Morphogenetic study of brachiopods

In this work we discuss the results of ontogenetic and morphobiological approaches to phylogenetic reconstructions of articulate brachiopods on the basis of morphogenetic data. These data provide the basis for generalizations concerning phylogeny and system of orders. The ontogenetic approach was the subject of criticism mainly because of arbitrary establishment of the homology of brachiopods. The constraints of the morphobiological approach are associated with the phenomena of morphological evolution without adaptive explanation so far. As an example of these phenomena, homeomorphism of brachiopods can be considered. Prospects for morphogenetic studies of brachiopods can be connected with the study of characteristic elements of their shell structure, such as porosity and mantle channels.     

Determination of paleoseasonality of fossil brachiopods using shell spiral deviations and chemical proxies

Brachiopods have been extensively used in paleoclimatic and paleoecological reconstructions, but their utility would greatly increase if paleoseasonality information could be obtained from their shells. Determining seasonal seawater temperature variations from fossil brachiopods requires knowledge of specimen ontogenetic ages, which is difficult to determine compared to other organisms secreting a shell by accretion. In this study, the combination of the spiral deviation methodology and chemical proxies is tested for determining specimen ontogenetic ages and paleoseasonality using two species of fossil brachiopods, Laqueus rubellus and Terebratula terebratula, of Pleistocene and Late Miocene age, respectively. Spiral deviations were obtained for Laqueus and Terebratula using an R program developed for modern taxa, and well-preserved shells were analyzed using oxygen isotopes and Mg/Ca ratios as chemical proxies for past seawater temperature. Results reveal that locations of spiral deviations on shells of L. rubellus displayed a strong direct relationship with Mg concentrations, and resulting Mg/Ca-derived paleotemperatures were seasonal. Conversely, specimens of T. terebratula did not show a consistently strong relationship between Mg concentrations and spiral deviations, although resulting paleotemperatures agreed with those from previous studies. Overall, the results from this study indicate that the spiral deviation methodology combined with chemical proxies presents great potential for utility in past seasonal seawater temperature reconstructions in pristinely preserved, biconvex fossil brachiopods.     

Morphogenetic regulation in the shells of bivalves and brachiopods: evidence from the geometry of the spiral

Ackerly. S. C. 1992 07 15: Morphogenetic regulation in the shells of bivalves and brachiopods: evidence from the geometry of the spiral.
Analyses of the spiral geometry in shells of the mollusc Pecten maximus and the brachiopod Terebratulina retusa indicate a relative reduction in morphological variability within the population during growth. The spiral, as measured by a model of exponential radial expansion, tends to converge on a particular adult form, irrespective of irregularities during early growth phases. The recurrence of this pattern of variability in populations from two separate phyla (molluscs and brachiopods) suggests a common mechanism controlling shell form. Brachiopoda. Mollusca, coiling, spiral. morphogenetic regulation, growth .     

The protegulum and juvenile shell of a Recent articulate brachiopod: patterns of growth and chemical composition

Patterns of shell formation and the chemical composition of the shell deposited during early post-larval life were investigated in laboratory-reared cultures of the Recent articulate brachiopod Terebraralia transversa (Sowerby). A non-hinged protegulum averaging 148 pm in length is secreted by the mantle within a day after larval metamorphosis. The inner surface of the protegulum exhibits finely granular, non-fibrous material. A rudimentary periostracum constitutes the outer layer of the primordial shell. and concentrically arranged growth lines are lacking. By four days post-metamorphosis, a brephic type of juvenile shell develops from periodic additions of shell material to the anterior and lateral edges of the protegulum. Imbricated secondary fibers occur throughout the inner layer of the newly formed juvenile shell, and a rudimentary hinge apparatus is present posteriorly. The external surface of the shell exhibits concentric growth lines anterior to the caudally situated protegulum, and unbranched punctae begin to form in the subperiostracal region of the shell. At 23 days post-metamorphosis, the shell weighs an average of 1.7 μg and measures 318 μm in length. Electron microprobe analyses reveal that the protegulum is calcified. Minor amounts of sulfur, magnesium, iron, chlorine, aluminum, and silicon are also present in protegula and juvenile shells. Based on electron diffraction data, the mineral phase of juvenile shells consists of calcite, and protegula also appear to contain calcite.     

