ORAL PRESENTATIONS * Jonathan M

3rd International Trilobite Conference (Oxford, U.K., 2001)

Abstracts ORAL PRESENTATIONS * Jonathan M. Adrain and Stephen R. Westrop...... 3 * J. Javier Álvaro and Daniel Vizcaïno...... 3 W. Douglas Boyce...... 4 * Kevin D. Brett and Brian D. E. Chatterton...... 4 David K. Brezinski...... 5 * Derek E. G. Briggs , Matthew A. Wills and Christoph Bartels...... 5 * David L. Bruton and Winfried Haas ...... 6 * David L. Bruton and Winfried Haas...... 6 P. Budil...... 7 Brian D. E. Chatterton...... 7 Duck K. Choi...... 8 * Euan N. K. Clarkson , Cecilia M. Taylor and John Ahlgren...... 8 Desmond Collins...... 9 Catherine Crônier...... 9 Michael B. Cuggy...... 10 Malte C. Ebach...... 10 * Gregory D. Edgecombe and Gonzalo Giribet...... 11 Artem V. Fedoseev...... 11 Raimund Feist...... 12 Terence P. Fletcher...... 12 Richard A. Fortey...... 13 * Diego C. García-Bellido and Desmond Collins...... 13 Øyvind Hammer...... 13 * Wayne G. Henderson and Nigel C. Hughes...... 14 J. Stewart Hollingsworth...... 15 * Nigel C. Hughes , Giuseppe Fusco and Alessandro Minelli...... 15 * Nigel C. Hughes , Shanchi Peng, O.N. Bhargava and S.K. Parcha...... 16 * Brenda R. Hunda and Nigel C. Hughes...... 16 J. Keith Ingham ...... 187 Peter A. Jell...... 18 Peter A. Jell...... 18 * Talia S. Karim and Stephen R. Westrop ...... 18 * Joanne Kluessendorf and Donald G. Mikulic...... 19 Igor V. Korovnikov...... 19 Hans-Hartmut Krueger...... 20 * Dong-Chan Lee and Brian D. E. Chatterton...... 20 Bruce S. Lieberman...... 21 J. D. Loch...... 21 * Kenneth J. McNamara , Yu Fengý and Zhou Zhiyiý...... 22 * Donald G. Mikulic and Joanne Kluessendorf...... 22 * Alessandro Minelli , Giuseppe Fusco, Nigel C. Hughes and Mark Webster...... 23 Pham Kim Ngan...... 23 * Alan W. Owen and Tim McCormick...... 24 Helje Pärnaste...... 24 * Shanchi Peng , Loren E. Babcock and Huanling Lin...... 25 Richard A. Robison...... 25 * David M. Rudkin , Graham A. Young, R. I. Elias and Edward P. Dobrzanski...... 26 Andrew C. Sandford...... 26 * Paul A. Selden and Derek J. Siveter...... 27 * Alberto M. Simonetta , Marta Pacini and Lavinia Tinalli...... 27 * David J. Siveter , Dieter Walossek and Mark Williams...... 28 * Derek J Siveter , Derek E. G. Briggs, David J. Siveter and Mark D. Sutton...... 28 Jana Slaví ková...... 28 * Mark D. Sutton , Derek E. G. Briggs, David J. Siveter and Derek J. Siveter...... 29 J. F. Taylor...... 29 S. T. Turvey...... 30 Mark Webster...... 30 * Yuan Wenwei , Zhou Zhiyi and Zhou Zhiqiang...... 31 * Stephen R. Westrop and Ed Landing...... 31 * Zhou Zhiyi , Zhou Zhiqiang and Yuan Wenwei...... 32 Posters Alison Bowdler...... 33 Abigail M. Brown...... 33 Abigail M. Brown...... 34 Maria G. P. de Carvalho, John G. Maisey, L. Borghi and Emma Edwards...... 34 Terence P. Fletcher and George Theokritoff...... 35 Jozsef Gal, Gabor Horvath, Euan N. K. Clarkson and Otto Haiman...... 35 * Renato Pirani Ghilardi and Marcello Guimarães Simões...... 36 R. Gozalo, E. Liñán and M.E. Dies...... 36 Ole A. Hoel...... 37 David J. Holloway...... 37 Paul Hong, Jeong Gu Lee and Duck K. Choi...... 37 Yumiko Iwasaki...... 38 Nadezhda P. Lazarenko and Tatyana V. Pegel...... 38 Dong-Chan Lee and Brian D. E. Chatterton...... 39 Seung-Bae Lee and Duck K. Choi...... 39 Kristina Mansson...... 40 Andrew C. Sandford...... 40 Jana Slaví ková and Petr Kraft...... 40 J. F. Taylor, D. K. Brezinski and B. K. Sell...... 41 M. Franco Tortello and Susana B. Esteban...... 42 S. T. Turvey...... 42 M. Vidal and A. Loi...... 43 Daniel Vizcaïno and J. Javier Álvaro...... 43 Anthony B. Windberg...... 44 ORAL PRESENTATIONS

The ‘cryptogenesis’ problem and higher trilobite phylogeny. 1* 2 Jonathan M. Adrain and Stephen R. Westrop 1 Department of Geoscience, University of Iowa, Iowa City 2 Museum of Natural History, University of Oklahoma, Norman, Oklahoma, USA The majority of post-Cambrian trilobite orders appeared during the Early Ordovician, but their relationship to Cam- brian taxa is unknown and their origin is obscure, or ‘cryptogenetic’. As a result, the high-level phylogeny of trilobites is largely unresolved, and cryptogenesis is the most significant outstanding problem in the evolutionary history of the group. The difficulties in bridging the Cambro-Ordovician phylogenetic ‘gap’ are so profound that it has even been suggested that post-Cambrian clades represent iterative derivations from soft-bodied trilobitomorph ancestors. The early ontogeny of post-Cambrian trilobite clades is well known, and larval synapomorphies help define all of the major groups. In contrast, ontogenetic information is lacking for most Cambrian taxa. It has been suggested that new finds of Cambrian larvae offer the best hope for resolving cryptogenesis. Here we present the first evidence for the occurrence of two major post-Cambrian trilobite orders in Cambrian rocks, based on complete silicified growth series of Marjuman age from Nevada, USA. The fauna records all ontogenetic stages for at least 27 species, including the first unequivocal Cambrian members of the orders Proetida, and possibly Phacopida. The discoveries suggest that ‘post-Cambrian’ groups may in fact be quite common in the Laurentian Upper Cambrian. Additional recent discoveries of silicified faunas in the Cambrian of the Great Basin offer hope for resolution of the cryptogenesis problem, and a better understanding of the major features of Cambro-Ordovician trilobite evolution.

Why the one-eyed are not necessarily the kings in the ‘kingdom’ of blind trilobites? 1* 2 J. Javier Álvaro and Daniel Vizcaïno 1 CNRS, Université de Lille, France 2 Carcassone, France The Middle Cambrian conocoryphid biofacies can be considered as an autochthonous benthic assemblage of blind and normally eyed trilobites, which exhibit similar degrees of disarticulation and fragmentation, episodically associated with agnostoids. In support of normal oxygenation is the fact that the blind and small-eyed fauna is associated with other benthic organisms: the fauna inhabiting the conocoryphid-bearing shales consists of abundant phosphatic brachiopods, carpoids, hyoliths and rarer eocrinoids, sponges, chancelloriids and soft-bodied metazoans. The presence of articulated normally eyed and blind trilobites testifies to relatively quiet bottom conditions. In addition, certain beds show much evidence of burrowing by soft- Middle Cambrian biotic turnovers of the western Mediterra- nean area is the increase of blind forms after regressive episodes in oxygenated muddy sediments. Some blind trilobites evidently enjoyed greater survivorship than did normally eyed taxa, giving rise to distinct trilobite replace- ments.

Preliminary trilobite-based biostratigraphic zonation of Cambrian sequences, West Newfoundland, Canada. W. Douglas Boyce Regional Geology Section, Geological Survey of Newfoundland and Labrador, St. John’s, Newfoundland, Canada A composite biostratigraphic zonation is outlined for Cambrian siliciclastic and carbonate platform rocks exposed in southeast Labrador, and on the Great Northern and Port au Port peninsulas, in west Newfoundland. Nineteen trilobite zones (two in the Early Cambrian, nine in the Middle Cambrian, and eight in the Late Cambrian) are recognized in the Labrador and Port au Port groups; these are based on more than 500 collections obtained between 1976 and 1999. Each zone is named for its most common and/or distinctive species; the base of each zone is defined by the first appearance datum (FAD) of this species. The top of each zone is defined by the base of the succeeding zone. Bi- ostratigraphic data from the following areas was used: Port au Port Peninsula, Goose Arm, Gros Morne National Park, Hawkes Bay, Eddies Cove East, and Canada Bay.

Parabolops, a new asteropygine trilobite from southern Morocco with an unusual trident-like anterior cephalic frontal process. * Kevin D. Brett and Brian D. E. Chatterton Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada Well-preserved specimens of complete dorsal exoskeletons of two new species of comurid-type asteropygines allow for descriptions of a new genus, Parabolops. The type species, P. neptunis, and P. hammii, occur only at one locality in the Lower Devonian of southern Morocco. The cladistic relationships of the new genus were investigated using a character matrix of 44 characters and 12 taxa. These were analysed using PAUP, producing a single, most parsimonious tree, resolving the new genus and its relationships with Comura, Hallandclarkeops, Philonyx, Psychopyge, and Tolkienia. Parabolops is found to be a monophyletic genus, most closely related to the more problematic Comura. It differs from Comura mainly in unique modifications of the cephalic border and rostral plate into a three-tined prong. The possible functions of the frontal process are discussed, with sexual recognition and protective/defensive strategies being the most likely. Sensory, hydrodynamic, and feeding functions are not completely ruled out. Further- more, the two species occur in the same strata, which may provide evidence for sexual dimorphism.

Evolutionary, palaeozoogeographical and palaeoecological significance of phylogenetic analysis of the Late Palaeozoic trilobite genus Paladin. David K. Brezinski Maryland Geological Survey, Baltimore, Maryland, USA The cosmopolitan Carboniferous and Permian trilobite Paladin has been previously subdivided into three subgenera: Paladin, Kaskia, and Neokaskia. Phylogenetic analysis utilising an outgroup of Thigriffides roundyi and an ingroup of 11 North American species of Paladin produced two most parsimonious trees each composed of two distinct clades. The first clade consists of species assigned to the subgenus Kaskia. Because this clade is so distinct from the other Paladin clade, Kaskia is herein returned to the genus level. The second clade is composed of species that con- form more closely to the original diagnosis of the genus Paladin. Palaeo-zoogeographic evaluation of the ingroup demonstrates a substantial environmental proclivity, with the Kaskia clade being distributed within shallow-water cyclothemic strata, and the Paladin clade occurring in outer shelf and shelf-edge environments. Inclusion of several non-North American Visean and Permian Paladin species within the ingroup analysis resulted in the creation of two additional clades. European Visean to Namurian species form a clade which is separate from the North American Paladin clade, but suggest a close common ancestry. A clade formed by Permian species assigned to the subgenus Neokaskia appears to have closer ancestral relationships with Kaskia, and should be elevated to the genus level.

