Fossil Brachiopods Research Articles

Post settlement behaviour of brachiopods on hard and soft substrates

This paper describes the variation in shell and pedicle morphology of three species of brachiopods. Two are specialists that live on hard or soft surfaces, respectively, and the third is a generalist that can live on either. The interaction between behaviour and substrate explains (1) the morphology of the specialists, (2) variability in the lifestyle of the generalists, and (3) diversity in fossil brachiopods.

Brachiopod diversity patterns from Carboniferous to Triassic in South China

AbstractIt has long been recognized that the trend of marine diversity from the Carboniferous to the Triassic includes an approximately 100‐myr‐long stable biodiversity stage ranging from the Late Carboniferous to the late Middle Permian, the most severe end‐Permian mass extinction in the Phanerozoic (pre‐Lopingian crisis and end‐Changhsingian mass extinction together), a bleak stage in the Early Triassic and a rapid recovery stage in the Middle Triassic. However, little attention has been paid to smaller diversity fluctuations among relatively stable stages in the Carboniferous and Permian. Here, we establish a database of the brachiopod fossil records from the Carboniferous to Triassic in South China, including 104 families, 373 genera, 2081 species recorded by 7948 occurrences with relatively detailed biostratigraphic controls. Analyses based on the raw taxonomic richness at familial, generic and specific levels, proportional and total extinction/origination/turnover rates, and rarefaction analyses for 21 different intervals from the Carboniferous to Triassic reveal that the brachiopod diversity trends can be generally divided into two distinctly different stages. Brachiopods were highly diversified during the Carboniferous and Permian Periods, whereas they were dramatically reduced in diversity after the end‐Changhsingian mass extinction. Brachiopods were abundant during the Early Carboniferous Tournaisian and Viséan, and were characterized by many genera extending from the Late Devonian. This was followed by a significant simple diversity decline in the Serpukhovian Stage. The Early Permian (either in Sakmarian or Artinskian) diversity decline previously perceived by coral and fusulinid workers is indicated by the raw generic and familial richness, and taxonomic richness per million years. However, it is not expressed by the rarefied brachiopod trajectory, which is probably affected by sampling effect or taxonomic selectivity. Brachiopods apparently declined from Capitanian to Early Wuchiapingian. Thus, the brachiopod diversity trajectory from Pennsylvanian Bashkirian to Late Guadalupian Capitanian generally characterises a long stable stage. Brachiopods are extremely abundant in the Late Wuchiapingian and Changhsingian in view of raw taxonomic richness, but a rarefied trajectory reveals a flat step following the pre‐Lopingian (end‐Guadalupian) crisis until the end‐Changhsingian mass extinction. Therefore, the previously widely perceived Lopingian radiation after the pre‐Lopingian crisis appears to be at least partly over‐stated. Brachiopods experienced a long bleak stage in the Early Triassic, followed by a rapid recovery in the Anisian, and reached their acme in the Norian, but never recovered to such a flourishing degree during the Carboniferous and Permian Periods. Brachiopods were eliminated in South China by the end‐Triassic withdrawal of the sea from this region. Copyright © 2006 John Wiley & Sons, Ltd.

Are the most durable shelly taxa also the most common in the marine fossil record?

This paper tests whether the most common fossil brachiopod, gastropod, and bivalve genera also have intrinsically more durable shells. Commonness was quantified using occurrence frequency of the 450 most frequently occurring genera of these groups in the Paleobiology Database (PBDB). Durability was scored for each taxon on the basis of shell size, thickness, reinforcement (ribs, folds, spines), mineralogy, and microstructural organic content. Contrary to taphonomic expectation, common genera in the PBDB are as likely to be small, thin-shelled, and unreinforced as large, thick-shelled, ribbed, folded, or spiny. In fact, only six of the 30 tests we performed showed a statistically significant relationship between durability and occurrence frequency, and these six tests were equally divided in supporting or contradicting the taphonomic expectation. Thus, for the most commonly occurring genera in these three important groups, taphonomic effects are either neutral with respect to durability or compensated for by other factors (e.g., less durable taxa were more common in the original communities). These results suggest that biological information is retained in the occurrence frequency patterns of our target groups.

