Trilobite Species Research Articles

Biogeographical and Biostratigraphical Significance of a New Middle Devonian Phacopid Trilobite from the Naidaijin Formation, Kurosegawa Terrane, Kyushu, Southwest Japan

Abstract. A newly discovered trilobite from the Naidaijin Formation in the Kurosegawa Terrane of southwest Japan is referred to Toxophacops (Atopophacops) fujiwara sp. nov. The trilobite occurs in strata 2 m below a level with detrital zircons that yield an age of 383.9±4.4 Ma that is likely Givetian (late Mid-Devonian). Elsewhere, Early to Mid-Devonian trilobite species of T. (Atopophacops) and T. (Toxophacops) have been recorded from the Nakazato Formation of the South Kitakami Terrane of northeast Japan, and from the Zhusilenghaierhan region of western Inner Mongolia, North China. The new trilobite species extends the geographical range of the phacopid subfamily Echinophacopinae, and supports the affinities of some Devonian Japanese trilobites with those of north China. The occurrence of Toxophacops in the Lower Member of the Naidaijin Formation, combined with other trilobite evidence, confirms a clear biostratigraphical distinction between the Lower Member (upper Lower and Middle Devonian) and Upper M...

Revision of the Cambrian Agnostina (Trilobita?) from Russia

Cambrian genera and species of Agnostina (?Trilobita) found in Russia are revised. Agnostid trilobite species are used as index taxa in chronostratigraphic subdivisions of the traditional Middle and Upper Cambrian in both regional and global stratigraphic scales. The correlation of the regional and international stratigraphic schemes largely depends on the state of knowledge of the regional agnostid fauna. Therefore, an up-to-date revision of this group based on the Russian collections taking into account their global diversity is very timely. For this study we reexamined the type collections of agnostids, including the holotypes of species described by Russian authors. This paper contains new photographic images of the holotypes housed in Russian museums. The compiled data offered solutions for some difficult taxonomic problems of the families Agnostidae, Ptychagnostidae, Peronopsidae, and some genera of Pseudagnostidae, Diplagnostidae. Apart from listing the diversity, this paper serves as the basis for studying the biogeography and evolution of this interesting arthropod group.

Dispersal in the Ordovician: Speciation patterns and paleobiogeographic analyses of brachiopods and trilobites

The Middle to Late Ordovician was a time of profound biotic diversification, paleoecological change, and major climate shifts. Yet studies examining speciation mechanisms and drivers of dispersal are lacking. In this study, we use Bayesian phylogenetics and maximum likelihood analyses in the R package BioGeoBEARS to reanalyze ten published data matrices of brachiopods and trilobites and produce time-calibrated species-level phylogenetic hypotheses with estimated biogeographic histories. Recovered speciation and biogeographic patterns were examined within four time slices to test for changes in speciation type across major tectonic and paleoclimatic events. Statistical model comparison showed that biogeographic models that incorporate long-distance founder-event speciation best fit the data for most clades, which indicates that this speciation type, along with vicariance and traditional dispersal, were important for Paleozoic benthic invertebrates. Speciation by dispersal was common throughout the study interval, but notably elevated during times of climate change. Vicariance events occurred synchronously among brachiopod and trilobite lineages, indicating that tectonic, climate, and ocean processes affected benthic and planktotrophic larvae similarly. Middle Ordovician inter-oceanic dispersal in trilobite lineages was influenced by surface currents along with volcanic island arcs acting as “stepping stones” between areas, indicating most trilobite species may have had a planktic protaspid stage. These factors also influenced brachiopod dispersal across oceanic basins among Laurentia, Avalonia, and Baltica. These results indicate that gyre spin-up and intensification of surface currents were important dispersal mechanisms during this time. Within Laurentia, surface currents, hurricane tracks, and upwelling zones controlled dispersal among basins. Increased speciation during the Middle Ordovician provides support for climatic facilitators for diversification during the Great Ordovician Biodiversification Event. Similarly, increased speciation in Laurentian brachiopod lineages during the Hirnantian indicates that some taxa experienced speciation in relation to major climate changes. Overall, this study demonstrates the substantial power and potential for likelihood-based methods for elucidating biotic patterns during the history of life.

