Ordovician Trilobite Faunas Research Articles

Diversity dynamics, faunal turnover and radiation pattern of the Middle Ordovician trilobites in South China

Available data on the temporal and geographical distribution of Middle–early Late Ordovician trilobites in South China were reviewed under a high-resolution biostratigraphical framework to investigate the diversity dynamics and explain the faunal turnover and radiation pattern of trilobites during the Middle Ordovician. Three macroevolutionary phases are recognized on the basis of the diversity changes at taxonomic levels. Cluster analysis shows three trilobite groups, two distinct trilobite faunas and three faunal turnovers through nine time slices. Three trilobite groups (Groups A, B and C) are coupled with three macroevolutionary phases, and characterized by different proportions of the Whiterock Fauna. Two distinct trilobite faunas (Early–Middle Ordovician and Late Ordovician Trilobite Faunas) and three faunal turnovers could be recognized at different similarity coefficients, their replacements were mainly affected by changes of sea level and substrate conditions. The trilobite radiation was manifested by the development, expansion and domination of the Whiterock Fauna (part of the Paleozoic Evolutionary Fauna) through the Middle Ordovician. The first diversity acme of trilobites occurred during the Dapingian–early Darriwilian, while the radiation centre gradually shifted from inner platform to outer platform environments. From the end Darriwilian onwards, elements of the Whiterock Fauna had further developed and dominated all environmental settings from the inner platform to the lower slope, coinciding with the second and more extensive radiation of trilobites in South China. Two phases of radiation may have been directly triggered by two major transgressions during the late Dapingian–early Darriwilian and the late Darriwilian–early Sandbian respectively. In addition, climate cooling and various substrate conditions, as well as the increased oxygen levels in the atmosphere and marine water, nutrients and tectonic movements during the Middle Ordovician may have provided essential conditions for the trilobite radiation.

Lower to Middle Ordovician trilobite faunas along the Ural border of Baltica

Lower to Middle Ordovician trilobite faunas along the Ural border of Baltica

Late Ordovician trilobites from the Xiazhen Formation in Zhuzhai, Jiangxi Province, China

Trilobites from mudstone of the Upper Ordovician Xiazhen Formation of South China are described. The reef-associated, unique fauna comprises 25 species, 14 genera, and ten families. Five new species are named: Remopleurides xiazhenensis sp. nov., Hibbertia aodiensis sp. nov., Vietnamia yushanensis sp. nov., Ceraurinus zhuzhaiensis sp. nov., and Pliomerina tashanensis sp. nov. The paucity of trilobites in reef-associated carbonates is interpreted that the trilobites diversified after the reef system decimated. Compared to the Late Ordovician trilobite faunas in other areas of South China, the Xiazhen mudstone fauna is unique in that the phacopids including Vietnamia, Ceraurinus, and Pliomerina account for 75% of the specimens collected. The occurrence of the same trilobite assemblage at different sampling localities along the dip direction of the formation suggests that the outcrops may be overlapped due to structural movement. The Xiazhen trilobite fauna is unique among the Late Ordovician fauna in that i...

Trilobite faunal successions across the Cambrian–Ordovician boundary intervals in Korea and their correlation with China and Australia

The Cambrian–Ordovician boundary in Korea lies within the Choson Supergroup exposed in the Taebaeksan Basin and has been recognized in the Taebaek and Yongwol groups. The Taebaek and Yongwol groups show slightly different trilobite faunal successions across the putative Cambrian–Ordovician boundary intervals. In the Taebaek Group, saukiid-dominated, Missisquoia/ Onychopyge, and kainellid-dominated faunas occur successively in the basal part of the Tongjom Formation. While the remaining part of the Tongjom Formation is poorly fossiliferous, the succeeding Tumugol Formation yields fairly diverse trilobite faunal assemblages of late Tremadocian age. This implies that the Cambrian–Ordovician boundary in the Taebaek Group should be placed somewhere within the interval yielding the kainellid-dominated fauna. In the Yongwol Group, an uppermost Cambrian Fatocephalus fauna is more or less contemporaneous with the saukiid-dominated fauna of the Taebaek Group, while three Tremadocian trilobite faunas, i.e. Yosimuraspis, Kainella, and Shumardia zones in ascending order, are well represented in the Mungok Formation. The occurrence of Jujuyaspis in the Yosimuraspis Zone provides a firm basis for locating the Cambrian–Ordovician boundary at the base of the Mungok Formation. These Cambrian–Ordovician trilobite faunas of Korea are in general well correlated with those of China and Australia.

Ordovician trilobite faunas and depositional history of the Taebaeksan Basin, Korea: implications for palaeogeography

The Taebaeksan Basin occupies the central-eastern part of the Korean peninsula and was a low-relief shallow marine carbonate shelf on which the Cambro-Ordovician Choson Supergroup was deposited. In the Taebaeksan Basin trilobites are among the most dominant fossil groups in the Lower Ordovician, but they become less important in Middle Ordovician faunal assemblages. The Early Ordovician trilobite faunas of the Taebaeksan Basin are characterised by the common occurrence of pandemic genera such as Jujuyaspis, Leiostegium, Asaphellus, Protopliomerops, Hystricurus, Apatokephalus, Shumardia, Asaphopsoides, and Kayseraspis. Biogeographically significant trilobite taxa include Yosimuraspis, Dikelokephalina, Koraipsis, and Chosenia. These Ordovician trilobite faunas, which thrived in shallow marine environments, show a remarkable similarity with faunas from North China, implying that the Taebaeksan Basin was connected through contiguous shallow waters to North China. These Sino-Korean faunas exhibit a close biogeographic connection with Australian faunas, with which they share some endemic genera, whereas they are more distantly related to the faunas of South China, South America, and North America. Based on these palaeobiogeographical features, it is suggested that in the early Palaeozoic much of the present Korean peninsula including the Taebaeksan Basin belonged to the Sino-Korean block, while part of the peninsula was derived from the Yangtze block.