Shell structure, patterns and trends of oxygen and carbon stable isotopes in modern brachiopod shells

This study investigates δ 13C and δ 18O variations in the shells of modern brachiopods representing all extant groups of calcite-precipitating brachiopods, collected live from 8 locations. SEM examinations determined the ultrastructural characteristics of each species prior to isotope analyses. δ 13C and δ 18O analyses of shell carbonate were carried out with samples representing disparate morphological features and ultrastructural shell layers of both ventral and dorsal valves. Generally, δ 18O values from the fibrous secondary or prismatic tertiary shell layers of the articulated Terebratulida and Rhynchonellida species were in oxygen isotopic equilibrium with ambient seawater. Isotopic temperatures extrapolated from these values are close to measured annual mean seawater temperatures. δ 18O values were relatively unaffected by shell specialisation. The only exception was Antarctic species Liothyrella uva, which did not have a complete tertiary shell layer typical of this genus and had δ 18O values of the innermost layer strongly correlated with δ 13C and mostly not in oxygen isotopic equilibrium with ambient seawater. With the exception of the rhynchonellid Notosaria nigricans, the outer primary layer material was depleted in δ 13C and δ 18O and highly variable. Inclusion of this material even as part of a whole shell sample could lead to misinterpretation of seawater temperature, therefore only fossil secondary layer material should be used. The anomalous articulated thecideidine brachiopod Thecidellina barretti is composed of mainly primary shell material and was not in oxygen isotope equilibrium. δ 18O values from the laminar secondary layer material of the inarticulated Craniida are highly variable. Therefore, these species are not recommended for use as palaeoenvironmental proxies. This study suggests caution when employing fossil brachiopod shells with similar ultrastructures to modern craniid and thecideidine brachiopods. The carbon isotope composition is highly variable in all of the brachiopods studied. Analysis of samples from specialised regions of the secondary shell layer show a pattern of depletion in 13C relative to non-specialised secondary material. The carbon isotope variability is independent of δ 18O and is repeated in most of the articulated species regardless of geographical location. This is possibly a vital effect produced by metabolic prioritisation.

Ontogenetic trace element distribution in brachiopod shells: an indicator of original seawater chemistry

Articulated fossil brachiopod shells have been used extensively to extract primary chemical information of Phanerozoic seawater. Despite the selection of well-preserved shells using trace element, microstructure and cathodoluminescence criteria, there are still concerns as to whether the selected brachiopod shells do indeed contain original seawater signals. Analyzed in-situ by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LAICPMS), Sr, Na, Mg, Mn, B and Ba distribute symmetrically in shell transects of the modern brachiopods Magellania flavescens and Terebratulina septentrionalis. Symmetry of the trace element distribution pattern is considered an intrinsic and original ontogenetic property of the brachiopod shell chemistry. The trace element distribution is symmetrical in a well-preserved shell of the Devonian brachiopod Independatrypa lemma, indicating that the selected shell by the conventional criteria has preserved its original seawater signal for 400 Ma. In another specimen of I. lemma that is considered diagenetically altered, trace element concentrations are asymmetrically distributed in the shell. The agreement between the distribution criteria and the conventional methods indicates the latter can be used to select brachiopod shells with original seawater chemistry. The average element concentration in the whole shell of unaltered brachiopods should be a reflection of the seawater chemistry, while its change in different part of a shell reflects ontogenetic effect, and its high frequent fluctuations in a transect are results of changes in environmental parameters with seasonal or annual characteristics.

