Christian C. Emig

δ18O and REE contents of phosphatic brachiopods: a comparison between modern and lower Paleozoic populations

δ18O values of both carbonate (18.7–25.1‰) and phosphate (15.1–16.7‰) components of the francolite from the fossil brachiopod shells are interpreted as the result of a partial resetting of pristine isotopic compositions. The similarity of hat-shape REE patterns of some lower Ordovician linguloids with those of extant littoral specimens suggests the preservation of a 500 Myr-old record of REE marine chemistry. In agreement with the known paleogeography, the phosphatic brachiopods have been deposited in a coastal environment under shallow and oxygenated marine waters. However, the contents and distribution of REE in some strongly altered brachiopod shells reveal an alteration of the original negative Ce anomalies and both Nd and Sm enrichments that transformed the initial hat-shape patterns of linguloids into strongly convex or bell-shape patterns.

Determination of oxygen isotope fractionation between water and phosphate from living lingulids: potential application to palaeoenvironmental studies

Abstract Lingulids are inarticulate brachiopods, with phosphatic shells, which live exclusively in marine waters. Their distribution is generally restricted to the continental shelf, within the 40° belt from temperate to equatorial areas. They show a range of morphological, physiological, and behavioral features that have remained remarkably constant since the Cambrian. The oxygen isotope fractionation between water and phosphate from living lingulids was determined as a tool to investigate the temperature and/or salinity of past coastal seawater. Oxygen isotope measurements were performed according to the silver phosphate method on a collection of lingulids coming from well-known and varied marine environments. A global δ18O variation of 3.5‰ was found for these lingulids which proves their good sensitivity to environmental factors namely the oxygen isotope composition and the temperature of seawater. Oceanographic data provided average temperature and salinity values in the living sites of the studied specimens. Least squares treatment of the data gave the following fractionation equation: T(°C) = 112.2 ± 15.3 − 4.20 ± 0.71[δ18O(PO4) − δ18O(H2O)]; which is similar to the equations determined by Longinelli and Nuti (1973a) and Kolodny et al. (1983) for other phosphate-bearing invertebrates and fishes. All these results suggest that a unique equation describes the phosphate-water fractionation of many marine organisms except for mammals.

δ18O values of coexisting brachiopods and fish: Temperature differences and estimates of paleo–water depths

To estimate vertical thermal gradients and paleo–water depths to marine platforms we present a new method based on the difference between δ 18 O values of contemporaneous brachiopod carbonate and fish phosphate. Present-day marine fauna of well-known ecology from the surface to the sea floor record isotopic temperatures that agree with measured temperatures. We predict distributions of isotopic data that result from sampling strategy, basin morphology, and fauna ecology and discuss limitations. Application of the method to the Jurassic Paris-London basin gives vertical thermal variations of up to 14 °C associated with depths varying from a few meters to 170 ± 30 m. The estimated depths are minimum values and are greater than those estimated from sedimentological criteria for this ancient epicontinental sea.

Réflexions critiques sur l'écologieet la systématique des Lingules actuelles et fossiles

Abstract New topics on ecology and systematics of recent and fossil Lingulids lead to an obvious revision of our knowledges on this zoological group. At first, the recent species need systematics and taxonomy on the bases of new described specific criteria (as, morphology of deltidial areas, muscle disposition); the results are briefly indicated. But, in fossil species, disorder and disparity of used characteristics are emphasized. The general conceiving on ecology of Lingulids are reviewed and discussed, especially on bathymetry and salinity; sediment and oxygenation conditions; taphocoenosis and lingulid «communities. On recent species, all these points are also studied, especially some ecological requirements (salinity, bathymetry, grain size), and mechanism of burrowing ability, burrow living positions in the sediments, as shell preservations after death and fossilization, to facilitate the paleobiotope interpretations. Recent animals are euryhalin, surviving at salinities from about 13 to 42‰; they could be considered as well adapted to waters with strong salinity fluctuations. They show preference to fine sand bottoms (lowest particle size about 40–60 μm). Their bathymetric distribution occurs between 0 and about 500 m (Lingula especially between 5–50 m; Glottidia 15–70 m). The isotherms 8–10°C seem to restrict their geographical and bathymetric distribution. Therefore, some post-palaeozoic lingulid bedsare studied or redescribed on the bases of the above discussed characteristics, and new interpretations on the environmental situation are given (Trias of Vosges Mountains; Oligocene from Japan; Eocene of London Basin). More caution must be used in study of fossil Lingulids that are not especially animals living in infralittoral bottoms with low salinity and deficient oxygenation, as generally accepted.

