The Hunneberg Stage (Ordovician) in the area east of St. Petersburg, north-western Russia

The bio- and lithostratigraphy of the poorly known early Ordovician (Arenig) Hunneberg Stage is described from the area east of St. Petersburg (Putilovo Quarry and Lava river), where the Lakity Beds (Leetse Fm.) consist of glauconitic sands and silty clays. The described fauna includes graptolites, conodonts, brachiopods, acritarchs, foraminifers, and several problematic groups. The Lakity Beds are unique within the lower Ordovician sequence of the East Baltic in the abundance of graptolites, co-occurring with conodonts. The conodonts from the lower part of the Lakity Beds belong to the uppermost subzone (Oelandodus elongatus — Acodus deltatus deltatus) of theParoistodus proteus Zone, coinciding with the lower part of theTetragraptus phyllograptoides Zone. This suggests that there is a hiatus between the Lakity Beds and the underlying Nazya Formation. The lower Lakity Beds also contain the brachiopodsLeptembolon lingulaeformis andEosiphonotreta cf.acrotretomorpha, which suggest that they may be correlated with the Joa Member of the Leetse Formation in North Estonia. In the upper part of the Lakity Beds, conodonts of thePrioniodus elegans Zone co-occur with graptolites indicating the upper subzone of theTetragraptus phyllograptoides Zone in the Scandinavian sections. There are still problems of defining and correlating the base of the Billingen Regional Stage, which are outside the scope of this paper.     

Occurrence of Giant Borings of Osprioneides kampto in the Lower Silurian (Sheinwoodian) Stromatoporoids of Saaremaa,Estonia

The distribution of Osprioneides is more environmentally limited than that of Trypanites in the Silurian of Baltica. Osprioneides probably occurred only in large hard substrates of relatively deepwater muddy bottom open shelf environments. Osprioneides were relatively rare, occurring in 4.7% of all stromatoporoid specimens in that environment, in contrast to small Trypanites-Palaeosabella borings, which occur in 88.4% of stromatoporoids and 88.9% of heliolitid corals. Osprioneides is reported only from the lower Sheinwoodian stromatoporoids of the exposed Silurian of Saaremaa (Wenlock to Pridoli). Osprioneides borings probably played a minor role in the general bioerosion in the Silurian of Baltica.     

Pattern of some Silurian bioevents

The best‐known Silurian bioevent occurred at the end of the Wenlock: the lundgreni event, together with the nassa‐ludensis crisis, was established among planktic graptolites. The East Baltic data show several peaks of high diversity (especially triangulatus, turriculatus, scanicus zones) and three levels of low diversity of graptolites (antennularius, radians, ludensis zones). These are more or less coincident with sea‐level changes. Energetic innovation of the shallow shelf corals started in the early Silurian. The late Wenlock regression seems not to affect them seriously but the late Silurian decline coincides with the aridization of the climate and a regression of the shelf seas. The Agnatha had strong radiations in the Wenlock (ludensis Zone) and Ludlow (leintwardinensis Zone), the fishes in the Pridoli. Many Silurian vertebrates were long‐ranging and extinction rate was relatively low; only at the late leintwardinensis level and in the latest Ludlow did considerable extinctions occur.     

Age of the Silurian Wuxiahe Formation in Langao,Northwest China: New conodont data

A recent study of conodonts from the Wuxiahe Formation (lower to middle part) in the Ziyang-Langao region suggested its age of middle Telychian (Llandovery) to lower Sheinwoodian (Wenlock), contradicted by subsequent graptolite studies indicating an age of late Telychian for the same interval. New samples from the Qiaoxi section for conodonts to re-access the age of the Wuxiahe Formation collected in this study show that the lower to middle part of the formation belongs to the Pterospathodus amorphognathoides amorphognathoides Biozone, suggesting the age of late Telychian; thus, the Llandovery–Wenlock boundary in the section is most probably higher than previously estimated, but its precise position is not determined since the identification of the Wenlock graptolite Cyrtograptus cf. lundgreni in the section is to be further confirmed. Based on the conodont faunas recognized in the Qiaoxi and Tianwancun sections, the base of the Wuxiahe Formation in the Ziyang-Langao region is diachronous, i.e., not higher than the upper Telychian Pterospathodus amorphognathoides amorphognathoides Biozone at Qiaoxi, but not lower than the lower Sheinwoodian Kockelella ranuliformis Biozone at the Tianwancun setion.     

