Trilobiten.de

[Jens]

Clarkson ENK, Taylor CM, Ahlberg P (1997): Ontogeny of the trilobite Parabolina spinulosa (Wahlenberg, 1818) from the upper Cambrian Alum Shales of Sweden. - TRANSACTIONS OF THE ROYAL SOCIETY OF EDINBURGH-EARTH SCIENCES, 88: 69-89 Part 2.

Abstract: The ontogeny of Parabolina spinulosa is described on the basis of material from Andrarum (Skane) and Jamtland in Sweden. Protaspides are rare, and indifferently preserved, but well-preserved isolated tagmata and complete specimens from the early meraspid stages onwards were available for study. Whereas the ontogeny is broadly similar to that of the earlier stages wahlenbergi gi, there are subtle differences, notably in a greater spinosity from the earlier stages and a gradual, rather than a sudden, change of surface sculpture in the early holaspid. P. spinulosa at all stages of growth is much more variable than is Olenus. Meraspides have larger articulating half-rings anteriorly and the first thoracic segments are of greater sagittal length than in the adult; these were adaptations which enabled Parabolina to undergo cylindrical enrollment from an early stage. Parabolina is considered to have arisen from the earlier genus Olenus, and on the basis of comparative ontogeny many, though not all, features of Parabolina appear to be of paedomorphic origin. These include the reduction of the preglabellar field, retention of the visual surface, position of the eyes set close to the glabella, retention of a conterminant hypostome, yoking of the librigenae, spinosity of the thorax and pygidium, more numerous glabellar furrows and reduction in number of thoracic segments. Olenus attenuatus has several features intermediate between those of earlier Olenus species and Parabolina, and the origin of the latter genus is best considered in terms of a mosaic paedomorphocline.

[Jens]

Fortey R (2000): Olenid trilobites: The oldest known chemoautotrophic symbionts? - PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 97 (12): 6574-6578.

Abstract: 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.

Addresses: Fortey R (reprint author), Nat Hist Museum, Dept Palaeontol, Cromwell Rd, London, SW7 5BD England
Nat Hist Museum, Dept Palaeontol, London, SW7 5BD England

[Jens]

Eklof J, Rydell J, Frojmark J, et al. (1999): Orientation of agnostid shields in Alum Shale (Upper Cambrian): Implications for the depositional environment. - GFF 121: 301-306 Part 4.

Abstract: Polar angles (azimuth orientations) and vertical positions (convex side up or down) of cephala and pygidia of Agnostus pisiformis were recorded from 18 shale surfaces within a 0.85 m sequence of Upper Cambrian Alum Shale in Vastergotland, Sweden. The absence of articulated specimens, and of thoracic segments, on the surfaces suggest that the agnostids did not live in the depositional area, but that exuviae had been transported into this area, possibly following storms. Two of the surfaces, where most of the shields were deposited with the convex side down, indicated absence of bottom currents. On the other 16 surfaces shields were deposited with the convex side up, indicating that their position had been affected by currents. On 12 of these 16 surfaces the orientations were significantly bipolar, suggesting a wave regime. Hence the results indicate that the sediments forming the Alum Shale (of the A. pisiformis Zone) were deposited above storm wave base (<50 m deep).

Addresses: Eklof J (reprint author), Univ Gothenburg, Dept Zool, Box 463, Gothenburg, SE-40530 Sweden
Univ Gothenburg, Dept Zool, Gothenburg, SE-40530 Sweden
Univ Tubingen, Inst Geol, Tubingen, DE-72076 Germany
Yale Univ, Kline Geol Lab, New Haven, CT 06520 USA

[Jens]

Axheimer N, Ahlberg P (2003): A core drilling through Cambrian strata at Almbacken, Scania, S. Sweden: trilobites and stratigraphical assessment GFF 125: 139-156 Part 3.