The Ordovician trilobite fauna of the Great Paxton Borehole, Cambridgeshire

SummaryThe Ordovician trilobite fauna of the Great Paxton Borehole, Cambridgeshire, consists of twelve species including the seven new species; Segmentagnostus stubblefieldi, Trinucleus bicallis, Bergamia artemis, Protolloydolithus salax, Ogygiocaris macrops, Merlinia anxia and Bohemilla tridens. The fauna recalls that from the lower Llanvirn of the Shelve area, Shropshire, but the possibility of an upper Llanvirn age remains.

Geography and Faunal Provinces in Tremadoc Epoch: ABSTRACT

A major change took place in trilobite faunas during Late Cambrian and Early Ordovician time, that is, during the Tremadoc Epoch. The majority of preexisting families died out shortly before or during this epoch. They were replaced by several short-lived, new groups and the earliest members of other families which dominated succeeding Ordovician trilobite faunas. The dissimilarities between samples of Tremadoc trilobite faunas from 18 areas in the world were analyzed by a nonmetric multidimensional scaling technique. Groupings obtained by such analyses reveal faunal provinces of the Ordovician, and for the early part of the period 4 provinces were recognized. The analyses of Tremadoc faunas should reveal whether or not changes in provinces occurred during this epoch. The ssumption that a faunal province originally extended over the shallow seas surrounding a single continental mass is used, with palaeomagnetic data, to propose a model for Tremadoc paleogeography. End_of_Article - Last_Page 662------------

Trilobites of the Upper Cambrian Ptychaspid Biomere Wilberns Formation, Central Texas

Trilobites collected during the past 20 years from the Morgan Creek, Point Peak, and San Saba Members of the Wilberns Formation comprise 89 species assigned to 45 genera belonging to zones of the upper Franconian and Trempealeauan Stages of the Upper Cambrian Croixan Series. New zonal names are proposed in the interest of a regionally applicable nomenclature. Although none of the zonal nomenclature is identical to that of the 1944 Cambrian Correlation Chart of Howell et al., the four zones recognized in central Texas are equivalent to the eight highest zones on the Chart. Stratigraphically lowest is the Franconian Taenicephalus Zone, with a locally recognized Parabolinoides Subzone at its base; this zone is equivalent to the Conaspis Zone of the Correlation Chart. The Franconian Idahoia Zone, with a locally recognized Idahoia lirae Subzone at its base, is equivalent to the Ptychaspis Subzone of the Ptychaspis-Prosaukia Zone of the Correlation Chart. The sparsely fossiliferous Ellipsocephaloides Zone corresponds to the Prosaukia Subzone of the Ptychaspis-Prosaukia Zone on the Chart. Almost two-thirds of the trilobite species described occur in the Trempealeauan Saukia Zone, which corresponds to the five highest zones of the Correlation Chart; local subzones, in ascending order, are the Saukiella pyrene Subzone, the Saukiella junta Subzone, the Saukiella serotina Subzone, and the Corbinia apopsis Subzone.The succession of ptychoparioid trilobite faunas within these zones characterizes the Ptychaspid Biomere. The base of the biomere is at the base of the Taenicephalus Zone; the top coincides with the lowest occurrence of an Ordovician trilobite fauna. Trilobite families that characterize the Ptychaspid Biomere are the Ptychaspididae and the Parabolinoididae.Systematic descriptions include two new subfamilies, Drumaspidinae and Ptychaspidinae, and eight new species, Conaspis leptoholcis, Idiomesus infimus, Euptychaspis frontalis, Keithiella scapane, Saukiella serotina, Prosaukia remora, Calvinella prethoparia, and Westonaspis? texana.

Contribution a l'etude stratigraphique et paleontologique du synclinal d'Ancenis (Massif armoricain)

Abstract The schists and quartzites which form the northern and southern flanks of the Ancenis syncline on the right bank of the Loire river (France), have yielded sandy, micaceous nodules which contain a middle Ordovician trilobite fauna. This discovery indicates a similarity between the quartzites and the Calymenella bayani sandstone of the more northern folds of the Saint-Georges-sur-Loire synclinorium; but the volcanic schists which overlie the C. bayani sandstone are not represented in the Ancenis syncline. Contrary to what has been thought until now, the schists and quartzites rest unconformably on the Brioverian basement complex. The Brulis limestones, present as lenses interbedded in the schist-quartzite band on the south flank, are considered middle or upper Ordovician. The Ecochere jasper and calcareous schist with limestone lenses are directly transgressive on the middle Ordovician and contain a fauna typical of the Frasnian (upper Devonian). The Frasnian Cope-Choux limestone with Hypothiridina cuboides of the north flank seems to be directly related to fissile shales identical to those containing the Ecochere limestones. Continental deposits of the lower Culm, which contain Rhodea hochstetteri, occupy the core of the syncline and are principally Dinantian, but may extend into the lower Namurian. The absence of upper Namurian and Westphalian deposits suggests the intervention of a new orogenic phase (Erzgebirgian?). The Llandeilian trilobites Placoparia zippei, Colpocoryphe aragoi, and Pricyclopyge binodosa are described from the nodules. Pricyclopyge binodosa is the first representative of the Cyclopygidae reported from the Armorican massif.