Crinoid Diversity Research Articles

Substrate type and palaeodepth do not affect the Middle Jurassic taxonomic diversity of crinoids

Crinoids are largely considered as good indicators for determining environmental conditions. They are robust proxies for inferring changes in salinity and sedimentation rate and for inferring substrate type. Some crinoid groups (e.g., certain comatulids, cyrtocrinids, millericrinids) have a depth preference, thus, making them useful for palaeodepth estimation. The hypotheses that crinoid distribution is substrate-dependent (rock type) or palaeodepth-dependent is tested here based on (a) archival Bathonian-Callovian (Middle Jurassic) crinoid occurrences from Poland and (b) newer finds from five boreholes from eastern Poland. Qualitative data suggests that isocrinids and cyclocrinids occur in both carbonate and siliciclastic rocks. The cyrtocrinids and roveacrinids occur within carbonate rocks, whereas the comatulids are exclusive to siliciclastics. In terms of palaeodepth, most crinoid groups dominate in shallow environments with the sole exception of cyrtocrinids, that are ubiquitous and occur in both shallow (near shore and shallow marine) and slightly deeper (deeper sublittoral to open shelf) settings. The occurrences of the cosmopolitan taxa, Chariocrinus andreae and Balanocrinus subteres (isocrinids), is independent of both substrate type and palaeodepth. Quantitative analyses (Analysis Of Variance; ANOVA) based on substrate type, i.e., substrate-dependency (claystones, sandstones and limestones), and palaeodepth i.e., palaeodepth-dependency (near shore, shallow-marine, mid-ramp and offshore), corroborate qualitative results. Statistical analysis suggest that the distribution of crinoids shows a strong substrate-dependency but not for palaeodepth, although very weak significance (low p value) is noted for near shore and shallow marine settings and crinoid distribution.

Inventory of the specimens of the Class Crinoidea (Echinodermata) deposited at the Invertebrates collection at the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”

The invertebrate collection of the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (MACN-In) is one of the most important in Latin America. It has more than 1411 type batches with ~90 type specimens of echinoderms. For the present study we analyzed 56 lots of crinoids from the MACN-In. We also checked and updated the identification, when necessary. Seven species belonging to 6 genera were identified; 23 specimens remain unidentified. The diversity of crinoids for Chile, Uruguay and Brazil and Antarctica is discussed. The MACN-In has several lots of crinoids from different parts of the world and numerous specimens of the 2 representative species from Argentina, Isometra vivipara Mortensen, 1917 and Phrixometra nutrix (Mortensen, 1918). This is the first published inventory of crinoids from samples deposited at the MACN-In collection, which will be a useful tool for future studies regarding echinoderms, particularly crinoids.

Crinoid diversity and their symbiotic communities at Bangka Island (North Sulawesi, Indonesia)

Members of the order Comatulida (Echinodermata: Crinoidea) are widely distributed on Indo-Pacific reefs, where they host a highly diverse and understudied cryptofauna, which makes them a potential source of hidden biodiversity. In this study, shallow-water crinoid populations and their symbiotic communities from the Bangka Archipelago (North Sulawesi, Indonesia) were investigated. Presence and diversity of the symbionts, focusing on their host selectivity patterns, were assessed. A total of 39 comatulid species belonging to six families were found. Overall, symbiont fauna included 70 species belonging to 11 families within eight orders. The results showed variable host specificity among symbionts’ families, and patterns correlated with host size for some symbiont taxa. This study provides the first baseline dataset of crinoid assemblages and their symbiont diversity in the understudied region of North Sulawesi, within the Coral Triangle.

