Methodological advances in the use of faunal gradient analysis for regional high-resolution correlation in the type Cincinnatian Series (Upper Ordovician)

Historically, strata of the type Cincinnatian Series have not been correlated with precision because of an assumption that individual beds are not regionally persistent. In an effort to establish a regional chronostratigraphic framework for the Cincinnatian, a technique has been developed recently that uses gradient analysis of fossil abundance data to compare vertical trends in biotic composition among five localities that span a distance of 65 km. Using faunal data to establish correlations below the meter-scale has been problematic, because variability in the lateral expression of many beds has made it difficult to sample equivalent fossiliferous strata at all localities.

Here, this correlation technique is modified in an attempt to draw meter-scale correlations of the Kope and lower Fairview Formations. This modification involves grouping fossil census samples into stratigraphic intervals, such that the stratigraphic spacing of samples is identical at all localities. Samples are binned using two protocols: one that groups samples into 0.5 m thick intervals, and another that groups samples by lithologically delineated meter-scale cycles. Gradient analysis of binned samples using both protocols produces curves in which patterns in faunal composition below the meter-scale can be correlated with success only for limited intervals at select localities. The inability to consistently correlate at high resolution might indicate that correcting for regional variations in the expression of strata is not enough. Alternatively, the ability to correlate some intervals below the meter scale suggests that other problems, such as fine-scale lateral variations in biotic composition, might be impeding correlation. In addition, gradient analysis techniques are employed at a new locality to extend the lateral breadth of the existing, broader-scale chronostratigraphic framework by approximately 40 km. Although interpreted to be in an up-ramp direction from previously measured localities, this new locality does not have an overall shallower water faunal assemblage until just below the Kope/Fairview contact.     

Quantitatively comparing morphological trends to environment in the fossil record (Cincinnatian series; Upper Ordovician)

Determining whether morphological trends in fossil species represent evolution within a lineage or lateral shifts in morphologically variable populations through time requires a thorough examination of the details of both morphology and paleoenvironment in time and space. The purpose of this study is to explore at high resolution the relationship between morphology of the trilobite Flexicalymene granulosa and paleoenvironmental conditions in Upper Ordovician deposits of southwestern Ohio and northern Kentucky. This is achieved by using geometric morphometrics to measure high-resolution morphological changes and by using gradient analysis to capture environmental gradients underlying faunal distribution patterns. Quantitatively comparing the outcomes of these two techniques provides an assessment of whether shape changes relates to environment. Results indicate that a significant amount of shape change, seen as an anteromedial movement of the eye region over time, corresponds to ordination scores. This suggests a relationship between certain aspects of morphology and environment. The combination of these quantitative techniques has provided the foundation for determining whether morphological trends within F. granulosa represent evolution or temporal shifts in geographic variation. Future work will involve examining this relationship in greater detail both geographically and stratigraphically.     

A quantitative paleoecological approach to high-resolution cyclic and event stratigraphy: the Upper Ordovician Miamitown Shale in the type Cincinnatian

Stratigraphic cycles form an underlying high-resolution chronostratigraphic structure for much of the sedimentary record. However, before their chronostratigraphic utility can be realized they must be reliably correlated. A new integrated cyclic, quantitative lithologic and faunal method of correlating meter-scale cycles has been developed for a 12 m interval of the Miami-town Shale in the Upper Ordovician of the Cincinnati, Ohio area. First, using lithologic criteria alone, six flooding-surface-bound (shale-on-limestone) shoaling-upward (shale-to-limestone) cycles were delineated and correlated between seven outcrop sections within a 30 km radius; many correlations were ambiguous. Unusual fossil occurrences constrain correlations of cycles 3 and 4, and the limited presence of a dalmanellid, Heterorthina fairmountensis , shows that the flooding surface above cycle 3 lies 10 cm below the lithologic limestone-shale contact. Cluster analysis of faunal abundance data constrained correlations between all cycles and showed a major transition at the top of cycle 2, again below the lithologic limestone-shale contact. Finally, faunal depth gradient fluctuations interpreted from ordination of faunal abundance data confirmed and clarified the nature of cycle correlations; the major transition at the top of cycle 2 is a transgressive surface, and the middle part of cycle 3 includes the interval of maximum water depth. These features delineate a larger, 10-m-scale, cyclicity. The smaller, meter-scale cycles, interpreted as averaging 40–100 ka in duration, demonstrate the potential of a ten-to twenty-fold increase in the resolution of the type Cincinnatian stratigraphic record. Ecostratigraphy, faunal cyclicity, cyclic stratigraphy, event stratigraphy epiboles, benthic paleoecology, Upper Ordovician, Maysvillian, Caradocian, Ashgillian, Cincinnati.     

