Renbin Zhan

Chapter 11 Biodiversity, biogeography and phylogeography of Ordovician rhynchonelliform brachiopods

Abstract The phylogeographical evolution and the consequent changing distribution and diversity of rhynchonelliform brachiopods through the Ordovician are linked to the dynamic palaeogeography of the period. The Early Ordovician (Tremadocian and Floian) is characterized by globally low-diversity faunas with local biodiversity epicentres, notably on the South China Palaeoplate; low-latitude porambonitoid-dominated faunas with early plectambonitoid and clitambonitoid representatives, as well as high-latitude assemblages mostly dominated by orthoids, can be recognized, but many taxa are rooted in Late Cambrian stocks. The Early Ordovician displays a steady increase in rhynchonelliformean biodiversity, which was mostly driven by the increasing success of the Porambonitoidea and Orthoidea, but the billingsellids and early plectambonitoids also contributed to this expansion. During the Early to Mid Ordovician (Dapingian–Darriwilian), marine life experienced an unprecedented hike in diversity at the species, genus and family levels that firmly installed the suspension-feeding benthos as the main component of the Palaeozoic fauna. However, this may have occurred in response to an early Darriwilian annihilation of existing clades, some of which had been most successful during the Early Ordovician. New clades rapidly expanded. The continents were widely dispersed together with a large number of microcontinents and volcanic arcs related to intense magmatic and tectonic activity. Climates were warm and sea-levels were high. Pivotal to the entire diversification is the role of gamma (inter-provincial) diversity and by implication the spread of the continents and frequency of island arcs and microcontinents. The phylogeographical analysis demonstrates that this new palaeogeographical configuration was particularly well explored and utilized by the strophomenides, especially the Plectambonitoidea, which radiated rapidly during this interval. The porambonitoids, on the other hand, were still in recovery following the early Darriwilian extinctions. Orthides remained dominant, particularly at high latitudes. Biodiversity epicentres were located on most of the larger palaeoplates, as well as within the Iapetus Ocean. Provincial patterns were disrupted during the Sandbian and early Katian with the migration of many elements of the benthos into deeper-water regimes, enjoying a more cosmopolitan distribution. Later Katian faunas exhibit a partition between carbonate and clastic environments. During the latest Katian, biogeographical patterns were disrupted by polewards migrations of warm-water taxa in response to the changing climate; possibly as a consequence of low-latitude cradles being developed in, for instance, carbonate reef settings. Many clades were well established with especially the strophomenides beginning to outnumber the previously successful orthides, although this process had already begun, regionally, in the mid to late Darriwilian. At the same time, atrypoid and pentameroid clades also began to radiate in low-latitude faunas, anticipating their dominance in Silurian faunas. The Hirnantian was marked by severe extinctions particularly across orthide-strophomenide clades within the context of few, but well-defined, climatically controlled provincial belts. Supplementary material: The individual localities and a reference list for the data sources are provided at: http://www.geolsoc.org.uk/SUP18667

Biotic diachroneity during the Ordovician radiation: evidence from South China

Zhan R. & Harper, D.A.T. 2006 09 12: Biotic diachroneity during the OrdovicianRadiation: evidence from South China. Lethaia, Vol. 39, pp. 211 226. Oslo. ISSN 0024-1164.The Ordovician radiation was one of the most marked and sustained increases inPhanerozoic biodiversification; nevertheless it occurred against a background of minimalglobal climatic and environmental perturbations. Detailed investigations of theOrdovician successions on the Yangtze Platform of the South China palaeoplate indicatethat: (1) the brachiopod a- and b-diversity changes are diachronous; (2) macroevolu-tionary patterns were different across the South China palaeoplate, with the EarlyOrdovician brachiopod radiation first occurring in normal marine, shallow-waterenvironments and then moving gradually to both nearer-shore and offshore locations;(3) the main contributors to the initial Ordovician brachiopod radiation were theOrthida and Pentamerida; the typical Ordovician brachiopod fauna, dominated by theOrthida and Strophomenida, did not appear until the late Mid Ordovician (Undulo-graptus austrodentatus Biozone) when the Strophomenida apparently replaced thedominant position of the Pentamerida within the fauna; (4) different ecotypes (e.g.,sessile benthos, mobile benthos together with pelagic and planktonic organisms)demonstrate substantially different macroevolutionary patterns. The Ordovician bra-chiopod radiation of South China was apparently earlier than that suggested by globaltrends together with the data available from other palaeoplates or terranes, which may berelated to its unique palaeogeographic position (peri-Gondwanan terrane graduallymoving to equatorial latitudes). I Brachiopods, diachroneity, a-diversity, b-diversity,Ordovician radiation, South China.Renbin Zhan, State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute ofGeology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China,[rbzhan@nigpas.ac.cn]; David A. T. Harper, Geological Museum, Oster Voldgade 5 7,DK-1350 Copenhagen K, Denmark, [dharper@snm.ku.dk]; 14th November 2005, revised6th March 2006.