Abstract: A core drilling at Almbacken in the village Sodra Sandby, Scania, southern Sweden, penetrated a c. 30 in thick succession of upper lower Cambrian and middle Cambrian strata. Only the uppermost part of the lower Cambrian (Gislov Formation) was recovered, comprising c. 1.50 m of unfossiliferous siltstones and a thin limestone bed at the base of the core. The core contains the most complete middle Cambrian succession so far documented in Scania. It contains a stratigraphical sequence from the Lejopyge laevigata Zone (upper Paradoxides forchhammeri Superzone) to the Holmia kjerulfi-group Zone (upper lower Cambrian). There is no faunal evidence for the presence of the Acadoparadoxides oelandicus Superzone. The middle Cambrian is 28.30 m thick and consists of dark grey to black mudstones and shales (Alum Shale) with stinkstones and limestone beds. Three major limestone beds were identified: the "Fragment Limestone" (0.35 m), the Exsulans Limestone (0.40 m), and the Andrarum Limestone (1.55 m). The middle Cambrian is richly fossiliferous, except in the lower six metres, and agnostoid trilobites generally dominate the faunas. Polymeroid trilobites and indeterminate lingulate brachiopods are abundant at some levels. The succession of trilobite species was used to erect a biostratigraphical subdivision into seven biozones. The preservation is generally good and 32 trilobites were identified to species level. The excellent preservation in the limestones allowed a description of growth stages in pygidia of Ptychagnostus punctuosus (Angelin, 1851).

Addresses: Axheimer N (reprint author), Lund Univ, Dept Geol, GeoBiosphere Sci Ctr, Solvegatan 12, Lund, SE-22362 Sweden
Lund Univ, Dept Geol, GeoBiosphere Sci Ctr, Lund, SE-22362 Sweden

[Jens]

Schovsbo NH (2001): Why barren intervals? A taphonomic case study of the Scandinavian Alum Shale and its faunas. - LETHAIA 34 (4): 271-285.

Abstract: The Scandinavian Alum Shale Formation (Middle Cambrian to Lower Ordovician) accumulated under generally low oxygen concentrations. Syndepositional changes in the oxygen concentrations of the bottom-water are reconstructed on the basis of the fossil fauna. Under relatively high oxygen concentrations, brachiopods and non-olenid polymerid trilobites inhabited the sea floor. Under lower oxygen concentrations the fauna was dominated by agnostids and at lowest oxygen levels by olenid trilobites. The enrichments of vanadium relative to nickel, as well as the enrichment of sulphur, match these faunal changes. A geochemical classification of the dysoxic environment is presented. The abundance of calcareous fossils decreases with increasing bottom water oxygen concentrations, indicating that the preservation of calcareous hard parts is most likely at the lowest oxygen concentrations. The poor preservation of calcareous fossils at relatively high oxygen concentrations is explained by the generation of corrosive pore waters during the reoxidation of sulphide compounds. Trilobitic and non-trilobitic intervals alternate up through the shale. Non-trilobitic intervals are either barren or contain non-calcareous fossils (phosphatic brachiopods, phosphatic 'ostracodes' and graptolites). The stratigraphical variation of trilobitic and non-trilobitic intervals is interpreted to reflect major changes in oxygen levels that might be linked to sea-level and climatic fluctuations.

Addresses: Schovsbo NH (reprint author), Univ Copenhagen, Geol Museum, Oster Voldgade 5-7, Copenhagen, DK-1350 K Denmark
Univ Copenhagen, Geol Museum, Copenhagen, DK-1350 K Denmark

[Jens]

Schovsbo NH (2002): Uranium enrichment shorewards in black shales: A case study from the Scandinavian Alum Shale. - GFF, 124: 107-115, Part 2.

Abstract: The Scandinavian Alum Shale Formation (Middle Cambrian to Lower Ordovician) contains high levels of organic carbon (up to 25 wt.%) and syngenetic enriched trace elements. A regional survey of the uranium and organic carbon content reveals that uranium is preferentially enriched in sections located palaeo-shorewards compared with sections located farther offshore. This type of enrichment mode is evident in the Upper Cambrian (above the A. pisiformis Zone) and Tremadoc interval. In the Middle Cambrian no significant regional variation in uranium level is present. In the most enriched Upper Cambrian biozone (Peltura scarabaeoides Zone) the average concentrations of uranium (100 to 300 ppm) are inversely correlated to zone thickness. The variable bed thicknesses are believed to represent primary differences in the rate of deposition and the relationship thus indicates a strong time-dependency in the enrichment processes governing uranium incorporation in sediments. The high uranium levels generally found shorewards are interpreted to reflect a more vigorous bottom water circulation that promoted higher rates of mass-transfer across the sediment/water interface relatively to the mud deposited farther offshore. Very high levels of uranium (1000 to 8000 ppm) concentrated in discrete beds (known as kolm) are interpreted to reflect resuspension of sediment in an anoxic water column that enhanced diffusive exchange between suspended particles and sea-water. A Late Silurian to Early Devonian thermal overprint towards the Caledonian Front affected the total organic carbon (TOC) content but appears to have no effect on the uranium distribution in the thermally mature sections.