Deciphering kinetic, metabolic and environmental controls on stable isotope fractionations between seawater and the shell of Terebratalia transversa (Brachiopoda)

This study presents carbon and oxygen stable isotope data obtained from high-resolution sampling (<500 μm) of the brachiopod Terebratalia transversa from the San Juan Islands (Washington State, USA). The aim of this study is to unravel the respective effects of physiological and environmental controls on the stable isotopic composition of brachiopod shell calcite. Based on an SEM study of the shell, a three-dimensional sampling was performed in order to investigate carbon and oxygen isotope variations along isochrons and ontogenetic transects.The primary as well as the outer part of the secondary shell layer display large and variable isotopic offsets as high as −7‰ for δ13C and −6‰ for δ18O relative to expected equilibrium values. The significant positive correlations between δ18O and δ13C values indicate that the isotopic compositions of these shell domains are mainly controlled by kinetic isotope fractionation effects. The ontogenetic δ13C and δ18O variations can be used to establish a growth curve of the studied specimen whose age is estimated close to 8 years. The extent of apparent O-18 disequilibrium observed in this study is about as large as any yet measured in any organism, which makes this brachiopod an interesting and important case.The carbon and oxygen isotope compositions increase from the outer towards the inner part of the secondary layer, where they reach values of 0–0.8‰ and −0.8‰ to −0.2‰, respectively. Corresponding calculated temperatures are between 12 and 13.8 °C and fall in the range of seawater temperatures recorded off the San Juan Islands (7–13 °C). These results suggest that the calcite fibres were secreted more and more slowly during the thickening of the shell throughout the animal's life, finally approximating isotopic equilibrium.This study illustrates that the stable isotopic composition of the modern brachiopod T. transversa is predominantly influenced by kinetic fractionation and, to a minor degree, by metabolic effects. Except for the innermost part of the shell, the measured isotope ratios do not reflect environmental conditions during shell precipitation. It remains to be tested by comparable studies whether other modern brachiopod species or even fossil brachiopods reflect comparable fractionation effects. These results point out the need for re-examination of Paleozoic oceanographic conditions.

Lopingian (Late Permian) stratigraphy, sedimentation and palaeobiogeography in southern Tibet

Investigations of the Permian-Triassic sections and limestone blocks scattered in the Indus-Tsangbo Suture Zone in southern Tibet show widespread distribution of the Lopingian strata. The Lopingian deposits mostly contain rich brachiopod fossils and characteristic conodonts of the Mesogondolella shenz Zone of latest Changhsingian age in the topmost part. Brachiopod assemblages are largely comparable with those known from the upper Wargal and Chhidru Formations of the Salt Range, Pakistan, the Zewan Formation of Kashmir, the upper part of the Kuling Group in Spiti of India and the Hardman Formation of Western Australia. A revised Lopingian (Late Permian) age is proposed for the Selong Group and its equivalents in southern Tibet. The Lopingian deposits in southern Tibet can be grouped into three different sedimentary types, each of which reflects different sedimentary environments from coastal to continental shelfal settings on the northern peri-Gondwanan margin. The Qubu-type sequence represents marine coastal and proximal barrier-lagoon sediments during a gradual sea-level rise. Micaceous sandstone and shale of regressive origin, with abundant palynomorphs and acritarches, developed during the Late Lopingian sea-level lowstand, which is followed by a major rapid transgression at the very end of Permian. The Selong-type sequence in the Selong area consists of bioclastic limestone and calcareous shale in the lower part, and crinoid grainstone in the upper part. The latter part is believed to have been formed in a high-energy inner shelf shoal setting. The Chitichun-type sequence, sporadically distributed along the Indus-Tsangbo suture zone as small limestone blocks, consists of pure bioclastic sparite with the ammonoid Cyclolobus fauna. It is interpreted as the break-up products of sea-mounts and/or small isolated carbonate build-ups developed on the outer shelfal settings.