Phylogeny and evolutionary history of diplobathrid crinoids (Echinodermata)

AbstractOrder Diplobathrida is a major clade of camerate crinoids spanning the Ordovician–Mississippian, yet phylogenetic relationships have only been inferred for Ordovician taxa. This has hampered efforts to construct a comprehensive tree of life for crinoids and develop a classification scheme that adequately reflects diplobathrid evolutionary history. Here, I apply maximum parsimony and Bayesian phylogenetic approaches to the fossil record of diplobathrids to infer the largest tree of fossil crinoids to date, with over 100 genera included. Recovered trees provide a framework for evaluating the current classification of diplobathrids. Notably, previous suborder divisions are not supported, and superfamily divisions will require significant modification. Although numerous revisions are required for families, most can be retained through reassignment of genera. In addition, recovered trees were used to produce phylogeny‐based estimates of diplobathrid lineage diversity. By accounting for ghost lineages, phylogeny‐based richness estimates offer greater insight into diversification and extinction dynamics than traditional taxonomy‐based approaches alone and provide a detailed summary of the ~150 million‐year evolutionary history of Diplobathrida. This study constitutes a major step toward producing a phylogeny of the Crinoidea and documenting crinoid diversity dynamics. In addition, it will serve as a framework for subsequent phylogeny‐based investigations of macroevolutionary questions.

Testing reduced evolutionary rates during the Late Palaeozoic Ice Age using the crinoid fossil record

In 2003, Stanley & Powell reported depressed rates of origination and extinction in marine invertebrates during the Late Palaeozoic Ice Age (LPIA). Using a database of crinoid genera, rates of origination, extinction and genus duration were calculated at the stage level from the Early Devonian to the Late Permian. This 165 m.y. time span includes non-glacial intervals before and after the LPIA, which spanned the Serpukhovian to Sakmarian, providing background rates for comparison. Data generated on crinoid evolutionary rates during the Middle to Late Palaeozoic were analysed and compared to Stanley & Powell's data to determine whether crinoid evolutionary patterns support their findings or suggest an alternative hypothesis. Rates of origination and extinction in all crinoid clades were reduced during the LPIA compared to the combined background intervals before and after the LPIA. However, crinoid diversity was higher during the LPIA than the surrounding time intervals. The difference in diversity trends between crinoids and other marine invertebrates is due to the advanced cladids clade. Unstable, fluctuating environmental conditions during the LPIA may have created habitats suitable for opportunistic crinoid genera that reduced both the probability of origination and extinction. The increased diversity of the advanced cladids is likely due to their unique adaptation of muscular arm articulations, which allowed them to thrive in marine settings with increased siliciclastic influx brought on by the Alleghenian orogeny. Despite the advanced cladids’ departure from the expected diversity count, the results of analyses performed on the updated crinoid database provide independent confirmation of Stanley & Powell's original hypothesis of depressed evolutionary rates in marine invertebrates during the LPIA.

Filling the Gondwanan gap: paleobiogeographic implications of new crinoids from the Castillejo and Fombuena formations (Middle and Upper Ordovician, Iberian Chains, Spain)

AbstractA diverse crinoid fauna is described from the Upper Ordovician (Katian) Fombuena Formation from the eastern Iberian Chains of Spain. New crinoids include the diplobathrid cameratesFombuenacrinus nodulusn. gen. n. sp.,Goyacrinus gutierrezin. gen. n. sp.,Dalicrinus hammannin. gen. n. sp., andAmbonacrinus decorusn. gen. n. sp.; the monobathrid camerateEopatelliocrinus hispaniensisn. sp.; and the cladidPicassocrinus villasin. gen. n. sp. A new occurrence ofHeviacrinus melendeziGil Cid, Domínguez Alonso, and Silván Pobes, 1996 is also documented from the Castillejo Formation (Darriwilian, Middle Ordovician) from the eastern Iberian Chains of Spain. The Fombuena Formation comprises a Gondwanan crinoid assemblage from a high paleolatitude and has the highest crinoid diversity of any currently known Katian Gondwanan fauna. This assemblage is compared to other Katian age faunas around the globe, and its paleobiogeographic implications are discussed.