新疆柯坪和甘肃平凉上奥陶统底部附近的牙形刺

新疆柯坪大湾沟和甘肃平凉官司庄剖面是Nemagraptusb gracilis带及上奥陶统底界的重要剖面,研究这两剖面的牙形刺具有十分重要的意义。本文描述了采自新疆柯坪大湾沟和甘肃平凉官司庄剖面上奥陶统底界附近的牙形刺共13属18种。     

Evenness and diversity in Upper Cambrian – Lower Ordovician trilobite communities from the Central Andean Basin (Cordillera Oriental,Argentina)

Community evenness has recently received much attention, either because it is related to ecosystem functioning or because it may affect estimation of diversity. Temporal and environmental trends in diversity and evenness of trilobite communities during the Late Cambrian – Early Ordovician of the Cordillera Oriental (north‐western Argentina) are here analysed. Richness and evenness increase through time in both deep subtidal (between fair‐weather and storm wave base) and offshore (below storm wave base) communities. Two significant patterns are superimposed on this general trend: (1) the magnitude of the increase in evenness is much more pronounced in deep than in shallower settings, and (2) richness and evenness trajectories are decoupled (while a significant rise in evenness is recorded in the middle Tremadocian (Tr2), an increase in richness is delayed until the late Tremadocian (Tr3)). In contrast to expectations, a single family (Olenidae) is dominant in samples associated with this earlier rise in evenness relative to richness. Hence, this trend is explained neither by the number of families present in the communities nor by the familial identity of the most abundant taxon. Large‐scale comparisons of the timing and geographical components of these trends are restricted to the patterns recognized in Laurentian North American studies. Results from the Cordillera Oriental mirror those of Laurentia regarding the rise in both metrics in deep marine settings. Nevertheless, the timing of this increase in richness and evenness is delayed in the Cordillera Oriental, supporting the idea that palaeogeographical regions differed in the nature and timing of ecological changes. Finally, the rise in trilobite alpha‐diversity through the Late Cambrian – Early Ordovician of the Cordillera Oriental supports the idea that trilobite alpha‐diversity did not decline worldwide, suggesting that the relative decline in trilobite alpha‐diversity is most probably caused by the dilution effect.     

Foliomena Fauna (Brachiopoda) from the Upper Ordovician of Sardinia

The late Ordovician brachiopod assemblage from Sardinia is one of the youngest members of the deep-water Foliomena fauna and is characterized by the following core taxa: Christiania , Cyclospira , Dedzetina and Foliomena . The fauna also contains Epitomyonia , Leangella , Glyptorthis and Skenidioides , which are more typical of shallower-water environments during the late Ordovician but occupied deeper-water niches during the Silurian following the termination of the Foliomena fauna. The suprafamilial placement of the family Chrustenoporidae is discussed and the new species Dedzetina serpaglii and Leangella ( Leangella ) fecunda are established. In common with many mid-Ashgill Foliomena faunas the Sardinian assemblage shows significant differences from other faunal developments of this type, reflecting its geographical position and shallower water conditions than those of the classic early Ashgill Foliomena faunas. The brachiopods occur with abundant trilobites belonging to a variant of the cyclopygid fauna. The faunas developed on part of a complex of microcontinents derived from peri-Gondwana during the Ordovician.     

Unusual trilobite biofacies from the Lower Ordovician of the Argentine Cordillera Oriental: new insights into olenid palaeoecology

Balseiro, D., Waisfeld, B.G. & Buatois, L.A. 2010: Unusual trilobite biofacies from the Lower Ordovician of the Argentine Cordillera Oriental: new insights into olenid palaeoecology. Lethaia, Vol. 44, pp. 58–75. The study of biofacies has proven to be relevant in the understanding of trilobite palaeoecology, palaeobiogeography and macroevolution. The widespread Olenid biofacies is one of the best known, and is usually interpreted as occuring in dysoxic environments. Tremadocian successions of the Argentinian Cordillera Oriental bear a diverse and long‐studied olenid‐dominated fauna. Based on cluster analysis, five distinct biofacies are defined for the middle Tremadocian (Tr2 stage slice), distributed from shelf (below storm wave base) to lower‐shoreface settings (above fair‐weather wave base). Ordination shows biofacies along two gradients, a bathymetrical one and another related to oxygen content. All of them are dominated both taxonomically and ecologically by olenids. This detailed quantitative palaeoecological study challenges current views suggesting instead that the Olenidae dominated a broad range of environments, from oxygenated shallow‐marine to dysoxic deep‐marine. Comparisons with largely coeval trilobite records from geodynamically and palaeobiogeographically disparate sites suggest that siliciclastic sedimentation appears as the most influential controlling environmental factor upon olenid distribution and dominance. Further comparisons across different climatic belts show that siliciclastic input controlled trilobite diversity gradients, even more than latitude. From an autoecological viewpoint distribution of traditional olenid morphotypes shows no relation to depth or to oxygen content, and at least some members of the group appear to have had the possibility of coping with low oxygen content, rather than being restricted to oxygen‐deficient environments. The analysis performed herein, together with recent research on the group, demonstrate that factors controlling olenid distribution are more complex than previously envisaged. □Biofacies, diversity, Olenidae, palaeoecology, Tremadocian, trilobite.     

