A new holocrinid (Articulata) from the Paris Biota (Bear Lake County,Idaho, USA) highlights the high diversity of Early Triassic crinoids

After the end-Permian crisis and the extinction of their four Paleozoic subclasses, crinoids rapidly recovered. This group is classically believed to have radiated from a small surviving clade and to have diversified during the Middle and Upper Triassic from two lineages. Nevertheless, recent findings suggested that several lineages of crinoids had already diversified during the Early Triassic, and that their diversity has been overlooked. Here we describe a new form of holocrinid, Holocrinus nov. sp., from the earliest Spathian (Early Triassic) of southeastern Idaho (USA). So far, the exceptional completeness of sampled specimens, with skeletal elements of arms and stem in connection, is unique for the Early Triassic. They show that derived morphological features had already evolved ∼1.3 million years after the Permian–Triassic boundary, supporting the scenario of a rapid Early Triassic diversification of crinoids.     

New data from Oman indicate benthic high biomass productivity coupled with low taxonomic diversity in the aftermath of the Permian–Triassic Boundary mass extinction

A new Early Triassic marine fauna is described from an exotic block (olistolith) from the Ad Daffah conglomerate in eastern Oman (Batain), which provides new insights into the ecology and diversity during the early aftermath of the Permian–Triassic Boundary mass extinction. Based on conodont quantitative biochronology, we assign a middle Griesbachian age to the upper part of this boulder. It was derived from an offshore seamount and yielded both nektonic and benthic faunas, including conodonts, ammonoids, gastropods and crinoid ossicles in mass abundance. This demonstrates that despite the stratigraphically near extinction at the Permian–Triassic Boundary, Crinoidea produced enough biomass to form crinoidal limestone as early as middle Griesbachian time. Baudicrinus, previously placed in Dadocrinidae, is now placed in Holocrinidae; therefore, Dadocrinidae are absent in the Early Triassic, and Holocrinidae remains the most basal crown‐group articulates, originating during the middle Griesbachian in the Tethyan Realm. Abundant gastropods assigned to Naticopsis reached a shell size larger than 20 mm and provide another example against any generalized Lilliput effect during the Griesbachian. Whereas the benthic biomass was as high as to allow the resumption of small carbonate factories, the taxonomic diversity of the benthos remained low compared to post‐Early Triassic times. This slow benthic taxonomic recovery is here attributed to low competition within impoverished post‐extinction faunas.     

New data on crinoid assemblages from the oldest sedimentary rocks of the Polish Outer Carpathians (Jurassic-Cretaceous)

Crinoids (Crinoidea) preserved in the so-called Cieszyn Beds (Tithonian-Hauterivian; southern Poland) are relatively numerous, especially in some levels, but not highly diversified. They are absent in the Lower Cieszyn Shale (Tithonian) and the Upper Cieszyn Shale (Valanginian-Hauterivian). The Lower Cieszyn Limestone (Tithonian) yielded crinoid remains classified as Isocrinus cf. amblyscalaris (Thurmann) and Isocrinida indet. In the Upper Cieszyn Limestone (Berriasian) crinoids are much more numerous and diversified. The following taxa are recorded: Isocrinus? annulatus (Roemer), Balanocrinus subteres (Münster), B. cf. smithi Hess and Gale, and Hemicrinus sp. The presence of specimens resembling Isocrinus amblyscalaris (Thurmann) in the Tithonian strata is surprising since the last occurrence of this taxon was reported from the Kimmeridgian. The Lower Cieszyn Limestone crinoidal assemblage is dominated by isocrinids (Isocrinida). This probably reflects the much shallower sedimentary environment of these sediments compared to that of the Upper Cieszyn Limestone, where excepting isocrinids, hemicrinids (Hemicrinidae, Cyrtocrinida) typical for deep marine environments were found. It is consistent with the analytical results from the foraminiferal assemblages, among which the benthic forms known from shelfal and paralic epicontinental environments first dominated, and then were supplanted by deep-sea taxa at the turn of the Jurassic and Cretaceous.     

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.     