Biodiversity of Mississippian (Lower Carboniferous) crinoids from Bradford Dale, Derbyshire, UK

Crinoid diversity and abundance was higher during the Early Carboniferous (Mississippian) than at any other time. Due to the systematic focus on more complete specimens of crinoids, some areas, like the White Peak of Derbyshire and Staffordshire, UK, have erroneously been considered poor in fossil crinoids. Indeed, cups and crowns have only rarely been found in this area, but many limestones and cherts from the White Peak are rich in disarticulated crinoid remains. Screwstones (=fossiliferous cherts) collected in Bradford Dale, Derbyshire, yielded the disarticulated stem fragments, preserved as natural moulds, of seven crinoid morphotaxa, which is more than half of the known species richness of the whole White Peak. Considering that the material studied herein came from one locality, it is thus probable that the diversity of Mississippian crinoids in the White Peak is somewhat higher than previously recognized. This study shows that disarticulated stem fragments can be used as a proxy to test the crinoid diversity of an area, and that with further study of not only cups and crowns, some areas preserve a diversity of crinoids that is more than previously known.

Diversity dynamics of post-Palaeozoic crinoids – in quest of the factors affecting crinoid macroevolution

Following the end-Permian biotic crisis which led to the near extinction of crinoids, this echinoderm class rebounded rapidly during the Mesozoic, resulting in forms with important morphological and behavioural novelties. However, quantitative patterns of crinoid diversity during the Mesozoic remain largely unexplored. Here, we report results of analyses of the evolutionary dynamics of post-Palaeozoic crinoid genera spanning a time interval between 250 and 70 Myr. We show that crinoids reached their Mesozoic peak of genus-level richness during the Late Jurassic. We also document a major reorganization of different ecological crinoid groups in the Mesozoic. More specifically, the diversity of sessile forms generally increased towards the mid-Mesozoic but decreased significantly starting in the Cretaceous, whereas the number of motile crinoid genera increased linearly during the Mesozoic. The possible role of biotic and abiotic factors in crinoid evolution is discussed.

The oldest post-Palaeozoic Crinoid and Permian-Triassic origins of the Articulata (Echinodermata).

The Crinoidea are the most primitive class of living echinoderms, and suffered a severe crisis during the Late Permian mass extinction event. All post-Palaeozoic crinoids, including living species, belong to the Articulata, and morphological and recent molecular studies demonstrate that they form a monophyletic clade. The Articulata originated from Palaeozoic cladid crinoids, but the nature and timing of their origination remains obscure. Problems with understanding the origin and early evolution of the Articulata have arisen because the Permian-Triassic crinoid fossil record is particularly poor. We report on a new genus and species from the earliest Triassic, which is the oldest known post-Palaeozoic articulate crinoid and fundamentally alters our understanding of the early evolution of the Articulata. Prior to this study, the most primitive post-Palaeozoic articulate was thought to be Holocrinus of the order Isocrinida. Unexpectedly, the new taxon belongs to the order Encrinida, which reveals a previously hidden diversity of crinoids in the earliest Triassic. Its discovery implies either a dramatic radiation of crinoids in the immediate post-extinction aftermath, when environmental conditions were at their most severe, or a pre-extinction origin of the crown group articulates and survival of multiple lineages.

Circumpolar dataset of sequenced specimens of Promachocrinus kerguelensis (Echinodermata, Crinoidea)

This circumpolar dataset of the comatulid (Echinodermata: Crinoidea) Promachocrinus kerguelensis (Carpenter, 1888) from the Southern Ocean, documents biodiversity associated with the specimens sequenced in Hemery et al. (2012). The aim of Hemery et al. (2012) paper was to use phylogeographic and phylogenetic tools to assess the genetic diversity, demographic history and evolutionary relationships of this very common and abundant comatulid, in the context of the glacial history of the Antarctic and Sub-Antarctic shelves (Thatje et al. 2005, 2008). Over one thousand three hundred specimens (1307) used in this study were collected during seventeen cruises from 1996 to 2010, in eight regions of the Southern Ocean: Kerguelen Plateau, Davis Sea, Dumont d’Urville Sea, Ross Sea, Amundsen Sea, West Antarctic Peninsula, East Weddell Sea and Scotia Arc including the tip of the Antarctic Peninsula and the Bransfield Strait. We give here the metadata of this dataset, which lists sampling sources (cruise ID, ship name, sampling date, sampling gear), sampling sites (station, geographic coordinates, depth) and genetic data (phylogroup, haplotype, sequence ID) for each of the 1307 specimens. The identification of the specimens was controlled by an expert taxonomist specialist of crinoids (Marc Eléaume, Muséum national d’Histoire naturelle, Paris) and all the COI sequences were matched against those available on the Barcode of Life Data System (BOLD: http://www.boldsystems.org/index.php/IDS_OpenIdEngine). This dataset can be used by studies dealing with, among other interests, Antarctic and/or crinoid diversity (species richness, distribution patterns), biogeography or habitat / ecological niche modeling. This dataset is accessible through the GBIF network at http://ipt.biodiversity.aq/resource.do?r=proke.