Late Wenlock (Middle Silurian) global Bioevent: Possible chemical cause for mass graptolite mortalities

Graptolites nearly became extinct in the latest Wenlock in all preserved stratigraphic sequences of this age. Graptolite mortalities occurred along the western coast of Laurentia and at sites that surrounded the Proto‐Tethys. Graptolite mass mortalities took place among deep‐water, open ocean dwelling organisms. After the mass mortalities, only the Pristiograptus dubius group and retiolids surface or near‐surface dwellers, survived. For a period of time, little speciation or diversification occurred. The base of the Ludlow is marked by diversification, with appearances of S. colonus, M. nilssoni and other groups which occur in near surface waters. None of the extensive plate movements postulated for the Silurian readily explain the mass extinctions that occurred. During the Silurian, global temperatures were warmer than present and atmospheric oxygen concentrations were lower, creating extensive oceanic anoxia. Below the oxygenated surface layers of the ocean, was an anoxic, non‐sulfidic zone (i.e. nitrate‐reducing) above a sulfidic zone. Graptolites lived over a range of depth from the oxygenated zone to either near or in the nitrate‐reducing zones. As the oxygen concentration declined through the Silurian, the depth of the oxic zone would have become shoaler with expanding anoxia. Late Wenlock graptolites that were unable to migrate to shallower depths, living in borderline oxygen conditions, could have been killed, resulting in the mortalities of the late Wenlock. Only those graptolites that were surface dwellers survived, adapted and reradiated.     

西藏南部聂拉木志留纪笔石新材料*

西沙群岛琛航岛琛科二井(CK-2)有878.3 m厚的新生代珊瑚礁灰岩(Cenozoic reef limestone)。新生代珊瑚礁灰岩自上而下包括了第四系的全新统和更新统以及新近系的上新统和中新统。其中, 中新统厚514.3 m, 产19属石珊瑚(Scleractinia corals)。更新统厚215.6 m, 产21属石珊瑚(Scleractinia)和1属八射珊瑚(Octocorallia)。珊瑚是营底栖固着生活的动物, 在地层断代方面它没有能像一些浮游动物(例如浮游有孔虫等)那么“精准”。但也有一些珊瑚的地质历程相对比较短暂的, 它们在地层划分和对比方面还是能起到一定的重要作用。根据本文的研究在琛科二井井深364–878.3 m的这一段中新世地层中就鉴定出有好几个只见于中新世或者常见于中新世的珊瑚, 如: 星日珊瑚(Astrhelia)、安的列斯珊瑚(Antillophyllia)和大安的列斯珊瑚(Antillia)等。另外在井深21.4–237 m的更新世地层中也发现了好几个只限于第四纪的珊瑚, 如: 叶状珊瑚(Lobophyllia)、合叶珊瑚(Symphyllia)、轮沙珊瑚(Trochopsammia)和苍珊瑚(Heliopora)等。上述那些珊瑚的地质分布与有孔虫(Foraminifera)生物地层鉴定的结果以及古地磁(Palaeomagnetism)和同位素(Isotope)年代地层测定的数据完全吻合。此外, 珊瑚除了在地层的划分对比方面(subdivision and correlation of the stratigraphy)能够起到一些关键的作用外, 更重要的是它在恢复和解释古地理(Palaeogeography)、古气候(Palaeoclimatology)和古生态(Palaeoecology)等方面也都能起到非常重要的作用。     

Anatomy and phylogenetic significance of Eoconularia loculata, a conulariid from the Silurian of Gotland

The type material of Eoconularia loculata (Wiman, 1895), a conulariid with high, bifurcated septa, was originally found in an erratic boulder, hence the source-rock is as yet unidentified. Recently, a rich material of the species has been discovered at eleven localities in the Silurian Hemse Beds of Gotland Another two localities in the Slite Beds (Wenlockan, Sheinwoodian) revealed what is assumed to be the ancestor of E loculata. This ancestral form probably constitutes a separate taxon distinguished from E. loculata in having simple, unbranched septa. E. loculata is re-described, and four ontogenetic stages in septal development are recognized. During stage 1, the most juvenile stage, the septa are simple. The septa in stages 3 and 4, the adult stages, are coarse and bifurcated. The affinities of conulariids are discussed, with the conclusion that the group shares a number of similarities with modem scyphomans. The microstructures of the exoskeleton show several similarities with coronatids, and the septa are interpreted to be homologous with the internal structures of stauromedusids. The stratigraphical distribution of all currently known septate conulariids suggests that septa were a primitive morphologic feature ranging from early? Ordovician to late Silurian. The simplest type, however, persisted at least into the early Permian. Five of the eleven described septa types have been found only among the conulariids from Gotland. □Conulariida, EOCONULARIA LOCULATA, bifurcated septa, taxonomy, ecology, morphology, Scyphozoa, Sweden, Gotland, Silurian.     

