bluuebunny/crossref_metadata_2025_split huggingface dataset:
The palaeozoic pelecypod family Rhombopteriidae and the evolution of the Ostreina
Authors: Johnston Paul A. 
Published: January 2018

Though long suspected to be critical to the understanding of the evolution of the pelecypod subclass Pteriomorphia, the mid-Palaeozoic family Rhombopteriidae was too poorly known to allow clarification of its relationships. Furthermore, numerous species were assigned to the nominate genus, Rhombopteria, many of which belong in other genera or even other subclasses. Consequently, the morphologic concept entailed by Rhombopteria was confused as were functional morphologic investigations.Silicified rhombopteriids discovered in the Lower Devonian of Australia are referred to a new genus, and reveal internal shell characters essential for understanding rhombopteriid relationships. The family Rhombopteriidae is revised to include only three genera, Rhombopteria, Prantliella and the new Australian genus.New data provided by the Australian material indicate that rhombopteriids were non-byssate, dimyarian pteriomorphs that lived pleurothetically on the left valve as do gryphaeid oysters. The Rhombopteriidae are assigned to the Ostreina and are the sister group of all other ostreinans including the Ostreoidea, Pseudomonotidae and Terquemiidae. Important characters common to rhombopteriids and gryphaeid oysters include: 1) left-sided pleurothetic habit; 2) absence of byssal notch or sinus throughout ontogeny; 3) Quenstedt muscle scar; 4) proximal gill weal; 5) circumferential curb; 6) commissural shelf; and 7) posteroventral palliobranchial fusion as evidenced by a branchitellum and posterior radial fold and sulcus. Outgroup comparison with Umburridae indicate that characters 1–4 are symplesiomorphic for the Order Ostreoida. Characters 5–7 are autapomorphies for a clade including the Rhombopteriidae, Pseudomonotidae, Terquemiidae and Ostreoidea.Rhombopteriids were probably derived from left-sided pleurothetic, umburrid-like ancestors which, in turn, descended from primitive, equivalved, orthothetic prionodonts. Thus, a right-sided pleurothetic stage was never part of the evolutionary pathway of oysters. The inequivalved shell of eupteriomorphs evolved initially for a left-sided pleurothetic semi-infaunal habit. Retained as an adaptation in rhombopteriids and oysters, the inequivalved shell is an exaptation in Pterioida (winged shells), Pectinina (scallops) and Pseudomonotidae, having been coopted for a right-sided pleurothetic orientation, and having the effect of enhancing stability in an epifaunal habit. Evolution of right-sided pleurothetic pteriomorphs, including the Pseudomonotidae, Pectinina and Pterioida, from separate left-sided pleurothetic rhombopteriid-like or umburrid-like ancestors, is explicable by paedomorphic retention of the byssus and epifaunal habit of the early post-larva. A right-sided pleurothetic orientation would follow ‘automatically’ owing to hydrodynamic and mechanical constraints on the already evolved, inequivalved shell, byssally attached by the anterior margin on the substrate surface.
Biogeographic analysis of middle Visean articulate brachiopod genera
Authors: Kelley Patricia H. , Sablock Peter E. , Raymond Anne , Isaacson Peter E. 
Published: January 2018

Climate models as well as the distribution and migration patterns of land plants and articulate brachiopods from the Early and Middle Carboniferous suggest that Visean latitudinal temperature gradients were relatively weak, and that the high latitudes may have been warmer than they were during the late Namurian and Westphalian. Biogeographic analysis of middle Visean brachiopod genera from Laurussia and North China supports these conclusions. Cluster analysis, multidimensional scaling and principal components analysis reveal longitudinal differentiation among brachiopod assemblages from Laurussia and the North China plate. Based on their faunal similarity, localities from the east coast of Laurussia (Urals, Moscow Basin, Donets Basin) and North China group together; localities from south central coast of Laurussia (Maritime Canada, England, Ireland and Belgium) group together, and localities from the southwest and west coast of Laurussia (Canada and the United States) group together. On recent Early Carboniferous reconstructions, the east Laurussian localities lie in equatorial, subtropical, and middle latitudes, but exhibit no paleolatitudinal differentiation. This may be the expected result for a biogeographic unit on the east coast of a large paleocontinent during an interval with a well-developed circum-equatorial current. On recent Early Carboniferous reconstructions, all of the localities from south central Laurussia lie near the paleoequator.West Laurussian assemblages show paleolatitudinal differentiation, which may be the expected result for a biogeographic unit along the west coast of a large paleocontinent influenced by high-latitude westerlies. Within the cluster analysis, assemblages from the Appalachians, Midwest, and Southwest clustered separately from Cordilleran (Idaho, Utah, Montana, Wyoming and Nevada) assemblages. Recent paleogeographic reconstructions for the Early Carboniferous suggest that the Cordilleran localities were paleoequatorial and that the Appalachian, Midwestern and Southwestern localities lay in the southern paleo-subtropical belt. However, the relative diversity of assemblages from these two clusters suggests that the Early Carboniferous paleoequator lay to the south of the Cordilleran localities. Throughout the Early and Middle Carboniferous, individual assemblages within the Appalachian-Midwest-Southwest cluster have higher diversities than individual assemblages within the Cordillera cluster.We have avoided a hierarchical ranking of these biogeographically distinct groups of assemblages into realms and provinces pending species and community level-analyses of Visean brachiopod communities which are in progress.
An isotopic biogeochemical study of the Oxford Clay Formation (U.K.)
Authors: Kenig Fabien , Hayes John M. , Summons Roger 
Published: January 2018