Camerate crinoids from the Nunn Member (Tournaisian, Osagean) of the Lower Mississippian Lake Valley Formation, New Mexico

The Nunn Member (early Osagean) of the Lake Valley Formation of New Mexico is known for its abundance and diversity of crinoids. Although crinoids were first reported in the late 1800s, no comprehensive study of the crinoids has been conducted and a complete list of the crinoid taxa does not exist. All subclasses of crinoids occur in the Lake Valley, but the camerates are by far the dominant group. Study of the Macurda collection from the University of Michigan, the Laudon collection from the University of New Mexico, and new collections provided more than 7000 specimens, 4,500 of which were identifiable camerates. Sixty-one species of camerates are recognized in the Nunn Member, including five new species: Blairocrinus macurdai, Iotacrinus novamexicanus, Agaricocrinus alamogordoensis, Uperocrinus kuesi, and Collicrinus laudoni. This camerate fauna is very similar to that of the lower Burlington Limestone of the Mississippi Valley. An update of the crinoid taxa in the Lake Valley Formation allows for a better understanding of the temporal and geographic relationships of crinoid faunas across North American during the Early Mississippian when camerates were at their global diversity maximum. The majority of the camerates come from the western New Mexico outcrops where the Nunn Member is thicker and the marine shelf was shallower, but several also occur in association with the deep-water Waulsortian mounds.

<p><strong>Crinoid diversity in the Upper Cretaceous Yezo Supergroup, Hokkaido, northern Japan*</strong></p>

New data, principally from ‘local’ encrinites in the Yezo Supergroup of Hokkaido, northern Japan, suggest that many relict ‘Jurassic-type faunas’ identified in Europe and central Japan might have persisted in the Late Cretaceous deep-water (> 100 m) muddy sandstone facies found throughout the island of Hokkaido. For example, Isocrinus and Balanocrinus occur in the outer shelf sandy mudstone facies of the Turonian-Coniacian Saku Formation and the Coniacian- Campanian Haborogawa Formation, of the Mikasa area (central Hokkaido), respectively. Isocrinus is also found in the Turonian-Coniacian deep-water siltstones and sandy siltstones of the Nishi-chirashinai Formation of the Nakagawa area (northern Hokkaido). In contrast, Isselicrinus, which belongs to ‘Late Cretaceous type-faunas’, occurs in the uppermost Creta­ceous (Campanian) outer shelf mudstone facies of the Upper Yezo Supergroup around Hobetsu (south-central Hokkaido). Although collections of crinoids from the chalks of northern Europe are themselves largely free from sampling biases, Cretaceous crinoid diversity data have been markedly influenced by fossils preserved in the relatively homogeneous chalk facies where the faunal differences between the deep-water Danish, English and north German chalks (> 250 m) and the shallow-water facies found around Maastricht, the Netherlands (< 50 m) are slight. The results of this preliminary report on the crinoid faunas of Hokkaido suggest that global crinoid diversity reported from the Upper Cretaceous might be influenced by sampling and facies biases.