A Laurentian Iocrinus Hall (Crinoidea,Disparida) in the Dapingian or Darriwilian (Middle Ordovician,Arenig) of Oman

Abstract: Early and early Middle Ordovician crinoids are rare globally, and are best known from North America and the British Isles. The first Arenig crinoid from the Arabian Peninsula is Iocrinus sp. cf. I. subcrassus (Meek and Worthen), known from two near‐complete individuals, and numerous fragmentary specimens and ossicles. These are the stratigraphically oldest Iocrinus specimens, and provide an unexpected extension of the palaeogeographical range of a genus known otherwise from slightly younger deposits in Laurentia (North America) and Avalonia (Wales). The Oman specimens differ from Gondwanan Heviacrinus melendezi Gil Cid et al., currently classified as a maennilicrinid, but morphologically close to Iocrinus, in having arms that branch at least seven times instead of four and in having columnals typical of Iocrinus. Three species from Wales and the Welsh Borders, previously placed in Iocrinus, but differing in having smooth, conical dorsal cups, are reclassified as Margoiocrinus Donovan gen. nov., type species Iocrinus shelvensis Ramsbottom.     

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.     

A re‐interpretation of the ambulacral system of Eumorphocystis (Blastozoa,Echinodermata) and its bearing on the evolution of early crinoids

Recent debates over the evolutionary relationships of early echinoderms have relied heavily on morphological evidence from the feeding ambulacral system. Eumorphocystis, a Late Ordovician diploporitan, has been a focus in these debates because it bears ambulacral features that show strong morphological similarity to early crinoid arms. Undescribed and well‐preserved specimens of Eumorphocystis from the Bromide Formation (Oklahoma, USA) provide new data illustrating that composite arms supported by a radial plate that bear a triserial arrangement of axial and extraxial components encasing a coelomic extension can also be found in blastozoans. Previous reports have considered these arm structures to be restricted to crinoids; these combined features have not been previously observed in blastozoan echinoderms. Phylogenetic analyses suggest that Eumorphocystis and crinoids are sister taxa and that shared derived features of these taxa are homologous. The evidence from the arms of Eumorphocystis suggests that crinoid arms were derived from a specialized blastozoan ambulacral system that lost feeding brachioles and strongly suggests that crinoids are nested within blastozoans.     

Host-specific pit-forming epizoans on Silurian crinoids

Brett, Carlton E. 197807 15: Host-specific pit-forming epizoans on Silurian crinoids. Lethaia , Vol. 11. pp. 217–232. Oslo. ISSN 0024–1164.
Circular-parabolic pits occur commonly on the endoskeletal remains of certain Paleozoic crinoids. Detailed study of several hundred specimens, representing about 30 pelmatozoan species from the Upper Silurian Rochester Shale of New York and Ontario, reveals that such pits occur exclusively in seven species of crinoids. Furthermore, there are consistent differences in the morphology and orientation of holes occurring on the different crinoid species. This suggests that distinct epizoan species settled selectively on given hosts. The relationship between the hole-producing epizoans and crinoid hosts is inferred to have been a form of dependent commensalism. Preliminary surveys of other Paleozoic crinoid assemblages reveal similar host-selectivity by pit-producing epizoans. Crinoidepizoan pairs apparently co-evolved through considerable spans of geologic time as related genera and species of different ages, from Silurian to Pennsylvanian, exhibit similar pits.     

Escalating predation on crinoids in the Devonian: negative community-level evidence

Previous morphological studies suggest that predation on stalked crinoids increased in the Devonian. However, there was no concomitant decline in the occurrence of dense, shallow-water stalked crinoid assemblages in North America from the Ordovician and Silurian to the Mississippian. The evolution of crinoid defensive adaptations may have kept pace with rising durophagy, forestalling the expected decline of crinoid communities. It is also possible that the demise of reefs after the Frasnian-Famennian mass extinction indirectly decreased predation pressure on crinoids by removing shelter for predatory fish. A third possibility is that stalked crinoid abundance was affected neither by new predators nor by the decline of reefs. □ Crinoidea, dense crinoid assemblages, Echinodermata, North America, Paleozoic, predation.     

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 231–252 mya 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.     

New crinoids from the Baltic region (Estonia): fossil tip‐dating phylogenetics constrains the origin and Ordovician–Silurian diversification of the Flexibilia (Echinodermata)