EPIPUNCTAE AND PHOSPHATIZED SETAE IN LATE ORDOVICIAN PLAESIOMYID BRACHIOPODS FROM ANTICOSTI ISLAND, EASTERN CANADA

Abstract Epipunctae, a new type of shell perforation, are well developed in typical taxa of the family Plaesiomyidae, a group of common orthide brachiopods from Laurentia and some other tropically located tectonic plates of Late Ordovician age. These minute, prominently elongate, tubular structures are similar to endopunctae in size and density, but differ in being oblique, intersecting the shell surface at a relatively low angle, and being confined largely to the outer portion of the shell wall. The tubules are similar in orientation to aditicules within the same shells but are much smaller and denser, usually aligned along fine growth lines and arranged in crude longitudinal columns. Exceptionally preserved phosphatic molds of bundled setal canals inside epipunctae and aditicules, described for the first time in this paper, are direct evidence that these two types of tubular structures of different sizes had the same function of housing sensory setae along the shell margin, but both the setae and the tubules became abandoned in the outer portion of the shell wall through burial by the secondary shell layer when the shell margin migrated forward. Epipunctae have been found so far only in plaesiomyid shells, but aditicules are common in many groups of the order Orthida. The taxonomic value of epipunctae is shown by a reassessment of Pionorthis Schuchert and Cooper, 1932. The hypotype previously regarded widely, but erroneously, as the archetype of ‘Orthis sola’ Billings, 1866, the type species of Pionorthis, is allied to Plaesiomys Hall and Clarke, 1892. It bears the characteristic epipunctae. The holotype of Orthis sola is a dalmanelloid shell with true punctae, assignable to Mendacella Cooper, 1930. This warrants rejection of the genus Pionorthis.

Surviving the end-Ordovician extinctions: evidence from the earliest Silurian brachiopods of northeastern Jiangxi and western Zhejiang provinces, East China

Earliest Rhuddanian (Silurian) brachiopods are recorded from the basal part of the Lower Llandovery Shiyang and Anji formations in western Zhejiang and northeastern Jiangxi provinces, East China. Associated graptolites including Normalograptus jerini indicate the lowest Rhuddanian Akidograptus ascensus Biozone. The surviving brachiopod fauna includes 19 genera dominated by orthids and strophomenids, whereas pentamerids and atrypids that inhabited mainly warmer water regimes, and were almost absent in the cool/cold Hirnantia Fauna, occur rarely in the studied fauna. Each family is represented by a single genus that seeded their recovery. The predominance of these long-ranging and widely distributed genera is one of major characters of the brachiopod survival in east China. From qualitative and quantitative analysis of faunal composition, diversity and abundance, with evidences from palaeoecology and palaeogeography, the Levenea qianbeiensis Association, Katastrophomena-Leptaena-Levenea Association, and Glyptorthis-Epitomyonia-Levenea Association are recognized and assigned to BA (Benthic Assemblage) 2, BA3, and an ecozone close to the BA3-4 boundary respectively. No Lazarus genera are recorded in this study. Skenidioides and Epitomyonia were chiefly regarded as deeper-water taxa in the Ordovician and Silurian, but are recorded from shallow-water in east China during the early Rhuddanian, indicating an ecologic experiment with these taxa migrating from deep into shallower, better-oxygenated sites at the crisis time and during the subsequent survival interval. This study further demonstrates that the brachiopod faunal turnover after the end-Ordovician extinctions may not have been completed until the late Rhuddanian in South China.