Fixed, free, and fixed: The fickle phylogeny of extant Crinoidea (Echinodermata) and their Permian–Triassic origin

Although the status of Crinoidea (sea lilies and featherstars) as sister group to all other living echinoderms is well-established, relationships among crinoids, particularly extant forms, are debated. All living species are currently placed in Articulata, which is generally accepted as the only crinoid group to survive the Permian–Triassic extinction event. Recent classifications have recognized five major extant taxa: Isocrinida, Hyocrinida, Bourgueticrinina, Comatulidina and Cyrtocrinida, plus several smaller groups with uncertain taxonomic status, e.g., Guillecrinus, Proisocrinus and Caledonicrinus. Here we infer the phylogeny of extant Crinoidea using three mitochondrial genes and two nuclear genes from 59 crinoid terminals that span the majority of extant crinoid diversity. Although there is poor support for some of the more basal nodes, and some tree topologies varied with the data used and mode of analysis, we obtain several robust results. Cyrtocrinida, Hyocrinida, Isocrinida are all recovered as clades, but two stalked crinoid groups, Bourgueticrinina and Guillecrinina, nest among the featherstars, lending support to an argument that they are paedomorphic forms. Hence, they are reduced to families within Comatulida. Proisocrinus is clearly shown to be part of Isocrinida, and Caledonicrinus may not be a bourgueticrinid. Among comatulids, tree topologies show little congruence with current taxonomy, indicating that much systematic revision is required. Relaxed molecular clock analyses with eight fossil calibration points recover Articulata with a median date to the most recent common ancestor at 231–252mya in the Middle to Upper Triassic. These analyses tend to support the hypothesis that the group is a radiation from a small clade that passed through the Permian–Triassic extinction event rather than several lineages that survived. Our tree topologies show various scenarios for the evolution of stalks and cirri in Articulata, so it is clear that further data and taxon sampling are needed to recover a more robust phylogeny of the group.

Predator-induced macroevolutionary trends in Mesozoic crinoids

Sea urchins are a major component of recent marine communities where they exert a key role as grazers and benthic predators. However, their impact on past marine organisms, such as crinoids, is hard to infer in the fossil record. Analysis of bite mark frequencies on crinoid columnals and comprehensive genus-level diversity data provide unique insights into the importance of sea urchin predation through geologic time. These data show that over the Mesozoic, predation intensity on crinoids, as measured by bite mark frequencies on columnals, changed in step with diversity of sea urchins. Moreover, Mesozoic diversity changes in the predatory sea urchins show a positive correlation with diversity of motile crinoids and a negative correlation with diversity of sessile crinoids, consistent with a crinoid motility representing an effective escape strategy. We contend that the Mesozoic diversity history of crinoids likely represents a macroevolutionary response to changes in sea urchin predation pressure and that it may have set the stage for the recent pattern of crinoid diversity in which motile forms greatly predominate and sessile forms are restricted to deep-water refugia.

Assessment of hidden diversity of crinoids and their symbionts in the Bay of Nhatrang, Vietnam

Crinoid associates represent an abundant and diverse, but poorly explored, component of the hidden biodiversity of coral-reef ecosystems. We studied data from 5 years of collecting in the Bay of Nhatrang (BN), Vietnam, to assess the diversity of crinoids and their symbionts, to compare it with other areas of the Indo-West Pacific, and to elucidate the extent to which the observed diversity of crinoids and their symbionts corresponds to their true diversity. In total, about 2,287 specimens of symbionts belonging to 70 species were found on 203 specimens of crinoids belonging to 33 species. Among the crinoids, the most numerous species were Himerometra robustipinna (36 specimens) and Cenometra bella (29 specimens), among the symbionts the polychaete Paradyte crinoidicola (c. 850 specimens) and the galatheid crustacean Allogalathea elegans (180 specimens). Species accumulation curves suggest that we have sampled most of the crinoid diversity in the BN, whereas the diversity of their symbionts remained undersampled. Estimated species richness of crinoids was higher than previously observed richness, and varied from 39 (estimated by bootstrap) to 46 (jackknife 2). Estimated species richness of symbionts was higher than observed richness, and varied from 71 (bootstrap) to 93 (jackknife 2). We suggest a slight increase in the number of crinoid species to result from more detailed studies of nocturnal species, and an increase in the number of symbiotic species when studies of nocturnal crinoid associates and sibling species among decapods are included. Our study revealed a rather rich crinoid fauna in the bay compared to other areas of the Indo-West Pacific, and the highest species richness of crinoid associates known from anywhere in the World Ocean.