The oldest known digestive system consisting of both paired digestive glands and a crop from exceptionally preserved trilobites of the Guanshan Biota (Early Cambrian, China).

The early Cambrian Guanshan biota of eastern Yunnan, China, contains exceptionally preserved animals and algae. Most diverse and abundant are the arthropods, of which there are at least 11 species of trilobites represented by numerous specimens. Many trilobite specimens show soft-body preservation via iron oxide pseudomorphs of pyrite replacement. Here we describe digestive structures from two species of trilobite, Palaeolenus lantenoisi and Redlichia mansuyi. Multiple specimens of both species contain the preserved remains of an expanded stomach region (a “crop”) under the glabella, a structure which has not been observed in trilobites this old, despite numerous examples of trilobite gut traces from other Cambrian Lagerstätten. In addition, at least one specimen of Palaeolenus lantenoisi shows the preservation of an unusual combination of digestive structures: a crop and paired digestive glands along the alimentary tract. This combination of digestive structures has also never been observed in trilobites this old, and is rare in general, with prior evidence of it from one juvenile trilobite specimen from the late Cambrian Orsten fauna of Sweden and possibly one adult trilobite specimen from the Early Ordovician Fezouata Lagerstätte. The variation in the fidelity of preservation of digestive structures within and across different Lagerstätten may be due to variation in the type, quality, and point of digestion of food among specimens in addition to differences in mode of preservation. The presence and combination of these digestive features in the Guanshan trilobites contradicts current models of how the trilobite digestive system was structured and evolved over time. Most notably, the crop is not a derived structure as previously proposed, although it is possible that the relative size of the crop increased over the evolutionary history of the clade.

Behavioural asymmetry in Devonian trilobites

The cephalon of the trilobite Phacopidae was usually separated from the thorax during moulting, and abandoned near the trunk. We statistically evaluated the distribution pattern of the cephala of Omegops cornelius, and found that near 70% of the total cephala were displaced on the right side, from the Upper Devonian deposits of the western Junggar in Northwest China. Omegops cornelius might have actively pushed the cephalon to the right of its body during moulting, indicating their preference to move counterclockwise. This preferred movement direction manifested the behavioural asymmetry in trilobites. A different type of asymmetry has been observed in Phacopidae Plagiolaria nandanensis from the Lower Devonian of Guangxi in South China, where about 67% of the cephala were found on the left side of the trilobite trunks. So the behavioural asymmetry may be diverse (or opposite) in different species of trilobites, and the reasons for the asymmetric moulting and movement patterns of the above two trilobites are likely related to their body structures, or their living environments. These new materials provide evidence for studying the origin and evolution of behavioural asymmetry.

Appendages of an early Cambrian metadoxidid trilobite from Yunnan, SW China support mandibulate affinities of trilobites and artiopods

AbstractAppendage anatomy contributes crucial data for understanding the evolution and ecology of Euarthropoda. The Palaeozoic trilobites show a great diversity of exoskeletons in the fossil record. However, soft parts, especially appendages, have only been discovered from a few trilobite species. Here we report extraordinarily preserved appendages in the trilobite speciesHongshiyanaspis yiliangensisZhang & LininZhanget al. 1980 (Redlichiida, Metadoxididae) from a single mudstone layer of the Xiazhuang fossil assemblage within the Hongjingshao Formation (Cambrian Series 2, Stage 3) near Kunming, Yunnan, SW China. The appendages exhibit the common architecture revealed by other trilobites and artiopods by consisting of a pair of uniramous antennae followed by a series of paired homonomous biramous limbs. The antennae in holaspid individuals comprise up to 27 spinous podomeres and their ontogeny occurs by lengthening of the podomeres. The post-antennal biramous limbs are similar to those in other polymerid trilobites and artiopods by having a single-segmented protopodite and an endopodite comprising seven segments, but possess a unique wide tripartite exopodite with long setae. Sophisticated appendage anatomy, including the body–limb junction, fine setae, putative muscle bundles and duct-type tissues, are also revealed. Appendages of trilobites, artiopods and other upper stem-group euarthropods are compared and summarized. TheH. yiliangensisappendages highlight the high morphological disparity of exopodites and the conservativeness of endopodites in trilobites and artiopods. This morphological pattern, together with similar body patterning seen in crustaceans but not in chelicerates, supports the mandibulate affinities of trilobites and at least some artiopods.