Lipids from a suite of 12 representative samples from the Lower Oxford Clay (LOC) and from the Middle and Upper Oxford Clay (MUOC) were extracted with organic solvent, separated, and analyzed qualitatively and quantitatively using gas chromatography-mass spectrometry (GC-MS) and isotopically using isotope-ratio-monitoring gas chromatography-mass spectrometry (irmGCMS). Determination of molecular structures allowed identification of compounds which retained enough chemical structural information to be recognizable as having a biochemical origin related to a specific organism or group of organisms (biomarkers). By allowing assignment of each compound to a portion of the local carbon cycle (production, sedimentation, and alteration), isotopic analyses of individual compounds provided further information regarding their origins. The 12 samples were chosen to represent the various macrofaunal assemblages define by Duff (1975) and to cover the total range of variability of the bulk geochemical parameters measured on sediments from LOC and MUOC (Kenig et al., this symposium).A relatively high content of unsaturated hydrocarbons, as well as the abundance of biogenic forms of molecular stereoisomers such as ββ hopanes and ααα steranes and other molecular indicators, confirms the low level of maturity of organic matter in the LOC. Contributions from the two main sources of sedimentary organic matter already identified from bulk geochemical data, marine phytoplankton and terrestrial organic matter, can be recognized in the saturated hydrocarbon fraction of all the samples analyzed. However, contributions from these two sources vary as a function of the TOC content, the HI, and the δ13C of organic matter. Saturated hydrocarbon fractions of high-TOC samples, formed during periods of high marine productivity, are mainly dominated by pristane and phytane and by tetra- and pentacyclic biomarkers. This dominance decreases with the TOC content and the 13C abundance. Conversely, the relative abundance of compounds indicative of terrigenous input increases. In samples with lower TOC, n-alkanes with a strong odd-carbon preference, peaking at C27, are particularly prominent in the saturated hydrocarbon fraction.Biosynthetic products with n-alkyl carbon skeletons are found in nearly all organisms. Accordingly, sedimentary n-alkanes are likely to derive from multiple sources. These can be partly distinguished by isotopic analysis of individual n-alkanes. In particular, marine and terrestrial sources can be resolved. Considering the variation of their relative abondance and of their isotopic composition as a function of TOC, δ13C of total organic matter and hydrogen index, the origins of n-alkanes, pristane and phytane as well as those of other biomarkers will be discussed. The paleobiological assemblage responsible for the production and alteration of the organic matter will be tentatively reconstructed.
Comparison of Cretaceous and Oligocene endolithic reef communities from Puerto Rico
Authors: Krumm Debra K. 
Published: January 2018

The question of the response of endolithic reef communities to changes in primary framework builders that serve as hosts prompted a study to compare two different types of frameworks from two formations, one Cretaceous and the other Oligocene, from Puerto Rico. The primary framework builders from the Cretaceous Cotui Formation of western Puerto Rico are rudistid bivalves, with corals and stromatoporoids also serving as supporting organisms to a lesser extent. Both larger endolithic organisms such as lithophagid bivalves and smaller endoliths such as clionid sponges are common throughout the study area. All three framework types serve as hosts. However, actual densities of endoliths, especially the bivalves, are low per host.Corals are the primary framework builders in the Upper Oligocene Lares Formation of northwestern Puerto Rico. In the study area, two types of coral frameworks were observed. The main reef was composed of massive coral heads, while facies interpreted as lower-energy patch reef and lagoonal environments were comprised of more delicate branching poritid-like corals. Oysters were common in both facies. Few larger endoliths were found in the branching coral. By contrast, boring bivalves including lithophagids, occurred in high densities in many of the massive coral heads. Some of the oysters were riddled by clionids.The comparison revealed that while the composition of the two endolithic communities was similar, the abundances and differences in density of the individual endolithic organisms was markedly different. This is attributed primarily to differences in the host substrates themselves. Hosts were abundant in both the Cotui and the Lares. However, the exoskeletons of rudistids differ considerably from corals, as do stromatoporoids. External influences such as environment, may have had some impact as well.
Biological and evolutionary responses to transgressive-regressive cycles
Authors: McGhee George R. 
Published: January 2018