Non-trilobite arthropods from the Lower Devonian Hunsrück Slate of Germany. 1* 2 3 Derek E. G. Briggs , Matthew A. Wills and Christoph Bartels 1 Department of Earth Sciences, University of Bristol, UK 2 Department of Biology and Biochemistry, University of Bath, UK 3 Deutsches Bergbau-Museum, Bochum, Germany The Lower Devonian (Lower Emsian) Hunsrück Slate yields one of the most important assemblages of Palaeozoic fossils. The extraordinary preservation provides unusually complete information on the anatomy of marine arthropods, echinoderms and vertebrates, as well as less abundant taxa. The arthropods (c.16% of the fauna) described to date include Marrellomorpha (Mimetaster and Vachonisia); Phyllocarida (Crustacea; eight species in six genera, of which two are undetermined); Trilobita (20 species and subspecies in 11 genera), Xiphosura (one species), Eurypter- ida (one species), Scorpionida (one species), Cheloniellon (unplaced cheliceriform), and Pycnogonida (three species in three genera). Four new arthropods (the first to be reported from the Hunsrück Slate since the description of the pycnogonid Palaeothea devonica in 1980) are characterised by a body of just two tagmata, a cephalon and a large number of similar trunk somites; the affinities of three lie with the crustaceans, the fourth is an arachnomorph. These new taxa confirm that morphologies other than those represented by trilobites and modern arthropod groups per- sisted long after the Cambrian, at least in muddy bottom marine settings.

The puzzling eye of Phacops. 1 2* David L. Bruton and Winfried Haas 1 Paleontological Museum, Oslo, Norway 2 Institut für Paläontologie, Bonn, Germany Using well preserved material of Phacops from the Middle Devonian of Germany, we have analysed the anatomy of the schizochroal compound eye with a view to image-vision, stereo-vision, light-vision, point-vision, and nocturnal- versus diurnal-vision in phacopid trilobites. A refined method of measuring the axes of each individual lens of the eye is described. Our results confirm previous views on overlapping of the visual fields of ommatidia in the vertical rows, but this did not lead to stereovision as supposed. Instead, we believe the large ommatidia, with low F- number (focal length/aperture) resulted in what we define as puzzle-vision. This means that each individual lens formed a unit which, when assembled with others, produced a picture image. Details of the capsule below the ommatidia are given together with the lamellar nature of the lens. We cannot confirm the presence of a Huygensian interface in the schizochroal eye lens and suggest that the so-called intralensar bowl is a preservational artefact. The refractive index of the lens changes towards the centre producing what is known as a gradient index lens (GRIN-lens).

Making Phacops come alive. 1* 2 David L. Bruton and Winfried Haas 1 Paleontological Museum, Oslo, Norway 2 Institut für Paläontologie, Bonn, Germany Careful preparation of the ventral surface of well preserved specimens of Phacops from the Middle Devonian of Germany reveals details of exoskeletal articulation and muscle attachment sites. In the cephalon two pairs of legs are attached to apodemes, the first leg pair being attached directly to the exoskeleton. Paired apodemes for leg attachment occur on each of the eleven thoracic segments and one pair on the pygidium. The remaining legs of the pygidium are attached to the exoskeleton. The hypostoma extends backwards beyond the occipital ring, is attached to the doublure and held rigidly in place by long wing processes. Articulation of thoracic segments is afforded by an anterior articulation groove and axial process, and a posterior flange and socket. These structures lie on the same axis of rotation. Enrollment entails gliding of the lateral facets with imbrication being controlled by panderian protru- berances; pleural tips are modified to allow a close fit of the first three segments under the cephalon and for those of the remaining segments into the vincular notch of the doublure. Details of appendages and stomach are shown from X-ray photographs and other studies of Phacops from the Lower Devonian Hunsrück Slate. The long, flexible antennae must have been folded under the thorax during enrollment. During partial enrollment, movement of the gill filaments attached to legs of the pygidium allowed water to be circulated to the gills of the thorax. When the body was extended each gill, consisting of a flap-like shaft with attached lath-shaped filaments, curved and hung down inside the vaulted exoskeleton, the filaments imbricating posteriorly. Each walking leg consisted of six podomeres, the last with a claw and two articulated flanking hooks. The ventral surfaces of all podomeres were covered in spines used to filter food particles. Given the size of legs, varying shapes of apodemes and the need for enrollment, it is possible to suggest a basic arrangement of muscles needed to allow Phacops to function. New reconstructions show the ventral longitudinal muscle attached to intersegmental folds of the ventral integument. The dorsal longitudinal muscle is attached to the dorsal lateral parts of the articulating ring furrows, with branches extending midway on the cephalon and to the anterior axial rings of the pygidium. Extrinsic leg muscles were attached to the apodemes with extensions to areas below the dorsal furrow. The legs of the cephalon are attached far back and the mouth was forward of these. This gives room for a short oesophagus leading into a stomach lying below the glabella. Leg and gill movements are those associated with a filter feeder.

The dalmanitid and acastid trilobites of the Ordovician and Silurian of the Prague Basin (Czech Republic). P. Budil Czech Geological Survey, Prague, Czech Republic A revision of the Bohemian representatives of the Dalmanitidae and Acastidae is presented. No new taxa are described, but several species and two subgenera are included in the synonymy, especially because of observed pheno- typic variability, ontogeny, and preservation. All the ten genus-group taxa of the Dalmanitidae (Chattiaspis?, Dalma- nitina, Delops, Eudolatites, Mucronaspis, Ormathops (Ormathops), O.(Mirops), Sokhretia, Toletanaspis?, and Ze- liszkella) and four genera of the acastid trilobites (Dreyfussina?, Duftonia, Kloucekia, and Phacopidina) are distinguished in the time interval from the Arenig to the Ludlow (Gorstian Stage). The reasons for assigning some species to the Pterygometopidae are not accepted, and the assignment of Dreyfussina into the family Phacopidae is rejected. Lithofacies dependence was observed in some species only. These trilobites are considered as mostly benthic and/or nectobenthic, with supposed modes of life as scavengers to opportunistic predators.

Cryptic behaviour in trilobites. Brian D. E. Chatterton Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta Canada Some trilobites were predators but all were potential prey. Predators of trilobites include: cephalopods, cnidarians, asterozoans, other arthropods, worms, jawed fishes, and possibly larger trilobites. Physical dangers included strong currents and turbid waters. Specimens from the Cambrian Burgess Shale occur with agnostid and eodiscid trilobites inside empty worm tubes (work with Des Collins). These trilobites have their heads towards the narrow ends of the tubes, perhaps hiding to escape a turbidity flow. They show that mature agnostids and eodiscids were benthic. Speci- mens from Anticosti Island show Acernaspis orestes in burrows made by other organisms. In one specimen, 27 moults, piled up to three deep, are preserved in an L-shaped portion of a burrow. This trilobite entered open burrows of other organisms to moult and hide. Some cavity fillings of ancient reefs are almost entirely composed of trilobite sclerites. These cavities were refuges for trilobites, perhaps particularly when they moulted. Trilobites also used camouflage to hide, with sculpture, colour patterns and epiphytic organisms all helping. Finally, some trilobites had specialised eyes that may have been adapted for low light conditions. Perhaps they hid during the day and were active at night, escaping predators with poor night vision.

Early Palaeozoic trilobite faunas and palaeogeography of the Korean Peninsula. Duck K. Choi School of Earth and Environmental Sciences, Seoul National University, Korea There is a general consensus that the Sino-Korean and Yangtze blocks were separated during the Palaeozoic. In these palaeogeographic models, the Korean Peninsula was either included in the Sino-Korean block or simply divided into the two parts, placing North and South Korea to the Sino-Korean and Yangtze blocks respectively. Trilo- bites of the Korean Peninsula have been well known to comprise two contrasting assemblages in the Cambrian. The Cambrian fauna of the Taebaek Group belongs to the Hwangho faunal province that is characterised by endemic taxa representing shallow shelf habitats, whereas that of the Yongwol Group is comparable to the Jiangnan fauna that is dominated by cosmopolitan and pelagic forms indicating deep-water oceanic environments. On the other hand, the Ordovician trilobite faunas of the Taebaek and Yongwol groups are similar, and further they show a close affinity to those of North China and Australia. The juxtaposed occurrence of the contrasting Cambrian trilobite biofacies has been interpreted as resulting from the difference in depositional environments in that the Taebaek Group was formed in the shallow water (inner shelf), whereas the Yongwol Group was deposited in the deeper water (outer shelf to slope). The Ordovician faunal similarity between the two areas was attained by progressive shallowing of the Yongwol area, while the shallow marine setting was maintained in the Taebaek area. These Cambrian and Ordo- vician shallow marine faunas suggest a close biogeographic connection of Korea and North China.

Spiny olenid trilobites from the upper Cambrian of Sweden. 1* 1 Euan N. K. Clarkson , Cecilia M. Taylor and John Ahlgren 1 Department of Geology and Geophysics, University of Edinburgh, UK 2 Floby, Sweden The Upper Cambrian Alum Shales of Scandinavia are replete with olenid, and some agnostid trilobites, which are often found well preserved, especially in the ‘orsten’ calcareous concretions which occur throughout the sequence. Whereas the earlier olenids are of relatively standard morphology, their descendants may be of bizarrely spinose appearance, in particular the genus Ctenopyge. New material of Ctenopyge, from two separate areas in Sweden has added significantly to our understanding of these extreme forms. It has been possible to undertake detailed ontogenetic studies, which have shown that the spines originate at an early stage of development. Ctenopyge ceciliae is one of the smallest trilobites known, the largest adult cranidium being only 1.7mm broad. In this very spinose form, not only is the adult miniaturised, but the ontogenetic stages are far smaller than those of other olenids. Ctenopyge is known mainly from disarticulated material, and from a relatively few intact specimens, preserved flattened in shale. A rich new fauna in the Peltura minor Zone has been discovered in Västergötland, central Sweden, by John Ahlgren. There are four species of Ctenopyge, and many of the specimens are preserved intact and at all stages of growth. This has allowed the ontogeny to be worked out in great detail, and both juvenile and adult forms have been fully reconstructed in three dimensions. In Ctenopyge (Eoctenopyge) angusta long genal spines develop at an early stage, and being horizontal and parallel with the outstretched thorax would have allowed the animal to rest on the sea floor. For this species several moulting clusters have been distinguished. In C. (E.) modesta, very long genal and thoracic spines appear early in ontogeny, and in the final stages of growth the anterior thoracic spines develop broad flanges, which may have relevance for feeding strategies

Three new onychophorans from the Burgess Shale of British Columbia. Desmond Collins Department of Geology, Royal Ontario Museum, Ontario, Canada Three newly discovered marine onychophorans from the Middle Cambrian Burgess Shale of British Columbia fill the morphological gap between, a) Cambrian forms such as Aysheaia with annulate bodies and fat, annulate, claw- bearing lobopods typical of living onychophorans, and b) others such as Hallucigenia and Microdictyon with thin, cylindrical bodies and thin, non-annulate, flexible legs. The spiny arms and anchoring rear legs on two of the new onychophorans indicate that they climbed sponges and reached out into the water column for their food, whereas the third was an active sea-floor feeder. Other morphological features suggest a connection to primitive arthropods.