[Jens]

Choi, DK, Lee, JG, Sheen, BC. (2004): Upper Cambrian agnostoid trilobites from the Machari Formation, Yongwol, Korea. - GEOBIOS-LYON, 37 (2): 159-189.

Abstract:
The Middle to Upper Cambrian Machari Formation in Korea is well known for abundant and diverse trilobites along with other invertebrate fossils. Based on recent reappraisal on the trilobites of the Machari Formation, eight trilobite zones have been proposed for the Upper Cambrian sequence: i.e., in ascending order the Glyptagnostus stolidotus, Glyptagnostus reticulatus, Proceratopyge tenuis, Hancrania brevilimbata, Eugonocare longifrons, Eochuangia hana, Agnostotes orientalis and Pseudoyuepingia asaphoides zones. Trilobites from the lower five zones and part of the Pseudoyuepingia asaphoides Zone have been already published elsewhere. In this paper, we describe the agnostoid trilobites of the upper three zones, Eochuangia hana, Agnostotes orientalis and Pseudoyuepingia asaphoides zones, of the Machari Formation. These comprise 24 species belonging to 13 genera, including one new genus (Yongwolagnostus) and ten new species (Homagnostus? sulcatus, Ivshinagnostus alatus, Ivshinagnostus quadratus, Yongwolagnostus stenorhachis, Yongwolagnostus dubius, Nahannagnostus pratti, Pseudagnostus? dividuus, Pseudagnostus medius, Pseudorhaptagnostus? urceus and Ammagnostus serus). These biozones correlate well with middle Upper Cambrian zones established in South China, Australia, Kazakhstan, Siberia, and Canadian Rocky Mountains.

[Jens]

Choi DK, Kim DH, Sohn JW (2001): Ordovician trilobite faunas and depositional history of the Taebaeksan Basin, Korea: implications for palaeogeography. - ALCHERINGA 25 (1-2): 53-68.

Abstract: 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.

[Jens]

Geyer G, Shergold J. (2000): The quest for internationally recognized divisions of Cambrian time. - EPISODES, 23 (3): 188-195.

Abstract: Although regional stadial schemes are available, and widely used, on all the major Cambrian continents, Armorica, Australia, Avalonia, Baltica, China, Kazakhstania, Laurentia, Siberia, the system currently has no formally agreed internationally recognized divisions. Since the IUGS Commission on Stratigraphy requires the definition of Global Boundary Stratotype Sections and Points (GSSPs), it has become the prime objective of the International Subcommission on Cambrian Stratigraphy to commence to document suitable biostratigraphic horizons within the system which might assist in achieving this goal. In this paper we suggest the consideration of four teen late Early Cambrian-terminal Cambrian levels, and document their stratigraphical and biogeographical distributions. Once agreement within the Subcommission is reached on which are the most suitable, it will be necessary to search for appropriate stratotype sections, bearing in mind the necessity to calibrate the biostratigraphy by way of non-biological correlation techniques, such as chemostratigraphy and magnetostratigraphy.

[Jens]

Geyer G, Malinky JM (1997): Middle Cambrian fossils from Tizi n'Tichka, the High Atlas, Morocco .1. Introduction and trilobites. - JOURNAL OF PALEONTOLOGY, 71 (4): 620-637.