Transgressive-regressive cycles involve environmental change and therefore, under the predictions of the theory of natural selection, biological response is expected. The nature, magnitude, and instrumentation of that response is, however, less well understood and difficult to predict. Generally the magnitude of biological response would be expected to be a direct function of the magnitude of the environmental change produced by alterations in sea level. However, this may not be the case. Moreover, the magnitude of environmental perturbation seen may itself not be a direct function of the magnitude, range, or even rate of sea level rise or fall.Biological responses to transgressive-regressive cycles are highly variable, yet may be empirically demonstrated. Although the reality of faunal changes can be observed, the precise forcing mechanism or mechanisms driving those changes may be hypothetical at best. The observed iterative morphological series seen in shallow water Jurassic ammonites, for example, appear to be produced by a complex interplay of species adaptation to changes in local habitat and response to immigration from oceanic realms, both of which are ultimately driven by relative sea level. Likewise, changes in diversity and species composition in Devonian shallow marine communities appear to be produced by the effect of variable sedimentation rates and shifts in the oxygen minimum zone, both of which also are related to changes in relative sea level.Published onlap-offlap sequence curves, as such, may offer very little to the paleobiologist interested in the evolutionary behavior of marine organisms. Additional geographic and areal data are required if any rigorous quantitative relationship between relative sea level and evolutionary biology is to be formulated. In the Devonian, for example, it can be demonstrated that a total lack of correlation exists between the evolutionary biology of major benthic marine organisms (brachiopods) and relative sea level as projected from onlap-offlap curves. It could be hypothesized that the rate of change of sea level is more important to organisms than relative sea level itself, though most hypotheses concerning the biological effect of sea level are explicitly framed in terms of relative sea level (usually invoking the species-area effect). Again, onlap-offlap curves alone offer little in testing such a rate hypothesis, as it can also be demonstrated that no correlation exists between the derivative of the Devonian relative sea level curve and the evolutionary biology of the Brachiopoda.
Onshore-offshore patterns during the Ordovician radiations: a worldwide assessment
Authors: Miller Arnold I. 
Published: January 2018

To understand the evolutionary significance of apparent temporal trends in global biotic diversity, it is important to delve beneath the umbrella of synoptic, global-scale compilations. Specifically, when evaluating a measurable increase or decrease on a global diversity curve, we must determine whether it reflects a transition that was truly global in scope and space-transcendent, or, alternatively, whether it is the manifestation of change associated with particular geographic or environmental regime(s).Previous analyses of the Ordovician faunal radiations have suggested that an onshore-offshore environmental overprint was associated with the diversity increase: trilobite-dominated biotas, which were ubiquitous during the Cambrian, became progressively restricted to deepwater through the Ordovician as diversifying, articulate brachipod-dominated faunas came to dominate shallower, open marine settings. At the same time, a less rapid proliferation of mollusc-rich biotas enabled them to become particularly diverse in nearshore settings. Additional analyses of diversification conducted for post-Paleozoic biotas have yielded onshore-offshore signals associated with diversification of a variety of taxa, suggesting the existence of a general evolutionary pattern associated with marine diversification that transcends taxonomy and time.However, to date, evaluations of Ordovician onshore-offshore patterns have been based on data limited primarily to North America, and, thus, to the Paleozoic continent of Laurentia. Thus, it is reasonable to ask whether this pattern was unique to Laurentia, or whether diversification proceeded similarly in Ordovician seas around the world.To analyze possible patterns of environmental and geographic selectivity associated with episodes of Ordovician diversification and extinction, I am currently compiling a database on the paleogeographic and paleoenvironmental distributions of Ordovician genera. Although this compilation is still in its infancy, preliminary analyses suggest that, in aggregate, paleoenvironmental patterns exhibited elsewhere are comparable to those recognized for Laurentia. However, the data remain scanty for many parts of the world; as the database grows, a province-by-province analysis of diversification patterns will be conducted. This analysis will not only permit determination of the degree to which onshore-onshore patterns transcended paleogeographic boundaries, but, more generally, will enable exploration of the relationship between local diversity trends and global-scale trends already documented for the Ordovician with synoptic data.
Actuopaleontological investigations of shallow water Red Sea echinoids
Authors: Nebelsick James H. 
Published: January 2018