Upper Devonian phacopine trilobites. Catherine Crônier Laboratoire de Paléontologie, Université de Rennes, France Much progress has recently been made in the understanding of the ontogeny of Upper Devonian phacopine trilobites. The best insight into their development has been obtained from a growth series of Trimerocephalus lelievrei, a Famennian species from Morocco, where the size and shape changes have been clearly quantified by morphome- try. In the present study, a morphometric approach based on the outline has been used to establish the patterns of developmental variations in Weyerites ensae, another Famennian species from Germany. Moreover, the ontogenetic trajectories of these two species have been compared to establish the patterns of developmental and evolutionary changes within these two closely related species derived from Phacops, and to determine quantitatively, how much of the morphological difference is due to ontogeny. Most of the difference is related to structural changes that re- mained constant during ontogeny and independent of the rate of development and probably linked to ecological adaptation. A minor shape change appears canalised in these two species and could be explained in terms of relative differences in timing or rate of development. The results suggest that ecological adaptation might be studied by ex- amining the developmental changes occurring within species through time and space.

The problem of trilobite species stability in taxonomy. Michael B. Cuggy University of Saskatchewan, Saskatoon, Canada It has been suggested by Hughes and Lababdeira (1995), that most trilobite species are vastly oversplit. This conclu- sion was based on a re-evaluation of the suite of described Dikelocephalus species. Their revision reduced the number of species from its high of 26, to one. They used this as evidence that trilobite species are, in general, oversplit. They attribute oversplitting to the naming of species on the basis of inadequate material. Since most Dikeloce- phalus species were identified by Ulrich and Resser, and because they identified more than three times the number of species that any previous or subsequent worker, the question becomes: ‘Is oversplitting a general problem in trilobite systematics, or a problem of some individual workers?’. To test this, other works of Charles Resser were chosen for examination. Three Cambrian trilobite genera were used in this study. Two, Arapahoia and Bynumia, include species largely described by Resser; the third, Aphelaspis, was studied by Rasetti. These genera were selected since all include a large number of species, and all are rather generalised trilobites. The taxonomic stability of these trilobites is then tested to see if the pattern identified by Hughes and Lababdeira for Dikelocephalus is generally applica- ble to Cambrian trilobites.

Plate tectonics and palaeobiogeography. An area cladistic example using harpetid trilobites. Malte C. Ebach University of Melbourne, Australia Area cladistics is an exciting new development in cladistic biogeography. It aims to reconstruct the Earth’s past using information about various fossil and extant groups. It is not designed to discover the past of one particular group or even of two closely related species. Congruence in the form of biogeographic patterns is the result of allopatric (geographic) speciation. Vicariance, dispersal and combinations of both, are recognised causes for allopatric speciation. An area cladistic approach highlights the concept that all these events occur in response to the changes of plate tectonics either directly, by geographical boundaries, or indirectly, at the level of ocean currents. The com- bination of several directly affected groups, with particular reference to harpetid trilobites, yields a general area- gram; a branching diagram that depicts the relationship of areas.

Phylogeny of the extant Arthropoda: combining eight molecular loca and morphology. 1* 2 Gregory D. Edgecombe and Gonzalo Giribet 1 Australian Museum, Sydney, Australia 2 Harvard University, Cambridge, Massachusetts, USA Molecular systematic studies of arthropods are beginning to overcome the depauperate taxonomic sampling that marred early efforts. Still, analyses to date have relied upon only one or two well-sampled loci, and attempts to com- bine sequence data with morphology have made extensive groundpattern assumptions. A synthesis of the well- sampled molecular markers for arthropods employs eight genes: ribosomal 18S rRNA, 28S rRNA and snRNA U2, mitochondrial 16S rRNA and Cytochrome c oxidase I, and the nuclear coding genes Elongation factor 1-alpha, Poly- merase II and Histone H3. Forty-eight arthropod terminals, plus tardigrade and onychophoran outgroups, have at least four of these genes sampled, and are analysed together with 303 morphological, developmental, ultrastructural and gene order characters using Direct Optimization in POY. The most congruent parameter set for combined analysis of the eight genes and non-sequence data retrieves the monophyly of Pantopoda + Euchelicerata, Mandibulata, Myriapoda and Pancrustacea (=Hexapoda + Crustacea). These clades are, however, sensitive to analytical parameters, few withstanding a range of gap and transition/transversion costs.

Middle Cambrian agnostids of the northeastern part of the Siberian Platform. Artem V. Fedoseev Oil and Gas Geology Institute, Novosibirsk, Russia The same kinds of agnostid trilobites occur in such distant regions as North and South America, Australia, Antarcti- ca, Europe, Kazakhstan, Siberia and China. Agnostid trilobites are very abundant in the Middle Cambrian Kounam- ka Formation of the northeastern part of the Siberian Platform. On the base of phylogenetic linkages between members of the Ptychagnostidae in this study region, a series of forms demonstrating regular morphological changes may be recognised. The first representative here of the ptychagnostids is Pentagnostus proanabarensis which appears in the sequence in the lower part of the Kounamkites Zone. Up section it is accompanied first by Pentagnostus anabarensis. P. praecurrens appears in the upper part of the Kounamkites Zone and is present until the advent of Triplag- nostus gibbus. Further up section a diverse ptychagnostid assemblage is found which includes Tomagnostus fissus, Triplagnostus pictinatus, T. contortus, and Acidusus atavus. Further ptychagnostid development gave rise to Triplag- nostus arctus which is morphologically similar to Lejopyge. These stages of ptychagnostid development are represented as the following phylozones and interval zones: Pentagnostus proanabarensis, P. anabarensis, P. praecurrens, Triplagnostus gibbus, Tomagnostus fissus - Acidusus atavus, and Triplagnostus arctus. Factual and literature data confirm that the lower and upper boundaries of the Triplagnostus gibbus Zone are of great biostratigraphic significance. Study of this group of trilobites has potential for construction of a general stratigraphical scheme for the Middle and Upper Cambrian of the world.

Clustered trilobite assemblages formed under shelter : case studies of palaeoecological behaviour. Raimund Feist Institut des Sciences de l’Evolution, Université de Montpellier, France Life activities of trilobites sheltering within or under biotic hard-part remains on the sea floor, or in cavities of carbonate build-ups, are deduced from their orientation, diversity, size frequency and functional morphology. Trilobites from late Early Devonian shallow water limestones in the Montagne Noire, southern France, are known exclusively from accumulations under the outer 30mm fringe of large, flat tabulate or rugose coral colonies. All of the complete individuals and most of the exuviae are positioned dorsal side down, embedded parallel to the lower surface of the corals. This suggests that the trilobites fed on nutrients on the underside of the corals. The colonies appear to have attracted trilobites, sheltering under them during moulting in a nutrient enriched environment. Head shields and bone plates of Late Devonian arthrodires in the Tafilalet area, southern Morocco, are often densely surrounded by remains of phacopine and cyrtosymboline trilobites of various ontogenetic stages. These accumulations, that do not occur in the adjacent matrix, resulted presumably from preferential gathering of trilobite communities for moulting adjacent to a food source. Likewise, evidence for both reproduction and moulting in a protected area, as well as a scavenging mode of nutrition, is indicated by in situ preservation of densely packed mass accumulations of larval stages and articulated adult carapaces within body chambers of cephalopod conchs. Many of the larger empty am- monoid shells of Manticoceras and of Platyclymenia annulata, which were deposited on the muddy sea floor in an offshore environment of the southern Moroccan Maider Basin, attracted trilobites that hid in the downward-facing umbilical void. A cavern-dwelling mode of life can be deduced for monospecific mass occurrences of scutelluid populations which inhabited pockets in mud-mounds that developed on the Hamar Laghdad Ridge, southern Moroc- co. On the correlation of olenellid and paradoxidid sequences. Terence P. Fletcher Dunbar, East Lothian, UK Global correlation of Cambrian rocks is hindered because they have been subjected to tectonic movements responsible for the destruction of oceanic sequences. The best preserved sequences are those developed on the more stable continental platforms, where biota responded to local conditions to form distinct ‘faunal provinces’. Shelf sequences characterised by Olenellus have been recognised as distinct from those with paradoxidids with little basis for accurate correlation. However, some olenellids occur below paradoxidids and, therefore, their ranges have been treated as marking divisions of Cambrian time – Olenellus = Lower Cambrian, Paradoxides = Middle Cambrian. Succes- sions representing outer shelf-slope environments occur in the New York Taconics, southeastern Newfoundland, Morocco and Siberia, and provide evidence for correlating separate continental successions. Such environments, marginal to the oceanic gene pool contain common agnostid trilobites that are the Cambrian correlatives of the graptolites and ammonoids of later periods. Specific agnostids from both suborders (Agnostina, Eodiscina) occur with Olenellus and with Acadoparadoxides to demonstrate that the paradoxidids first appear at a time coeval with a position within the Bonnia – Olenellus Zone.

Feeding habits in trilobites: progress and problems. Richard A. Fortey Department of Palaeontology, Natural History Museum, London, UK The determination of feeding habits in trilobites was described by Fortey and Owens (1999) by the discrimination of three modes of hypostome attachment. Hypostomes rigidly buttressed against the cephalic doublure in conterminant or impendent condition were associated with scavenging/predating habits; such hypostomes often developed appro- priate modifications (forks, ‘grinders’) of the posterior margin. Natant hypostomes were comparatively conservative and unmodified from Cambrian to Carboniferous; they were associated with a particle-feeding mode of life. A third group of suspension feeders was identified with trinucleid/harpid morphology featuring a subcephalic vault and sus- pended thorax. Experimental testing of a current circulation model for the latter yielded equivocal results, and did not support the idea of the trinucleid fringe as having an exhalant function. Hydrodynamic experiments have also been devised to test whether dorsal terrace ridges are consistent with other data on life habits. A progress report on this work will be presented.

A new study of Marrella splendens from the Burgess Shale, British Columbia, Canada. 1* 2 Diego C. García-Bellido and Desmond Collins 1 Departamento de Paleontologia, Universidad Complutense de Madrid, Spain 2 Department of Geology, Royal Ontario Museum, Ontario, Canada The study of over 1000 specimens of Marrella splendens, out of the more than 6000 collected by the Royal Ontario Museum since 1975, has produced new details of the anatomy, functional morphology, behaviour and population biology of the most common arthropod in the Burgess Shale. Among new features are the presence of sessile eyes, a distinction between the alimentary canal and the circulatory system, interpretation of the second pair of antennae as a pair of swimming appendages, and a larger range of size, from 1ꞏ1 to 24mm in length. There is one unique specimen that is preserved in the act of moulting. The ROM collections extend the geographical distribution and stratigraphical range of Marrella.