Abstract: New finds of the trilobites Cobboldites tichkaensis Geyer, 1988, Pseudocobboldia pulchra (Hupe, 1953), Protolenus (Protolenus) densigranulatus Geyer, 1990, Latoucheia (Latoucheia) tichkaensis Hupe, 1953, and Acanthomicmacca neltneri Hupe, 1953, from the basal Middle Cambrian near the peak of Tizi n'Tichka in the central High Atlas, Morocco, supplement the known morphology of these species; the trilobites Acanthomicmacca new species, Oreisator tichkaensis new genus and species, and ''Parasolenopleura'' sp. from that locality are new. Acanthomicmacca neltneri is the first-species of the genus and family that is described and figured in detail in terms of morphologic plasticity and ontogeny; Oreisator tichkaensis is the first ptychopariacean trilobite formally described and based on material from Africa. Trilobites and other fossils from the locality suggest a strong affinity to other Mediterranean and to Avalonian faunas, which is well supported by helcionelloid and hyolith genera.

[Jens]

Ahlberg P, Ahlgren J. (1996): Agnostids from the Upper Cambrian of Vastergotland, Sweden. - GFF, 118: 129-140, Part 3.

Abstract: Fourteen agnostid species are described from the Upper Cambrian of Vastergotland, Sweden. They are assigned to eleven genera: Agnostus, Homagnostus, Trilobagnostus, Lotagnostus, Kormagnostus, Glyptagnostus, Hypagnostus, Peratagnostus, Cristagnostus, Pseudagnostus, and Aspidagnostus. Cristagnostus and Aspidagnostus have not previously been recorded from Scandinavia. The majority of the species are from the lower part of the Upper Cambrian, i.e., the Agnostus pisiformis, the Olenus and Homagnostus obesus, and the Parabolina spinulosa Zones. Agnostids are very rare in the upper part and only three species seem to be represented, viz. Trilobagnostus rudis, T. holmi, and Lotagnostus trisectus.

Ahlberg P (reprint author), DEPT GEOL HIST GEOL & PALAEONTOL, SOLVEGATAN 13, LUND, S-22362 SWEDEN
HOGSKOLAN SKOVDE, DEPT ART & MEDIA, SKOVDE, S-54128 SWEDEN

[Jens]

Ahlberg P, Ahlgren J (2000): Lotagnostus? mystacinus, a rare agnostid from the Upper Cambrian of Sweden. - ACTA PALAEONTOLOGICA POLONICA 45 (1): 91-96.

Abstract: Agnostids afford the best means of correlating Cambrian strata, and they are widely used for intercontinental correlations, They are most common in open-marine deposits and reached a maximum diversity during the Middle and early Late Cambrian, About twenty species of agnostids are known from the Upper Cambrian of Scandinavia, Lotagnostus? mystacinus Tjernvik, 1953 is a rare agnostid from the Upper Cambrian Agnostus pisiformis Zone of south-central Sweden. It is redescribed following examination of the holotype and an additional pygidium. The outline and morphology of especially the pygidial posteroaxis, which is distinctly trilobate by a pair of deep notular furrows, suggest that the species is best classified as a species of Lotagnostus. If correctly assigned to Lotagnostus, it would be the oldest known species of that genus.

[Jens]

Nielsen AT (1997): A review of Ordovician agnostid genera (Trilobita). -TRANSACTIONS OF THE ROYAL SOCIETY OF EDINBURGH-EARTH SCIENCES, 87: 463-501, Part 4.

Abstract: The definition and scope of Ordovician genera of agnostid trilobites are discussed, and the generic affiliation of Ordovician species and well-illustrated material referred to in open nomenclature is assessed. Some 198 Ordovician species plus 25 species of uncertain latest Cambrian/earliest Ordovician age are enumerated, representing 24 genera and subgenera, of which Geragnostus (Novoagnostus) n.subg. and Lotagnostus (Semagnostus) n.subg. are new. Geragnostella is ranked as a subgenus of Geragnostus. The species of Arthrorhachis are tentatively divided among a tardus species group and an elspethi species group. Species of Dividuagnostus are divided among a sensu stricto group and an early species group. Pseudorhaptagnostus Lermontova, 1951 is restored as senior synonym of Neoagnostus Kobayashi, 1955. It is concluded that Ordovician agnostids were largely adapted to temperate and colder water habitats.