High frequency of drill holes in brachiopods from the Pliocene of Algeria and its ecological implications

The fossil record holds a wealth of ecological data, including data on biotic interactions. For example, holes in the skeletons of invertebrates produced by drilling activities of their enemies are widely used for exploring the intensity of such interactions through time because they are common and easily distinguished from non-biotic holes or holes produced by other types of interactions. Such drill holes have been described in numerous studies of Palaeozoic brachiopods but rarely in those focusing on brachiopods of the post-Palaeozoic, a striking pattern given that in the late Mesozoic and Cenozoic drilling gastropods diversified and frequencies of drilled molluscs increased dramatically. During the past several years, however, drilled brachiopods were reported in several studies of the Mesozoic and Cenozoic, suggesting that this phenomenon may be more common than has been previously assumed. Here we report on drilled brachiopods from a Pliocene locality in Algeria where 90 of 261 (34.5%) specimens of Megerlia truncata show evidence of predatory drilling. These data confirm that Cenozoic drilling frequencies of brachiopods may be locally high and, when taken together with other published data, that drilling frequencies are highly heterogeneous in space and time.

Conditions de fossilisation du genre Lingula (Brachiopoda) et implications paléoécologiques

Abstract In the light of recent ecological investigations on Recent lingulid brachiopods, some general concepts on lingulid paleoecology are reviewed. Under drastic environmental changes fossilization occurs (1) in life-position, e.g. rapid temperature decrease, salinity increase, desiccation or emersion of the subtratum, very fine sedimentation, (2) in flatlaying shells, e.g. prolonged reduction in salinity, coarse-size sedimentation, storms. Tolerances of lingulid populations, distribution and species characteristics are briefly discussed in regard to the lingulid occurrences in Recent and fossils ecosystems. It is suggested that morphological conservatism of Lingula since the Paleozoic is related to the niche continuum in deltaic or estuarine ecosystems and to a large degree of independence of environmental constraints.

Distributional patterns along the Mediterranean continental margin (upper bathyal) using Gryphus vitreus (Brachiopoda) densities

Abstract The Gryphus vitreus biocoenosis occurs in two types of profiles of the bottom topography on the continental slope. The density of G. vitreus can be divided into five zones directly related to the velocity of the bottom-current. The direction of the current over the Gryphus vitreus biocoenosis suggests three models according to the distributional limits of the density zones; the upper limit is always the continental shelf-edge (100–120 m) and the zonal limits are related to the slope gradient below 150 m. The bathymetric and spatial distribution of the density zones are analysed in relation to the current velocity and direction.

Triassic lingulide brachiopods from the Iberian range (Spain)

Abstract During the Middle Triassic marine transgression in Spain, several lingulide populations were fossilized in the Iberian Range (western part of Sephardic Province) and the recorded specimens have been described previously under several specific names. The paleontological aspects of the Jalance (Valencia province) section have been studied for the first time. Its exceptionally large population was fossilized in situ as flat-lying valves and can be interpreted as an autochthonous association related to a very shallow marine environment. The lingulide specimens belong to the genus Lingularia Biernat & Emig , 1993 , but the species name remains under debate, probably Lingularia smirnovae. Internal morphology and shell characters are described and compared with other Lingularia species.

Offshore brachiopods investigated by submersible

The distributional limits and densities of the brachiopod Gryphus vitreus (Born) are investigated for the first time by submersible, along transects over the “Banc du Magaud” (east of Hyeres islands, Provence, France). The offshore bottoms, on which the G. vitreus biocoenosis occurs (110 to 250 m), can be divided into three zones. The highest density (up to 600 individuals·m−2) is observed in large ripplemarks under strong bottom currents (1.5-2 knots) in Zone 2 (130–180 m), while the density is lower (< 10·m−2) in Zone 1 (110–130m) and Zone 3 (180–250 m, on a Quaternary thanatocoenosis) where the currents are weaker (0.5-1 knot). The ecological requirements of G. vitreus, a stenotopic species, are high hydrodynamic conditions (inducing a weak sedimentation, high nutrients supplies, sandy sediment with small hard substrata) and an annual constancy of temperature and salinity. The arrangement of the shells in relation to the current (Zone 2) is analysed. Paleoecological implications for branchiopods are suggested. A green alga is recorded to depths of 190 m.

Tools for linguloid taxonomy: the genus Obolus (Brachiopoda) as an example

This study points out some basic problems of linguloid systematics and proposes solutions for them. A taxonomic examination of the unique species of the genus Obolus found in the Upper Cambrian of Estonia and Russia, O. apollinis (= O. ruchini, O. transversus, O. rebrovi and Ungula convexa) is used as an example of a methodology employing all of the characters valid for distinguishing species of both extant and fossil Lingulidae. These characters are: - umbonal region; - body musculature; - septa or ridges; - main mantle canals - as established and figured by EMIG (1982, 1983) and BIERNAT and EMIG (1993). All of them have been determined to be taxonomically stable and have been studied and compared to take into account intraspecific variability; they should be used to describe or to redescribe any taxon of the superfamily Linguloidea. Characters of the shell and valves, such as shape, size, and dimensional ratios have no taxonomic value.