Graptolite Taxa Research Articles

First Palaeozoic Phyllocarid Crustaceans and Pterygotid Eurypterids in Serbia

Palaeozoic phyllocarid crustaceans and pterygotid eurypterids from the Gethicum Zone of Carpatho-Balkanides in Serbia are herein documented for the first time. The described and illustrated phyllocarid remains consisting of a coupled telson and furcal rami were collected from upper Silurian (?) shale. This specimen is fragmented and poorly preserved to allow identification to species level, and has thus been assigned to Ceratiocaris sp. indet. The eurypterids are represented by part of a fragment, showcasing the distinct scale-like ornamentation of the pterygotids, and a segment of a walking leg. The pterygotid remains were found together with a few graptolite taxa (Monograptus sudeticus Porębska, “M.” microdon microdon Reinh. Richter, Neomonograptus aequabilis (Přibyl), Uncinatograptus hercynicus (Perner), U. subhercynicus (Willefert)), which are characteristic for the lower part of the U. hercynicus graptolite zone (Lochkovian, Lower Devonian). There are at least two species in this stratigraphic interval that correspond to the pterygotid eurypterids remains from Serbia – Acutiramis perneri Chlupáč and Pterygotus cf. barrandei Semper, but without the chelicerae, it is impossible to make precise identification. These new finds from eastern Serbia, together with the Bulgarian ones, are a further confirmation of peri-Gondwanan origin of pre-Variscan Palaeozoic sediments in the West Srednogorie Unit in Bulgaria and in the Gethicum Unit in Serbia.

First record of Pridolian graptolites from South America: Biostratigraphic and paleogeographic remarks

Graptolites were planktonic organisms that constitute one of the essential biostratigraphic tools used in Paleozoic successions worldwide. Notably, Pridolian (upper Silurian) graptolites have been globally recognized in several geological units, but completely absent from South American sections until now. This study introduces the first Pridolian graptolite assemblage in this subcontinent. The Rinconada Formation, from the Eastern Precordillera of San Juan Province, Argentina, has an abundant fossil content that includes: graptolites, brachiopods, bivalves, trilobites, corals, plant remains, and microfossils. Two graptolite taxa have been identified and described, including Skalograptus parultimus (Jaeger) and cf. Enigmagraptus. Both genera are mentioned for the first time in South America. As a result, the S. parultimus Biozone is recorded from the upper outcropping levels of the Rinconada Formation at its eponymous section, indicating an early Pridolian age. This discovery represents the first mention of Pridolian graptolites for South America, and increases the knowledge about the graptolite content of the studied formation as well. In addition, the assemblage might represent the faunal recovery interval after the Kozlowskii-Lau Event, a globally recorded episode of biotic crisis. The co-occurrence of graptolites and plant remains within the same stratigraphic levels in the Rinconada Formation represents the first and oldest record in western Argentina. Finally, the age of the Rinconada Formation is reviewed, and a local, regional, and global correlation is proposed with several Pridolian sections around the globe.

Geographic dynamics of some major graptolite taxa of the Diplograptina during the Late Ordovician mass extinction in South China

The study of graptolite paleobiogeography is important for understanding the relationship between geography and evolutionary dynamics in graptolites. However, there have been few detailed studies of graptolite paleobiogeography during the Late Ordovician, or the role that geography played in the Hirnantian Mass Extinction (HME). In this study, in order to investigate the geographic dynamics of major graptolite taxa during the HME, a data-set of graptolite occurrences in the late Katian–Hirnantian from 61 localities in South China was compiled using the GBDB online database. The minimum polygon method was used to reconstruct 14 distribution maps of 5 major taxa belonging to the Diplograptina. The geographic dynamics of most diplograptine taxa show a small reduction in their geographic ranges from the Dicellograptus complexus Zone to the Paraorthograptus pacificus Zone, probably because of the contractions in the distribution areas of the coeval marine sediments. A substantial reduction in the distributions of most diplograptine taxa from the P. pacificus Zone to the Metabolograptus extraordinarius Zone mainly represents the effect of the major extinction event. Our study also demonstrates a reduction in the geographic ranges of each taxon to the center of the Yangtze epicontinental sea during the HME. The changes in geographic ranges are mirrored by a similar reduction in species-level total diversity during the study interval.