NEW DATA ON THE FOLIOMENA FAUNA (BRACHIOPODA) FROM THE UPPER ORDOVICIAN OF SOUTH CHINA

Abstract A newly discovered Late Ordovician (early Ashgill) brachiopod assemblage from the Linhsiang Formation in the middle part of the Yangtze Platform, South China, bridges the paleobiogeographical gap between the early Ashgill Foliomena-bearing associations known previously from the upper and the lower parts of the Yangtze Platform. Characterized by minute shells in calcareous to siliciclastic mudstones, the fauna contains 13 brachiopod genera, of which two plectambonitoids are new: Hadroskolos and Jingshanella. Cluster and principal component analyses, based on 29 global occurrences of the Foliomena fauna in Laurentia, Avalonia, Kazakhstan, Baltica, Sardinia, Bohemia, Sibumasu, North China, and South China, revealed broad trends of spatial and temporal faunal differentiation in terms of taxonomic compositions. The analyses demonstrate for the first time that early Foliomena-bearing associations of Caradoc age occupied primarily deepwater (distal shelf) environments with a siliciclastic or calcareous mud substrate. The fauna attained its widest paleogeographical distribution and paleoecological range (midshelf to shelf margin settings) during the early Ashgill.

The Central Guizhou and Yi- chang uplifts, Upper Yangtze region, between Ordovician and Silurian

The Central Guizhou and Yichang Uplifts are present in central Guizhou to western Hubei. Biostratigraphic evidences from more than 20 sections in 14 counties of this region provide the data about the duration of these uplifts. Although this duration differs from locality to locality, it is mainly from Ashgillian to Rhuddanian. The uplifts result from a horizontally driven movement to the South China Paleoplate from an uncertain block in southeast. Global sea-level drop during the end of the Ordovician made the uplifts obvious, particularly the Central Guizhou Uplift. It might have emerged above sea level in the short interval between the Ordovician and Silurian.

Taxonomic reassessment of two virgianid brachiopod genera from the Upper Ordovician and Lower Silurian of South China

Abstract Reexamination of type and topotype material revealed the presence of well-developed ventral and dorsal interareas in two virgianid brachiopods from South China, Eoconchidium jiangshanensis Liang (in Liu et al., 1983) and Paraconchidium shiqianensis Rong, Xu, and Yang, 1974, of Late Ordovician and Early Silurian ages, respectively. A cladistic analysis of the common virgianid taxa, incorporating new data on the development of interareas, confirms Paraconchidium Rong, Xu, and Yang, 1974 as a valid genus (not a junior synonym of Pseudoconchidium Nikiforova and Sapelnikov, 1971) and warrants E. jiangshanensis as the type species of Deloprosopus new genus (not allied to either Eoconchidium or Tcherskidium as previously believed). Our preliminary survey on the suborder Pentameridina, based on available material or illustrations of well-preserved, disarticulated (typically silicified) valves, indicates that 1) the interareas are more commonly developed in the superfamily Pentameroidea than was reported previously, especially in the families Virgianidae and Subrianidae; 2) the ventral and dorsal interareas commonly do not occur as paired planar surfaces in the Pentameroidea, as they do in the superfamily Stricklandioidea; and 3) despite the common absence of a ventral interarea, the development of a sharply delimited dorsal interarea appears to be ubiquitous in the Pentameroidea and possibly in the suborder Pentameridina. In the currently adopted classification, the presence of matching ventral and dorsal interareas is treated as one of the diagnostic characters that separate Stricklandioidea from other superfamilies of the Pentameridina. The new data presented herein on the development of interareas imply the need to reevaluate the taxonomic and evolutionary significance of the ventral and dorsal interareas, pending a thorough survey on their distribution in the suborder Pentameridina.

