Ordovician Bivalves Research Articles

New Ordovician bivalves from the Indochina Palaeoplate in Dali, western Yunnan, Southwest China and their palaeogeographic significance

A centre of radiation for Ordovician bivalves is identified based on an abundant and diverse fauna from the Hsiangyang Formation (Darriwilian, Middle Ordovician) of Dali, western Yunnan, Southwest China. It consists of 22 species of 18 genera including 1) one new genus and four new species: Rhomboconcha tresdentes n. gen. n. sp., Fasciculodonta curvata n. sp., Glyptarca symmetrica n. sp., and Paracyclas initium n. sp.; 2) three taxa known from elsewhere but initially found in Dali: Praeleda sp., Glyptarca sp., and Redonia deshayesi; 3) other taxa previously reported by Fang and Cope (2004). Numerical analysis of the distribution of 11 Middle Ordovician bivalve faunas from different regions shows two distinct faunal groups, the HPL group, representing the bivalves that lived in higher palaeolatitudes, and the LPL group (including Australia and South China) in lower palaeolatitudes. The bivalve fauna from Dali correlates with both groups, indicating that the Indochina Palaeoplate was located between these two groups, and in middle–high palaeolatitudes. Thus, the Indochina Palaeoplate was probably an isolated centre for bivalve radiation during the Middle Ordovician; those genera confined to Dali did not then spread to other palaeoplates.

A new pustulose bivalve from the Late Ordovician of the Prague Basin (Czech Republic) and remarks on the diversification of pteriomorphids

The new genus Alena Polechová, Zicha and Rak, with its type species Alena pustulosa nov. gen., nov. sp., is described from the Sandbian Letná Formation of the Prague Basin (Czech Republic) as a new Late Ordovician bivalve with pustules. Alena pustulosa nov. gen., nov. sp. appears to be an endobyssate bivalve based on its functional morphology. It is placed within Cyrtodontida (Pteriomorphia) and included in the diversified Modiolopsis draboviensis Association from the Letná Formation, which comprises eleven bivalve species. The bivalve association from the Letná Formation is formed predominantly by pteriomorphids (now six species out of eleven) and shows that pteriomorphian groups also radiated strongly in shallow-water sands and silts in mid-latitude areas. All main groups of Pteriomorphia are already known from the Early Ordovician and diversified rapidly during the Ordovician. The Gondwana and peri-Gondwana margins with two Early Ordovician radiation centers (Central Australia and Northwestern Argentina) played important roles in their early diversification and dispersion to other palaeocontinents. The function of the sculpture in bivalves is discussed with an emphasis on the Ordovician bivalves. The ornamentation in bivalves serves several purposes such as supporting the stable position of the shell in a substrate, helping in burrowing, strengthening of shell, and protecting against predators. In the Ordovician bivalves, the main function of the sculpture is to stabilise the shell in the substrate.

Late Ordovician molluscs of the central and eastern Anti-Atlas, Morocco

Abstract More than 30 species of tergomyan, gastropod, bivalve and cephalopod molluscs are described from the Late Ordovician of central and eastern Anti-Atlas, Morocco. For the cephalopods this represents the first systematically known taxa of the region. Tergomyans and gastropods are most common in the more shaly part of the Lower Ktaoua Formation, while bivalves are more frequent in the sandy part of the Lower Second Bani Formation. A southern Gondwana aspect is evident for the tergomyan, gastropod and bivalve assemblages, sharing many taxa with Bohemia, while no clear signal is present for the cephalopods. The latter reflects insufficient knowledge of the fauna of large parts of these areas. The widely recognized Holopea ? antiquata is transferred to the genus Radvanospira gen. nov.; other new gastropod taxa include Allossospira gen. nov., Tritonophon grandis sp. nov., Radvanospira baniensis sp. nov. and Lophospira latilabra sp. nov. Most of the diverse bivalve fauna and the few cephalopods are left in open nomenclature but new taxa include the bivalve Praenucula pojetai sp. nov. and the cephalopods Wadema tattai sp. nov. and Tafadnatoceras tiouririnense gen. et. sp. nov. The Late Ordovician bivalves from Morocco are dominated by pteriomorphs and protobranchs, inhabiting infaunal, semi-infaunal and epifaunal niches.