Growth rate and substrate-related mortality of a benthic brachiopod population

Collins, M. 1991 01 15: Growth rate and substrate-related mortality of a benthic brachiopod population. Lethaia , Vol. 24, pp. 1–11. Oslo. ISSN 0024–1164.
Vital staining and careful examination of potential substrates enabled an accurate census of Terebratulina retusa to be made and prompted a study of their population dynamics. Seasonal samples of T. retusa from a deep water Modiolus -brachiopod assemblage were always dominated by small (>1 mm) individuals as growth rate of the post-larvae, estimated from changes in mean cohort length. was unexpectedly slow. Six months after settlement the animals had barely doubled in length, a rate of increase consistent with laboratory studies, but an order of magnitude less than conventional estimates. As the attainment of a size refuge is the only documented strategy by which articulate brachiopods counter overgrowth or disturbance this observation has profound implications for survival. Mortality of T. retusa in the Firth of Lorn, from different substrates, followed an unexpected pattern. Virtually the only substrate on which adult T. rehusa were recorded was the surface of M. modiolus shells, although juvenile T. retusa attached to this substrate suffered enhanced levels of mortality. Grazing pressures and spatial competition, believed to be reduced on complex surfaces, may account for the elevated mortality levels of M. modiolus-attached post-larvae prior to the apparent size refuge at a length of 2 mm. * Brachiopoda, Terebratulina, growth rate, disturbance, ecology, population structure .     

Variable pedicle morphology in a population of the Recent brachiopod Terebratulina septentrionalis

Extremely variable pedicle morphology is described in a large sample of the Recent articulate brachiopod Terebratulina septentrionalis (Couthouy) from off the coast of Nova Scotia. The majority of these specimens were attached to the shells of living or dead scaphopods by a dense network of pedicle rootlets. Other brachiopods had been lying on the sea-floor anchored solely by the weight of sediment enmeshed within the bush-like network of pedicle rootlets. Some brachiopod larvae had settled on the exposed pedicle rootlets of adults, presumably because of the scarcity of other suitable substrate. Such a mode of life is thought 'to indicate that these brachiopods could survive a further reduction in the available substrate and it is suggested that, should such conditions persist, changes in hard-part morphology would enable descendants of the species to adopt a predominantly free-lying mode of life. Likely morphological adaptions are suggested, based on examples from the fossil record. This evolutionary trend, from attached to free-lying and perhaps vice versa, has occurred many times in the history of the Phylum Brachiopoda, and it is suggested that the mode of life of this T. septentrionalis population provides an important insight into at least one of the possible evolutionary pathways which bring about such transformations.     

The relationship between major lamellae and epithelial regressions in some articulate brachiopods

Brunton, C. Howard C. & Alvarez, Fernando 1989 07 15: The relationship between major lamellae and epithelial regressions in some articulate brachiopods. Lethaia , Vol. 22, pp. 247–250. Oslo. ISSN 0024–1164.
Hiller (1988, Lethaia , Vol. 212) proposed three relationships between the secretory epithelium of articulate brachiopods and the shell surface ornamentations of growth lines, lamellae and spines. None of his models satisfy the growth of strongly lamellose athyrid shells and we propose a fourth involving strong regressions effecting both primary and secondary shell layers. In Recent Tegulorhynchia we suggest a growth function for the 'frayed' shell of Hiller occurring immediately in front of the spines.     

Microstructure, growth banding and age determination of a primnoid gorgonian skeleton (Octocorallia) from the late Younger Dryas to earliest Holocene of the Bay of Biscay

A fossil primnoid gorgonian skeleton (Octocorallia) was recovered on the eastern Galician Massif in the Bay of Biscay (NE Atlantic) from 720 m water depth. The skeleton shows a growth banding of alternating Mg–calcitic and organic (gorgonin) increments in the inner part, surrounded by a ring of massive fibrous calcite. Three calcite-dominated cycles, bounded by thick organic layers, consist of five light-dark couplets of calcite and gorgonin. Two AMS-¹⁴C datings of the fossil skeleton give ages of 10,880 and 10,820 ± 45 ¹⁴C years before present (BP). We arrive at a calibrated age range of 11,829–10,072 cal. years BP (two σ), which comprises the late Younger Dryas to the earliest part of the Holocene. The cyclic calcitic–organic growth banding may be controlled by a constant rate of calcite secretion with a fluctuating rate of gorgonin production, possibly related to productivity cycles. The skeletal fabric change of alternating calcitic–organic increments to massive fibrous calcite may be the result of hydrographic changes during the deglaciation as reflected by preliminary stable isotope data. If this hypothesis proves to be correct, primnoid gorgonians are able to match with varying hydrodynamic conditions by changing their biomineralisation mode.     