Models for the developmental genetics of lateral inhibition in trilobites – cuticular and ommatidial patterning. Øyvind Hammer Paleontological Museum, Oslo, Norway Trilobite cuticles are positioned in a spacing pattern, as revealed by spatial statistics. Similar spacing between sensory bristles, due to lateral inhibition, is well known in insects, and the genetic basis for these patterns has recently been an important field of study in developmental biology. Assuming that similar genetic principles are in operation for the positioning of peripheral neuronal elements in all arthropods, it can even be speculated that genes with functions similar to delta, notch, and scute were active in trilobite cuticular patterning. In some trilobites, terrace ridges seem to display transitions into granulation, indicating that these two types of structure share as underlying pattern formation mechanism reminiscent of reaction-diffusion systems. Such patterns are seen very well in specimens of Paradoxides forchammeri. Lateral inhibition has also been proposed as the mechanism responsible for the spacing of trilobite ommatidia, and a similar system in Drosophila provides a possible model for the developmental mechanism responsible. Such developmental scenarios can imply hypothetical developmental constraints and degrees of freedom that should be kept in mind by taxonomists.

Saukiid-dikelocephalid trilobites and their implications for Late Cambrian palaeogeographic and palaeoen- vironmental reconstructions. Wayne G. Henderson* and Nigel C. Hughes Department of Earth Sciences, University of California, Riverside, California, USA Genera assigned to the Saukiidae and the Dikelocephalidae have long been considered closely related. Among Dike- locephalidae, a markedly expanded cephalic doublure is synapomorphic for dikelocephalids, and the Saukiidae, as currently defined, is probably paraphyletic. Nevertheless, the saukiid cranidium has a distinct morphology and, while the Dikelocephalidae are exclusively Laurentian, trilobites with the saukiid glabellar morphotype occur globally in equatorial regions. This distribution is particularly surprising as Cambrian polymerid trilobites are generally considered to show high degrees of continental endemism, and saukiids are particularly known for their preference for nearshore habitats. Ulrich and Resser (1933) first described the Saukiidae in detail, erecting 104 species in five genera from the Upper Mississippi Valley. An additional 25 genera and 200 species of saukiids have since been described, occurring across both the equatorial core and outboard Gondwana, Laurentia, Siberia, and Kazakhstan; they have been extensively employed for biostratigraphic zonation. Saukiid taxa have frequently been described as endemic to these regions even though there are few, if any, morphological features to distinguish them from species found on other palaeocontinents. Accordingly, there is a critical need to refine species concepts. We are: 1) evaluating character variation within large collections from single bedding planes to establish the bounds of intrapopulation variation, and 2) constructing a character matrix for phylogenetic analysis of all well-preserved saukiids based strictly on morphological criteria. Such analysis will point to the resolution of taxonomic relationships within these groups and provide the basis for evaluating Late Cambrian endemism and biogeographic links.

Early Cambrian Holmiidae and related trilobites in Nevada : evolutionary trends and possible correlations. J. Stewart Hollingsworth Grand Junction, Colorado, USA The Monetzuman Stage in Laurentia offers an opportunity to observe the appearance of the fallotaspidid, holmiid and nevadiid trilobites in a fairly continuous section. The stage begins in a deep-ramp siliciclastic environment, which is interrupted by a moderate regression; in the rapid transgression following this event, holmiids and nevadiids appear. An intermittent carbonate bank developed after the middle of the Montezuman, but off-shelf or slope deposits have not been found. The first holmiids to appear are forms which have a broad cephalon and narrow thor- th th ax with a massive spine on the 12 or 13 segment, some of which resemble Schmidtiellus from Baltica. Esmeral- dina rowei soon appears accompanied by several other species of this genus and Palmettaspis. Higher, Esmeraldina is replaced by a new genus of holmiid in which the L3 lobe disappears in a greatly inflated anterior lobe. Holmiella, a genus with strongly advanced genal spines, appears in the middle Montezuman and seems to persist to the end of the stage, which is marked by the extinction of all nevadiids and holmiids in Laurentia. Meraspides are uncommon, but late-stage meraspides of the earliest holmiid are quite similar to same-stage meraspides of Fallotaspis near the beginning of the Montezuman Stage.

The dynamics of post-cephalic segment accretion in trilobites. 1* 2 2 Nigel C. Hughes , Giuseppe Fusco and Alessandro Minelli 1 Department of Earth Sciences, University of California, Riverside, California, USA 2 Department of Biology, University of Padova, Italy Trilobites generally developed hemianamorphically, i.e. only the early moults were accompanied by an addition of new thoracic segments (meraspid period = anamorphic phase), then the animal continued to moult without further addition of thoracic segments (holaspid period = epimorphic phase). Adult Aulacopleura konincki (Proetida, Aulaco- pleuridae; Middle Silurian) show marked variation in segment number, there being from 18 to 22 in the thorax. A scatter-plot of the number of thoracic segments against glabellar length has been interpreted as the result of anamorphic development protracted into adulthood (Hughes and Chapman 1995), with an ontogenetic threshold occurring at a certain body size, when segment increment rate dropped significantly in all individuals, regardless of the number of segments they had when reaching that size. This interpretation rested on two hypotheses, which are not necessarily associated: a) the meraspis to holaspis trigger was size-dependent; and b) the holaspis increased in the number of segments, although at a rate lower than the meraspis. Testing the first point is difficult, but hypothesis b) implies that some moults resulted in segment addition, while some others not, without any evident regular schedule. Such growth is unknown amongst Recent arthropods. By reference to the postembryonic development of Recent arthropods, we suggest a more parsimonious hypothesis for the dynamics coupled with ontogenetic variability in the switch (whatever its nature was) turning the trilobite from the anamorphic to the epimorphic developmental phase, leading to an intraspecific polymorphism for the final (adult) number of thoracic segments.of postcephalic segment accretion in A. konincki, in terms of hemianamorphosis.

The oldest and the youngest Cambrian trilobites known from the Himalaya. 1* 2 3 4 Nigel C. Hughes , Shanchi Peng , O.N. Bhargava and S.K. Parcha 1 Department of Earth Sciences, University of California, Riverside, California, USA 2 Institute of Geology and Palaeontology, Nanjing, China 3 Harayana, India 4 Wadia Institue of Himalayan Geology, Dehra Dun, Uttar Anchal, India Several important new trilobite collections have been made from the Himalaya since the publication of the mono- graph ‘Himalayan Cambrian Trilobites’ (Jell and Hughes 1997). These extend both the temporal and geographic range of Cambrian deposits known from that region. A collection from the Nigali Dhar syncline of the Lesser Hima- laya in Himachal Pradesh includes Qingkouia zhangyangouensis, Dolerolenus (Malungia) cf. D. (M.) malungensis, and, from slightly higher in the section, Protolenella sp. These specimens suggest an age of latest Chiungchussian to earliest Tsanglangpuian, and predate Paokannia magna, previously considered to be the oldest trilobite known from the Himalaya. Cambrian trilobites are now also known from Bhutan, some 1000km farther east than any previously reported Himalayan trilobite. These forms resemble Prochuangia and suggest an age no older than early Changsha- nian. Until now the youngest Cambrian trilobites known from the Himalaya were from Kashmir and of early Kusha- nian age. Lastly, new collections of some 700 specimens from limestones at the classic Parahio Valley section in Spiti show limited deformation and will be permit greater confidence in taxonomic determinations than has generally been available with other Himalayan Cambrian trilobites; they will also permit detailed comparison with forms from the Yangtze block. Together, these new collections indicate the potential of the Himalayan region for yielding a substantial Cambrian record. The discovery of late Cambrian trilobites from Bhutan is critical because it falsifies the general notion that deformation in the eastern Himalaya was too severe to permit preservation of Lower Palaeozoic fossils, and provides a potential link with faunas and sections in Sibumasu. Further faunal and sedimentary work along the Himalayan margin may establish whether the Qiangtang and Lhasa blocks of Tibet collided with India in late Cambrian time, and whether they were contiguous with Sibumasu, as in the Cimmerian model.

Event-bed deposition in the Cincinnatian Series: implications for taphonomic processes and assessing microe- volutionary changes within Flexicalymene. Brenda R. Hunda* and Nigel C. Hughes Department of Earth Sciences, University of California, Riverside, California, USA Despite intense scientific interest, there are currently little high-resolution data available to understand how organ- 3 6 isms responded to multiple episodes of environmental change at time-scales ranging from 10 to 10 years. The pre- requisites for such a study include exceptional preservation of multiple fossiliferous horizons and a high-resolution stratigraphic framework. Recent stratigraphic analyses of the Cincinnatian Series now provide an exceptionally precise spatial and temporal framework for assessing micro-evolutionary changes within individual species and species lineages. Initial studies in the area have shown that storm-related episodes of rapid mud deposition smothered populations of live Flexicalymene, preserving unique and substantial samples of contemporary individuals which were alive some 450 million years ago. Thin section analysis has revealed a similar depositional regime at Mt. Orab, within the Arnheim Formation, with at least seven gradational beds within a 0.46m mudstone unit. Differences in size distribution, density, and attitude of the trilobites suggests that the Mt. Orab beds differ from the specific behavioural aggregations seen within the ‘granulosa’ bed of the Kope Formation, although both are thought to represent contemporaneous populations. Similar ‘event-bed’ preservation occurs throughout the Cincinnatian Series, offering the possibility of repeated sampling of contemporary populations, sequentially throughout the Series. Morphometric analysis of these contemporary populations of Flexicalymene will constrain patterns of morphological variability at the population level, providing a firm basis for understanding the morphological variation evident within Flexicaly- mene from the Cincinnatian, and its relationship to multiple episodes of environmental change within a sequence- stratigraphic framework.

Ellipsotaphrus and its allies. J. Keith Ingham Division of Earth Sciences and Hunterian Museum, University of Glasgow, UK Following Fortey and Owens (1987), the Ellipsotaphrinae of Kobayashi and Hamada (1970) [=Gamopsidae Snajdr,1976] is established as a valid taxon within the Cyclopygidae, but it is interpreted to exclude Amicus (a pricy- clopygine) and Psilacella (tentatively a micropariine). A characteristic feature of typical included genera is the to- tally circumscribed fore-glabella incorporating extended S1 furrows. Typical genera, like most cyclopygids, are re- markably conservative in form throughout their Arenig to Ashgill ranges and are geographically widespread. All occur only in deeper water sediments with open oceanic access. Girvanopyge [=Cremastoglottos, Nanlingia ] is demonstrated, partly on the basis new material from the latest Caradoc to earliest Ashgill of Girvan, to be an ellipsotaphrine and not a remopleuridid; the last known species - G. problematica - evidently permanently retains what is otherwise normally the last thoracic segment in the pygidium. Gamops is revived for an unusual tuberculate Czech Llandeilian form and a smooth Abereiddian precursor, which together with a late Arenig form from south Wales, all show linkages to both Girvanopyge and Ellipsotaphrus. E. zhongguoensis from the late Caradoc of Hunan Province, China, is shown to be a synonym of the almost coeval E. pumilio from the early Ashgill of Girvan, both of them being members of the E. infaustus species group. Two new, rare ellipsotaphrine genera from the Girvan upper Ordovician are documented.