Burrowers from the Past: Mitochondrial Signatures of Ordovician Bivalve Infaunalization

Bivalves and gastropods are the two largest classes of extant molluscs. Despite sharing a huge number of features, they do not share a key ecological one: gastropods are essentially epibenthic, although most bivalves are infaunal. However, this is not the ancestral bivalve condition; Cambrian forms were surface crawlers and only during the Ordovician a fundamental infaunalization process took place, leading to bivalves as we currently know them. This major ecological shift is linked to the exposure to a different redox environoments (hypoxic or anoxic) and with the Lower Devonian oxygenation event. We investigated selective signatures on bivalve and gastropod mitochondrial genomes with respect to a time calibrated mitochondrial phylogeny by means of dN/dS ratios. We were able to detect 1) a major signal of directional selection between the Ordovician and the Lower Devonian for bivalve mitochondrial Complex I, and 2) an overall higher directional selective pressure on bivalve Complex V with respect to gastropods. These and other minor dN/dS patterns and timings are discussed, showing that the Ordovician infaunalization event left heavy traces in bivalve mitochondrial genomes.

A new Middle Ordovician bivalve–siliceous sponge–microbe reef-building consortium from North China

A new reef-building consortium from a Middle Ordovician succession of the western North China Platform is described, consisting mainly of bivalves, siliceous sponges, and microbial carbonates (Epiphyton-like, Renalcis-like and Girvanella calcified microbes, and microcrystalline microstromatolites), in addition to minor brachiopods, Amsassia and Rhabdotetradium. The bivalves are thin-walled and mostly articulated, indicating in situ preservation. The siliceous sponges are characterized by regularly spaced spicule networks embedded within micrite, which partly grade into peloidal textures. Three main types of bivalve–sponge associations are found: (1) larger bivalves (2–13mm) encrusted by sponges, (2) sponges occupying internal spaces of larger bivalves, and (3) smaller (0.2–0.4mm) bivalves embedded within sponge spicule networks. Microbial carbonates either cover the upper surfaces of siliceous sponges and bivalves, or occur independently as centimeter-scale patches. The reefal boundstones were constructed mainly by bivalves, siliceous sponges and microbes, which were subsequently encrusted and stabilized by additional sponges and microbes. Extensive early marine cementation forming fibrous cement helped stabilize the reef framework. The co-occurrence of bivalves and siliceous sponges is possibly analogous to modern-day counterparts in which sponges encrust bivalves or bivalves are living within sponges, suggesting a symbiotic relationship. The bivalve–siliceous sponge–microbial reefs of this study, together with other Ordovician reefs, represent the changeover from microbial- to skeletal-dominated reefs during the Middle Ordovician. The current example may represent an ancestral association of bivalve–siliceous sponge–microbe reefs, similar to those in the Mesozoic and Cenozoic, thus shedding light on the roots of such associations.

Distribution and palaeoecology of Ordovician bivalves and gastropods from Girvan, SW Scotland

ABSTRACTMolluscs from the Middle and Upper Ordovician succession of Girvan, SW Scotland are common and diverse in some localities. The mollusc fauna consists mainly of gastropods, bivalves and various univalved molluscs (mimospirids and tergomyans), along with scarcer polyplacophorans, rostroconchs and cephalopods. The present study gives an overview of the distribution and palaeoecology of bivalves, gastropods and univalved molluscs and compares them with mollusc faunas worldwide. Gastropods, mimospirids and tergomyans are present from the Darriwilian (mid Llanvirn) onwards in both siliciclastic and carbonate facies, and increase in diversity through the Sandbian (Caradoc) and into the Katian (Ashgill). Bivalves first appeared in Girvan in the late Darriwilian (early Caradoc) in deep water siliciclastic facies; where they continued to be more abundant and diverse than in equivalent carbonate facies. Molluscs are initially Laurentian in aspect, though peri-Gondwanan faunal elements occur, particularly during the Sandbian. The pattern of bivalve and gastropod diversity found in the Ordovician of Girvan generally follows that of the known global diversity for these groups.

Paleolongitudinal estimates for paleocontinents derived from interplate distances based on Late Ordovician bivalves

The geographic distribution of 293 Modern bivalve genera has been analyzed and found to be statistically correlated with distance. In particular, a least-squares regression analysis of the data indicates that the distance between faunal realms (D) in kilometers can be estimated using the equation D = (ln(d) + 0.4233)/−0.00013, where d is the Dice coefficient of faunal similarity. Analysis of 59 genera of Late Ordovician bivalves indicates that the above equation also describes their biogeographic distribution.Using this formula, the distance between Laurentia and Scotland/Northwest Ireland was estimated to be 5500 kilometers. This is consistent with the reconstruction of a connection among these areas during the Late Ordovician based on brachiopod and graptolite biogeographic data.Paleomagnetic and paleoclimatic data also suggest that Avalonia, Baltica, and Laurentia were at tropical latitudes. Distances between these paleocontinents can therefore be used to estimate paleolongitudes. If the location of England on the eastern side of Avalonia is used as zero degrees paleolongitude for the Late Ordovician as it is today, the paleolongitude for South America, Laurentia, Scotland and northwest Ireland, and Baltica would be 125°W, 45°W, 10°W, and 15°E, respectively. Because of drifting of the Avalonia plate, these paleolongitudes probably do not coincide with the longitudinal grid used today. The paleolongitudes indicate only the relative spacing between continents in the past. The methodology in this study should be useful for improving the accuracy of paleogeographic reconstructions for the Late Ordovician throughout the Cenozoic, and especially the Paleozoic periods for which magnetic seafloor anomaly data are not available.