Cope's rule in the Ordovician trilobite family Asaphidae (order Asaphida): patterns across multiple most parsimonious trees

Cope's rule defines lineages that trend towards an increase in body size through geological time. The trilobite family Asaphidae is one of the most diverse of the class Trilobita and ranges from the Upper Cambrian through to the Upper Ordovician. The group is one trilobite clades that displays a large size range and contains several of the largest trilobite species. Reduced major axis correlations between the lengths of cephala and pygidia and the total sagittal length of complete individuals have high support and were used to standardise all incomplete specimens to total axial length. Phylogenetic studies into Cope's rule tend to use supertrees, composite trees or a single tree selected through a fit criterion. Here, for the first time, all trees recovered from a maximum parsimony analysis were analysed equally. Maximum likelihood was used to fit four evolutionary models: random walk, directional, Ornstein–Uhlenbeck (evolution towards an adaptive optimum) and stasis. These were compared equally using Akaike weights. Fitting of evolutionary models by maximum likelihood supports stasis as consistently the most likely model across all trees with low support for directionality.     

Some ostracodes from the Gur'yanovka Formation (Upper Ordovician) of northeastern Gorny Altai

Ostracodes from the Gur'yano-ka Formation (Upper Ordo-ician, Sandbian and Katian stages) of Gorny Altai, Russia, are studied for the first time. Some localities with fossil ostracodes of this age are described briefly. Ele-en new species of the genera Ballardina, Eurychilina, Laccochilina, Bolbina, Retiprimites, Pseudozygobolbina, Bullaeferum, Soanella, Egoro-ella, and Allertemmysa are described and figured. The pre-iously described species Leperditella aff. par-ipunctata V. Ivanova, 1959, Grammolomatella valdari V. Ivanova et Melnikova 1977, Longidorsa? baltica Meidla, 1996, and Steusloffina cuneata (Steusloff, 1895) and ostracodes in open nomenclature, Bollia sp., Klimphores sp., Rectella sp., Longiscula sp., are only figured.     

A 17‐element conodont apparatus from the Soom Shale Lagerstätte (Upper Ordovician), South Africa

Abstract:  Natural assemblages of a new conodont taxon, Notiodella keblon, from the Upper Ordovician Soom Shale Lagerstätte of South Africa contain 17 elements. This is the first time that a 17‐element apparatus plan has been unequivocally demonstrated in conodonts. The apparatus comprises paired P₁, P₂, P₃, M, S₁, S₂, S₃ and S₄ elements and an unpaired, axial S₀ element and provides a new template for use in the reconstruction of apparatuses from the collections of dispersed elements, particularly for those with icrion‐bearing P₁ elements and perhaps for other balognathids.     

Geometric optics of trilobite eyes: a theoretical study of the shape of the aspherical interface in the cornea of schizochroal eyes of phacopid trilobites

A general method is given to determine theoretically the shape of the aspherical interface that eliminates spherical aberration in an optionally shaped thick lens. The theory is applied to trilobite eyes. On the basis of the geometric optical method presented, the refractive indices and focal length of the original corneal lenses of trilobites can be determined. The shape of the aspherical interface in the cornea of some phacopid trilobites with schizochroal eyes is investigated. The theoretical aspherical interfaces agree well with the real ones.     