Phylogeny of Early and Middle Cambrian trilobites. Peter A. Jell Queensland Museum, Brisbane, Australia Several early redlichioid genera are demonstrated to resemble earlier olenelloid genera more closely than they do other redlichioids, provoking the question ‘did facial sutures evolve more than once among trilobites’? From consid- eration of the earliest olenelloids and redlichioids as against later members of those groups it is argued from ontogenetic, outgroup and stratigraphic data that the detached (natant) hypostomal condition is primitive and the attached (conterminant) condition derived. Some preliminary speculations on evolutionary pathways between major groups in the Early and Middle Cambrian are outlined with almost all lineages progressing from detached to attached hypostomes.

History of erecting generic names for Cambrian trilobites. Peter A. Jell Queensland Museum, Brisbane, Australia There appear to be about 2900 names introduced for Cambrian trilobites to the end of 1999. Attempts to exclude misspellings and nomina nuda and the position of the Cambrian/Ordovician boundary are only two of the problems that prevent precision to the last name. Just over 2400 of the names were erected between 1935 and 1983, these being the dates of Kobayashi’s first major Cambrian work and the last of the Chinese palaeontological atlases (ex- cept for that of the already well-known North China), respectively. Analyses of geographic and temporal origins of these names are used to argue that few, if any, large blocks of generic names remain to be recognised globally. Esti- mation of the percentage of these names that may disappear into synonymy suggests that a great deal of work remains to be done in that area. Only recently have sufficient data become available to even begin to assess the phylogeny of many Cambrian groups and for most of them this task has not yet begun.

Taphonomy and palaeoecology of the Ordovician isoteline trilobite ‘Homotelus’ bromidensis. Talia S. Karim and Stephen R. Westrop* Museum of Natural History, University of Oklahoma, Norman, Oklahoma, USA The Bromide Formation of Oklahoma includes horizons composed of numerous complete exoskeletons of ‘Homote- lus’ bromidensis. At some horizons, exoskeletons have librigenae and hypostomes in place and are therefore car- casses rather than moults. Facing-directions of the exoskeletons are random, and the majority of specimens are convex-up. Other horizons are composed of moults, as indicated by opening of the facial sutures and separation of the cranidium from the remainder of the exoskeleton. Cut slabs show that the trilobite horizons are overlain by up to 200mm of lime mudstone that lacks skeletal debris. This indicates that the horizons were preserved by catastrophic mud-blanketing, probably during major storms. As with younger clusters of phacopid trilobites from the Devonian of New York State, they record behavioural aggregation of individuals for synchronous moulting and reproduction. The occurrence of clustering in species from such phylogenetically distant clades as the Asaphina and Phacopi- da indicates that pre-moult aggregation is likely to be a behavioural characteristic of trilobites in general.

Hydrodynamic controls on trilobite associations in Silurian reefs. 1* 2 Joanne Kluessendorf and Donald G. Mikulic 1 Department of Geology, University of Illinois, Urbana, Illinois, USA 2 Illinois State Geological Survey, Champaign, Illinois, USA

Trilobite occurrences in Silurian reefs globally display a strong taphonomic overprint that distorts their true abundance, distribution, and behaviour in these environments. In contrast to most other reef taxa, the majority of trilobite specimens occur in localised concentrations of abundant sclerites, having similar shapes, sizes, and orientations, typically dominated by a single taxon. Moults of modern arthropods and shells of selected other invertebrates were used as models in flume studies to determine hydrodynamic and depositional controls on the formation of these trilobite concentrations. Hydrodynamic sorting during transportation was found to be a primary control on the composition, size, and shape of sclerites in these accumulations. Specific orientation and concentration of sclerites is domi- nantly the result of depositional processes acting in conjunction with various sediment traps or current shadow zones. The co-occurrence of skeletal elements of other organisms with similar morphologies, as well as semi-buoy- ant shells of dead cephalopods, supports this model of formation. Reef trilobite composition can be significantly under- or over-represented depending on how these concentrations are considered. In addition, behaviour attributed to these trilobites should be interpreted based on mode of concentration. Other reported trilobite concentrations, especially in Ordovician reefs, may exhibit a wider range of formational controls than these.

Evolutionary patterns of Protolenidae from the Siberian Platform.

Igor V. Korovnikov Oil and Gas Geology Institute, Novosibirsk, Russia

Protolenids first occur in the Lower Cambrian of the Siberian platform in the Botomian Stage. Their appearance in the section is sudden, and their ancestors unknown. The first - Protolenus - occurs in the north of the platform. Nele- geria, Bergeroniellus and Bergeroniaspis occur a little higher in the sequence. The directions of development they show are different at various sites within this Siberian basin, and these sites belong to different facies. The types living in the deep-water part of the palaeobasin have a flat, wide exoskeleton, and wide fixigenal fields. In time, the frontal lobe of the glabella became a little longer, and the flat anterior border became wider. At the end of the Boto- mian to the beginning of the Toyonian these protolenids gave rise to Lermontovia, with L. dzevanovskii inheriting from them the wide flat exoskeleton and the forwardly extended glabella. The further expansion forward of the glabella to the anterior margin of the cranidium gave rise to the Paradoxididae (Anabaraspis) at the end of the Toyo- nian. Protolenids living in shallow water had convex exoskeletons and narrow fixigenal fields; the frontal lobe of the glabella is pointed and approaches the anterior border, which is flat, wide, and convex. In summary, from the evolution of the protolenids in the Early Cambrian of the Siberian Platform it is possible to recognise three important features: 1) their sudden appearance at the beginning of the Botomian, 2) the development of different morphotypes living in different facies of the basin, and 3) the probable evolution of the Paradoxididae from protolenids at the end of the Early Cambrian.

Development of the hypostome in Asaphus (A.), Asaphus (Neoasaphus) and Asaphas (Postasaphus).

Hans-Hartmut Krueger

Museum für Naturkunde der Humboldt-Universität, Berlin, Germany

The hypostome of Asaphus consists of the central body, the maculae, the anterior wings and two posteriorly di- rected, pointed processes, the so-called ‘furca’. Various researchers dealt with the hypostome between 1883 and 1901 (Novák, Brögger, Lindström and Schmidt). Subsequently, Born (1919) dealt with the hypostome of Chasmops odini and Rudolph (1992) with that of Toxochasmops. According to Fortey and Owens (1999), the morphology of the hypostome of trilobites is conservative in comparison to that of the dorsal exoskeleton. In recent years hypostomes of a variety of asaphid species originating from the Balto-Scandinavian region have been prepared, so as to be fully exposed. From the oldest, Asaphus (A.) bröggeri, to the youngest, A. (Postasaphus), the hypostome has been documented in relation the exoskeleton of the cephalon in 31 species. From the overall morphology and the distinctive surface sculptures, isolated hypostomes can be referred to one of the 31 species.

Taxonomy of the Hystricuridae.

Dong-Chan Lee* and Brian D. E. Chatterton

Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada Members of the Hystricuridae have been documented from Lower Ordovician (Ibexian or Tremadoc to early Areni- gian) strata in Laurentia, Siberia, Kazakhstan, and Gondwana excluding South America. The family is considered to be transitional between some Cambrian Ptychopariida and some (all?) post-Cambrian Proetida. Taxonomic revision of the Hystricuridae will contribute to resolving the ‘ptychopariid problem’. All the species that have been assigned to the Hystricuridae, and new materials from the Great Basin (western USA), are morphologically re-analysed in comparison with similar ptychopariides and proetides. The family contains 13 genera: Hystricurus, Hillyardina, Pa- chycranium, Parahystricurus, Pseudohystricurus, and eight new genera. Pygidia are associated for species of 11 of these genera. The pygidia of five of the stratigraphically youngest genera are characterised by the development of a ridge (serially homologous with the fulcral ridge of thoracic segments) that separates the inner and outer pleural fields. This pygidial feature appears to be taxonomically very informative, because it is rare in both the Ptychoparii- da and the Proetida. The pygidia of the other genera have a tubercle or tubercles, or simply show a relatively abrupt change of slope between inner and outer pleural fields in the part of the pygidium considered homologous with this ridge

Using phylogenetic palaeobiogeography of trilobites to study Cambrian global change.

Bruce S. Lieberman

Department of Geology, University of Kansas, Lawrence, Kansas, USA

During the Early Cambrian, in addition to the profound biological changes, there were profound geological changes, including a series of tectonic events and major oscillations in sea level. A modified version of Brooks Parsimony Analysis was applied to phylogenies of several Early Cambrian trilobite clades to study how these geological changes influenced evolution and to determine the relative timing of tectonic events during the Early Cambrian. To- wards the end of the Early Cambrian, trilobite biogeography indicates that vicariance was the dominant mode of diversification and there was very little dispersal. This vicariance was probably related to the fragmentation of Lauren- tia, Siberia, and Baltica due to rifting, and does provide a means for increasing speciation rates during the end of the so-called Cambrian radiation interval. However, in the early (trilobitic) part of the Early Cambrian, dispersal pre- dominates, particularly between Laurentia and different parts of the terranes marginal to Gondwana. The extensive dispersal during the early part of the Early Cambrian is compatible with the geological events associated with the as- sembly of Gondwana and rising sea levels. Although repeated dispersal should lower speciation rates, in earliest Early Cambrian trilobites they were high, albeit not phenomenally so.

Canyon narrows: implications for a proposed boundary stratotype for the Middle Ordovician Series.

J. D. Loch

Department of Earth Sciences, Central Missouri State University, Warrensburg, Missouri, USA

Finney and Ethington (2000) have proposed a GSSP for the base of the Middle Ordovician Series at the earliest occurrence of the conodont Tripodus laevis (= T. combsi) in a section at the Whiterock Canyon Narrows, Monitor Range, Nevada. Objections have been raised that this section contains a significant unconformity near the base of the Antelope Valley Limestone, thereby lessening its utility as a boundary stratotype. Detailed collecting in limestones within the underlying Ninemile Formation at this section has yielded 13 trilobite-bearing collections and a trilobite fauna of at least 10 species. Preliminary identifications indicate that the species ranges of Nileus hesperaffinis, Ampyxoides cf. A. occiputalis, Illaenus cf. I. auriculatus, and Poronileus vallancei extend down section below their previously reported occurrences in the overlying Antelope Valley Limestone. Further, these ranges overlap with those of Lachnostoma latucelsum and Raymondaspis sp. nov., which extend to the base of the section. The lack of a distinct faunal break in the upper Ninemile Formation at the Whiterock Canyon Narrows section should end any supposition that a major unconformity exists. Heterochrony and homoeotic evolution in the oryctocephalid trilobite Arthricocephalus from the Early Cam- brian of China.

1* 2 2 Kenneth J. McNamara , Yu Fengý and Zhou Zhiyiý

1 Western Australian Museum, Perth, Australia 2 Institute of Geology and Palaeontology, Nanjing, China

The ontogeny of four species of the Early Cambrian oryctocephalid trilobite Arthricocephalus is documented from the Balang Formation, eastern Ghuizhou, southwest China. This is the first description of the ontogeny of the group. Protaspid to holaspid ontogeny is known for A. chauveaui, while incomplete meraspid to holaspid ontogenies are known for A. xinzhaieensis, A. balangensis and A. pulchellus. These four species form an evolutionary trend from the oldest species, A. chauveaui, to the youngest, A. pulchellus. Morphological changes in this lineage occur by heterochrony, and as such represents one of the few documented examples in trilobites of species-species changes induced by this process. The changes involve both those in meristic characters (in the form of a paedo-morphocline in thoracic segment number and peramorphocline in pygidial segment number), and allometric changes, occurring as paedomorphic changes to cephalic traits. The occurrence of both paedomorphosis and peramorphosis in this lineage is one of the few examples of dissociated heterochrony documented in trilobite evolution. It is argued that, as in many other groups of metazoans, the dissociated heterochrony reflects a developmental trade-off. It is proposed that the underlying mechanism that produced this was a directional shift in homoeotic gene domains.