Patterns of sclerobiont colonization on the rugose coral Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian of Gotland,Sweden

Analysis of mushroom-shaped rugose corals Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian (Upper Visby Beds, Lower Wenlock, Sheinwoodian) of Gotland, Sweden, showed that they were colonized on both the upper (exposed) and lower (cryptic) sides by a variety of encrusting and boring (sclerobiont) biotas, represented by 10 taxa and at least 23 species. Bryozoans and microconchid tubeworms, the most abundant encrusters, dominated on the cryptic undersides of the corals, while the dominant endobionts responsible for Trypanites borings overwhelmingly dominated the exposed surfaces. Except for cnidarian sphenothallids, which were exclusive colonizers of the underside of only one coral host, no other encrusters could be referred to as obligate cryptobionts. Because the upper surface of these corals was likely covered by soft-tissues during life, in specimens lifted off the sea-floor sclerobionts must have settled on the cryptic sides first. They could colonize the upper side only after the coral’s death, unless it was covered by sediment as could be the case in some flat specimens. With time, the space on the underside of the coral skeleton may have progressively been filled by sediment as well, precluding further colonization by sclerobionts. In that respect, the colonization patterns of these corals by encrusters and borers were controlled by the complex interplay of environmental factors, sclerobiont dynamics and coral growth in a given Silurian habitat. Compared with Silurian stromatoporoid hosts, the sclerobiont diversity and abundance noted on the Schlotheimophyllum corals may be regarded as representative for the Silurian as a whole.     

塔里木盆地塔中台地上奥陶统海百合茎化石及其古生态*

聂拉木是西藏南部志留纪含笔石地层(石器坡组)的主要产地。近期在该地亚来村新发现一批笔石标本, 包括Normalograptus sp.、Glyptograptus sp.、Campograptus lobiferus、C. cf. lobiferus、C. cf. obtusus、C.? circularis、Lituigraptus cf. convolutus、Rastrites cf. perfectus、Stimulograptus sedgwickii、Streptograptus sp.和Torquigraptus decipiens。该组合面貌确定其属于志留系兰多维列统埃隆阶上部Lituigraptus convolutus带至Stimulograptus sedgwickii带。这一新材料的发现, 使西藏南部的志留纪地层得以作全球对比。     

Retiolitid graptolites from the collection of Hermann Jaeger II: <Emphasis Type="Italic">Cometograptus</Emphasis>, <Emphasis Type="Italic">Spinograptus</Emphasis> and <Emphasis Type="Italic">Plectograptus</Emphasis>

Graptolites from the Jaeger collection at the Museum für Naturkunde (Berlin, Germany) provide important information on structural details of Silurian (Wenlock–Ludlow) retiolitids as well as for the biostratigraphic and biogeographic distribution of these magnificent graptolites. Species of the genera Cometograptus, Spinograptus and Plectograptus are described from isolated glacial boulder material, collected in northern Germany and from shale specimens found in the Lower Graptolite Shale of Thuringia. The biostratigraphic placement of material derived from glacial erratic boulders, however, is far from being precise. The fauna associated with the neotype of Plectograptus macilentus in the ‘Unterer Graptolithenschiefer’ of Thuringia is discussed and illustrated. Cometograptus alfeisenacki from the Cyrtograptus lundgreni Biozone is recognized as a new species. The genus is discovered for the first time in North German glacial erratic boulders.     