Geochemistry of modern brachiopods: applications and implications for oceanography and paleoceanography

Modern Rhynchonellida, Terebratulida, Thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2–3940 m, from the equator to high latitudes covering the Atlantic, Pacific, Indian, Caribbean and Mediterranean Oceans/Seas. Well-preserved fibers of the secondary layer combined with Sr (450–1928 mg/kg), Mn (1–199 mg/kg) and Fe (1–610 mg/kg) contents confirm, with few exceptions, the excellent preservation of the modern brachiopod material. Evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations. It revealed that oxygen isotope incorporation into shell calcite (secondary layer) of modern articulated brachiopods, in most cases, occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions. Thecideida as a group (shallow water and low latitude) incorporate oxygen isotopes (−3.04‰ to +0.35‰) into shell calcite in equilibrium with their ambient water. A large majority of genera and species of the Terebratulida (shallow water and low-mid latitude) also incorporate oxygen (−2.30‰ to +3.48‰) into shell calcite in isotopic equilibrium with their surrounding water. In contrast, equilibrium incorporation of oxygen isotopes into shell calcite by the Rhynchonellida is uncertain, but a vital effect probably applies to the Craniida. The question of equilibrium/disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time. Isotope compositions range up to 4.5‰, 5.6‰ and 1.5‰ for δ 13C, and up to 5.5‰, 5.9‰ and 0.3‰ for δ 18O, for shallow-water low, mid, and high latitude brachiopods, respectively. Strontium isotopes of modern brachiopods, as expected, show no significant variation with location, latitude, water depth, temperature, salinity and general water conditions. Once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered, their isotopic/elemental values should be valuable diagenetic indicators and important oceanographic/chemostratigraphic proxies.

Long-term trends in the survival of immunological epitopes entombed in fossil brachiopod skeletons

We report the most comprehensive study of survival of peptide bonds and epitopes (antibody binding sites) in fossil shells from a semi-continuous New Zealand brachiopod sequence extending for 3 Ma. The study reveals for the first time long-term trends in proteins survival. The investigation focused on a sub-set of the total skeletal biomolecules, those protected from exposure to a strong oxidising agent (NaOCl); the so-called intra-crystalline component. The extent of peptide bond hydrolysis was compared with the declining immunological signal. The proportion of free amino acids increased very rapidly but between 5 and 10% of the amino acids remained peptide bound in all samples. The pattern of loss of immunological reactivity broadly mirrored the loss of peptide bonds, but overall loss of signal was much greater. Significant antibody response was observed in some but not all late Pliocene fossils (>3 Ma), but against a panel of antisera the pattern of reactivity was lost in samples >0.5 Ma. Alternative models of polypeptide chain scission were used in an to attempt to relate the rate of peptide bond hydrolysis to the loss of immunological determinants. The findings suggest that, despite early optimistic reports, the application of immunology to shell carbonates does not appear capable of extending into deep time.

Use of stable oxygen isotope determinations from brachiopod shells in palaeoenvironmental reconstruction

Stable oxygen isotope analyses were obtained from fossil brachiopod shells from a shallow marine deposit of Upper Pleistocene age (approximately 80 ka) in New Zealand as part of a palaeoenvironmental investigation. Bulk analyses of entire shells of Calloria inconspicua yielded highly variable results (a range of 2.30‰), rendering these data of limited use as palaeoenvironmental proxies. Attempts to obtain consistent oxygen isotope values by removing areas of the brachiopod shell thought to be prone to oxygen isotope disequilibrium effects (‘vital effects’) revealed that the matching anterior portions of ventral and dorsal valves from the same individual (which were secreted at the same time) also yielded different oxygen isotope ratios. The dorsal valve δ 18O values were higher and less variable than those obtained from the ventral valve of the same individual. The investigation was then extended to living representatives of the same species from a similar shallow water habitat from the South Island of New Zealand. The pattern of dorsal valves yielding higher and less variable oxygen isotope values than matching areas of the ventral valves was repeated in seven out of eight individuals investigated, although there was considerable variation in the absolute values from specimen to specimen. Contrary to common practice therefore, it seems that in this species it is the much thinner and lighter dorsal valve that provides a more consistent isotopic measurement. If converted into absolute temperature estimates, the dorsal valve measurements correspond to a temperature midway between the mean and maximum annual temperature experienced by this species in its present-day habitat, which may make it acceptable as a palaeoenvironmental indicator. The high level of variation between individuals (including an inferred temperature from one ventral valve above the mean maximum temperature experienced) indicates that a range of individuals needs to be investigated in any palaeoenvironmental investigation to avoid misleading interpretations. However, intra- and inter-specimen variation in isotopic composition may provide valuable palaeobiological information on growth rates, metabolism and possibly also pathological conditions in the past.