Some New Late Mississippian Trilobites from Oklahoma and Arkansas

ABSTRACT A new late Mississippian trilobite species, Kaskia pitkinensis, new species, is described from the Pitkin Formation of Arkansas. Kaskia pitkinensis, recovered from early Serpukhovian strata, is the youngest species of the Kaskia clade known in the United States. Kaskia c.f. K. wilsoni (Walter, 1924) also is illustrated. Cyrtoproetus kerhini, new species, from the upper Fayetteville Formation of Arkansas is also described. Richterella hindesvillensis Hessler, 1965, from the Hindesville Limestone of Oklahoma, is herein reassigned to the genus Cyrtoproetus Reed, 1943. Cyrtoproetus kerhini, new species, and C. hindesvillensis (Hessler, 1965) are the first known occurrences of Cyrtoproetus in North America.

Trilobites from the Redwall Limestone (Mississippian) of Arizona

ABSTRACT Trilobites from the Lower Mississippian (late Tournaisian) Redwall Limestone of Arizona are rare. Four identifiable specimens were recovered and studied. These specimens, in conjunction with recorded stratigraphic distributions of lost Redwall trilobites, allows for the assemblage of a range chart. Identifiable trilobite species include: Aprathia sp., Phillipsia peroccidens (Hall and Whitfield, 1877), Cummingella? sp., and Cummingella sp. The Redwall trilobites in this small collection exhibit a much closer taxonomic affinity to the late Tournaisian forms known from Europe than they do to species from strata of similar age in the eastern, central, and southern United States. This suggests that during the late Tournaisian the inferred geographic barrier known as the Transcontinental Arch prominently separated the Redwall depositional location from that of the central and eastern United States. This barrier appears to have contributed to the endemism of trilobites of the eastern United States.

The Lower Cambrian of the Salair and Gorny Altai (Siberia) revisited

This paper discusses the fossil record, stratigraphy and sedimentary environments of lower Cambrian sequences that crop out in the Salair and Gorny Altai, southern part of western Siberia (Russia). Numerous and well-preserved archaeocyaths and a few small shelly fossils (SSF) have been discovered in carbonate sequences that crop out nearby the Gavrilovka village, Salair. The presence of the Gordonicyathus howelliarchaeocyath Zone is established for the first time in this thick sequence of biogenic carbonates, in addition to the Nochoroicyathus mariinskii Zone, which was known previously from the Gavrilovka Formation. Both of these zones are Atdabanian in age. It is likely that accumulation of the Gavrilovka Formation took place in relatively shallow waters, along reef buildups surrounded by lagoons with archaeocyaths. In the Ak-Kaya section of the Gorny Altai, the trilobite species Alacephalus contortus and Poliellaspis rotundata, known previously from the upper Atdabanian, were discovered, only a few meters above horizons bearing lower Botoman trilobites. We may consider that the previously known age range of these two species is slightly longer and should be extended up to the lower Botoman. Alternatively, on the basis of their paleoecological affinity for agitated waters, these trilobites may be interpreted as reworked in lower Botoman strata.

Early Ordovician trilobites from the Iruya area (Cordillera Oriental, northwestern Argentina) and their stratigraphic significance

