Early Ordovician Trilobites Research Articles

Early Ordovician trilobites from Barnicarndy 1 stratigraphic well of the southern Canning Basin, Western Australia

Twenty-three trilobite taxa are described here from the Early Ordovician (Tremadocian to Floian) Nambeet Formation retrieved from the Barnicarndy 1 drillcore, Canning Basin, Western Australia. This includes one new genus, Veeversaspis gen. nov., and six new species: Asaphellus zheni sp. nov., Madiganaspis lauriei sp. nov., Norasaphus (Norasaphus) jagoi sp. nov., Rodingaia leggi sp. nov., Sanbernardaspis excalibur sp. nov., and Veeversaspis jelli gen. et sp. nov. This fauna can be divided into three stratigraphically distinct assemblages, the Apatokephalus sp.–Veeversaspis jelli gen. et sp. nov. Assemblage (2177.50–2382.94 m depth), Asaphellus trinodosus Assemblage (2030.07–2177.52 m depth), and Asaphellus zheni sp. nov. Assemblage (1595.83–2001.88 m depth). The two stratigraphically lowest assemblages are consistent with a late to latest Tremadocian age (both within the Paroistodus proteus Zone). The third, and highest, assemblage is consistent with a mid-Floian age (within the Oepikodus communis Zone). This systematic contribution refines previous biostratigraphic work based on an age-diagnostic conodont fauna and demonstrates the stratigraphic utility of using multiple taxonomic groups for more robust biostratigraphic age estimates. P.M. Smith [ Patrick.Smith@austmus.gov.au ], Palaeontology Department, Australian Museum Research Institute, Sydney, New South Wales, 2010, Australia, and Department of Biological Sciences, Macquarie University, Sydney, New South Wales, 2109, Australia. H.J. Allen [ heidi.allen@dmirs.wa.gov.au ], Geological Survey of Western Australia, Department of Mines, Industry Regulation and Safety, Mineral House, 100 Plain Street, East Perth, Western Australia, 6004, Australia.

Floian, Early Ordovician trilobites from the Olongbluk Terrane, northwest China

Floian, Early Ordovician trilobites from the Olongbluk Terrane, northwest China

Contrasting Early Ordovician assembly patterns highlight the complex initial stages of the Ordovician Radiation

The Early Ordovician is a key interval for our understanding of the evolution of life on Earth as it lays at the transition between the Cambrian Explosion and the Ordovician Radiation and because the fossil record of the late Cambrian is scarce. In this study, assembly processes of Early Ordovician trilobite and echinoderm communities from the Central Anti-Atlas (Morocco), the Montagne Noire (France), and the Cordillera Oriental (Argentina) are explored. The results show that dispersal increased diachronically in trilobite communities during the Early Ordovician. Dispersal did not increase for echinoderms. Dispersal was most probably proximally triggered by the planktic revolution, the fall in seawater temperatures, changes in oceanic circulation, with an overall control by tectonic frameworks and phylogenetic constraints. The diachronous increase in dispersal within trilobite communities in the Early Ordovician highlights the complexity of ecosystem structuring during the early stages of the Ordovician Radiation. As Early Ordovician regional dispersal was followed by well-documented continental dispersal in the Middle/Late Ordovician, it is possible to consider that alongside a global increase in taxonomic richness, the Ordovician Radiation is also characterized by a gradual increase in dispersal.

Rediscovery of Ordovician and Silurian trilobites from the Nares Arctic Expedition of 1875-6 from Ellesmere Island and western Greenland

Recent reorganisation of the trilobite collections in the Natural History Museum, London UK, led to the discovery of two drawers of specimens from ‘Arctic America’. These fragmentary specimens had remained unincorporated within the systematic trilobite collections. Original labels identified them as the H.W. Feilden Collection from the Arctic Expedition of 1875-6, led by Sir George Nares with HMS Alert and HMS Discovery. Some of the specimens were described but not illustrated by Robert Etheridge in 1878 but his determinations were approximate at best. The early Ordovician trilobites are an important historic collection, as the first collected from so far north. They are re-described and figured here. They have close affinities with species from East Greenland, Svalbard and western USA. A Silurian pygidium from western Greenland is identified as Ekwanoscutellum agmen. All indicate an origination in shallow carbonate facies of Laurentia.

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.

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.

An Early Ordovician Trilobite assemblage from the Lashkarak Formation, Damghan area, northern Iran

A low diversity Lower Ordovician trilobite assemblage is described from the middle part of the Lashkarak Formation at Simeh-Kuh, northwest of Damghan, northern Iran. Co-occurrence with conodonts of the lowermost Paroistodus proteus Biozone suggests an uppermost Tremadocian age. This assemblage includes four taxa, including one new genus and two new species, Damghanampyx ginteri nov. gen. nov. sp. and Asaphellus fecundus nov. sp. The third diagnosable species from the formation is Taihungshania miqueli (Bergeron, 1894) which has previously been reported from southern France and the Turkish Taurides, suggesting north Gondwanan faunal affinities.