Moulting behaviour and disarticulation patterns of Silurian calymenids: implications for interpreting trilobite ecology and taphonomy.

1* 2 Donald G. Mikulic and Joanne Kluessendorf

1 Illinois State Geological Survey, Champaign, Illinois, USA 2 Department of Geology, University of Illinois, Urbana, Illinois, USA

Calymenids, among the most common trilobites in Silurian rocks of central North America (e.g. the Racine Dolo- mite), typically are represented in both reef and non-reef environments by semi-articulated specimens having a distinctive swayback profile. These specimens share features such as convex-up orientation, downward flexure of pygidium, arching of the posterior six segments, downward sag of thorax centre, up-turn of the first three to four thoracic segments, down-turn of cephalon, in-turning of free checks, and an upward displacement of hypostome; they represent moults not dead individuals. Additional specimens show progressive disarticulation from this stage, commonly ultimately as a separate flexed pygidium with a few arched segments occurring close to other isolated parts. Disartic- ulation occurs in a specific pattern allied to sutures and stress points affected by moulting. In contrast to many other described examples of trilobite moulting, calymenid exuviae initially retain all their parts, including hypostomes, in near life position and are primarily identified as moults by their conspicuous swayback posture. Recognition of moults has major implications for population and behavioural studies and for determination of depositional and environmental conditions. For example, the abundance of articulated calymenid moults compared to rarity of articulated specimens of co-occurring trilobites may derive simply from differences in the articulating/locking nature of the thoracic segments. Recognition of moults also provides evidence for behaviour, such as sheltered moulting within cephalopod shells. The preservational pattern of these calymenid moults provide evidence for a firm substrate, relatively slow rates of sedimentation, and low levels of current or storm activity.

Tagmata and segment specification in trilobites. 1* 1 2 2 Alessandro Minelli , Giuseppe Fusco , Nigel C. Hughes and Mark Webster

1 Department of Biology, University of Padova, Italy 2 Department of Earth Sciences, University of California, Riverside, California, USA

While variation in the number of trilobite cephalic segments remains debatable, it is clear that the postcephalic region exhibited wide variation in segment numbers among different clades. Intraspecific variability in the number of thoracic segments (by two to five segments) is known for at least 25 species (mainly of Cambrian age), so that the boundary between thorax and pygidium was placed at a different segment in different adults of the same species. The thorax to transitory pygidium boundary also shifted during ontogeny. Amongst Recent arthropods, intraspecific variability in segment number is known in several clades, but in all cases tagmata have definitive boundaries as soon as they become expressed as distinct morphological entities. Equating trilobite body regions with ex- pression domains of Hox genes is not straightforward, because although the dorsal exoskeleton is apparently divided into two posterior units, the thorax and the pygidium, the ventral appendages associated with these units share a similar basic structure. A similar mismatch between dorsal and ventral structures is also known among Recent arthropods, but trilobites are apparently unique in that the regional identity of individual postcephalic segments changed during their ontogeny, as segments formed in the transitory pygidium were later released into the thorax. As in some Recent arthropods, the shape of the adult appears more tightly constrained through ontogeny than the number of segments: in holaspid Aulacopleura konincki, specimens with from 18 to 22 thoracic segments shared almost identical sagittal proportions. These results suggest that there was some developmental flexibility in trilobite body architec- ture, thus raising the question of whether trilobite postcephalic tagmata are strictly comparable to those of the remaining arthropods.

New data on trilobites from Late Cambrian sediments in Vietnam and neighbouring areas.

Pham Kim Ngan

Research Institute of Geology and Mineral Resources, Hanoi, Vietnam

Late Cambrian sediments in North Vietnam belong to two facies, the Changpung facies in north and northwest Viet- nam, and the Thansa facies in northeast Vietnam. The shallow shelf sediments of the Changpung facies are domi- nantly micritic, dolomitic, and oolitic limestones interbedded with shale, siltstone and calcareous sandstone. Togeth- er they yield the Changpung Fauna, which is composed of the following nine assemblages; 1, Drepanura premesnili - Damessella brevicaudata - Blackwelderia sinensis - Cyclolorenzella tonkinensis; 2, Billingsella tonkiniana; 3, Pro- chuangia mansuyi - Mansuyia sp. - Chuangiella sp. nov.; 4, Irvingella sp. - Pagodia meovacensis - Caulaspina sp. nov.; 5, Haniwa quadrata - Obolus sp.; 6, Proceratopyge cylindrica -Kaolishaniella sp. - Billingsella sp.; 7, Prosau- kia angulata - Quadraticephalus teris; 8, Tsinania cancus - Dictyites sp. - Dictyella mansuyi; and 9, Calvinella wal- cotti - Eoorthis doris. The shelf slope sediments of the Thansa facies are composed of thinly-bedded shale and marl shale, interbedded with a few thin beds of limestone and sandstone, and they contain the Thansa Fauna which includes only the three following assemblages of ceratopygid, olenid and agnostid trilobites; 1, Proceratopyge sp. - Haniwa ambolti; 2, Hedinaspis regalis - Charchaqui norini; and 3, Lotagnostus asiaticus - Agnostus hedini. The Changpung Fauna has been reported also from southeast Yunnan, North China, and the Thansa Fauna is closely related to that of northwest Hunan, Guizhou and Tianshan, China.

Ordovician trilobite biodiversity change in the British Isles.

Alan W. Owen* and Tim McCormick

Department of Geology, University of Glasgow, UK Analysis of a relational database founded on the occurrence of species at localities enables the patterns of trilobite species and generic diversity to be assessed, stage-by-stage through the Ordovician of the British Isles. In the British sector of Avalonia (the Welsh and north of England basins), a late Arenig to early Llanvirn increase in diversity included the highest species-to-genus ratios and was contemporaneous with both a rise in global diversity and the rifting of Avalonia from Gondwana. A late Abereiddian dip in diversity was followed by recovery during the Llandeili- an to early Caradoc and an apparent decline during the late Caradoc to early Ashgill, the latter being at least partly a reflection of the limited rock record for that interval and the restriction of most of the preserved faunas to those from deep-water environments. The greatest diversity was in the palaeoenvironmentally differentiated Rawtheyan, and was followed by the diversity crash seen in the Hirnantian throughout the world. Although a more restricted range of palaeoenvironments is represented, a broadly similar pattern is shown by the Llanvirn (upper Abereiddian) to early Silurian trilobites of the Girvan district which was part of a terrane on the Laurentian margin of Iapetus. Assessment of the changing generic diversities within families provides a regional test of the published global patterns.

On the systematic position of cyrtometopinine (Cheiruridae) trilobites.

Helje Pärnaste

Institute of Geology, University of Tartu, Tallinn, Estonia

The Cyrtometopinae was separated from the Cheiruridae by Öpik (1937) based on the possession of a transverse furrow or line of pits on the thoracic pleurae. The significance of this character had been emphasized previously by Schmidt (1881) and Barton (1913). Lane (1971) noted that the range of variability of cyrtometopinines is extremely wide, comparable to that of the entire family, and thus he regarded Cyrtometopinae as junior synonym of Cheiruri- nae. Krattaspis and related transverse furrow-bearing genera (Actinopeltis, Cyrtometopella, Cyrtometopus, Hemi- sphaero-coryphe, Reraspis,, Sphaerocoryphe,) are very similar to each other in morphology but clearly distinct from cheirurinids, acanthoparyphinids, and sphaerexochinids. However, Deiphon, regardless of some specific features (pleurae not in contact with each other), is supposedly a descendant of Sphaerocoryphe, and thus Cyrtometopinae may be taken as the junior synonym of Deiphoninae. On the other hand, if Deiphoninae is to be kept monotypic like Areiinae, the cyrtometopinids could well form a separate subfamily. Another possibility is to accept Lane's opinion that the orientation of the thoracic pleural furrows is insignificant, when, in my opinion, both Cyrtometopinae and Deiphoninae should be included in Cheirurinae, and the other subfamilies (Acanthoparyphinae, Areiinae, Eccopto- chilinae, and Sphaerexochinae) should be regarded as a natural group. In this case, it might be reasonable to change the rank of these two groups to the family level.

Cambrian shumardiid trilobites from western Hunan, China.

1* 2 Shanchi Peng , Loren E. Babcock and Huanling Lin

1 Institute of Geology and Palaeontology, Nanjing, China 2 Department of Geological Sciences, Ohio State University, Columbus, Ohio, USA Two new species of trilobite belonging to the Shumardiidae are present in the Upper Cambrian of western Hunan, China. The new forms, which include the earliest known representatives of the family, are important because they reveal characteristics present at an early stage in the evolution of the group. One new species, which also represents a new genus, occurs in the upper part of the Huaqaio Formation, where it is closely associated with trilobites indica- tive of the Glyptagnostus stolidotus Zone (lower Upper Cambrian: Youshuian), and thus is the oldest shumardiid known. Important features of the new species are the presence of palpebral lobes and facial sutures. Previously, most shumardiids were considered to be blind, variably facial-suture-bearing trilobites, with palpebral lobes observed only in the early holaspid stage of the Akoldinioidia didymacantha (Lotagnostus punctatus - Hedinaspis regalis Zone; upper Upper Cambrian: lower Taoyuanian). The new species from the Huaqaio Formation indicate that shumardiids retained eyes in their early evolutionary history. A new species of Akoldinioidia occurs in the upper part of the Shen- jiawan Formation, where it occurs below Onchopyge (upper Upper Cambrian: upper Taoyuanian). This species has facial sutures, yoked librigenae, and five thoracic segments in the holaspid stage. A hypostome, which has not been recorded previously from shumariids, is present; it has a small middle body and a long posterior border. An ontogenetic series reveals that the third and fourth thoracic segments are developed as macropleural in the meraspid stage. This characteristic suggests that the new species represents an evolutionary stage midway between the paedomorphic development of Acanthopleurella from Akoldinioidia.

Abrupt interspecific variation in Ptychagnostus (Cambrian Trilobita): a case for hybridisation.

Richard A. Robison

Department of Geology, University of Kansas, Lawrence, Kansas, USA

Ptychagnostus atavus is one of the most widespread and most commonly encountered Cambrian trilobites. P. occultatus, is a very similar but less common and seemingly less widespread species that primarily differs from P. atavus by the presence of four prominent exoskeletal spines. Although these species have partly overlapping stratigraphic ranges, most of their occurrences are mutually exclusive, even where repetitious in the same stratigraphic section. The one observed exception is in a single mid Middle Cambrian collection from the western United States (Marjum Formation, House Range, Utah) which contains hundreds of specimens of either P. atavus, P. occultatus, or intermediate morphs with all gradation of characters at different growth stages. Ecophenotypy, hybridisation, and sexual dimorphism are considered as possible causes for this variation, with a preponderance of evidence favouring hybridisation. This is the oldest suggested example of hybridisation in the fossil record.