Ontogeny of growth hormone, prolactin, luteinizing hormone, and testosterone secretory patterns in the ram

The ontogenetic changes that occur in secretory patterns of growth hormone (GH), prolactin (Prl), luteinizing hormone (LH), and testosterone (T) in rams maintained in constant photoperiod were examined. Nine ram lambs were moved to individual pens in a controlled environment (12L: 12D cycle; 18-24 degrees C temperature) at 66 days of age. Blood samples were collected via indwelling cannulae at 15-min intervals for an 8-h period at 80, 136, 192, 248, and 304 days of age. Plasma concentrations of GH, Prl, LH, and T were quantitated and parameters of the secretory patterns determined. Mean concentration of GH tended to decline with age, probably because the amplitude of secretory peaks was significantly reduced with age. There were no age-associated changes in basal concentration of GH or incidence of GH peaks. There was an increase in Prl secretion (as estimated by mean concentration) at 136 and after 248 days of age. Significant age-associated changes occurred in all parameters of LH and T secretion. At the younger ages, testosterone concentrations were low and LH concentrations were elevated. At the older ages the relationship was reversed, with LH low and testosterone high. There were no significant correlations between frequency and magnitude of LH and T peaks. The significant correlations present among parameters of LH and T secretion were between basal concentration of LH and overall mean concentration and basal concentration of T. These results suggest that LH may not be the sole tropic stimulator of acute T secretion.     

Borings produced by brachiopod pedicles, fossil and Recent

Bromley, R. G. & Surlyk, F.: Borings produced by brachiopod pedicles, fossil and Recent.
Characteristic etching traces are produced in hard calcareous substrates by the pedicles of brachiopods belonging to several groups. It was previously unsuspected that the ability to bore was widespread within the brachiopod phylum. Five species were investigated from the Norwegian Sea: Terebratulina retusa and T. septentrionalis (Terebratulacea), Hemithyris psittacea (Rhynchonellida), and Macandrmia cranium and Dallina septigera (Terebratellacea). Fossil traces with closely similar morphology occur in the Cretaceous and are probably also the work of brachiopods. The most characteristic form is designated Podichnus centrifugalis n. ichnogen., n. ichnosp.     

The origin and geometry of radial ribbing patterns in articulate brachiopods

Ackerly, S. C. 1992 07 15: The origin and geometry of radial ribbing patterns in articulate brachiopods.
Geometric models for simple. radial ribbing in articulate brachiopods include (1) ribs radiating isometrically from the shell umbo. (2) divergence of thc ribs from some 'point' within the shell, and (3) reorientation of the ribs at right angles to the shell margin. Analyses of the Orthida, the ancestral taxon of articulate brachiopods, indicate that rib geometries are isometric in Early Cambrian taxa (model 1). but that by the Early Ordovician rib orientations are generally perpendicular to the shell margin (model 3). A combination of functional and morphogenetic Factors explains the ribbing geometries observed in orthide brachiopods.     

The Recent Terebratulina Community in the rocky subtidal zone of the Bay of Fundy, Canada

A distinctive rocky subtidal benthic community (the Terebratulina Community) is described from the Bay of Fundy, Canada. It is shown to consist of three closely intcrspersed sub-communities: a cavity sub-community, characterised by chitons, coelenterates, brachiopods, bryozoans, chordates and annelids; a rock-face subcommunity, similar in composition but enriched in brachiopods and sponges; and an upper-surface subcommunity, dominated by algae, chitons, bivalves and echinoids.
Comparison with recently described Jurassic, Cretaceous and Recent (Mediterranean) hard-ground communities suggests a relative constancy in composition, in terms of higher taxa, since the Mesozoic. Development of these (sub-)communities occurs wherever crevice or cavity systems on hard substrates lead to microenvironments differentiated mainly on the basis of water energy and light.
The composition and trophic structure of the community and the life habits of Terebratulina septentrionalis (Couthouy) are related to aspects of the environment. Marked differences in composition between the living cavity sub-community and the death assemblage in the sediments are shown to be due to differential preservation, fragmentation, population dynamics and limited local transportation.     

Interpreting skeletal growth in the past from a functional and physiological perspective

The study of juvenile skeletal remains can yield important insights into the health, behavior, and biological relationships of past populations. However, most studies of past skeletal growth have been limited to relatively simple metrics. Considering additional skeletal parameters and taking a broader physiological perspective can provide a more complete assessment of growth patterns and environmental and genetic effects on those patterns. We review here some alternative approaches to ontogenetic studies of archaeological and paleontological skeletal material, including analyses of body size (stature and body mass) and cortical bone structure of long bone diaphyses and the mandibular corpus. Together such analyses can shed new light on both systemic and localized influences on bone growth, and the metabolic and mechanical factors underlying variation in growth. Am J Phys Anthropol, 2013. © 2012 Wiley Periodicals, Inc.     