The palaeobiogeography of Late Cretaceous and Cenozoic brachiopods from Western Australia

Recent research on the Late Cretaceous and Cenozoic fossil brachiopods from the Carnarvon, Perth, Bremer and Eucla sedimentary basins in Western Australia has added much to our understanding of their systematics and biodiversity. Fifty-eight species, including one new family, two new genera and 30 new species, have been described from these sources. Four, possibly five, genera and one species from the Late Cretaceous of Western Australia are common to the Late Cretaceous deposits of the Antarctic Peninsula. This evidence suggests that in the Late Cretaceous there was a continuous shelf environment extending from the Antarctic Peninsula to the Carnarvon Basin of Western Australia. These southern shelf environments formed the high latitude southern circum-Indo-Atlantic faunal province. In this area, brachiopods evolved genera and species differing from those of the northern hemisphere. Many subsequently dispersed into northern areas of the Indian, Atlantic and, finally, Pacific Oceans. Examination of Cenozoic material from the Carnarvon Basin indicates that there is a strong correlation with Cenozoic material from the Antarctic Peninsula. At least six brachiopod genera are common to the two areas. If the distribution of brachiopod genera in Australia and New Zealand is analysed, they first appear in the northwest of Western Australia. They then appear in chronological order in the south-western, south-eastern basins of Australia and finally New Zealand. The apparent migration of brachiopods south and then eastward was most likely due to the Proto-Leeuwin and Great Australian Bight Currents. Fifteen species are common to south-western Australia and south-eastern Australia. Brachiopods may well have used various migration mechanisms from the earliest breaching of the gap between Australia and Antarctica to be transported into the Tasman Sea and hence to New Zealand. This included attachment to living specimens and dead objects as well as possible extended larval life in lower temperature waters. Factors such as light avoidance, food availability and competition with bivalves may provide an explanation for the small number of species and specimens of brachiopods in some deposits.

GHOSTS OF THE PAST, PRESENT, AND FUTURE IN BRACHIOPOD SYSTEMATICS

Three historical phases can be distinguished in the study of brachiopod systematics over the past 75 years. Prior to 1956, systematic neontologists and paleontologists struggled to reconcile differences in perceived evolutionary patterns (and thus classifications) based largely on static morphological differences observed separately among living brachiopods and among fossil brachiopods. Following 1956, patterns of morphological distribution began to be interpreted relative to the processes by which they were formed, and a more dynamic view of brachiopod phylogeny and classification resulted. Over the past decade, newer methodologies (phylogenetic systematics) have allowed older phylogenetic hypotheses to be tested and evaluated. The major challenges that brachiopod systematists now face are not unique to brachiopods; they concern improving the methods of phylogeny (and classification) reconstruction so that all the sources of data available to paleontologists can be utilized more effectively. In the future, I predict that more intensified, global fossil collecting, together with further investigation of the embryology and development of brachiopods, and molecular systematic research, will play an increasingly larger role in revising the classification currently in use.

Ghosts of the past, present, and future in brachiopod systematics

Three historical phases can be distinguished in the study of brachiopod systematics over the past 75 years. Prior to 1956, systematic neontologists and paleontologists struggled to reconcile differences in perceived evolutionary patterns (and thus classifications) based largely on static morphological differences observed separately among living brachiopods and among fossil brachiopods. Following 1956, patterns of morphological distribution began to be interpreted relative to the processes by which they were formed, and a more dynamic view of brachiopod phylogeny and classification resulted. Over the past decade, newer methodologies (phylogenetic systematics) have allowed older phylogenetic hypotheses to be tested and evaluated. The major challenges that brachiopod systematists now face are not unique to brachiopods; they concern improving the methods of phylogeny (and classification) reconstruction so that all the sources of data available to paleontologists can be utilized more effectively. In the future, I predict that more intensified, global fossil collecting, together with further investigation of the embryology and development of brachiopods, and molecular systematic research, will play an increasingly larger role in revising the classification currently in use.