AbstractThe middle part of the Santa Rosita Formation (Tremadocian) is well exposed in the Iruya area, northwestern Argentina. At the Pantipampa and Rodeo Colorado localities, it is composed of shale and sandstone representing a wave-dominated shelf with influence of storm activity. Twenty-two trilobite species are described from these localities. Low-diversity assemblages from the lower part of the succession (Kainella meridionalisKobayashi,Asaphellus catamarcensisKobayashi,Leptoplastides marianus[Hoek]) are diagnostic of the early TremadocianKainella meridionalisZone. Trilobites from the middle part of the sequence are much more diverse.Kainella teiichiiVaccari and Waisfeld,Gymnagnostus kobayashiin. sp.,Conophryssp. indet.,Asaphellus clarksonin. sp.,A.stenorhachis(Harrington),A.isabelaeMeroi Arcerito, Waisfeld and Balseiro,Ogygiocaris?iruyensisn. sp.,Niobe(Niobella)inflecta(Harrington and Leanza) n. comb.,Metayuepingia riccardiin. sp.,Pseudokainella keideliHarrington,Apatokephalus rugosusn. sp.,Onychopyge acenolazain. sp.,O.gonzalezaen. sp.,Nileus cingolaniin. sp.,N.ericin. sp.,Leptoplastides marianus,Parabolinellasp. indet.,Hapalopleurasp. indet., and Ceratopygidae gen. et sp. indet., occur at different levels of theKainella teiichiiZone. This biostratigraphic unit includes the oldest records ofNileusDalman andOgygiocaris? Angelin;MetayuepingiaLiu,Niobe(Niobella) Reed, andOnychopygeHarrington are here first reported from the Tremadocian of southwest Gondwana. Finally, the uppermost part of the succession is characterized by the absence of the genusKainellaWalcott and the occurrence ofBienvillia tetragonalis(Harrington),Asaphellus stenorhachis,Pseudokainella keideliandLeptoplastidessp. indet., which are indicative of the middle TremadocianBienvillia tetragonalisZone. The trilobites described in this paper provide a basis for the refinement of correlations with other Lower Ordovician sections of the Cordillera Oriental. The genera recognized have their closest affinities with faunas from Scandinavia, Great Britain, and China.

Morphological assessment of the Cambrian trilobites Oryctocephalus indicus (Reed 1910) from China and Oryctocephalus ‘reticulatus’ (Lermontova 1940) from Siberia

Oryctocephalus indicus is a widespread trilobite species described from the lower–middle Cambrian (provisional Cambrian Stage 5) of south China, North Korea, India, USA and possibly North Greenland. Principal component analysis (PCA) and thin-plate splines (TPSs) based on a pooled sample of 359 specimens from four sections in the Guizhou Province, south China, demonstrated that the shape of this species is very constant, and only a small difference is detected in specimens from deeper part of the basin. Most of the variation is taphonomically controlled, and only the specimens from Sanwan Section show a modest natural difference due to a slightly different depositional environment. A comparison between the Chinese specimens and Oryctocephalus ‘reticulatus’ from the Molodo Section, Siberia, has been carried out. PCA and TPS show that O. ‘reticulatus occupies the same morphospace of O. indicus. However, the canonical variates analysis and the analysis of similarities detect small differences between the Siberian and Chinese populations, indicating a minor geographical variation caused by different environmental settings. The ontogenic variation is also described from early meraspids to holaspids. The most substantial changes take place during the first period of the early meraspid development, in which the glabella changes from a bell-like shape to a cylindrical shape. The ocular ridge changes from poorly defined in early meraspid to well developed in late merapids. The results indicate that O. ‘reticulatus’ is a junior synonym of O. indicus, suggesting that the base O. indicus of Siberia can be correlated with the O. indicus Zone of south China.

Self-regulation of trilobite diversity in Murero (middle Cambrian, Spain) due to compensatory extinction

As species accumulate in a community, competition for available ecospace is expected to prevent the addition of new species and to facilitate species extinction, thus producing a dynamic equilibrium of diversity. This mechanism remains under debate since its empirical support comes mainly from indirect or partial evidence, with very few direct tests at the species level. Here a new method is described to detect the presence of selfregulation feedbacks between species richness and turnover rates. It consists of Monte Carlo simulations which randomize the distribution of species ranges among stratigraphic intervals, providing predictions which allow the detection of genuine self-regulation feedbacks in the real data. Since the simulations include any potential bias due to preservation, sampling, or change in depositional environment, and these biases would also affect the real dataset, they are thus ruled out as explanations for any difference found. This method is applied to one of the best known fossiliferous sequences worldwide, the Rambla de Valdemiedes in Murero (RV1 section, middle Cambrian, Spain), a classic locality that has been studied for more than 150 years and which stands out due to its excellent sampling density, continuous deposition, and homogeneous fossil preservation. The results show that trilobite species richness was self-regulated due to positive feedback with extinction rate, which implies that compensatory extinction regulated this fauna in spite of the on-going Cambrian radiation. The lack of evidence of any origination feedback suggests ecological opportunities were not limiting for new species to colonize this Cambrian community