Biogeography of the recent brachiopods

The vertical, latitudinal, and circumcontinental zonality of the distribution of the species, genera, and families of recent brachiopods is considered. The distortions of the latitudinal and meridional symmetry of the biogeographic structure of the ocean are analyzed in view of the patterns of the global circulation of the surface and intermediate waters. Thus ancient faunas may be reconstructed based on data on the structural characteristics of the taxocene of recent brachiopods. The features of the paedomorphic evolution of brachiopods from the different families in extreme habitats (interstitial, underwater caverns, submarine rises, abyssal depths, hydrothermal areas, and margins of habitats) are discussed. The biogeographic structure of bottom dwellers is shown to simplify with depth as well as with simplification of the hydrological structure of the ocean. The important role of the bathyal oceanic zone (slopes of continents, islands, submarine mountains, ridges, and rises) in the preservation of faunal relicts is shown. The historical change from brachiopods to bivalves that occurred from the Paleozoic to the Mesozoic and Cenozoic is shown to have resulted not from competitive exclusion, but from complex and global changes in the plankton composition, which were unfavorable for articulate brachiopods, which had already developed specialized feeding habits, feeding on food that led to the production of almost no metabolic waste products; they had even partly lost their alimentary canal. The development of shelly plankton and, especially, of diatoms hampered the post-Paleozoic revival of large assemblages of articulate brachiopods in shallow-water habitats. The unfilled ecological niches were colonized by bivalves, which were widely adapted to feeding on live phyto-and zooplankton. Recent articulate brachiopods, which are adapted to feeding on the products of decay of dead plankton, form a belt of densely populated settlements of the organic biofilter outside the photic zone on the seaward edge of shelves and on the upper parts of the slopes of continents, islands, and submarine rises throughout the world.     

Life-History Traits of the Miocene Hipparion concudense (Spain) Inferred from Bone Histological Structure

Histological analyses of fossil bones have provided clues on the growth patterns and life history traits of several extinct vertebrates that would be unavailable for classical morphological studies. We analyzed the bone histology of Hipparion to infer features of its life history traits and growth pattern. Microscope analysis of thin sections of a large sample of humeri, femora, tibiae and metapodials of Hipparion concudense from the upper Miocene site of Los Valles de Fuentidueña (Segovia, Spain) has shown that the number of growth marks is similar among the different limb bones, suggesting that equivalent skeletochronological inferences for this Hipparion population might be achieved by means of any of the elements studied. Considering their abundance, we conducted a skeletechronological study based on the large sample of third metapodials from Los Valles de Fuentidueña together with another large sample from the Upper Miocene locality of Concud (Teruel, Spain). The data obtained enabled us to distinguish four age groups in both samples and to determine that Hipparion concudense tended to reach skeletal maturity during its third year of life. Integration of bone microstructure and skeletochronological data allowed us to identify ontogenetic changes in bone structure and growth rate and to distinguish three histologic ontogenetic stages corresponding to immature, subadult and adult individuals. Data on secondary osteon density revealed an increase in bone remodeling throughout the ontogenetic stages and a lesser degree thereof in the Concud population, which indicates different biomechanical stresses in the two populations, likely due to environmental differences. Several individuals showed atypical growth patterns in the Concud sample, which may also reflect environmental differences between the two localities. Finally, classification of the specimens’ age within groups enabled us to characterize the age structure of both samples, which is typical of attritional assemblages.     