No vital effect on δ 18O and δ 13C values of fossil brachiopod shells, Middle Devonian of China

Biogenic fractionation (vital effect) of carbon and oxygen isotopes during metabolism is ubiquitous among marine organisms. Whether there is vital effect on the isotopic compositions of fossil brachiopods represents one of the most controversial issues in the carbonate stable isotope geochemistry. Furthermore, the problem involves not only the feasibility of the utilization of fossil brachiopod shells as analysis samples for obtaining the original carbon and oxygen isotopic compositions of carbonates, but also the credibility of the data and conclusions already achieved in the study field. With fossil brachiopods from Middle Devonian of China, this study investigates the vital effect by comparisons of δ 18O and δ 13C between the fossils of the same original living environment and the shell’s preservation at levels of species, genus, and family. No systematic differences of δ 18O and δ 13C between fossils were found, which led to the conclusion that no detectable vital effect occurred in the fossil brachiopod shells. The argument that the fossil brachiopod possibly has biogenic fractionation with the stable isotopes of carbon and oxygen resulted likely from studies of fossils that are different in the original living environment or the state of preservation.

Mitochondrial COI Sequences of Brachiopods: Genetic Code Shared with Protostomes and Limits of Utility for Phylogenetic Reconstruction

A 1230-bp region of the cytochrome c oxidase subunit I (COI) gene of mitochondrial DNA of each of 16 brachiopod species, representing all five living orders, was amplified by polymerase chain reaction and sequenced. Pairwise comparisons of sequence differences plotted against divergence times estimated from the brachiopod fossil record revealed that, although there are considerable variations in the expected substitution rate among different lineages, amino acid substitutions of the COI sequences may largely become saturated in 100 Ma, due mostly to multiple substitutions at the same site. Coinciding with this result, phylogenetic analysis indicated low bootstrap values for nodes corresponding to divergence events that occurred before 100 Ma, suggesting that COI sequences are suitable only for inference of phylogenetic events subsequent to the Mesozoic. Examination of brachiopod codons corresponding to invariant amino acids in the COI of various other animals suggest the nonuniversal codon relationships UGA = Trp, AUA = Met, AAA/G = Lys, and AGA/G = Ser. These are identical to those in mollusks, annelids, and arthropods, consistent with the conclusion that brachiopods are protostomes, as indicated by previous molecular analyses.

THE 1999 JOSEPH A. CUSHMAN AWARD

Research Article| January 01, 2000 THE 1999 JOSEPH A. CUSHMAN AWARD Pamela Hallock Pamela Hallock Department of Marine Science, University of South Florida, 140 Seventh Avenue South, St. Petersburg, FL 33701 Search for other works by this author on: GSW Google Scholar Author and Article Information Pamela Hallock Department of Marine Science, University of South Florida, 140 Seventh Avenue South, St. Petersburg, FL 33701 Publisher: Cushman Foundation for Foraminiferal Research First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 © 2000 Journal of Foraminiferal Research Journal of Foraminiferal Research (2000) 30 (1): 1–2. https://doi.org/10.2113/0300001 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Pamela Hallock; THE 1999 JOSEPH A. CUSHMAN AWARD. Journal of Foraminiferal Research 2000;; 30 (1): 1–2. doi: https://doi.org/10.2113/0300001 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search The Cushman Foundation for Foraminiferal Research announces the selection of Professor John J. Lee for the 1999 Joseph A. Cushman Award, in recognition of his lifetime contributions to foraminiferal research. John’s lifelong fascination with science began during his ninth summer, when he found fossil brachiopods in New York’s Catskill Mountains (USA). His father took John and his fossils to the American Museum of Natural History, where Dr. Normal Newell took the time to examine and explain the child’s treasures. John took away a crucial lesson and that was, no matter how busy as a parent or scientist, one must take... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Different fossil brachiopod skeletal microstructure of different information on carbon and oxygen isotope contents