The graptolite, conodont and sedimentary record through the late Ludlow Kozlowskii Event (Silurian) in the shale-dominated succession of Bohemia

AbstractThe shale-dominated hemipelagic succession exposed in the southwestern part of the Prague Synform preserves the most complete Ludfordian graptolite record so far encountered from peri-Gondwanan Europe. Four graptolite biozones – theNeocucullograptus inexpectatus,Nc. kozlowskii,Pseudomonoclimacis latilobus–Slovinograptus balticusandPristiograptus fragmentalisbiozones – are recognized in the middle and late Ludfordian, between theBohemograptus tenuisBiozone and the base of the Pridoli Series. Conodont occurrences are restricted to scattered limestone beds, but enable tentative integration of the graptolite and conodont biozonal schemes. Particular attention was paid to faunal and sedimentary changes and the carbon isotope record across the middle Ludfordian Kozlowskii extinction Event. The Kozlowskii Event caused the almost simultaneous extinction of graptolites with ventrally curved rhabdosomes. The generaBohemograptus,PolonograptusandNeocucullograptus, along withPseudomonoclimacis dalejensis, disappeared from the fossil record. The offshore conodont fauna recorded in the section was not strongly affected and similarly the pelagic orthocerids and nektonicCeratiocarispassed unaffected through the extinction interval. The abundant and widespread pelagic myodocopid ostracodEntomis, however, became extinct. The late Ludfordian graptolite recovery gave origin to a novel fauna of Pridoli type from taxa that emerged or just reappeared above the Kozlowskii crisis. In Všeradice and elsewhere in the Prague Synform, the recovery, manifested by the appearance ofPseudomonoclimacis latilobusandSlovinograptus balticus, closely postdates the end of the isotope excursion but pre-dates the first appearance of the conodont index ‘Ozarkodina’snajdri. Here the graptolite recovery was delayed relative to the recovery of the benthic fauna. A canalized intraformational limestone conglomerate corresponds with a gap in the sedimentary record above the Kozlowskii extinction and just below the graptolite recovery. The benthic faunas from the conglomerate matrix and pebbles permit correlation with the shallower part of the basin indicating a distinct fall in sea-level. The present data demonstrate the coincidence of the graptolite crisis with benthic faunal change and eustatic fall in sea-level manifested by facies change and the carbon isotope excursion.Polonograptus chlupacisp. nov., from theNc. kozlowskiiBiozone, is described and several other graptolite taxa are redescribed.

The sequence and correlation of Early Ordovician (Arenig) graptolite faunas in the Richardson Trough and Misty Creek Embayment, Yukon Territory and District of Mackenzie, Canada

Four graptolite biozones are recorded from the Arenig portion of the Road River Group in the Richardson and Mackenzie mountains in the Yukon and Northwest Territories. In ascending order, these zones are Tetragraptus approximatus, Pendeograptus fruticosus, Didymograptus bifidus, and Parisograptus caduceus australis (new). The Castlemainian stage may be represented by nongraptolitic massive bedded chert. The Arenig–Llanvirn boundary is drawn below the first occurrence of Undulograptus austrodentatus. Fifty-four graptolite taxa are present, and 16 of these species and subspecies are recorded for the first time in this deep-water biotope, namely, Didymograptus? cf. adamantinus, D. asperus, D. dilatans, D. cf. kurcki, D. validus communis, Holmograptus aff. leptograptoides, H. sp. A, Isograptus? sp. nov. A, I. ? dilemma, Keblograptus geminus, Pseudisograptus manubriatus harrisi, Ps. m. koi, Ps. m. janus, Ps. cf. tau, Xiphograptus lofuensis, and Zygograptus cf. abnormis.

Upper Darriwilian graptolite and conodont zonation in the global stratotype section of the Darriwilian stage (Ordovician) at Huangnitang, Changshan, Zhejiang, China

Investigation of the previously little known upper Darriwilian graptolite biozone succession in the Darriwilian GSSP at Huangnitang, Changshan, China has led to the recognition of three biozones above the basal Darriwilian Undulograptus austrodentatus Biozone, namely the Acrograptus ellesae Biozone, the Nicholsonograptus fasciculatus Biozone, and the Pterograptus elegans Biozone. The Hustedograptus teretiusculus Biozone has not been identified and the post-Darriwilian Nemagraptus gracilis Biozone is separated from the P. elegans Biozone by a stratigraphic interval without stratigraphically diagnostic graptolites. Several levels in the succession have yielded index conodonts, making it possible to recognize international conodont biozones in part of the sequence. The virtually complete Darriwilian graptolite biozone succession, the good to excellent preservation of many graptolite taxa, the comprehensive construction of facilities to facilitate the study of the section, and the designation of this section as a protected National Geopark make Huangnitang an internationally unique and important geological site.