INDIVIDUAL VARIATION OF ONTOGENIES: A LONGITUDINAL STUDY OF GROWTH AND TIMING

This study of growth and developmental time in the water strider Limnoporus canaliculatus (Heteroptera: Gerridae) is based on longitudinal data from specimens reared individually in the laboratory. I analyzed multivariate allometry using a common principal components approach. This technique identified patterns of variation that were uncorrelated both within and among instars and which remained fairly constant throughout the growth period; in contrast, the overall amount of variation increased from young to older instars. Negative correlations between size and subsequent growth increments indicated convergent growth in the first three instars, but there was a transition to positive correlations (divergent growth) in later instars. Analysis of covariation among measurements made in different instars showed strong ontogenetic autocorrelation and revealed patterns remarkably similar to those found in mammals and birds; yet corresponding analyses of growth increments showed mainly independent variation in different instars. Therefore, I conclude that the strong correlations among stage-specific measurements result from the part-whole relationships inherent to these cumulative size data, but do not reflect specific properties of the organisms studied. In contrast to size increments, instar durations of water striders were highly correlated throughout the larval period, indicating that individuals tended to develop at either relatively fast or relatively slow rates in all instars. The correlations between growth increments and instar durations were nil or negative, contrary to expectations from life-history theory. The results of these analyses of individual variation match the findings from other water striders and from interspecific comparisons in the genus Limnoporus, but information about physiological mechanisms of molting and growth in insects cannot completely explain the patterns observed.     

Mapping of recent brachiopod microstructure: A tool for environmental studies

Shells of brachiopods are excellent archives for environmental reconstructions in the recent and distant past as their microstructure and geochemistry respond to climate and environmental forcings. We studied the morphology and size of the basic structural unit, the secondary layer fibre, of the shells of several extant brachiopod taxa to derive a model correlating microstructural patterns to environmental conditions. Twenty-one adult specimens of six recent brachiopod species adapted to different environmental conditions, from Antarctica, to New Zealand, to the Mediterranean Sea, were chosen for microstructural analysis using SEM, TEM and EBSD. We conclude that: 1) there is no significant difference in the shape and size of the fibres between ventral and dorsal valves, 2) there is an ontogenetic trend in the shape and size of the fibres, as they become larger, wider, and flatter with increasing age. This indicates that the fibrous layer produced in the later stages of growth, which is recommended by the literature to be the best material for geochemical analyses, has a different morphostructure and probably a lower organic content than that produced earlier in life.In two species of the same genus living in seawater with different temperature and carbonate saturation state, a relationship emerged between the microstructure and environmental conditions. Fibres of the polar Liothyrella uva tend to be smaller, rounder and less convex than those of the temperate Liothyrella neozelanica, suggesting a relationship between microstructural size, shell organic matter content, ambient seawater temperature and calcite saturation state.     

Grazing bioerosion in Jurassic seas: a neglected factor in the Mesozoic marine revolution?

Grazing bioerosion, notably by chitons, gastropods and regular echinoids, is a powerful destructive force in many recent shallow-marine environments and impacts significantly on sessile epibionts through grazing predation and/or unselective dislodgement. Grazing bioerosion was an important component of a major phase of biotic escalation; the Mesozoic marine revolution. Recent investigations of hard substrates in southern British Jurassic marine formations have identified widespread ichnofossils attributable to grazing activity by gastropods and/or chitons, and regular echinoids. The co-occurring benthic macrofaunas include groups that would have been vulnerable to grazing disturbance and dislodgement; notably articulate brachiopods. The emerging ichnological evidence strengthens the argument for grazing bioerosion as a significant contributor to the Mesozoic–Cenozoic decline of the articulate brachiopods, and their retreat to deep-water and/or cryptic refugia.     

Bone Growth Dynamics of the Facial Skeleton and Mandible in <Emphasis Type="Italic">Gorilla gorilla</Emphasis> and <Emphasis Type="Italic">Pan troglodytes</Emphasis>

Adult craniofacial morphology results from complex processes that involve growth by bone modelling and interactions of skeletal components to keep a functional and structural balance. Previous analyses of growth dynamics in humans revealed critical changes during late ontogeny explaining particular morphological features in our species. Data on bone modelling patterns from other primate species could help us to determine whether postnatal changes in the growth dynamics of the craniofacial complex are human specific or are shared with other primates. However, characterizations of bone modelling patterns through ontogeny in non-human hominids are scarce and restricted to isolated data on facial and mandibular regions. In the present study, we analyse the bone modelling patterns in an ontogenetic series of Pan and Gorilla to infer the growth dynamics of their craniofacial complex during postnatal development. Our results show that both Pan troglodytes and Gorilla gorilla are characterized by species-specific bone modelling patterns indicative of a mainly forward growth direction during postnatal development. Both species show minor but consistent ontogenetic changes in the distribution of bone modelling fields in specific regions of the face and mandible, in contrast to other regions which show more constant bone modelling patterns. In addition, we carry out a preliminary integrative study merging histological and geometric morphometric data. Both approaches yield highly complementary data, each analysis providing details on specific growth dynamics unavailable to the other. Moreover, geometric morphometric data show that ontogenetic variation in the modelling pattern of the mandibular ramus may be linked to sexual dimorphism.