Jiayu Rong

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

Comparative analysis of the end-Permian and end-Ordovician brachiopod mass extinctions and survivals in South China

Abstract A comparative study of the pattern of brachiopod extinction, survival and recovery in the end-Ordovician and end-Permian mass extinctions reveals a variety of patterns, magnitudes and intensities in South China. The presence of many survivors and the absence of any ordinal extinction of brachiopods across the Ordovician–Silurian transition indicates a close taxonomic and ecological relationship of pre- and post-extinction brachiopod associations. Brachiopods recovered rapidly in Late Rhuddanian (Early Silurian) after a short survival period. The taxonomic composition, biodiversity and ecological levels in the radiation period largely mirror those prior to the end-Ordovician extinction. In contrast, elimination of four major brachiopod orders, 20 superfamilies and almost all Permian-type genera after a short survival interval in the early Griesbachian and the absence of survival, Lazarus and progenitor genera suggest a great revolutionary turnover between Late Permian and Triassic brachiopod associations. Brachiopods underwent a long bleak interval from late Griesbachian to the beginning of the Middle Triassic. The brachiopod groups in the Anisian (Middle Triassic) recovery–radiation period are taxonomically linked to those in the Permian only at family or higher levels. Therefore, the taxonomic and paleoecological effects of the end-Ordovician extinction were of a lesser magnitude than for the end-Permian extinction of Brachiopoda in South China.

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.

The earliest known Stegerhynchus (Rhynchonellida, Brachiopoda) from the Hirnantian strata (uppermost Ordovician) at Borenshult, Östergötland, Sweden

Abstract Stegerhynchus eoborealis sp. nov. from the Dalmanitina Beds (Hirnantian, uppermost Ordovician), Borenshult, Östergötland, Sweden, is described in this study as the earliest known species of Stegerhynchus, within the family Rhynchotrematidae. This implies that Stegerhynchus originated during the latest Ordovician mass extinction event, and radiated in the Silurian Period to become one of most common rhynchonellide brachiopod genera in shallow tropical seas. In the early evolutionary stage of the genus, Stegerhynchus eoborealis already exhibited a notable reduction in the size of septalium compared to the closely related genus Rhynchotrema. Compared to its Silurian counterparts (e.g. Stegerhynchus borealis and S. peneborealis), Stegerhynchus eoborealis has some variable characters within single populations, particularly in the number of costae in the sulcus and on the fold, implying a morphological plasticity during the early evolutionary stage of the genus. During the Hirnantian mass extinction events, five rhynchonellide families were represented by small taxonomic groups, but only the Rhynchotrematidae and Trigonirhynchiidae diversified into many highly successful clades of rhynchonellides during the Silurian and Devonian. However, the Ancistrorhynchidae, Orthorhynchulidae, and Sphenotretidae largely disappeared by the end of the Ordovician, with a few species (such as Plectothyrella sp.) surviving into the earliest Silurian but shortly becoming extinct.

A New Survivor Species of Dicoelosia (Brachiopoda) from Rhuddanian (Silurian) Shallower-Water Biofacies in South China

Abstract The brachiopod genus Dicoelosia is generally considered a typical deep-water taxon. New data suggest that some species of the genus may have invaded relatively shallow-water habitats during its geological history. However, there is scant evidence for its invasion of shallow-water environments after the terminal Ordovician mass extinction. Dicoelosia occurs in the shallower-water benthic shelly assemblages of the lower Niuchang Formation (upper Rhuddanian, Llandovery) of Meitan County, northern Guizhou Province, South China. Evidence of a move to shallow water includes its morphology and population structure, regional paleogeography, sedimentology, together with the abundance and diversity of its shallow-water associates. Following the biotic crisis, deep-water environments were barely habitable, and may have driven Dicoelosia into shallower-water niches. The taxon endured the less suitable shallow-water environments until the deep-water benthic zones ameliorated after the recovery, implying a sha...

A new early Silurian brachiopod genus, Thulatrypa, from Norway and South China, and its palaeobiogeographical significance

Huang, B., Baarli, B.G., Zhan, R.B. & Rong, J.Y., October 2015. A new early Silurian brachiopod genus, Thulatrypa, from Norway and South China, and its palaeobiogeographical significance. Alcheringa 40, xxx–xxx. ISSN 0311-5518. The smooth atrypoid brachiopod Thulatrypa gen. nov. incorporates two species, a younger (T. gregaria) from Norway, and an older (T. orientalis) from South China, which collectively span the middle Rhuddanian through Aeronian. In Baltica, the genus thrived just below the storm wave base in a tropical BA4 setting extending slightly into BA3 and BA5 respectively, whereas in South China, its representative occurs in a much shallower assemblage (BA2–3). Their palaeobiogeographical implications are carefully investigated. This study supports the arguments that Thulatrypa may have originated in South China in the middle Rhuddanian and extended its range to eastern Baltica in the late Rhuddanian. Larvae may have drifted along a channel from the east to the southwest of Baltica, which supports the reconstructions of palaeocurrents in the early Silurian in previous palaeogeographical studies. Bing Huang [bhuang@nigpas.ac.cn], Ren-bin Zhan [rbzhan@nigpas.ac.cn] and Jia-yu Rong [jyrong@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing, 210008, PR China; B. Gudveig Baarli [gudveig.baarli@williams.edu], Department of Geosciences, Williams College, Williamstown, MA 01267, USA.