[Jens]

Hier ein wichtiges Zitat mit frei erhältlichen PDF (url siehe unten). Es sind eine Reihe von seltenen Arten und Gattungen beschrieben, von einigen hab ich bisher noch nie was gehöhrt.

OLE A. HOEL (1999): Trilobites of the Hagastrand Member (Toyen Formation, lowermost Arenig) from the Oslo Region, Norway. Part II: Remaining non-asaphid groups. - Norsk Geologisk Tidsskrift, 79 (4): 259 - 280.

Autor: Paleontologisk Museum, Sars gate 1, N-0562 Oslo, Norway

Abstract:

This is Part II of a two-part description of the trilobite fauna of the Hagastrand Member (Tøyen Formation) in the Oslo, Eiker-Sandsvær, Modum and Mjøsa areas. In this part, the non-asaphid trilobites are described, while the asaphid species have been described previously. The history and status of the Tremadoc-Arenig Boundary problem is also reviewed, and I have found no reason to insert a Hunnebergian Series between the Tremadoc and the Arenig series, as has been suggested by some workers. Descriptions of the localities yielding this special trilobite fauna are provided. Most of the 22 trilobite species found in the Hagastrand Member also occur in Sweden. The 12 non-asaphid trilobites described herein belong to the families Metagnostidae, Shumardiidae, Remopleurididae, Nileidae, Cyclopygidae, Raphiophoridae, Alsataspididae and Pliomeridae. One new species is described; Robergiella tjernviki n. sp.

Der Link führt zur Abstract-Seite der Norsk Geologisk Tidsskrift,
unter entire-Document findet man das PDF. Bei mir wollte es sich nicht öffnen, aber ich habe den Button mit der rechten Maustaste angeklickt und dann unter speichern unter als pdf-Datei abgespeichert. Das klappt problemlos.

Grüsse,

Jens

http://taylorandfrancis.metapress.com/app/home/contribution.asp?wasp=a8612r45fg7tnl5f381y&referrer=parent&backto=issue,5,6;journal,5,8;linkingpublicationresults,1:103276,1

[Jens]

Auch nicht uninteressant ist folgender Artikel:

Richard Arnold Davis, R. H. B. Fraaye, Charles Hepworth Holland (2001): Trilobites within nautiloid cephalopods. - Lethaia, 34 (1): 37-45.

A1 College of Mount St. Joseph, 5701 Delhi Road, Cincinnati, Ohio, 45233-1670, USA
A2 Oertijdmuseum 'De Groene Poort', Bosscheweg 80, NL 5283 WB Boxtel, The Netherlands
A3 Department of Geology, Trinity College, Dublin 2, Ireland


Abstract:

'Sheltered preservation' of the remains of trilobites within the shells of nautiloid cephalopods is not especially uncommon. In most cases, of course, both the trilobites and the nautiloids were dead, and the association, merely due to post-mortem happenstance. However, on the basis of state of preservation and occurrence, a number of live individuals of the trilobite genera Acidaspis, Flexicalymene, and Isotelus from the Ordovician of the United States and of Alcymene and Encrinuraspis from the Silurian of Wales and the Czech Republic seem to have entered conchs of dead cephalopods, presumably for refuge.

Keywords:

BEHAVIOUR NAUTILOID CEPHALOPODS TAPHONOMY TRILOBITA

Kommentar: Auch von Gotland kenne ich Beispiele, daß man vollständige Trilobiten in den Wohnkammern von Nautiloiden finden kann. Es macht Sinn, daß Trilobiten in der gefährlichen Phase (nach der Häutung) sich vor Freßfeinden versteckt hielten und abwarteten, daß der neue Panzer aushärtet.

Von Gotland kenne ich Calymene tuberculosa, Calymene blumenbachi neotuberculata und Proetus cf. granulatus aus Nautiloiden-Gehäusen. Eine großwüchsige Calymene hatte sich anscheinend im Gehäuse verklemmt und es nie wieder verlassen. In einem anderen Gehäuse fand sich der Proetus als Häutungsrest, das Pygidium fehlte.


Grüsse,

Jens