Whether there is isotope fractionation caused by metabolism (vital effect) of brachiopods in geologic time with their shells’ δ18O and δ13C has been studied intensively in the field of carbonate isotope geochemistry in the last decade. The approach to dealing with the problem is by comparing isotopic compositions between different fossil brachiopods with their secondary shells which usually consist of two kinds of layers: prismatic layer composed of prismatic low-Mg calcite crystals, and fibrous layer comprising fibrous ones. The isotopic compositions of the two secondary layers have been investigated by comparison of carbon and oxygen isotopic compositions between five genera of Atrypidae collected from Givetian, Middle Devonian in Longmenshan, Sichuan Province, China. Due to different microstructures of the two secondary layers, their abilities to prevent from being altered by diagenesis are also different, thus in their state of preservation. The fibrous layer is more susceptible to the diagenetic alternation than the prismatic one in the way of microfracture filling between fibrous crystals in the elongated direction. Consequently, the isotopic compositions of the fibrous layer are systematically lower than those of the prismatic layer in their δ18O and δ13C by (0.53 ± 0.08)‰ and (0.12 ±0. 04)‰, respectively. This suggests that further studies of vital effects with brachiopod in geological times by comparison of isotopic compositions in the secondary shell take into consideration of the different states of preservation between the fibrous and the prismatic layer.

PROBLEMS IN STUDIES ON CARBON AND OXYGEN STABLE ISOTOPES IN CARBONATES

Carbon and Oxygen stable isotopes in carbonates have long been the important geochemical tracers. Studies on the isotopic compositions can provide insights into the paleoclimatic processes, the paleoceanic environmental processes and the geological processes as well. Researches of more than four decades in the field, especially from the early 1980s on, during which the analysis of the isotopes in fossil brachiopods and early diagenetic cements has contributed much to the knowledge, achieved appreciable progress. However, problems still remained with how to explain the data that already existed on the isotopic compositions of carbonates, on which there is a dichotomy between those who advocate that the data represent the original characteristics of the isotopes and those who argue that the data have been altered diagenetically; with how to select the samples of carbonate for analysis of the isotopic ratios, which has a set of criteria, namely, the microstructure, the Cathodoluminescence and trace elements, for tests of the sample preservations; with whether the fossil brachiopods′ shells have vital effects on the isotopic compositions, on which there is a tendency toward the existence in recent years; with to what extent the living environment variations of the fossil affect their carbon and oxygen isotopic ratios and with the utilization of early diagenetic cement as analyzing samples. Along with the problem raising, this paper reviewed the methods on, and new developing trends toward, the problem solvings, as well as the up to date advances of studies on each problem.

Original shell colouration in Late Pleistocene terebratulid brachiopods from New Zealand

A Late Pleistocene locality (approx. 80 ka) in the Wanganui Basin, New Zealand, has yielded large numbers of the brachiopod Calloria inconspicua displaying original shell colouration. In total 78% out of a collection of 377 fossil shells show orange-red colouration that represents a partial degradation of the stronger red colour found in living representatives. Investigation of a modern-day population of the species from New Zealand from an intertidal habitat indicates that recently deceased individuals rapidly lose all of their colouration. Only 57% of 281 individuals collected from the sediment surface beneath this modern population retained any trace of shell colour, and this proportion dropped to 46% of the 321 shells in the top 50 mm of sediment. As other brachiopods and molluscs at the Late Pleistocene locality also revealed traces of original colouration, preservational conditions must favour the survival of the pigments responsible for shell colouration. The colouration of Calloria inconspicua is caused by a caroteno-protein embedded within the shell, which is susceptible to degradation in the presence of light and oxygen. Rapid burial may retard the processes of degradation, and such an interpretation is consistent with the occurrence of the fossil brachiopods in an intertidal pebble bed. Colouration of the shell may help camouflage the brachiopod; the same colouration in the free-swimming larvae may offer protection from radiation damage.

δ 18O and REE contents of phosphatic brachiopods: a comparison between modern and lower Paleozoic populations

δ 18O 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.