Testing the plateau: a reexamination of disparity and morphologic constraints in early Paleozoic crinoids

Studies of crinoid morphology have been pivotal in understanding the constraints on the range of morphology within a clade as well as the patterns of disparity throughout the Phanerozoic. Newly discovered and described faunas and recent study of early Paleozoic crinoid diversity provide an ideal opportunity to reanalyze Ordovician through Early Silurian crinoid disparity with more complete taxonomic coverage and finer stratigraphic resolution. Using the coarse stratigraphic binning of Foote (1999), the updated morphologic data set has a similar disparity pattern to those previously reported for the early Paleozoic. However, with the more resolved stratigraphic binning used by Peters and Ausich (2008), a significant difference exists between the original and current data sets. Both data sets have a pronounced disparity high during the late Middle Ordovician. However, the updated disparity curve has a much higher initial disparity during the Early Ordovician and a pronounced rise in disparity during the Silurian recovery. Examination of differential sampling, proportions of the crinoid orders through time, and methods of coding characters indicate these factors have little effect on the pattern of crinoid disparity. The Silurian morphospace expansion occurs primarily within disparids and coincides with the origination of the myelodactylids. These findings corroborate the rapid expansion of morphospace during the Ordovician. However, crinoid disparity did not remain static and, although less frequent than during the initial radiation, new body plans evolved following the Ordovician Extinction (e.g., the myelodactylids). These results are consistent with the hypothesis of ecology constraining the limits on morphologic disparity at the class level.

COULD A STALKED CRINOID SWIM? A BIOMECHANICAL MODEL AND CHARACTERISTICS OF SWIMMING CRINOIDS

Modern stalked crinoids represent a relict fauna of once considerably higher diversity, as seen in their extensive fossil record. Comatulid crinoids, which lack a stalk and dominate modern crinoid diversity, have been interpreted as an evolutionary success story due to the increased mobility afforded by stalk loss. This mobility includes effective crawling and also swimming, often interpreted as anti-predatory escape strategies. Until recently it was assumed that stalked crinoids were incapable of active locomotion, but observations of an extant isocrinid have demonstrated that some can crawl relatively rapidly, perhaps in order to escape from benthic predators. Because the mechanics of crawling in stalked crinoids resemble the mechanics of swimming in comatulids, it is worth investigating whether a stalked crinoid would be capable of swimming. The feasibility of this scenario is tested using a biomechanical model of swimming in a stalkless crinoid and by applying the model to a stalked crinoid. The model demonstrates that the stalk imposes a heavy burden that limits the ability of a stalked crinoid to swim. Evolutionarily this might suggest that stalk loss was a key innovation that facilitated swimming; however, stalk loss alone is not sufficient to allow a crinoid to swim. Swimming would have allowed greater capability for escape from benthic predators than crawling. An evolutionary scenario is considered in which swimming evolved in a stalked crinoid to allow more effective escape from benthic predators subsequent to evolution of rapid crawling, precipitating eventual stalk loss.

A re-evaluation of Famennian echinoderm diversity: implications for patterns of extinction and rebound in the Late Devonian