Revised correlation of Silurian Provincial Series of North America with global and regional chronostratigraphic units and δ13Ccarb chemostratigraphy

Cramer, B.D., Brett, C.E., Melchin, M.J., Männik, P., Kleffner, M.A., McLaughlin, P.I., Loydell, D.K., Munnecke, A., Jeppsson, L., Corradini, C., Brunton, F.R. & Saltzman, M.R. 2011: Revised correlation of Silurian Provincial Series of North America with global and regional chronostratigraphic units and δ¹³C_carb chemostratigraphy. Lethaia, Vol. 44, pp. 185–202. Recent revisions to the biostratigraphic and chronostratigraphic assignment of strata from the type area of the Niagaran Provincial Series (a regional chronostratigraphic unit) have demonstrated the need to revise the chronostratigraphic correlation of the Silurian System of North America. Recently, the working group to restudy the base of the Wenlock Series has developed an extremely high‐resolution global chronostratigraphy for the Telychian and Sheinwoodian stages by integrating graptolite and conodont biostratigraphy with carbonate carbon isotope (δ¹³C_carb) chemostratigraphy. This improved global chronostratigraphy has required such significant chronostratigraphic revisions to the North American succession that much of the Silurian System in North America is currently in a state of flux and needs further refinement. This report serves as an update of the progress on recalibrating the global chronostratigraphic correlation of North American Provincial Series and Stage boundaries in their type area. The revised North American classification is correlated with global series and stages as well as regional classifications used in the United Kingdom, the East Baltic, Australia, China, the Barrandian, and Altaj. Twenty‐four potential stage slices, based primarily on graptolite and conodont zones and correlated to the global series and stages, are illustrated alongside a new composite δ¹³C_carb curve for the Silurian. Conodont, graptolite, isotope, New York, Ontario, series, Silurian, stage.     

Population structure of graptolite assemblages

Graptolite rhabdosomes display a diverse suite of morphologies. The range of morphotypes present within most moderate- to high-diversity assemblages from the Ordovician and Silurian is similar, despite the different taxonomic composition of the faunas at different times. Survivorship analyses of graptolite faunas from the Ordovician and Silurian demonstrate strong similarities in the mortality rates of unrelated graptolites of similar functional morphology. They also show a strong correlation between decreasing mortality rates among more mature colonies with increasing rhabdosome complexity. This similarity in both functional morphology and life history of graptolites suggests that they lived within a very stable planktic community structure.     

Aeronian (Llandovery, Lower Silurian) palynomorphs and graptolites from the Lipeón Formation, Eastern Cordillera, north-west Argentina

The lower levels of the Lipeón Formation, in the Eastern Cordillera, north-west Argentina, yield a marine-dominated palynomorph assemblage, together with graptolites of mid to late mid Llandovery age (Demirastrites convolutus and probably Stimulograptus sedgwickii zones). The palynomorph assemblage is dominated by acritarchs, but also contains algae and terrestrial cryptospores. Crassiangulina variacornuta, considered a potentially good global biostratigraphical marker for the Upper Llandovery is recovered for the first time from the Silurian of Argentina. The occurrence of this species in strata not younger than late Aeronian, and independently dated by graptolites, indicates an early first appearance for Crassiangulina variacornuta, in the Lipeón Formation, below the Aeronian/Telychian boundary. The lower part of the unit corresponds to a quiet marine environment; thus supporting that Crassiangulina variacornuta is a facies-sensitive acritarch.     

Placement of the Wenlockian/Ludlovian boundary in western New York State

Despite many years of detailed examination focused on the Silurian strata of New York State, the position of the Wenlockian/Ludlovian boundary has, to date, not been satisfactorily cstablished. Reccnt discovery of early Ludlovian graptoloid graptolites, however, provides the first conclusive biostratigraphic evidence for placement of this chronostratigraphic boundary within the New York sections. The carly Ludlovian genera Saetograptus and Spinograptus were recovered from a thin, but laterally persistent bed of argillaceous dolostone located near the base of the Goat Island Formation. This occurrencc indicates that the Wenlockian/Ludlovian boundary is at or near the contact between the Goat Island Formation and the underlying Gasport Formation, considerably lower than had previously been suspected. □ Silurian, Wenlockian, Ludlovian, graptolites, stratigraphy. biostratigraphy.     