Trilobite biofacies and sequence stratigraphy: an example from the Upper Ordovician of Oklahoma

There have been surprisingly few empirical investigations of the fundamental principle that the architecture of depositional sequences exerts considerable control on observed patterns of faunal distribution and replacement. In this paper, we examine trilobite associations in two sequences of the Upper Ordovician (Sandbian) Bromide Formation of southern Oklahoma. Cluster analysis and ordination of genus abundance data identified five lithofacies‐related biofacies that are also differentiated by diversity patterns. Biofacies of the transgressive system tract (TST) of successive sequences are more similar to each other than they are to biofacies in the highstand systems tract (HST) of the same sequence. This similarity likely records dominance of large, robust convex sclerites in taphonomically degraded samples from condensed, strongly winnowed grainstone and rudstone. Horizons with articulated exoskeletons of isoteline trilobites preserved by obrution deposits occur most commonly in the early HST and record behavioural aggregations. Grainstone and rudstone of the later HST are less winnowed than those of the TST and show less fragmentation and sorting of sclerites. These changes in taphonomic conditions preserve ecological patterns more clearly. In most biofacies, rarefied alpha diversity (samples) and gamma diversity (biofacies) of middle‐ and outer‐ramp HST deposits are greater than in the TSTs, and biofacies replace each other down ramp. Diversity patterns do not agree with model predictions and other data sets that indicate low beta and high alpha diversity in the TST, likely because of taphonomic degradation. Vertical replacement of biofacies is expressed by the appearance of peritidal facies in which trilobites are rare. Biofacies shifts also characterize sequence boundaries and are most profound in the inner‐ramp successions characterized by sharp facies offsets. Comparison with bathymetrically similar deposits in the Taconic foreland basin showed similar diversity trends along environmental gradients, with some differences in shallow‐water settings attributed to taphonomic differences.     

Oldest known Dicoelosia and Epitomyonia,deep water brachiopods from the Beiguoshan Formation (Middle Katian,Upper Ordovician), Shaanxi,north China

Abstract: A diverse brachiopod fauna from a relatively deep water carbonate facies of the Upper Ordovician Beiguoshan Formation (uppermost Caradoc – lower Ashgill, middle Katian) is characterized by small shells and contains the oldest known Dicoelosia and Epitomyonia, two diagnostic taxa of deep water brachiopod palaeocommunities during the Late Ordovician and Silurian. Three new species are recognized: Dicoelosia cordiformis sp. nov., Dicoelosia perbrevis sp. nov. and Epitomyonia fui sp. nov. These pioneer forms of the family Dicoelosiidae show a relatively high degree of morphological plasticity. The shells of Dicoelosia from the Beiguoshan Formation range from the typical slender‐lobed form with a concavoconvex profile to the strongly equibiconvex, fat‐lobed morphotype that was not known previously until the late Silurian. The Beiguoshan dicoelosiids point to an important attribute of the deep water brachiopods: small generalists with high morphological plasticity, which make them ideal candidates as progenitors for the evolution of shallow water brachiopod faunas in shelf and platform depositional environments.     

Ontogeny of the Furongian (late Cambrian) trilobite Proceratopyge cf. P. Lata Whitehouse from northern Victoria Land,Antarctica, and the evolution of metamorphosis in trilobites

There were multiple origins of metamorphosis‐undergoing protaspides in trilobite evolution: within the superfamilies Remopleuridioidea, Trinucleoidea, and within the Order Asaphida. Recent studies have revealed that the protaspides of the Cambrian representatives of the Remopleuridioidea and the Trinucleoidea did not undergo metamorphosis. However, ontogeny of the Cambrian members of the Order Asaphida has remained unknown. This study documents the ontogeny of the Furongian asaphoidean ceratopygid trilobite, Proceratopyge cf. P. lata Whitehouse, from northern Victoria Land, Antarctica. Two stages for the protaspid phase, five developmental stages for the post‐protaspid cranidia, and ten stages for the post‐protaspid pygidia have been identified. Interestingly, the protaspis directly developed into a meraspis without metamorphosis. A new cladistic analysis resulted in a single most parsimonious tree, according to which the presence of the bulbous commutavi protaspis turns out to be a synapomorphy for Asaphidae + Cyclopygoidea, not a synapomorphy for the Order Asaphida as previously suggested. In addition, it is inferred that there was convergent evolution of indirectly‐developing commutavi protaspides during the Furongian and Early Ordovician. Metamorphosis‐entailing planktonic larvae evolved in many different metazoan lineages near the Cambrian–Ordovician transition, due to the escalating ecological pressure of the Great Ordovician Biodiversification Event. Since the bulbous commutavi protaspid morphology is thought to be an adaptation for a planktonic life mode, the convergent evolution of the indirect development in the three trilobite lineages at this period might have been a result of adaptation to the early phase of the Great Ordovician Biodiversification Event.     