This study documents previously unknown taxonomic and morphological diversity among early Palaeozoic crinoids. Based on highly complete, well preserved crown material, we describe two new genera from the Ordovician and Silurian of the Baltic region (Estonia) that provide insight into two major features of the geological history of crinoids: the early evolution of the flexible clade during the Great Ordovician Biodiversification Event (GOBE), and their diversification history surrounding the end‐Ordovician mass extinction. The unexpected occurrence of a highly derived sagenocrinid, Tintinnabulicrinus estoniensis gen. et. sp. nov., from Upper Ordovician (lower Katian) rocks of the Baltic palaeocontinent provides high‐resolution temporal, taxonomic and palaeobiogeographical constraints on the origin and early evolution of the Flexibilia. The Silurian (lower Rhuddanian, Llandovery) Paerticrinus arvosus gen. et sp. nov. is the oldest known Silurian crinoid from Baltica and thus provides the earliest Baltic record of crinoids following the aftermath of the end‐Ordovician mass extinction. A Bayesian ‘fossil tip‐dating’ analysis implementing the fossilized birth–death process and a relaxed morphological clock model suggests that flexibles evolved c. 3 million years prior to their oldest fossil record, potentially involving an ancestor–descendant relationship (via ‘budding’ cladogenesis or anagenesis) with the paraphyletic cladid Cupulocrinus. The sagenocrinid subclade rapidly diverged from ‘taxocrinid’ grade crinoids during the final stages of the GOBE, culminating in maximal diversity among Ordovician crinoid faunas on a global scale. Remarkably, diversification patterns indicate little taxonomic turnover among flexibles across the Late Ordovician mass extinction. However, the elimination of closely related clades may have helped pave the way for their subsequent Silurian diversification and increased ecological role in post‐Ordovician Palaeozoic marine communities. This study highlights the significance of studies reporting faunas from undersampled palaeogeographical regions for clade‐based phylogenetic studies and improving estimates of global biodiversity through geological time.     

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.     

New fish assemblages from the Middle Permian from the Guadalupe Mountains,West Texas,USA

Late Wordian/Capitanian (Guadalupian, Middle Permian) fish assemblages are described from the “McKittrick Canyon Limestone”, Lamar Limestone and Reef Trail Members of the Bell Canyon Formation in the Patterson Hills and the PI section (Hegler/Pinery Members) along Highway 62/180 in the Guadalupe Mountains, West Texas. The assemblages contain chondrichthyan teeth of Stethacanthulus meccaensis, Texasodus varidentatus, Cooleyella cf. amazonensis, C. cf. peculiaris, and the new genus and species Lamarodus triangulus; and buccopharyngeal denticles of undetermined symmoriiform; chondrichthyan scales of eight morphotypes; fragment of an actinopterygian jaw, isolated teeth; the scales of Alilepis sp., Varialepis sp. and undetermined elonichthyid and haplolepid fishes. Using microtomography, the vascularization system has been observed for the first time for the teeth of Texasodus varidentatus and a new taxon Lamarodus triangulus. The distribution of chondrichthyan taxa was analyzed for the known fish assemblages of the Early, Middle, and Late Permian of the world. The end-Guadalupian crisis in the evolution of chondrichthyan fishes involved substantially more taxonomic change than the Permian–Triassic mass extinction.     

Reinterpretation of crinoid-platyceratid interaction

The well-known association of platyceratid gastropods with crinoids has traditionally been considered an example of coprophagous commensalism. The Occurrence of several crinoid 'stands' ( Platycrinites sp.) from closely spaced bedding surfaces in the upper Mississippian Wymps Gap Limestone member of the Mauch Chunk Formation of southwestern Pennsylvania encourages reinterpretation of this relationship. Crinoid calyces were collected from five separate clusters, two of which contained associated platyceratids. 'Infested' crinoids either died prematurely or were stunted, compared to crinoids in the 'uninfested' clusters. Platyceratid attachment apparently had an adverse effect upon crinoid growth. Serial acetate peels show positioning of the gastropod on the crinoid tegmen over a highly developed anal tube, or chimney. However, the terminus of the anal tube abuts the gastropod's shell and is poorly situated for fecal ingestion by the snail. We suggest that the snail probably pursued another trophic strategy, perhaps taking advantage of aerosol filtration by the crinoid and elevation above the substrate.     

Unusual tabulate‐crinoid biocoenosis from the Lower Devonian of Morocco

The Early Devonian (Pragian: sulcatus to pireneae conodont zones) crinoid–coral biocoenosis from Hamar Laghdad, Morocco contains fragments of crinoid stalks of various taxa encrusted by spherical and ellipsoidal coralla of the tabulate coral Hamarilopora minima. These corals were encrusting host crinoids syn vivo, and this is evidenced by pluricolumnals exceeding 30 elements overgrown from all sides. Most known to date crinoid–epibiont associations display various types of reaction to the epibiont, such as swellings and deformations. In the case discussed here, no clear interaction is visible; therefore, this association can be classified as paroecia. It can be inferred, however, that due to a change in mechanical properties of the crinoid stalk (losing flexibility), the epizoan influence on the host was negative, while the coral was profiting from the elevated position over the seafloor and nutrient‐bearing water currents. It can be supposed that this interaction was close to parasitism. No strict species‐specific relationship between the epizoan and the host was observed.     