The middle lower Cambrian (Ovetian)Lunagraulosn. gen. from Spain and the oldest trilobite records

AbstractThe type material ofAgraulos antiquusSdzuy, 1961 from the La Herrería Formation, northern Spain, is revised together with additional material and included in the new genusLunagraulos. The stratigraphical range ofLunagraulos antiquus(Sdzuy, 1961) – occurring below that of the trilobite species of the generaLunolenus,MetadoxidesandDolerolenusin the type locality of Los Barrios de Luna in the province of León, northern Spain – and the accompanying ichnofossil assemblage demonstrate an Ovetian age (lower part of Cambrian Stage 3, currently being discussed by the International Subcommission on Cambrian Stratigraphy) for this species. Moreover, the trilobiteLunagraulos tamamensisn. gen. n. sp. is found in the Tamames Sandstone near the village of La Rinconada in the province of Salamanca, central Spain. The biostratigraphical position of this new taxon and its accompanying ichnoassemblage is also analysed and assigned to the lowermost Ovetian Stage. The genusLunagraulosis therefore the oldest agraulid found in the fossil record. The exceptional presence ofLunagraulosin a marine coarse siliciclastic succession – a facies rather typical for the ichnofossilsCruzianaandRusophycus, some of the oldest signs of trilobite activity – suggests that first trilobite representatives may have inhabited high- to middle-energy, marine environments. This hypothesis may also explain both the taxonomic and biostratigraphic heterogeneity of the first trilobite genera appearing across the world, due to preservation problems in this type of facies. Comparison of theLunagraulos biostratigraphy with other coeval Spanish fossil assemblages allows us to propose its intercontinental correlation with the oldest records of currently known trilobites.

Devonian trilobites from the Amazonas Basin: systematic diversity, taphonomy, and biogeographic significance

Although the Devonian invertebrate biota of the Amazonas Basin is incompletely known, its unusual mixture of supposedly Malvinokaffric and Appalachian taxa is of considerable biogeographical interest. The history of research on Devonian trilobites from the Amazonas Basin is summarized. These fossils occur in the Maecuru (latest Emsian – early Eifelian) and Ererê (latest Eifelian – early Givetian) formations, representing the families Homalonotidae, Dalmanitidae, and Calmoniidae. Trilobite diversity is higher in the Maecuru (nine named plus six indeterminate taxa) than the Ererê Formation (with only two named taxa), which displays faunal impoverishment generally. None of the Devonian Amazonas Basin trilobite species is known from other Malvinokaffric sites, suggesting very high endemicity within this basin. A taxonomic revision of “Homalonotus” derbyi (Clarke, 1890) is presented and a lectotype is designated. A lectotype and paralectotype are also designated for Eldredgeia paituna (Hartt & Rathbun, 1875). Some taphonomic observations of fossils from the Maecuru Formation are made, and a brief biogeographic synopsis of the Devonian Amazonas biota is also given.

A review of the Carboniferous and Permian trilobites of Australia.

The first complete review of the Carboniferous and Permian trilobite species found within Australia is presented to assess the current standing of Australian taxa in a modern systematic context. The review consists of four families, 20 genera and 61 known species from the early Tournaisian to Moscovian (358.9 Ma to 304 Ma), throughout New South Wales, Tasmania, Western Australia and Queensland. The revision also includes a revised anatomical nomenclature for Australian Carboniferous trilobites. Emended diagnoses are provided for seven genera and 28 species. The genus Thalabaria is placed within the subfamily Archegoninae, and the genera Australokaskia and Planokaskia are placed within Cummingellinae. The subgenera Brachymetopus (Spinimetopus), Bollandia (Capricornia), Australokaskia (Longilobus) and Australokaskia (Planilobus) are suppressed within Brachymetopus, Bollandia, Australokaskia, respectively. All Brachymetopus (Brachymetopus) maccoyi subspecies are elevated to species. Species of Linguaphillipsia are considered sensu lato until there is adequate revision of the entire genus. New combinations include the following: Aprathia semicircularis is reassigned to Weania; Aprathia applanata is questionably reassigned to Carbonocoryphe; and Phillipsia squamata is tentatively reassigned to Palaeophillipsia. The following have been synonymised: Conophillipsia with Monodechenella; Megaproetus with Pudoproetus; Weberiphillipsia with Palaeophillipsia; Weania (Rosehillia) with Schizophillipsia; Conophillipsia breviceps dungogensis with Monodechenella breviceps; Linguaphillipsia raglanensis with Linguaphillipsia stanvellensis; and Weberiphillipsia girvanensis with Palaeophillipsia collinsi. Carbonocoryphe (Winterbergia) elegans, Carbonocoryphe (Winterbergia) keepitensis and Winterbergia? waterhousei are considered representatives of indeterminate genera.