The Early Ordovician trilobite distribution and zonation of the East Baltic

Biozones of the East Baltic Early Ordovician trilobites were studied based on the trilobite distribution in northwestern Russia, Estonia, and Sweden. New data on trilobite distribution reveal the diachroneity of the lowest calcareous sediments of the Maekula Member, which forms the upper part of the Leetse Formation in the East Baltic. Trilobites of the Tremadoc Apatokephalus serratus and Megistaspis (Ekeraspis) armata biozones are missing in the East Baltic, in contradiction to the suggestion of Balashova (Vopr. Paleontol., 1966, 5, 3-22). Some poorly preserved specimens probably belonging to Megistaspis (Para- megistaspis) planilimbata (Angelin) and also records of Pliomerops? linnarssoni (Wiman) indicate that the Arenig Megistaspis (P.) planilimbata Biozone of the Hunneberg Stage may be represented in some localities. The final delimitation of biozones in the Maekula and Paite members should improve when the ontogenetic and phylogenetic variation of the M. (Paramegistaspis) lineage has been fully documented. Until then the Evropeites lamanskii Biozone is used in the East Baltic following Balashova, as indicated by the appearance of that taxon in most studied localities, marking the beginning of the Billingen Age. The succeeding Megalaspides (Megalaspides) dalecarlicus Biozone is represented by the occurrence of at least its upper part in the Vassilkovo Beds in the St. Petersburg region, where Megalaspides paliformis Tjernvik occurs together with the index taxon (these taxa co-occur in the upper part of this zone in Sweden). The Paite Member in the East Baltic is correlated with the Megistaspis (P.) estonica Biozone of the upper part of the Billingen Stage in Sweden.

Adequacy of the Early Ordovician trilobite record in the southern Montagne Noire (France): biases for biodiversity documentation

ABSTRACTThe litho- and biostratigraphical subdivisions of the Tremadocian-Arenigian succession of the southern Montagne Noire are hereby revised. The Lower Ordovician diversity patterns are estimated through statistical analysis of 27 families, 64 genera and 132 species of trilobites across nine interval zones; from bottom to top: the Proteuloma geinitzi, Shumardia (Conophrys) pusilla, Euloma filacovi, Taihungshania miqueli, Taihungshania shui landyranensis, Colpocoryphe maynardensis, Neseuretus (Neseuretus) arenosus, Apatokephalus incisus and Hangchungolithus primitivus zones. Maximum trilobite diversity occurred within the E. filacovi and A. incisus zones, alternating with two sharp declines (S. (C.) pusilla and T.shui landyranensis zones), in both cases drastically related to transgressive-regressive trends. Trilobites attained their highest diversity in muddy outer-platform settings, decreasing in fine-grained sandstones and siltstones of shoreface environments, where trilobites could still be numerically abundant. Four major trilobite turnovers are recognised at the bottom of the P. geinitzi, S.(C.)pusilla, E. filacovi and T. shui landyranensis zones, in which survivors from previous intervals are not reported at specific level, and important generic replacements took place. Despite the relative incompleteness of the Lower Ordovician trilobite record, envisaged after analysing the high proportion of monotypic taxa and discontinuous ranges of some families, the trilobite record is representative enough to estimate diversity patterns, although a better understanding of the palaeoenvironmental control will greatly enhance biodiversity resolution.

Adequacy of the Early Ordovician trilobite record in the southern Montagne Noire (France): biases for biodiversity documentation

Adequacy of the Early Ordovician trilobite record in the southern Montagne Noire (France): biases for biodiversity documentation

Ordovician trilobite faunas and depositional history of the Taebaeksan Basin, Korea: implications for palaeogeography

The Taebaeksan Basin occupies the central-eastern part of the Korean peninsula and was a low-relief shallow marine carbonate shelf on which the Cambro-Ordovician Choson Supergroup was deposited. In the Taebaeksan Basin trilobites are among the most dominant fossil groups in the Lower Ordovician, but they become less important in Middle Ordovician faunal assemblages. The Early Ordovician trilobite faunas of the Taebaeksan Basin are characterised by the common occurrence of pandemic genera such as Jujuyaspis, Leiostegium, Asaphellus, Protopliomerops, Hystricurus, Apatokephalus, Shumardia, Asaphopsoides, and Kayseraspis. Biogeographically significant trilobite taxa include Yosimuraspis, Dikelokephalina, Koraipsis, and Chosenia. These Ordovician trilobite faunas, which thrived in shallow marine environments, show a remarkable similarity with faunas from North China, implying that the Taebaeksan Basin was connected through contiguous shallow waters to North China. These Sino-Korean faunas exhibit a close biogeographic connection with Australian faunas, with which they share some endemic genera, whereas they are more distantly related to the faunas of South China, South America, and North America. Based on these palaeobiogeographical features, it is suggested that in the early Palaeozoic much of the present Korean peninsula including the Taebaeksan Basin belonged to the Sino-Korean block, while part of the peninsula was derived from the Yangtze block.