Llandovery‐Ludlow graptolites from central Victoria: New correlation perspectives of the major formations

The Darraweit Guim Province of the Melbourne Trough contains a sequence of Uandovery ‐ early Ludlow clastic rocks. New biostratigraphic data permit revised correlations and reinterpretation of published and unpublished descriptions of the sequence. The sequence is divided into the Keilor Group, of Llandovery age, comprising the Deep Creek Siltstone, Springfield Sandstone and Chintin Formation; and the Dargile Group, of Wenlock ‐ early Ludlow age, comprising the Anderson Creek Formation, Wapentake Formation, Bylands Siltstone (new), Costerfield Siltstone, Yan Yean Formation and Melbourne Formation. Graptolite faunas from the sequence represent a greater number of bio‐zones than hitherto recognised, and trilobite faunas indicate a number of stratigraphically discrete shelly assemblages. A synthetic approach to biostratigraphic and lithostratigraphic data is adopted to alleviate reliance on lithostratigraphy in what is a lithologically monotonous, poorly exposed sequence; the approach facilitates the extensive revision of sequence boundaries in accord with the biostratigraphic data. New graptolite taxa described are: Monograptus ludensis yarraensis, Monograptus uncinatus praeprognatus, Bohemograptus (Egregiograptus) tsegelnuki, Saetograptus colonus heathcotensis and Pristiograptus jolimontensis. The distribution of graptolitic and benthic faunas accords with a history of deposition dominated by eustatic events.

Heterochrony, punctuated equilibrium, and graptolite zonal boundaries

Summary Many graptolite taxa are important biostratigraphically because their first appearances in stratigraphic sequences represent unique events that are recognizable and correlative worldwide. However, because the direct ancestry of many of these taxa are cryptic, the biostratigraphical value of their first appearances may be questioned. Astogenetic and ontogenetic studies of well-preserved, isolated specimens of Nemagraptus gracilis, Dicellograptus (four species), Leptograptus trentonenesis, Glossograptus ciliatus and Glyptograptus euglyphus from the middle Ordovician Athens Shale of Alabama show that considerable graptolite evolution occurs through heterochony. And, what are here considered to be small heterochronic changes, often produce large morphological discontinuities between ancestors and descendants. In turn the presence of these morphological discontinuities in graptolite sequences suggest that graptolite evolution follows the model of punctuated equilibrium, rather that that of phyletic gradualism. Whether nor not this is the case is here considered to be a matter of semantics. More importantly, heterochronic evolution is here considered to explain the cryptic ancestry of many graptolite taxa, and with this mode of evolution in mind, the graptolite biostratigrapher may find it easier to determine ancestor-descendent relations and thus recognize those first appearances that are valid for biostratigraphical correlation.

Early Devonian Conodont-Graptolite Collation and Correlations with Brachiopod and Coral Zones, Central Nevada

A range chart of some Early Devonian conodont and graptolite taxa from central Nevada is presented. It is based on the graphic correlation method of Shaw, and shows correlations with the established zones for brachiopods and corals as well as conodonts and graptolites. It indicates that the hesperius through pesavis conodont zones established for western North America are approximately equivalent to the Lochkovian of the Czechoslovakian sequence, and the Pragian begins approximately with the sulcatus zone. The chart also indicates that the zones based on different groups do not coincide, are of very unequal duration, and that intervals of rapid morphologic change correspond to intervals of higher diversity and greater morphologic variation. Species have significantly diff rent longevities, generally those originating during times of greatest morphologic variation being the shorter lived. The approximate duration of the species studied is 2 to 10 m.y. Use of the graphic correlation method permits better correlation of shelf and basin faunas and enhances the possibility for constructing accurate shelf margin histories and for correlating provincial shelf faunas with those in other parts of the world.