Trilobites from the Giles Creek Dolostone (Cambrian Series 3, Stage 5; Templetonian) Amadeus Basin, central Australia

AbstractTwelve trilobite species, plus rare agnostid arthropods, are described from the Giles Creek Dolostone (Cambrian Series 3, Stage 5; Templetonian) at Ross River Gorge and Gaylad Dam in the north‐eastern Amadeus Basin, Northern Territory, central Australia. Amphoton krusei sp. nov., Nepea ommacrada sp. nov., Penarosa oepiki sp. nov. and Schopfaspis shergoldi sp. nov. are described in association with Deiradonyx toddi Öpik, 1982, Dinesus sp., Kootenia sp., Pagetia silicunda Jell, 1975, Solenoparia sp., Tonkinella? sp., Xystridura filifera Öpik, 1975a, and Xystridura gayladia Öpik, 1975a, in addition to indeterminate agnostids. Pagetia silicunda and Xystridura filifera suggest an early Templetonian age, within the Pentagnostus anabarensis or Pentagnostus praecurrens Zone. This is supported by the co‐occurrence of Amphoton Lorenz, 1906, Deiradonyx, Öpik, 1982, Dinesus Etheridge, 1896 and Kootenia Walcott, 1889, all of which occur in Templetonian successions in the Georgina Basin (Northern Territory and Queensland), Gnalta Shelf (western New South Wales) and the Heathcote Greenstone Belt (Victoria). We argue that the Tempe Formation (central Amadeus Basin) and the Giles Creek Dolostone are not contemporaneous as previously suggested, indicating that regional stratigraphical schemes need to be amended.

The Naming of the Shrew by John Wright. Bloomsbury, London, 2014. No. of pages: xv+303. Price: UK£14.99. ISBN 978‐1‐4088‐1698‐1 (hardback)

There are those subjects that need learning in detail for examinations, but which are essential knowledge only for active practitioners. Once their days of usefulness to the student are over, the details of any arcane academic subject slip slowly away from memory as other, newly important facts and methodologies take their place in the mind. Thus, since my final examinations in 1980, the necessity for me to remember fine details of the classification of igneous rocks has been removed. Although I can still recognise diorites, andesites or granites used as building stones, these represent the extent of my limited ability to name igneous rocks. Which is why I welcome The Naming of the Shrew as an inspiring introduction for those, amateurs or academics, who might want to improve their knowledge of the Linnaean binomial classification of life or as an aid to the ailing memories of those who once knew more than they can remember. The intricacies of naming biological species, either live or fossil, is taught in universities, yet how swiftly the details must slip away for many after graduation. The Naming of the Shrew is a seamless way to explore biological nomenclature. Any reader will be entertained by the extraordinary array of instances which John Wright uses to illustrate his text. Every page abounds with examples that illustrate principles, clarify methodologies, and reiterate historical triumphs and errors, while fascinating and engaging the reader. For example, who wouldn't smile at a trilobite species named Han solo, a cuboid fungus Spongiforma squarepantsii and a wasp Pison eu? Wright's main interest is the fungi and, while he knows these best and can comment on their Linnean names with the greatest facility, The Naming of the Shrew is sprinkled liberally with the animal and vegetable, a few bacteria and a liberal selection of the palaeontological. Wright's text is highly readable, and he conveys the numerous aspects of biological nomenclature and classification by reference of only a minimum of relevant illustrations; his message is in the language of naming. Anyone who read Wonderful Life by the late Stephen Jay Gould (1989) will remember that he turned the systematics in the middle of the book into an account as gripping as any thriller. In The Naming of the Shrew, John Wright's virtuoso performance put me in mind of another late lamented author, Spike Milligan, whose verbal pyrotechnics in Puckoon (1965) made every page an adventure and a surprise. Wright has taken what in many hands would be the driest of subjects and turned it into a learned fireworks display.

