometric studies of fossil brachiopods

In different groups of fossil brachiopods new adaptations were formed by changes in size, shape, and proportions of morphological structures in ontogenetic and phylogenetic development.     

Biogeography of rotifers

The biogeography of rotifers is discussed in light of general biogeographical concepts. It is argued that, in spite of considerable abilities for passive dispersal, vicariance can develop well in this group. Examples selected from the Branchionidae illustrate the high levels of endemicity found in Australia and South America, while the Indian subcontinent and Africa have a predominantly cosmopolitan fauna. An explanation for these patterns is found in drifting continents and Pleistocene climatic changes.     

Ecophenotypic strategies of dalmanellid brachiopods

General ecophenotypic patterns, of particular interest when they apply to all, or most, taxa of the group concerned, can never be demonstrated until after monophyletic taxa have been recognized, that is, until after the initial stages of phylogeny construction have been carried out. In criticizing certain dalmanellid phylogenies, and based in large part on a study of five 'species subgroups'. Hurst & Watkins (1978; Geologica et Palaeontologica 12 ) postulate ecophenotypic patterns for Isorthis , and Hurst (1978; Palaeontology 21 ) postulates general patterns of ecophenotypic variation for dalmanellid brachiopods. These patterns may be invalid for four reasons: (1) Univariate and 'bivariate' statistical analysis of the samples used to define the five subgroups reveals no significant differences between subgroups, or vertical trends, for the very morphological characters claimed to exhibit the ecophenotypic patterns; (2) Hurst & Watkins' discriminant function analysis contains procedural errors and its results are ambiguous; (3) several of the five subgroups represent mixtures of unrelated taxa; (4) in recognizing the alleged patterns, Hurst & Watkins ignored contrary evidence from many taxa (and from many dalmanellid studies). □ Brachiopoda, Dalmanellidae, Silurian, ecology, evolution, systematics.     

Ontophylogenetic studies of the brachiopods of the order terebratulida

The patterns of ontophylogenetic change of the brachidium in Late Paleozoic, Mesozoic, and Cenozoic terebratulids are analyzed. The work of Russian specialists in establishing new evolutionary trends and working out terebratulid taxonomy on the basis of ontophylogenetic studies is discussed.     

Phylogeny and Biogeography of the Stapeliads

The stapeliads (Apocynaceae — Asclepiadoideae — Ceropegieae) form a group of highly succulent, practically leafless plants with a very diverse floral morphology. They are found in the drier parts of the Old World from southern Africa eastwards to Burma. 55 characters are selected on which a cladistic analysis is based and these are discussed in detail where necessary. From this a phylogeny is produced for the stapeliads. It is shown that they are monophyletic and that they are nested within a larger group among the tribe Ceropegieae of the subfamily Asclepiadoideae. Several of the important innovations that have led to the diversification of the stapeliads in semidesertic regions are discussed. The stapeliads appear to be mainly fly-pollinated. The methods of attraction of flies are mentioned and it is suggested that there are four basic floral types among the stapeliads.     

Plankton Biogeography of the Indian Ocean

Knowledge of plankton biogeography for the Indian and adjacent seas is necessary for an understanding of the regional characteristics and changes in the plankton composition. Some of the plankters will serve as good biogeographical indicator species. Some phytoplankters and tintinnids among zooplankton are promising for use as such labels for the presence of different waters in the Porto Novo (Coromandel coast, Bay of Bengal) region. A biogeographical classification of the local phytoplankton and peculiarities in the distribution of some rare tintinnids occurring there are discussed.     

Predatory asteroids and the decline of the articulate brachiopods

Various causes, such as increased predation pressure, the lack of planktotrophic larvae, a 'resetting' of diversity, increased competition from benthic molluscs and the decline of the Palaeozoic fauna, have been suggested to explain the failure of the brachiopods to reradiate following the Permo-Triassic mass extinction. Increased predation pressure has hitherto appeared improbable, because typical predators of brachiopods, such as teleostean fish, brachyuran crabs and predatory gastropods, did not undergo major radiation until the late Mesozoic and early Cenozoic. However, new evidence strongly suggests that one important group of predators of shelly benthic organisms, the asteroids, underwent a major radiation at the beginning of the Mesozoic. Although asteroids appeared in the early Ordovician, they remained a minor element of the marine benthos during the Palaeozoic acme of the brachiopods. However, these early asteroids lacked four important requirements for active predation on a bivalved epifauna: muscular arms (evolved in the early Carboniferous); suckered tube feet, a flexible mouth frame and an eversible stomach (all evolved in the early Triassic). Thus radiation of the Subclass Neoasteroidea coincided with both their improved feeding capability and the decline of the articulates. The asteroids were the only group of predators of brachiopods that underwent a major adaptive radiation in the earliest Mesozoic. The asteroids may therefore have contributed to inhibiting a Mesozoic reradiation of the brachiopods. Epifaunal species lacking a muscular pedicle may have been particularly vulnerable. Unlike bivalve molluscs, modern brachiopods show only a limited range of adaptations to discourage asteroid predation. □ Asteroidea, Brachiopoda, evolution, predation, functional morphology.     

Modeling the Biogeography of Fossil Baboons

We use a model of modern baboon socio-ecology to explore the behavioral ecology and biogeography of the extinct Plio-Pleistocene baboons (genera Parapapio, Gorgopithecus, Dinopithecus, and Papio). The model is based on the way climate affects the baboons’ time budgets, and focuses on intersite variability in behavior rather than on species-typical patterns of behavior, as most previous approaches have done. We use climate estimates for individual fossil sites based on matching modern habitats using faunal profiles and estimates of individual species’ body masses given in the literature. The model allows us to examine the minimum and maximum sizes of groups that individual species would have been able to support at particular localities, and hence the biogeography of a species on a continental scale. In doing so, the model allows us to examine which variables are most responsible for limiting a species’ ecological and biogeographic flexibility, and through this to explore a species’ capacity for coping with climate change. Feeding time is identified as the main constraint. In general, large-bodied species would have had more difficulty surviving in as wide a range of habitats as smaller-bodied species, and this may explain the limited geographical distribution of large-bodied baboons such as Gorgopithecus and Dinopithecus.     

Biogeography of the changing Phanerozoic world

Practically each one of the chapters in the book Historical Biogeography, Plate Tectonics, and the Changing Environment (Gray & Boucot 1979) would have deserved to be channelled to readers in the form of articles in periodicals, to be efficiently circulated among the most concerned specialists as offprints and to be abstracted and indexed by the secondary information services.     

New brachiopods from the Ordovician of northeastern Russia

New brachiopod taxa, Starnikoviella gen. nov., with the type species S. settedabanica sp. nov. (family Clitambonitidae), and Avdeevella gen. nov., with the type species A. mica sp. nov. (subfamily Glyptomeninae), from the Middle–Upper Ordovician boundary deposits of northeastern Russia are described.     

Morphobiological study of the brachiopods of the order Chonetida

A comparative morphological study of the brachiopods of the order Chonetida revealed a key part of the development of the shell structures connected with the feeding and respiration organs, such as the lophophore, musculature, and mantle, in the morphological evolution of the group. The general trends revealed in the development are adaptive and were restored based on morphofunctional analysis. Against the background of these trends, the correlative changes of the shell shape and its external ornamentation led to the repeated appearance of homeomorphs, whose similarity cannot be explained by adaptation. The phylogeny of the superfamily Anoplioidea is described as an example.