The Late Ordovician and Early Silurian pentameride brachiopod Holorhynchus Kiaer, 1902 from North China

Abstract Holorhynchus giganteus Kiaer, 1902, a common Late Ordovician (mid-Ashgill) pentameride brachiopod in the Baltic region, Kazakhstan, and southern Tien Shan, is documented for the first time from the Badanjilin Formation (mid-Ashgill) of western Inner Mongolia (Alxa block), North China. Serial sections of the Chinese material confirm the presence of a vestigial ventral median septum in the early growth stage of H. giganteus, but the septum becomes embedded in the secondary shell thickening at the adult growth stage. A survey of the type material from Norway and additional material from other regions indicates that the incipient ventral median septum is a much more commonly developed structure than was previously believed. The presence of a well-developed pseudodeltidium in the Tien Shan material of H. giganteus and the absence of such a structure in conspecific material from many other regions require a systematic revision of the generic group. Holorhynchus has rodlike crura (=brachial processes) that do not form flanges at their junctions with the inner hinge plates (=outer plates = crural plates) and outer hinge plates (inner plates). This, together with the development of a crude spondylial comb structure, points to its affinity to the Virgianidae rather than to the Stricklandiidae. Holorhynchus can be regarded as a Lazarus taxon because of its absence during the crisis (Hirnantian) and survival (early-middle Rhuddanian) intervals associated with the Late Ordovician mass extinction and its reappearance in Kazakhstan and North China during the Early Silurian (late Rhuddanian-early Aeronian). The mid-Ashgill Holorhynchus fauna, typified by a number of large-shelled pentamerides, was common in the Baltic region, the Urals, Kazakhstan, Tien Shan, Alxa, Qaidam, Kolyma, and east-central Alaska, but largely absent from Laurentia and Siberia (except for Taimyr) in the ancient tropical-subtropical regions. This paleobiogeographic pattern agrees with the general pattern of the Late Ordovician brachiopod provincialism.

Latest Ordovician brachiopod and trilobite assemblage from Yuhang, northern Zhejiang, East China: a window on Hirnantian deep-water benthos

A moderately diverse brachiopod and trilobite assemblage, the Leangella–Dalmanitina (Songxites) Assemblage, occurs in the upper Yankou Formation (Hirnantian, probably equivalent to the Normalograptus persculptus Biozone) at Shizi Hill, Yuhang, west of Hangzhou, northern Zhejiang, E China. The brachiopods are rare, characterised by minute, thin shells with very small body cavities, preserved in mudstones as moulds. They may have inhabited quiet, deep-water and dysaerobic slope environments with low levels of nutrients, equivalent to Benthic Assemblage 5. Most genera were adapted for life in deep water and either remained there or alternatively migrated into relatively shallower habitats to evade perturbations during the first phase of the end Ordovician extinctions. The slope environments were recolonised from outer shelf and upper slope communities during the early Hirnantian, but isolated biotas may also have survived in deeper-water habitats by reducing their population size and diversity during the crisis. The Leangella–Dalmanitina (Songxites) Assemblage provides an unique Hirnantian window through which we can monitor the changes in the deep-water biofacies following the first phase of the extinctions. Significantly, parts of the deep water marine environment may have survived intact, the end Ordovician extinctions.

Two new genera of Early Silurian stricklandioid brachiopods from South China and their bearing on stricklandioid classification and paleobiogeography

Abstract Restudy of two Early Silurian (Aeronian) stricklandioid species, Stricklandinia transversa Grabau, 1925 and Stricklandiella robusta Rong and Yang, 1981 from the Yichang area of South China, leads to the recognition of two new genera, Sinokulumbella and Sinostricklandiella. Two types of spondylia and four types of cardinalia are recognized for the Stricklandioidea and can be used for classification of the superfamily at the generic or even familial level. On the basis of these characters, five groups (typified by Stricklandia, Stricklandiella, Kulumbella, Microcardinalia, and Aenigmastrophia) can be recognized within the superfamily. Sinokulumbella n. gen., with a small, shallow, bowl-shaped spondylium and a pair of outer hinge plates that are discrete from the crura, is regarded to be affiliated with the Kulumbella group. Sinostricklandiella n. gen. has superimposed plicae and costae, although its internal structures are similar to the Stricklandiella group. A revised classification of stricklandioids implies that the Chinese pentamerides were characterized by strong provincialism during the early and middle Llandovery. This interpretation is supported further by the complete lack of true Stricklandia and Microcardinalia lineages in South China. Different stocks of stricklandioids in Baltica, Laurentia, South China, Siberia, and Kazakhstan may have experienced allopatric evolution, punctuated by several pulses of faunal migration or exchange between these paleoplates during the Llandovery. Evolution of the Stricklandia lineage is significantly different from that of Kulumbella and Sinokulumbella, particularly in that the outer plates disappeared earlier in the kulumbellids than in the stricklandiids.