Uppermost Ordovician bivalves from the Prague Basin (Hirnantian, Perunica, Bohemia)

Uppermost Ordovician bivalves from the Prague Basin (Hirnantian, Perunica, Bohemia)

Affinities and palaeobiogeographical significance of some Ordovician bivalves from East Yunnan, China

The four poorly known Ordovician bivalve genera erected by Guo (1988) from the Lower Ordovician (Floian) Hongshiya Formation of East Yunnan, China are redescribed, based on a re-examination of the type material, and their taxonomic position is clarified. This paper places the four genera in the superfamily Cycloconchoidea. Reinterpretation of the hinge structure of Baidiostraca allows us to recognize it as a cycloconchoid rather than a myophorid; the new family Baidiostracidae is proposed. Zhenxiongella gen. nov. is described based on Taselasmodum septatum Guo, 1988, because this species differs significantly from the type species Taselasmodum decussatum Guo, 1985. These two genera differ fundamentally from other cycloconchids in possession of a strong posterior internal septum in each valve and a pedal retractor scar at the posterior of the hinge-plate; they are included in the new subfamily Taselasmodinae. The poorly understood family Nyassidae Hall, 1885 is enlarged and discussed herein; it seems that this family forms a unique lineage in the Cycloconchoidea. Zadimerodiidae Guo, 1988 is a junior subjective synonym of Nyassidae Hall, 1885. On the basis of the bivalve faunas, East Yunnan was sufficiently far from West Yunnan to prevent interchange of most species, although one species is common to both plates. On the other hand, a common genus and the similarities between two cycloconchids suggest proximity of East Yunnan and Australia, although these regions have no species in common. New information on the duplivincular ligament of glyptarcids allows these to be classified with the superorder Pteriomorphia, rather than the Heteroconchia, as previously proposed. The comparisons between the eastern West Yunnan fauna and those of Western Europe, where glyptarcids are also important members of the fauna, suggest that the eastern West Yunnan fauna lay at a much higher palaeolatitude than the East Yunnan fauna.

An introduction to Ordovician bivalves of southern China, with a discussion of the early evolution of the Bivalvia

AbstractThis paper introduces the Ordovician bivalves of southern China to non‐Chinese colleagues, and then incorporates them into the global Ordovician bivalve database compiled by Cope (2004). This will provide a firmer basis for the discussion of the initial adaptive radiation of the Bivalvia. A new scenario for the early evolution of the class Bivalvia is advanced herein based on the integration of a wide variety of evidence concerning bivalves, including morphological features, ontogenetic trajectory, benthic environment and lithologic setting, so as to explain reasonably why the initial explosive radiation of bivalves in the Early Ordovician followed a long‐term macroevolutionary lag since their first appearance during the Cambrian explosion. The early evolution of the Bivalvia can be divided into three phases: (a) the origination and macroevolutionary lag phase in the Early and Middle Cambrian; (b) the crisis phase in the Late Cambrian; and (c) the Ordovician radiation phase, which can be subdivided into two radiation pulses or intervals (the Arenig and the Caradoc radiation intervals). It is the Cambrian substrate revolution that caused a transformation of shallow subtidal seafloors from more coherent Neoproterozoic‐style matgrounds to soupier Phanerozoic‐style mixgrounds, thus compelling Cambrian ‘archetype’ bivalves to sink into the infaunal realm and to adapt themselves to the development of the mixed layer in siliciclastic soft substrate environments. As a result, Cambrian ‘archetype’ bivalves entered a tight bottleneck and became extinct while the latest common ancestor of ‘modern‐type’ bivalves originated from a certain founder population somewhere in the Gondwanan shelf seas. The rapidly evolving founder population may be the place of origin of evolutionary novelties and it became the starting point of the evolution of ‘modern‐type’ bivalves. The macroevolutionary lag of the Bivalvia ended in the earliest Ordovician as a result of the successful invasion of the infaunal adaptive zone. The bivalve die of ‘modern‐type’ was cast during the Ordovician, when all principal clades and all four principal life‐habit groups underwent initial development. A series of morphological innovations, especially the evolution of the muscular hydraulic foot with burrowing adaptations, byssus, and feeding gill, are responsible for the initial adaptive radiation. It is these morphological innovations that provide evolutionary access to the new adaptive zone for bivalves. Copyright © 2006 John Wiley & Sons, Ltd.