The regular and irregular echinoid fauna of the Northern Bay of Safaga (Red Sea, Egypt) has been investigated within the framework of an actuopaleontological study of the flora, fauna, sediments and facies. The distribution of echinoids has been compared to grain size parameters as well as to the distribution of other organisms.The study area (ca. 10 × 7 km) was investigated using SCUBA-diving techniques along 55 transects with a total length of 126 km. Echinoid presence was quantified using weights of fragments (2 mm) originating from 67 standardized bulk samples distributed throughout the Bay. The complex morphology of the echinoid test and the spines allow the identification of fragmented material upon comparison to complete specimens. The resulting data was analyzed using correlation techniques as well as Q and R-mode multivariate statistical analysis. This method counters the difficulties originating from the cryptic habitats and patchy distributions.The results of the analysis show that echinoid distribution can be analyzed for both regular and irregular wchinoid taxa despite taphonomic bias and restrictions imposed by the analytic method. Time averaging in fact counters the difficulties arising from the patchy distributions of echinoids. There is a close correlation of echinoid distribution to sedimentary and bottom facies as well as to grain size parameters and other environmental factors. The distribution of irregular echinoids is highly differentiated with coarse coastal sand dominated by Clypeaster sp., Echinodiscus auritus, Fibularia ovulum, and Lovenia elongata; muddy sands by Laganum depressum, Clypeaster sp. and Echinocyamus crispus; and muds by members of the Schizasteridae. Regular echinoids, mostly Eucidaris metularia, Echinometra mathaei, Tripneustes gratilla, Heterocentrotus mammillatus and Diadema setosum, dominate the sediments found within, or near reefs, coral carpets and patch reefs.The methodology used in this actuopaleontological investigation should be useful in recognizing the distribution patterns of ancient echinoid faunas, especially in light of the significance of regular echinoids in the bioerosion of reefs and irregular echinoids in the bioturbation of sediments.
Palaeontology and palaeoecology of the Lower Cambrian Emu Bay Shale Lagerstätten, Kangaroo Island, South Australia
Authors: Nedin Christopher 
Published: January 2018

The last two decades have seen the status of deposits containing soft bodied Cambrian fossils rise from geological curios into one of the foundations of modern thinking on early metazoan evolution and ecology. Some thirty of these soft bodied assemblages or Lagerstätten, resembling the Burgess Shale fauna are now known. One of these is the Lower Cambrian Emu Bay Shale fauna from Kangaroo Island, South Australia.The Emu Bay Shale has been mapped in two localities approx. 8 km (5 miles) apart on the northern coast of Kangaroo Island, at Emu Bay and at Big Gully. Previous investigations into the numerically abundant Lagerstätten fauna at Big Gully have highlighted its unusually pauperate diversity, with only some seven species described. The preservation is also unusual, comprising replacement by iron stained calcite. The fauna is confined to a 10 m thick basal siltstone. The age of the deposit is believed to be mid to upper Botomian and is thus marginally older than Early Cambrian soft bodied assemblages found on the North American continent and predating the better known Middle Cambrian Burgess Shale.In late 1991, a study of the Emu Bay Shale was undertaken to document the palaeontology and palaeoecology of the fauna. Preliminary findings, whilst increasing the number of species, confirm the pauperate diversity of the fauna. The new forms include several specimens of anomalocarid appendages. These not only represent the first occurrence of this form in Australia, but also the first occurrence outside the Burgess Shale of anomalocarid appendages with 11 segments, as compared with the more common and widespread 14 segment appendages. This connection may be important in the light of recent palaeoreconstructions which show the west coast of Canada and eastern Australia in close proximity during the early Cambrian. Also the spatial arrangement of the appendages indicates that anomalocarids may have shoaled and hunted in groups. They appear to have fed on the sea bottom, possibly using their appendages to probe the muddy bottom for shallowly buried prey as well as for capturing and transporting prey to the mouth.The assemblage appears to be dominated by the preservation of hard or permineralized body parts. However, abundant calcified ribbon-like structures concentrated on some bedding planes have yet to be classified. Several exceptionally preserved specimens of Myoscolex appear to have a series of metamerically repeated ‘paddle-like’ appendages, similar to some forms from the Burgess Shale, thus casting doubt on an annelid affinity.The assemblage appears representative of a deep water, low oxygen environment prone to periodic anoxia, possibly similar to the accretionary environment of the Burgess Shale.The Emu Bay Shale at Emu Bay exhibits a shelly assemblage, mostly comprised of disarticulated Hsuaspis exuvia with occasional small Redlichia exuvia and hyolithids. No calcite replacement is evident. The location represents current swept, probably shallow water environment.