Facies of two important Early Triassic gastropod lagerstätten: implications for diversity patterns in the aftermath of the end-Permian mass extinction

Two important lagerstätten of Early Triassic gastropods, the Sinbad Limestone (Utah, USA) and the Gastropod Oolite (North Italy) yield about 40% of all described Early Triassic species. This great contribution to the global diversity and the exceptional good preservation render high information content, which characterizes fossil lagerstätten. The Smithian Sinbad Limestone contains the most diverse Early Triassic gastropod fauna. At the type locality, it occurs in single, probably storm-induced shell bed within a series of high energy deposits underlain by intertidal microbial mats and subtidal oolite/peloid shoals. The main shell bed contains about 40 invertebrate taxa. Gastropods, scaphopods, and bivalves are most abundant and form an assemblage, which is dominated by small neritaemorphs, the opisthobranch Cylindrobullina convexa and the scaphopod Plagioglypta (annulated tubes). This assemblage lived on shallow, subtidal soft-bottoms based on sedimentological and ecological characteristics. The Dienerian (to Smithian?) Gastropod Oolite Member (North Italy) has extremely abundant, probably salinity-controlled gastropod faunas with low species richness. Almost monospecific assemblages of Pseudomurchisonia kokeni as well as assemblages with about four species are present in the Gastropod Oolite. Modern hydrobiid mudsnail faunas which are adapted to strongly fluctuating salinity in intertidal to shallow subtidal coastal areas form probably a suitable model for the Gastropod Oolite biota. Gastropods from the Werfen- and Moenkopi-Formation lagerstätten are well preserved compared to other Early Triassic deposits. The high contribution to the global diversity of just two sites suggests very incomplete sampling and preservational bias. However, the low richness of the major faunas reflects depauperate Early Triassic faunas and slow recovery from the Permian/Triassic crisis.     

Filtration models, guilds, and biofacies: Crinoid paleoecology of the Stanton Formation (Upper Pennsylvanian), midcontinent, North America

Filtration models make several predictions concerning the distribution of crinoids among benthic habitats: (1) generally, higher energy shoreward settings should contain crinoid assemblages dominated by taxa with dense mesh filtration fans; (2) generally, lower energy offshore settings should be dominated by crinoids with open mesh filtration fans; (3) diversity should be highest in nearshore settings, which generally contain low energy microhabitats within high energy settings where both dense fan and open fan forms can co-occur, whereas offshore assemblages should be dominated by open fan taxa; thus, open fan forms should be more eurytopic than dense fan forms. Also, previous empirical models for crinoid distribution patterns note that nearshore assemblages are dominated by large forms whereas offshore assemblages are dominated by small forms. Filtration fan morphology and body size interact significantly to determine how and where crinoids feed and thus are used here as criteria for distinguishing late Paleozoic crinoid guilds. The distribution patterns of crinoid taxa and guilds among the benthic paleoenvironments of the Upper Pennsylvanian (Missourian) Stanton Formation were used to test the predictions of the filtration models.

The results of quantitative analyses show that large, dense fan crinoids are significantly more abundant in shoreward assemblages than smaller, open fan crinoids, which are more abundant in offshore assemblages; these results are consistent with the aforementioned models. However, diversity patterns are not consistent with the filtration models, indicating that mid-depth and aerobic offshore assemblages are more taxonomically and trophically diverse than nearshore and dysaerobic offshore assemblages, ostensibly due to the overlapping ranges of characteristically nearshore and offshore taxa. Analysis of guild distribution patterns also indicates some contradictions to predicted patterns of stenotopy and eurytopy, indicating additional complexities to late Paleozoic crinoid paleoecology.

Five recurrent crinoid assemblages, or biofacies, have been identified from the Stanton Formation of midcontinent North America. The guild structure and diversity of these biofacies are characterized here as: (1) a moderate diversity nearshore biofacies dominated by large calyx, dense fan guilds; (2) a high diversity midshelf biofacies characterized by equitable contributions of many taxa and guilds; (3) a moderate diversity offshore biofacies dominated by non-pinnulate and small calyx, open fan pinnulate guilds; (4) a low diversity offshore dysaerobic biofacies dominated by small calyx pinnulate guilds; (5) a depauperate offshore biofacies dominated by a unique stalkless species, Paragassizocrinus tarri. Except for Biofacies 5, the number of guilds appears to increase offshore; however, the equitability of taxa among and within the guilds generally decreases offshore. This pattern indicates that the heterogeneity of resources, or the recognition by taxa of different classes of resources, as reflected by the variety of functional types, increased from nearshore to offshore, but that the abundance or accessibility of these resources, and/or the relaxation of competition within guilds, increased from offshore to nearshore.     