Early Ordovician Trilobites from the Nazareno Area, Northwestern Argentina

The upper part of the Santa Rosita Formation (Ordovician, Tremadocian) in the Nazareno area, Cordillera Oriental, northwestern Argentina, records the vertical passage of high-energy, shallow water platform environments to offshore settings. Eighteen trilobite species are described from this locality for the first time. Although the taxa from the lower part of the succession (Leptoplastidessp.,Asaphellussp.) are scarce and non-age diagnostic, those from the upper part include diverse assemblages partially assigned to the late TremadocianNotopeltis orthometopaZone. Systematic descriptions of several species (Geragnostus nesossiiHarrington and Leanza,G. callaveiformisHarrington and Leanza,Asaphellus jujuanusHarrington,Notopeltis orthometopa[Harrington],Mekynophrys nannaHarrington,Ceratopyge forficuloidesHarrington and Leanza,Apatokephalus tibicenPřibyl and Vanĕk) are improved, the genusNileusDalman (includingN. australisn. sp.) is first reported from the Tremadocian of western Gondwana, and new species ofAsaphellusCallaway (A. nazarenensisn. sp.),ConophrysCallaway, andApatokephalusBrøgger are described. The trilobites have their closest affinities with faunas from Norway and Sweden.Notopeltis orthometopaandMekynophrys nannaare restricted to the uppermost part of the succession, well above the first records of most other trilobites recognized.

Early Ordovician Trilobites from the Nazareno Area, Northwestern Argentina

The upper part of the Santa Rosita Formation (Ordovician, Tremadocian) in the Nazareno area, Cordillera Oriental, northwestern Argentina, records the vertical passage of high-energy, shallow water platform environments to offshore settings. Eighteen trilobite species are described from this locality for the first time. Although the taxa from the lower part of the succession (Leptoplastides sp., Asaphellus sp.) are scarce and non-age diagnostic, those from the upper part include diverse assemblages partially assigned to the late Tremadocian Notopeltis orthometopa Zone. Systematic descriptions of several species (Geragnostus nesossii Harrington and Leanza, G. callaveiformis Harrington and Leanza, Asaphellus jujuanus Harrington, Notopeltis orthometopa [Harrington], Mekynophrys nanna Harrington, Ceratopyge forficuloides Harrington and Leanza, Apatokephalus tibicen Přibyl and Vanĕk) are improved, the genus Nileus Dalman (including N. australis n. sp.) is first reported from the Tremadocian of western Gondwana, and new species of Asaphellus Callaway (A. nazarenensis n. sp.), Conophrys Callaway, and Apatokephalus Brøgger are described. The trilobites have their closest affinities with faunas from Norway and Sweden. Notopeltis orthometopa and Mekynophrys nanna are restricted to the uppermost part of the succession, well above the first records of most other trilobites recognized.

The Cambrian of Bennett Island (New Siberian Islands)

The paper presents new data on the Cambrian stratigraphy of Bennett Island, one of the least explored East Arctic islands. The section, about 500 m of total thickness, comprises four lithological units that store a record of the deposition history: (1) clastic sediments including storm sandstones; (2) shallow-marine mudstone; (3) lagoonal variegated mudstone and limestone; (4) black shale. It is suggested to classify the units as formations with their proper names. The section spans all epoches of the Cambrian stratigraphy constrained by trilobite fossils. In the Cambrian, territory of the island belonged to Siberia rather than to some exotic terrane, judging by abundant endemic Siberian trilobite species in the Bennett section. This inference is supported by synchronicity in recorded deposition events of Bennett Island and northeastern Siberia (Kharaulakh Mountains). The Cambrian sediments of the two areas were deposited in different parts of a single shallow sea which extended as far as Taimyr.