The world's biggest trilobite: a giant among arthropods.

1* 2 3 4 David M. Rudkin , Graham A. Young , Robert I. Elias and Edward P. Dobrzanski

1 Department of Paleobiology, Royal Ontario Museum, Ontario, Canada 2 Manitoba Museum of Man and Nature, Winnipeg, Manitoba, Canada 3 Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada 4 Winnipeg, Manitoba, Canada In 1998, the largest trilobite specimen so far known was recovered from the Upper Ordovician (Richmondian) Churchill River Group of northern Manitoba, Canada. It is a virtually complete articulated dorsal exoskeleton over 700 mm in length (restored), belonging to a new species of Isotelus. The vast majority of described trilobites had adult lengths ranging from 30 to 100mm. The largest articulated trilobites documented previously have been in the range of 350 to 430mm, and all reports of trilobite lengths of 500mm or more have been estimates based on dimensions of partial exoskeletons or isolated sclerites. The new specimen is almost 70% longer than any previously documented complete trilobite and provides the first indisputable evidence of a trilobite exceeding half a metre in length. Comparisons with other species of Isotelus suggest the new specimen could represent as much as a 1200- fold increase in length from the protaspis until it reached c.720 mm at the time of death. It is not certain whether the animal had attained the maximum possible age and size for its species, but the extreme rarity of such exceptionally large specimens indicates that it must have been approaching the upper limit for trilobite dimensions.

Homalonotid trilobites from the Silurian and Early Devonian of southeastern Australia and New Zealand.

Andrew C. Sandford

School of Earth Sciences, University of Melbourne, and Museum of Victoria, Melbourne, Australia

The homalonotid fauna of the Silurian and Early Devonian of southeastern Australasia is of worldwide significance, with 18 taxa represented. In particular, the Llandovery and the Ludlow to Gedinnian taxa represent about half of all homalonotines described from these intervals; both are critical periods in the diversification of the subfamily. The fauna includes the earliest Dipleura, the two earliest Digonis, and two of the earliest Trimerus; these taxa provide new perspectives both on the definition of genera represented, and on the evolutionary trends in the subfamily. Evo- lutionary strategy of the subfamily is best illustrated in reiterative patterns in pygidial morphologies. Two patterns can be identified; the first is exemplified by Trimerus and Digonis, in which pygidial outlines become markedly elongate and acutely pointed through time, the second is exemplified by Parahomalonotus and Dipleura, in which pygidial outlines become shortened and increasingly rounded through time. With few exceptions these homalonotids occur either as dominant species in low diversity homalonotid-proetid-dalmanitid assemblages, or as rarer compo- nents of higher diversity assemblages. The Australian homalonotids are restricted in distribution to continental shelf settings on the southwestern margin of the Lachlan Fold Belt, inferring open water barriers to dispersal into the contemporary island arc settings of New South Wales and Queensland.

New fossil arachnids of Carboniferous (Westphalian D) age from Somerset, UK, and the restoration of de- formed fossils.

1* 2 Paul A. Selden and Derek J. Siveter

1 Department of Earth Sciences, University of Manchester, UK 2 University Museum, University of Oxford, UK

New fossil arachnid specimens, including a phalangiotarbid and a new spider, are reported from the Coal Measures (Westphalian D) of Writhlington, Somerset. Whilst phalangiotarbids are relatively common here, the record of a spider is the first from this site; it exhibits carapace features typical of the few described Carboniferous Araneae from Mazon Creek (Illinois) and Coseley (UK), and is probably a mesothele. Computer retrodeformation of the Writh- lington arachnids reveals that there are fewer morphotypes (genera) than previously suggested. Trilobita, Crustacea, Chelicerata, Myriapoda and Insecta?

Alberto M. Simonetta*, Marta Pacini and Lavinia Tinalli

Dipartimento di Biologia animale e Genetica. Università di Firenze, Italy

Debates concerning the phylogeny of arthropods and their classification have been lively through the years. How- ever, there has been little effort to make a systematic analysis of the comparative anatomy of both recent and fossil arthropods. Because of space limits, the present paper considers only three aspects of the morphology of arthropods and closely related taxa: 1) tagmosis, 2) the evolution of adaptations for respiration in terrestrial environments, and 3) some aspects of the evolution of appendages and mouthparts. In each case there is sound evidence to maintain that: a) both parallel and convergent evolution or homoplasies are quite common and they are almost impossible to sort into any kind of regularly branching pattern, probably at least by late Lower Cambrian; b) the characters considered have currently been used for over a century in order to group living taxa into the three great living classes Crus- tacea, Chelicerata and Insecta, while the position of myriapods, sensu lato has often been disputed. Actually morphology shows that none of these ‘classes’ may be considered as being an unquestionably natural one (that is monophyletic); c) it is, perhaps, possible to suggest a distant monophyletic origin for some of them, provided that we as- sume that such possible common ancestor had none of the diagnostic characters which now characterises each later taxon; and d) in several important instances it is impossible to decide whether a given morphology is primitive or derived. To conclude, it is argued that in each individual case the significance of every morphology should be assessed by the methods of classical comparative anatomy and tested against other lines of evidence, rather than built into matrixes.

A three-dimensionally preserved phosphatocopid crustacean with appendages from the Lower Cambrian of Shropshire, UK.

1* 2 3 David J. Siveter , Dieter Walossek and Mark Williams

1 Department of Geology, University of Leicester, UK. 2 Section for Biosystematic Documentation, University of Ulm, Germany. 3 British Geological Survey, Keyworth, Nottingham,UK.

A three-dimensionally preserved, phosphatised phosphatocopid arthropod, with appendages, has been recovered from the Lower Cambrian of Shropshire, England. The morphology of this species endorses the notion that phospha- tocopids are the sister group to the Eucrustacea and, therefore, that crown-group Crustacea were present in the early Cambrian. The find includes the oldest known occurrence of an animal with its body and complement of limbs preserved in three dimensions, and identifies an important, stratigraphically early Konservat-Lagerstätte.

Arthropods from the Herefordshire Lagerstätte, UK.

1* 2 3 4 Derek J Siveter , Derek E. G. Briggs , David J. Siveter and Mark D. Sutton

1 University Museum, University of Oxford, UK 2 Department of Earth Sciences, University of Bristol, UK 3 Department of Earth Sciences, University of Leicester, UK 4 Department of Earth Sciences, University of Oxford, UK The Silurian (Wenlock Series) Herefordshire Lagerstätte in the Welsh Borderland preserves 3D, non-biomineralized fossils. The specimens are preserved in calcite, and occur within carbonate concretions in a volcaniclastic depos- it. Traditional mechanical and chemical methods of preparation are unsuitable for recovery of the fauna, so that the morphologies of the specimens are being reconstructed by serial grinding, digital photography, and computer visual- ization. Four types of arthropod with limbs have been recognised: a chelicerate-like animal, a trilobite and two as yet enigmatic forms.

Exuviation of selected Bohemian trilobites.

Jana Slaví ková

Department of Palaeontology, National Museum, Prague, Czech Republic

Trilobite research in Bohemia began over 150 years ago and has resulted in numerous publications. Most are systematic studies, and few investigations have delved into trilobite taphonomy, palaeoecology, and especially exuviation. Recent study of trilobite communities in the Šárka Formation (Darriwilian) of the Prague Basin, has yielded new data concerning exuviation patterns of several trilobite species. The Šárka is a deep-water (below storm-base) formation, its fossil communities are part of the cold water Mediterranean Province. All the specimens studied are three dimensionally preserved in siliceous, organic rich, nodules so that all the observations concerning the exuviae must be significant. Preliminary study of Šárka communities indicates that at least some of the specimens and exuviae were buried in situ. Colpocoryphe bohemica is preserved with the incomplete post-cephalic exoskeleton con- cavely flexed. Finds of isolated moulted post-cephalic exoskeletons of Trinucleoides reussi are common. Exuviation in the rare species Plasiaspis bohemica in some cases resulted in the pygidium and/or pygidium with last thoracic segments inverted and rotated. Pricyclopyge binodosa commonly shed the rostral plate with the eyes, whilst leaving the post-cephalic exoskeleton intact. Preliminary results of the study show modifications and elaboration of known exuviation patterns that are illustrated by the well-developed three dimensional preservation.

The Silurian arthropod Offacolus: a three-dimensional exploration.

1* 2 3 4 Mark D. Sutton , Derek E. G. Briggs , David J. Siveter and Derek J.Siveter

1 Department of Earth Sciences, University of Oxford, UK 2 Department of Earth Sciences, University of Bristol, UK 3 Department of Earth Sciences, University of Leicester, UK 4 University Museum, University of Oxford, UK The small non-biomineralised arthropod Offacolus kingi is the most commonly occurring body fossil of the Here- fordshire (UK) Konservat-Lagerstätte. The recently published description is now supplemented by three-dimensional computer models obtained from serial grinding of specimens, providing detailed understanding of the external morphology of the animal. The dorsal exoskeleton comprises an arch-like cephalic shield, a thorax of three free tergites, and a triangular posterior tagma of ?five fused tergites, the last bearing a long posterior spine. Seven pairs of rami arise ventrally from the viscera beneath the cephalic shield in a ‘rosette’ pattern, around an oral cavity. The first (anteriormost) is short and presumed to be sensory or manipulative. The second to sixth are longer and termi- nate in a single spine; they are likely to have been ambulatory. The seventh is flap-like, distally setose, and projects posteriorly; functionally it is part of the thorax. A small pair of rami arises on the anterior of the cephalic viscera, and may be manipulative, working in opposition to the first rosette appendage pair. A further four pairs of relatively robust rami project anteriorly from under the cephalic shield; these are terminally spinose, and are assumed to have functioned in trapping food. Each thoracic tergite bears a pair of curved flap-like rami, from which up to four subsid- iary flap-like rami branch off ventrally, presumably functioning as gills. Similar but unbranched rami exist beneath the anteriormost three segments of the posterior tagma.

Uppermost Cambrian inner shelf faunas of the western United States.

J. F. Taylor

Geoscience Department, Indiana University of Pennsylvania, USA

Uplifts in Colorado, Wyoming, and Montana offer an onshore to offshore transect of inner shelf, mixed clastic-carbonate strata that span the Cambrian-Ordovician boundary. Innermost shelf faunas (Colorado) reveal a break at the top of the widespread Clinetop Stromatolite Bed where Saukiella serotina Subzone strata directly overlie beds of the Illaenurus Zone. Another unconformity omits the Eurekia apopsis and Missisquoia depressa Subzones, which are present in more distal sections in Wyoming and Montana. The usually rare euptychaspid Macronoda is common at the top of the Sunwaptan in the distal sections, allowing better characterisation of the pygidium and librigena than was previously possible. Larifugula leonensis dominates the E. apopsis Subzone, although this dominance, and the relatively low diversity of uppermost Sunwaptan faunas, may be more taphonomic than ecologic in origin. In one section, the Plethopeltis-dominated fauna of the M. depressa Subzone replaces that of the E. apopsis Subzone within the upper half of a metre-scale cycle, confirming the rapid nature of that turnover. Similarly, the replacement of Ple- thopeltis by Apoplanias at the base of the Missisquoia typicalis Subzone (top of the Ptychaspid Biomere) is every- where sharp. Scattered horizons with prolific faunas within the Symphysurina Zone (some within thrombolitic reefs) promise improved precision of correlation within this unit.