New trepostome Bryozoa from the Early Triassic (Smithian/Spathian) of Nevada

Two new bryozoan species of the trepostome family Dyscritellidae,Dyscritellopsis thaynesianus n. sp. andDyscritellopsis montelloensis n. sp., are described from the Early Triassic (Smithian/Spathian) Thaynes Limestone, Nevada (USA). The bryozoan fauna documents the survival of Paleozoic lineages into the earliest Triassic on northern open shelves outside the tropics. The fauna holds paleobiogeo-graphic connections to the Early Triassic bryozoan faunas of Spitsbergen.      

Presumed postlarval pentacrinoids from the Lower Devonian Hunsrück Slate,Germany

Several tiny crinoids with crowns as small as 1 mm, or less, in width are newly recognized from the Hunsrück Slate of southwestern Germany. The presence of erect arms above an amorphous calyx in some specimens can be inferred. Based on comparison with the size and gross morphology of developmental stages in living crinoids, these tiny Hunsrück crinoids are judged to be at an early postlarval stage that is analogous to the pentacrinoid stage just after development from the stalked, but armless, smaller cystidean larval stage found in both living comatulids and isocrinids. Some of these tiny crinoids have a stalk up to 4 mm long attached to a now pyritized former substrate. Their clustered occurrence suggests gregarious settlement of larvae. Taxonomic identification of these presumed pentacrinoids is not possible, even to the sub‐class level, although they are preserved with larger juveniles of the cladids Propoteriocrinus and Lasiocrinus. These larger juveniles exhibit 3‐D pyritized calcite plates, whereas the probable pentacrinoids appear to be preserved as flattened, micro‐crystalline pyritized dermal tissues that enclosed lightly calcified, porous ossicles. The pentacrinoids were likely buried within weeks or months of hatching, based on developmental stages in similar‐sized living crinoids. These tiny crinoids, presumably pentacrinoids, are a further example of the extraordinarily detailed preservation of delicate tissues in pyrite from the Hunsrück Slate. They are most likely the pentacrinoid stage from one or more of the crinoid taxa (30 genera) present in the Hunsrück Slate. Assuming these are not microcrinoids, they are the first report of pentacrinoids from the fossil record and document that a Palaeozoic sister group to modern crinoids had similar developmental stages.     

Revision Of Late Devonian (Famennian) And Some Early Carboniferous (Tournaisian) Crinoids And Blastoids From The Type Devonian Area Of North Devon

The crinoids and blastoids from the Pilton (Beds) Formation of the type Devonian of north Devonshire are revised. These fossils were monographed by the Rev. G. F. Whidborne in 1898, but have not been studied since that time. Recent studies on various groups of fossils from the Pilton and related rocks in North Devon confirm that the great majority of these fossils are Famennian, although three specimens from Fremington are probably Early Carboniferous (Tournaisian). We identify four blastoid taxa from a fauna that is sparse and poorly preserved; two spiraculates, one fissiculate, and one taxon unidentifiable at the ordinal level. Mesoblastus cf. M. crenulatus from the Gattendorfia Zone (Lower Carboniferous) near Fremington is the oldest known representative of this genus. The crinoid fauna is somewhat more diverse, but the preservation is equally poor. No changes are made in the flexible crinoids. Among camerate crinoids, one species is reassigned to Eumorphocrinus and one is retained in Actinocrinites. Specimens of some crinoids, such as Rhodocrinites and Megistocrinus, are so poorly preserved that certain identification was not possible. The hexacrinoid Adelocrinus, relegated to uncertainty for 150 years, is here shown to be a valid genus that is very similar to Arthroacantha, but not synonymous with it. Among the cladid crinoids, the dominant groups are those within the Superfamily Scytalocrinacea, which includes Bridgerocrinus, Sostronocrinus, and Scytalocrinus, all of which are placed in the new family Sostronocrinidae. One new species, Glossocrinus whidbornei, is named. Non‐pinnulate cladids, common in older Devonian rocks, do not occur. The fauna shows considerable similarity with faunas from eastern North America and Germany. It shows less resemblance to the extensive Famennian crinoid and blastoid fauna of north‐western China, despite some remarkable congruencies, especially the occurrence of very similar species of Actinocrinites in these widely separated areas.