A Curious Rusophycus (Arthropod Ichnofossil) Assemblage from the Upper Ordovician of Ontario,Canada

The ichnogenus Rusophycus includes a wide range of short bilobate excavations generally attributed to variable feeding behaviors of arthropods, especially trilobites. An unusual Rusophycus assemblage from Upper Ordovician Georgian Bay Formation in Ontario departs radically from previously described examples and presents new challenges for understanding the behavior represented by these traces. This specimen is unique in the arrangement of multiple Rusophycus burrows in a circular, lens-shaped array (as opposed to a linear or random arrangement typical of other Rusophycus assemblages). The size and shape of the individual Rusophycus components are consistent with traces attributed to the coeval trilobite Flexicalymene. Multiple Rusophycus assemblages likely reflect aggregations of trilobites in response to a local concentration of food. The topology of this particular Rusophycus assemblage suggests that the trilobites opportunistically exploited a rich and narrowly restricted food source, perhaps the decaying remains of a buried organism.     

Intraspecific variation of trunk segmentation in the oryctocephalid trilobite Duyunaspis duyunensis from the Cambrian (Stage 4, Series 2) of South China

A detailed exploration of growth and trunk segmentation of the oryctocephalid trilobite, Duyunaspis duyunensis Chang & Chien in Zhou et al. 1977, from the lower Cambrian (Stage 4, Series 2) Balang Formation in western Hunan Province, South China, is presented. Because of the excellent preservation, the complete post‐protaspid ontogenetic series from merapsid degree 0 to the holaspid phase is described. The ontogenetic series reveals new information on morphological changes such as the migration of the posterior branch of the facial sutures (from proparian to opisthoparian) and contraction of the posteromedial notch in the pygidium. The abundance of articulated specimens available from a narrow stratigraphical interval makes this material singularly useful for studying the morphogenesis and post‐embryonic growth of D. duyunensis in comparison with other oryctocephalids. Strong evidence that multiple numbers of pygidial segment are recognized in each meraspid degree as well as in the holaspid period showed unusual intraspecific variability in the rate of trunk segmentation, providing insights into how Cambrian subisopygous trilobites controlled their body patterning, including size, shape and trunk segment number in both thorax and caudal plate during growth.     

Decoupling of local and regional dominance in trilobite assemblages from northwestern Argentina: new insights into Cambro‐Ordovician ecological changes

Components of biodiversity are strongly scale dependent, but the relative importance of the patterns that operate at different scales and the links between them have been overlooked. To disentangle the ecological structure of Cambro‐Ordovician trilobite assemblages from the Argentine Cordillera Oriental at different scales, we explore patterns of abundance, dominance and occupancy across the onshore–offshore profile, and through three time intervals: Furongian, earliest Late Tremadocian (Tr2), latest Middle Floian–earliest Late Floian (Fl2–Fl3). At the regional scale, single taxa are overwhelming dominant in the Furongian (Parabolina) and in the earliest Late Tremadocian (Leptoplastides). Several dominants occur in the Floian, but just one (Famatinolithus) attains high occupancy and, rarely, high dominance. In contrast, only the Furongian records highly dominated local assemblages, whereas dominance distinctly decreases among Tr2 and Fl2–Fl3 ones. Thus, when both scales of analysis are combined, an unexpected scenario becomes evident: Tr2 assemblages resemble those of the Furongian at the regional scale, but mirror those of the Floian at the local scale. These results highlight a decoupling in local versus regional structures triggered by an earlier switch in dominance in local communities and a delayed change at the regional scale. Interestingly, this decrease in local dominance matches previous analyses accounting for a coeval step‐up in local evenness, suggesting that the Tr2 appears as a pivotal interval in the reorganization of communities in the Cordillera Oriental. This scenario emphasizes that biogeographical regions witnessed different regional‐scale processes, and suggests that scaling local and regional patterns provides new insights to unravel the history of biodiversity among benthic communities.     

The first articulated specimen of Plumulites canadensis (Woodward, 1889) from the Upper Ordovician of Ontario,with a review of the anterior region of Plumulitidae (Annelida: Machaeridia)

Abstract. Articulated plumulitid machaeridians are rarely preserved intact. Here, we describe a complete specimen of Plumulites canadensis (Woodward, 1889) retaining much of the head region. The two anteriormost pairs of shell plates are quite distinct from the rest in outline, density of concentric rugae, and especially the radial ornamentation of the second pair. We demonstrate that the latter condition is present in other complete plumulitids and therefore widespread, which elucidates a larger diversity in morphology of plumulitids than realized previously.