NEW BIVALVIA AND ROSTROCONCHIA FROM THE EARLY ORDOVICIAN (LATE TREMADOC–MIDDLE ARENIG) OF NORTHWESTERN ARGENTINA

Abstract New species of Early Ordovician bivalves and rostroconchs from the northwestern Argentina basin are described. Bivalves include the following species: Cienagomya bidentata new genus and species, Goniophorina tenuicostata, Lipanella purmamarcensis new genus and species, Ucumaropsis lermaensis new genus and species, and Coxiconchia babini new species. Among rostroconchs, Ribeiria pojetai new species is recognized. Cienagomya bidentata (late Tremadoc–early Arenig) may represent a phylogenetic link between the families Intihuarellidae and Cycloconchidae. The new family Lipanellidae is erected to include Lipanella n. gen. Recognition of Ucumaropsis n. gen. in the early Arenig attests to the important radiation of the Anomalodesmata in northwestern Argentina.

Early Ordovician bivalves from Dali, West Yunnan, China

A bivalve fauna of Early Ordovician (late Arenig) age is described from the Hsiangyang Formation of the eastern part of West Yunnan, China. The fauna contains elements in common with Early Ordovician faunas of southern Gondwanan areas such as the Montagne Noire and Morocco and with those of Avalonia, together with several previously undescribed taxa. The following taxa are new: Biseriodonta simplex gen. et sp. nov.; Glyptarca sinensis sp. nov.; Trigonoglyptarca magna gen. et sp. nov.; Erhaiconcha xiangyangensis gen. et sp. nov.; Fasciculodonta impressa gen. et sp. nov.; Yunnanoredonia laevis gen. et sp. nov.; Daliella gen. nov.; Goniophorina (Goniophorina) contracta sp. nov.; Haidongoconcha radialis gen. et sp. nov.; Eopterinea aequiconcha gen. et sp. nov. The bivalve fauna includes the most diverse glyptarcid fauna and the earliest nuculanid and paracyclid known hitherto. Eastern West Yunnan belonged to the Indochina terrane and it is concluded that the bivalve fauna represents a high‐latitude assemblage and that the Indochina terrane should be considered a component part of the Peri‐Gondwanan continent in the Ordovician; its bivalve faunas contrast with those of neighbouring terranes which have affinities with those of lower latitudes.

The bivalve Ambonychia in the Ordovician of New Zealand

A new bivalve species, Ambonychia hailesensis (Ambonychiacea: Ambonychiidae), is described from a boulder of Arthur Marble (Late Ordovician), Hailes Knob, northwest Nelson, South Island, New Zealand. The species is the first record of an Ordovician bivalve from New Zealand and the only confirmed Ambonychia presently known from Australasia. The occurrence of Ambonychia in Gondwanaland shelf seas may be explained by oceanic migration. It is suggested that although morphological affinities exist with North American and European specimens, specific differences in the New Zealand species probably resulted from isolation and consequental divergent evolution.

Middle Ordovician bivalves from Mid‐Wales and the Welsh Borderland

Middle Ordovician bivalves from Mid‐Wales and the Welsh Borderland

Diversification of bivalvesin the Ordovician

The Ordovician was the most significant Period in bivalve diversification. From a small Cambrianstock of palaeotaxodonts, the most fundamental radiation occurred in the early Ordovician. An intrinsic factor was the most significant, involving the evolution of the feeding gill within the palaeotaxodonts. This fundamental morphological change allowed development of more effective feeding strategies, permitting bivalves to take advantage of the increased Ordovician nutrient supply. This allowed rapid size increase and diversification, and colonization of a variety of habitats from entirely infaunal into semi-infaunal and epifaunal. By the end of the early Ordovician, seventeen families belonging to six subclasses have hitherto been recognised. Early Ordovician bivalves are restricted to peri-Gondwanan shelves and favoured inshore clastic sedimentary environments; it was not until the mid Ordovician that bivalves were able to migrate to other continents, but initially remained largely confined to nearshore clastic facies. The succeeding late Ordovician radiation was largely driven by extrinsic factors, as the development of low-latitude carbonate platforms promoted the evolution of many epifaunal groups, particularly the modiomorphoids and the pteriomorphians — the latter often characterized by a calcitic outer shell layer.

Early Ordovician Bivalve Radiations and Their Cause

Early Ordovician Bivalve Radiations and Their Cause

Transitional Ordovician Bivalve with Both Monoplacophoran and Lucinacean Affinities

The rare and problematic Ordovician molluscan genus Babinka is a probable evolutionary link between the bivalve superfamily Lucinacea and some monoplacophora-like ancestral mollusc. Babinka provides the first direct evidence of a transition between the class Bivalvia and more primitive molluscan ancestors.