Late Ordovician–Early Silurian facies development and environmental changes in the Subpolar Urals

The continuous Upper Ashgill–Sheinwoodian carbonate succession in the most eastern Kozhym River area in the Subpolar Urals comprises the Yaptikshor (Rawtheyan), Kamennaya baba (Hirnantian), Ruchej and Manyuku (Llandovery–?Sheinwoodian) formations. The facies of the deep subtidal Yaptikshor Fm. mark an abrupt sea‐level rise following emergence of the Bad’ya reef (Rawtheyan). Carbonate breccias at the base of the Kamennaya baba Fm. correlate with the beginning of the Hirnantian glaciation and change upwards towards the Ordovician–Silurian boundary with the development of light‐grey massive boundstone/packstone shoal deposits. An abrupt change in facies to the Rhuddanian–Aeronian Ruchej Fm. continental slope environment marked the start of a long‐term sea‐level rise. The uppermost Aeronian–?Sheinwoodian is represented by submarine canyon carbonate conglobreccias of the Manyuku Fm. unconformably underlying the Balban’yu reef. The rapid facies changes at the base of the Hirnantian and at the Ordovician–Silurian boundary were of global eustatic origin. In contrast, the abrupt changes in the Rawtheyan and the formation of the Manyuku Fm. conglobreccias were of local or regional origin associated with tectonics. They were followed by the start of a regional transgression (Yaptikshor Fm.) and a global transgression marked by the initiation of the Balban’yu Reef in the Sheinwoodian.     

Phylogenetic analysis reveals that Rhabdopleura is an extant graptolite

A phylogenetic analysis of morphological data from modern pterobranch hemichordates (Cephalodiscus, Rhabdopleura) and representatives of each of the major graptolite orders reveals that Rhabdopleura nests among the benthic, encrusting graptolite taxa as it shares all of the synapomorphies that unite the graptolites. Therefore, rhabdopleurids can be regarded as extant members of the Subclass Graptolithina (Class Pterobranchia). Combined with the results of previous molecular phylogenetic studies of extant deuterostomes, these results also suggest that the Graptolithina is a sister taxon to the Subclass Cephalodiscida. The Graptolithina, as an important component of Early–Middle Palaeozoic biotas, provide data critical to our understanding of early deuterostome phylogeny. This result allows one to infer the zooid morphology, mechanics of colony growth and palaeobiology of fossil graptolites in direct relation to the living members of the clade. The Subdivision Graptoloida (nom. transl.), which are all planktic graptolites, is well supported in this analysis. In addition, we recognize the clade Eugraptolithina (nov.). This clade comprises the Graptoloida and all of the other common and well‐known graptolites of the distinctive Palaeozoic fauna. Most of the graptolites traditionally regarded as tuboids and dendroids appear to be paraphyletic groups within the Eugraptolithina; however, Epigraptus is probably not a member of this clade. The Eugraptolithina appear to be derived from an encrusting, Rhabdopleura‐like species, but the available information is insufficient to resolve the phylogeny of basal graptolites. The phylogenetic position of Mastigograptus and the status of the Dithecoidea and Mastigograptida also remain unresolved. □ Biodiversity, Cambrian, Hemichordata, Deuterostomia, Ordovician.     

Graptolites from glacial erratics of the Laerheide area,northern Germany

Ordovician and Silurian glacial erratics of the Laerheide area (Lower Saxony, north-western Germany) bear well-preserved graptolites. The faunas provide important information on the origin and transport direction of the sediments preserved in a kame, representing the Drenthe stadial of the Saalian glaciation. The faunas even include species not commonly encountered in the successions of mainland Sweden, from where the erratics presumably originated. The most common graptolites are from Upper Ordovician (Sandbian to Katian) limestones and from Katian black shales. More common, however, are greenish limestones, sand- and siltstones, often combined in the term ‘Grünlich-Graues Graptolithengestein’, in which upper Wenlock to Ludlow (upper Silurian) graptolites are common.     

Horizon of the oldest known bryozoans (Ordovician)

Among the six species of fossil bryozoans described by Xia et al. [Xia, F.S., Zhang, S.G., Wang, Z.Z., 2007. The oldest bryozoans: new evidence from the late Tremadocian (Early Ordovician) of East Yangtze Gorges. Journal of Paleontology 81 (6), 1308–1326] from the Fenghsiang Formation of the Chenjiahe section of Yichang and the Guanzhuangping section, Liujiachang Town of Songzi, the Yangtze Gorges, Nekhorosheviella nodulifera occurs in the pristinus Conodont Subzone (lower Subzone of deltifer Conodont Zone) and the five other species are associated with the conodont Paltodus deltifer deltifer and the graptolites Acanthograptus sinensis and A. erectoramus. Based on the conodonts and graptolites, this bryofauna stratigraphically corresponds to the A. sinensis Graptolite Zone or P. deltifer Conodont Zone. The bryofauna is of Tremadocian Age (Early Ordovician) and represents the oldest bryozoans so far as known.     