Olenid trilobites: the oldest known chemoautotrophic symbionts?

Late Cambrian to early Ordovician trilobites, the family Olenidae, were tolerant of oxygen-poor, sulfur-rich sea floor conditions, and a case is made that they were chemoautotrophic symbionts. Olenids were uniquely adapted to this habitat in the Lower Paleozoic, which was widespread in the Late Cambrian over Scandinavia. This life habit explains distinctive aspects of olenid morphology: wide thoraces and large numbers of thoracic segments, thin cuticle and, in some species, degenerate hypostome, and the occasional development of brood pouches. Geochemical and field evidence is consistent with this interpretation. Olenids occupied their specialized habitat for 60 million years until their extinction at the end of the Ordovician.

An Early Ordovician trilobite faunule from the Choson Supergroup, Maepo, Tanyang area, Korea

This study reports an Early Ordovician trilobite faunule from the Choson Supergroup for the first time in Maepo, Tanyang area. The faunule is composed of trilobites, bellerophontoid gastropods and ostracods. Trilobites includeAsaphellus? sp.,Kayseraspis sp. cf.K. laticauda (Kobayashi, 1934),Asaphopsoides maepoensis n. sp., and asaphid gen. and sp. indeterminate. Comparable trilobite faunal assemblages have been known from theKayseraspis Zone of the Tumugol Formation in Taebaek-Samchok area, the upper part of the Yehli Formation in North China, and the lower part of the Emanuel Formation of Australia. This faunule indicates an early Arenig age.

Early Ordovician trilobite taxonomy and biostatigraphy of the Emanuel Formation, Canning Basin, Western Australia

Early Ordovician trilobite taxonomy and biostatigraphy of the Emanuel Formation, Canning Basin, Western Australia

Early Ordovician trilobite taxonomy and biostratigraphy of the Emanuel Formation, Canning Basin, Western Australia

Early Ordovician trilobite taxonomy and biostratigraphy of the Emanuel Formation, Canning Basin, Western Australia

The trilobiteAngelinaunstretched

The early Ordovician trilobite Angelina sedgwickii has hitherto been known only from stretched and squeezed specimens from North Wales. As a classic example of a deformed fossil, it has featured not only in palaeontological but also in structural geology textbooks, and various methodologies have been employed to attempt to restore it to its original shape. Recently discovered specimens from Shropshire, although flattened, are not sheared and preserve the original bilateral symmetry, affording for the first time an opportunity to find out what this trilobite might really have looked like.

Trilobite cuticle thickness in relation to palaeoenvironment

100 thickness measurements from thin sections of cephala or pygidia of early Ordovician trilobites occurring across an onshore to offshore environmental gradient show that progressively greater maximum cuticle thickness was characteristic of increasingly inshore sites. There is a 40-fold difference between the thinnest and thickest cuticles, and exclusively thin cuticles are confined to the offshore Olenid Biofacies. Variability in cuticle thickness increases offshore to onshore. Environmental control is shown to be more influential on cuticle thickness than is the overall length of the trilobite: some comparatively large trilobites having thin cuticles and small trilobites thick cuticles. The environmental factors which might be responsible for the pattern are briefly discussed. The thin cuticles dominating the offshore Olenid Biofacies were probably appropriate for dysaerobic conditions. Thick cuticles in the most inshore biofacies may have offered protection against predators and turbulence, but the additional presence there of trilobites with thinner cuticles is considered to reflect the greater heterogeneity of the epeiric habitat.

Early Ordovician trilobites and molluscs from the Poulsen Cliff Formation, Washington Land, western North Greenland

A well-preserved, shallow water bathyurid trilobite fauna of early Ordovician age, and associated gastropods and an undetermined hyolith are described from the Poulsen Cliff Formation of Washington Land, western North Greenland. Two new bathyurid species, Licnocephala sminue and Pe/tabellia elegans, and a new gastropod species, Plethospira(?) floweri, are described. Biolgina Maximova is considered a junior subjective synonym of Peltabellia Whittington. The distribution of the genus is an example of close relationship between shallow water trilobite faunas of Laurentia and the North-east Siberian platform in the early Ordovician.

Early Ordovician trilobites from the Wandel Valley Formation, eastern North Greenland

A small trilobite fauna is described from the Wandel Valley Formation of Kronprins Christian land, eastern North Greenland. It has a specific composition identical to the fauna from the Catoche Formation, western Newfoundland, which is typical of the shallow water bathyurid biofacies of the eastern part of the Ordovician Laurentian palaeocontinent. The fauna is of early Ordovician age, trilobite Zone H, equivalent to the early Arenig.