Abstract Critical to understanding long-term trends in diversity is a dataset that is both worldwide in scope and based on a sound taxonomic foundation. In this paper we re-evaluate the Famennian (Late Devonian) echinoderm dataset, which has changed radically in the past decade, and reinterpret patterns of Late Devonian echinoderm extinction and rebound based on these new data. Historically, Famennian (Late Devonian) and earliest Carboniferous echinoderms have been poorly known on a global basis leading to interpretations of prolonged rebound from the Devonian extinction events. Recent discoveries of abundant and diverse Famennian echinoderm faunas from northwestern China, Colorado, Australia and Iran, together with re-examination of previously known echinoderm faunas from Germany and England, have altered drastically our understanding of the patterns of extinction and rebound of Famennian and earliest Carboniferous echinoderm communities. Overall, Famennian echinoderm diversity at the generic level is nearly five times greater than reported in the 2002 Sepkoski compilation, and familial level diversity is more than seven times greater than previously thought. Despite the increases in diversity, Famennian echinoderm faunas show a reduced diversity of camerate crinoids that typify both Middle Devonian and Lower Mississippian faunas and portend the rise of cladid crinoid diversity later in the Carboniferous. Individual Famennian faunas are numerically dominated by blastoids, which also portends trends seen at various times later in the Palaeozoic. In general, we are able to recognize the following trends. Rebound from the Late Devonian extinction events in echinoderms was more rapid than previously thought, but seems to be concentrated in Asia. Palaeogeographically Famennian echinoderms can be grouped into two broad regions: one includes China, Australia and Iran, all of which bordered the Palaeotethys; the other includes regions from Laurussia (Europe and North America) and northern Africa (Morocco).

NEW CLADID AND FLEXIBLE CRINOIDS FROM THE MISSISSIPPIAN (TOURNAISIAN, IVORIAN) OF ENGLAND and WALES

Abstract: The modern study of fossil crinoids began with J. S. Miller who, in 1821, described specimens from southern England, nearby Wales and other regions, and named several common Early Carboniferous genera. Later, in 1950–60, James Wright monographed all known Early Carboniferous crinoids from the British Isles. In spite of such previous scrutiny, we recognize here two new genera among species already described: Glamorganocrinus gen. nov. (type species: Ophiurocrinus gowerensis Wright, 1960) from South Wales and Mendipocrinus gen. nov. (type species: Poteriocrinus latifrons Austin and Austin, 1847) from southern England. These new genera increase the number of advanced cladid genera in the Ivorian Substage of the Tournaisian in western Europe to 18, and the total number of crinoid genera to 36. A review of species assigned to Mespilocrinus has led to the recognition of M. granulifer De Koninck and LeHon, 1854 as a nomen dubium. A new species of Mespilocrinus, M. wrighti sp. nov., is described from the Ivorian of South Wales; this is the most highly derived species of the genus, as based on a phylogenetic analysis including ten species and 13 characters, with Pycnosaccus as the outgroup. A single, well‐ordered tree resulted from this analysis. Interpretation of this tree suggests that the centre of evolution for Mespilocrinus was North America, where three species appeared during the Kinderhookian (early Tournaisian), rapidly achieving morphological disparity within the genus. This radiation event was part of the overall explosive radiation of crinoids following the Late Devonian mass extinction event when crinoid diversity was at a global minimum during the Frasnian. Recovery began during the Famennian, followed by an explosive radiation in the Tournaisian.

New camerate crinoids from the Ordovician of Scotland and Wales

ABSTRACTTwo new broad-cupped camerate crinoids are reported from the Upper Ordovician (Ashgill, Rawtheyan) Lady Burn Starfish Beds of the Girvan district, Strathclyde, SW Scotland. These represent a significant addition to the limited crinoid diversity known from the Ordovician of the British Isles. The 20-armed diplobathrid Eodimerocrinites littlewoodi gen. et sp. nov. is similar to Silurian Dimerocrinites Phillips, but lacks median ray ridges and has a distinct calyx sculpture. Camerate sp. indet. differs from E. littlewoodi in the sculpture of the dorsal cup and the arrangement of the interbrachial plates, but it preserves insufficient information for it to be further classified with confidence.New specimens of the diplobathrid gen. et sp. nov. cf Botting from the Middle Ordovician (Llanvirn, Abereiddian) of central Wales, that illustrate hitherto unknown morphological features, including a distal rhizoidal holdfast and a geniculate proximal column, suggest that this species was a rheophilic filter feeder. One specimen is one of the most complete fossil crinoids known from the Ordovician of the British Isles.