PALAEOECOLOGY OF THE GRAPTOLITHINA, AN EXTINCT CLASS OF THE PHYLUM HEMICHORDATA

1. Whatever heirarchical system of classifying graptolites is adopted, perhaps even raising them to the rank of phylum, the hemichordates including Rhabdopleura and Cephalodiscus remain their closest relatives. 2. Benthonic graptolites preceded and outlasted the planktonic graptolites which exhibited spectacular morphological changes related to a change to a holoplanktonic mode of life and a probable hermaphroditism. 3. The resorption of the narrow-end of the larval skeleton (prosicular cauda) enabled the construction by an outer layer of secreting tissue (extrathecal tissue) of a hollow nema, the dark hollow rod which supported gas-filled tissue and which in turn conferred buoyancy on the colony. 4. The nema provided access to the exterior of the colony for extrathecal tissue which began to strengthen the outside of the prosicular and metasicular parts of the larval skeleton with laminated cortical deposits before the first non-sicular individual of the colony was budded. 5. Attachment of the larval stage in those graptolites having a basal disc or ‘roots’ was by the first-formed extrathecal tissue through a resorbed cauda. 6. Initial attachment of the larval stage in certain encrusting graptolites such as Idiotubus may have been by a larval individual lacking any scleroprotein periderm as a skeletal sheath. 7. After initial attachment the extrathecal tissue continued to secrete additional layers of cortical tissue mostly for the purposes of strengthening the colony. 8. Feeding in graptolites was by ciliated lophophore often positioned so as to take maximum advantage of currents flowing from the dorsal to the ventral side of the colony, for example in Dictyonema and Monograptus. 9. The main function of the nema, particularly of those nemata bearing vanes, was as a support for vacuolated tissue which imparted a holoplanktonic mode of life to planktonic (sensu Zato) graptolites. 10. Attachment of colonies (rhabdosomes) as groups of colonies (synrhabdosomes) was by the extrathecal tissue issuing from the tips of the nemata: such associations were probably sexual rather than for reasons of buoyancy. 11. Attachment of planktonic graptolites to floating algal fronds is an unnecessary hypothesis. Although an undoubted occurrence of graptolites in rocks containing large quantities of carbonaceous matter is beyond dispute, the plant or animal nature of this material has never been established. A symbiotic relationship of planktonic graptolites with a marine, formless alga, perhaps involving the extrathecal tissue, remains a possibility. 12. Although different species may have lived at different depths, the full vertical range of the holoplanktonic graptolites was probably small. The evidence advanced for depth zonation is considered inadequate. 13. Planktonic graptolites were essentially tropical to temperate in distribution with the bulk of the species and individuals in the former environment. 14. Automobility of graptolite rhabdosomes was an unlikely mechanism and does not readily account for the morphology and distribution of the graptolites. 15. Most planktonic graptolites were suspended beneath a nema coated in extrathecal, vacuolated (gas-filled) tissue: changes of position in the water were by passive response to ocean currents. 16. The nature of the graptolite zooid is considered unsolved, although it may have been essentially like that of the extant Rhabdopleura in having paired lophophores. 17. It is possible that a modified pre-oral lobe was capable of secreting both fusellar (inner) and cortical (outer) layers of the periderm. 18. The extrathecal tissue itself would in that case have been derived both from the nemal tube and the thecal individuals.     

Sea level and faunal changes during the latest Llandovery and earliest Ludlow (Silurian)

It is now recognized that the late Telychian and early Gorstian sea level changes are, like many others in the Silurian, of world‐wide extent. The 30–50 m deepening events at these times were between 1 and 2 Ma in duration, so melting continental ice caps appear to be the most probable cause. The faunal changes associated with the two events are respectively very close to the base and the top of the Wenlock Series and thus segregate many of the faunas diagnostic of the Llandovery, Wenlock, and Ludlow series. Permanent extinctions (often followed by radiations) are more prevalent in the graptolites, conodonts, and acritarchs, while benthic faunas are more affected by regional shifts in community distributions. This means that, in the benthos, slowly evolving lineages are the only reliable guides to time. Such phyletic evolution, however, appears to have been unaffected by sea‐level events.