Arenig to Llanvirn trilobite palaeoecology of the South China plate.

S. T. Turvey

Department of Earth Sciences, University of Oxford, UK Trilobite species abundance data were analysed to quantify assemblage composition for the Yangtze Platform and Jiangnan Transitional Belt regions of the South China Plate during the Arenig and Llanvirn series. Study material was collected from the Chaochiapa, Siliangssu, Dawan, Kuniutan and Jiuxi formations, from Shaanxi, Hubei and Hunan provinces, representing a range of depositional environments from the shallow inner shelf to slope. Along a progressively deepening palaeobathymetrical environmental gradient, a shallow-water neseuretus/asaphid assemblage is replaced by different isoteline, trinucleid and nileid-dominated assemblages, with slope deposits in Hunan characterised by deep-water cyclopygid assemblages. Further assemblage differentiation occurs within this framework, probably as a result of heterogeneity in substrate conditions at similar depths. Assemblage composition indicates biogeographical affinities for the South China Plate with the peri-Gondwanan regions of Tarim, Indo-China, the Middle East and Southern Europe, and the Gondwanan regions of South America and possibly New Zealand.

Allometric patterning in trilobite ontogeny: testing for heterochrony in Nephrolenellus.

Mark Webster

Department of Earth Sciences, University of California, Riverside, California, USA

Heterochrony relates specifically to evolutionary changes in the rate or timing of events along an otherwise con- served ontogenetic trajectory. Conservation of ancestral patterns of shape differentiation serves as a test by which heterochronic modification of ontogeny can be delimited rigorously from other evolutionary processes such as heterotopy. The Early Cambrian olenelloid trilobite Nephrolenellus geniculatus differs from its ancestral sister species N. multinodus in retention of fewer glabellar axial nodes, development of a stronger adgenal angle, and impingement of L4 into the anterior border; all of these features can be explained as simple extrapolation of ontogenetic trends present in the ancestral species. Under traditional criteria, this putative case of peramorphic evolution is one of the most strongly supported examples of heterochrony in trilobites. However, thin-plate spline analyses of ontogenetic shape-change show that N. geniculatus and N. multinodus differ significantly in allometric patterning from the earliest preserved ontogenetic stage. This proves that the descendant ontogeny was predominantly modified in spatial, rather than temporal, parameters. The hypothesis of evolution by pure heterochrony in Nephrolenellus is rejected, and alternative evolutionary processes such as heterotopy must be invoked. Failure of this case to meet the criterion of allometric conservation required which would rigorously demonstrate heterochrony suggests that the prevalence of this process may be considerably overestimated in trilobite evolution.

On the ontogeny of Ovalocephalus primitivus.

1 1 2 Yuan Wenwei *, Zhou Zhiyi and Zhou Zhiqiang

1 Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing, China 2 Institute of Geology and Mineral resources, X’ian, China Ontogenetic material of O. primitivus was collected from the Arenig Dawan Formation of Anhui, South China. The metaprotaspis is almost circular in outline, with three pairs of short equally-spaced fixigenal spines. Ovalocephalus , referred to the Hammatocneminae is, therefore, referred to the Pliomeridae. Morphological changes during ontogeny include successive abaxial and forward expanding of the glabella, the broadening and deepening of the lateral glabellar furrows, the posterior migration of the palpebral lobe, the shortening of the posterior fixigenal field, the out- ward migration of the posterior branch of the facial suture, the reduction of the fixigenal spines; the widening of the pygidial axis and the narrowing of the pygidium. Ovalocephalus has 11 species, ranging from Arenig to Ashgill in age, which occur in China, Poland, Kazakhstan, Uzbekistan, Thailand and Spain. Younger species have more anteriorly situated palpebral lobes, a longer posterior fixigenal area, narrower basal part of the glabella, narrower pygidial axis and relatively wider pygidium. They thus retain immature features of the ancestral form, suggesting that paedomorphosis plays an important role in the evolution of Ovalocephalus. .

Environmental patterns in the Early Cambrian diversification of trilobites.

1* 2 Stephen R. Westrop and Ed Landing

1 Museum of Natural History, University of Oklahoma, Norman, Oklahoma, USA 2 State Geological Survey, Albany, New Youk, USA

The Avalon Continent provides an excellent record of the Cambrian Radiation and offers new insight into the emer- gence of trilobite-dominated palaeocommunities in the Branchian Series. The earlier Placentian diversification of ‘small shelly fossils’ (SSF) occurred primarily in nearshore environments, where they reached peak species rich- ness. Low diversity SSF assemblages occurred in offshore facies. The Branchian appearance of trilobites is in the offshore facies, with continued dominance by SSF in nearshore sites. Trilobites did not displace SSF in the offshore, but rather the diversification of trilobites expanded the palaeocommunity composition, so that a decline in relative importance of SSF was a simple, and entirely passive process of dilution. Thus, the rise of trilobite-rich palaeocommunities during the Early Cambrian is a mirror image of the Ordovician Radiation, which saw a decline in the relative importance of trilobites through dilution when other groups, such as articulate brachiopods, diversified.

Latest Llanvirn to early Caradoc trilobites and biofacies of southwest Shaanxi, China.

1 2 1 Zhou Zhiyi *, Zhou Zhiqiang and Yuan Wenwei

1 Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing, China 2 Institute of Geology and Mineral resources, X’ian, China

Latest Llanvirn to early Caradoc trilobite faunas are recorded for the first time from southwest Shaanxi, South Chi- na; they contain 38 species assigned to 33 genera of which 29 better-preserved taxa including six new species are described or reviewed. Specimens were collected from carbonates of the Lower Pagoda Formation at six measured sections across the northwest margin of the Yangtze Block. Trilobites display strong southeast and central Asian affinities. They are also closely related to those from Central and Western Europe and share a few genera with Balto- scandian faunas. According to faunal composition and diversity, and relative abundance of genera, northwards from the northern margin of the Hannan old land, four trilobite biofacies are distinguished in relation to an environment gradient. The Agerina Biofacies occurs in tempestite beds comprising only a few benthic forms, indicating an inner shelf location. The Cyclopyge-rorringtoniid, Cyclopyge-Alceste and Cyclopyge-trinucleid biofacies are all characterised by the occurrence of abundant mesopelagic cyclopygids, and are distributed successively along a steep outer- shelf slope with faunal diversity gradually reduced; the relative abundance of cyclopygids increased seawards. POSTERS

Taxonomy of the Marrolithinae (Trinucleidae). Alison Bowdler Department of Geology, University of Glasgow, UK The Marrolithinae currently comprises 10 genera and some seventy species and subspecies, ranging in age from upper Arenig to Ashgill. The radiation of the subfamily was associated with the opening and widening of the Rheic Ocean and the rifting and northward drift of micro-continents from the Gondwanan margin. As a result, species are found in the Anglo-Welsh area, France, Iberia, Bohemia, Turkey, Russia (Urals), North Africa and South Ameri- ca. A strongly typological approach to species definition has led, in some instances, to an over-divisive classification, which leaves many specimens difficult to identify or forces quite similar individuals from the same horizon in- to separate ‘species’. The misidentification of specimens has also occurred through erroneous assumptions of species distribution. At the generic level, many of the supposedly diagnostic characters are not amenable to cladistic analysis, bringing the validity of some of them into question. A new, population-based, approach is being undertaken and takes into account ranges of variation within species and adopts a more rigorous approach to the definition of diagnostic characters. This will provide a more workable taxonomy which will underpin the understanding of the palaeogeographical distribution of species and enhance their stratigraphical usefulness.

The development of cuticular sensory structures through ontogeny in Paladin mylonicus and Baliothyreus cheilos. Abigail M. Brown Department of Geology and Geophysics, University of Edinburgh, UK Examination of two previously undescribed Carboniferous trilobites from Eyam in Derbyshire, UK, has revealed numerous potentially sensory cuticular structures that are observed to change throughout ontogeny, perhaps in response to changes in ecology or physiology. Cuticular structures described in various ontogenetic stages of Paladin mylonicus and Baliothyreus cheilos include pits, canals, granules, terrace ridges and cell polygons. The observed variations in cuticular sculpture through ontogeny of these species are compared with those already described by Clarkson and Xi-guang (1991) in a closely related Namurian species, Paladin eichwaldi shunnerensis. Further investigation of the sensory structures of this species, collected from Great Shunner Fell in North Yorkshire, has revealed pitting of the external ventral surface of the doublure, possible pore canal preservation in the pygidial margin, and terrace ridges bearing no pore canals. The cuticle of these species has predominantly been studied using the SEM, thin section, and EDTA etching. This research is being conducted in parallel with that of Robert Owens and John Tilsley who are currently preparing the two new species for publication; they kindly donated the Derbyshire material for this study.

Internal and external cuticular sensory structures of Ctenocephalus exsulans. Abigail M. Brown Department of Geology and Geophysics, University of Edinburgh, UK The Middle Cambrian Exsulans Limestone of Brantevik, Skåne, Sweden, has yielded numerous adult specimens of Ctenocephalus exsulans, displaying many interesting cuticular structures. These structures include an inter-granular anastomosing channel system recessed into the internal surface of the fixigena, which is interpreted as a potential alimentary prosopon. Moulds of the internal surface of the cranidium demonstrate that this surface was densely covered with small granules, interspersed with large pits. These are interpreted to be sensory with respect to the internal physiology of the trilobite. Arrays of pits and granules with a particular orientation have been observed, and are be- lieved to have had a sensory function. They are compared with similar arrays of angled setal pits observed in lobster carapaces, which are currently being studied as modern analogues. This poster informally presents ongoing preliminary research that is being conducted in parallel with the study of the development of cuticular sensory structures through ontogeny in Paladin mylonicus and Baliothyreus cheilos, using similar techniques. Any comments and suggestions regarding the significance of these structures, their potential function(s) and any similarities with other trilobites and analogies with other arthropods are invited.

Preliminary report on the trilobites of the Falkland Islands, collected during the American Museum of Natu- ral History expedition, February 2000. 1 1 2 3 Maria G.P. de Carvalho , John G. Maisey , Leonardo Borghi and Emma Edwards 1 American Museum of Natural History, New York, USA 2 Departamento de Geologia, Universidade Federal do Rio de Janeiro, Brasil 3 Port Stanley, Falkland Isles The Falkland Islands are a rich source of Devonian marine invertebrate fossils, which were first noted by Charles Darwin in 1833 and 1834. The few collections that were made in the early 20th century have formed the basis of practically all subsequent investigations. In 1913, J.M. Clarke observed that Devonian invertebrates from the Falk- lands closely resemble those from Bolivia, parts of Brazil, and especially South Africa. His pioneering studies would ultimately lead to recognition of a distinct austral cold-water biogeographic region, the Malvinokaffric Realm. In February 2000 a palaeontological expedition was undertaken by the American Museum of Natural His- tory, in co-operation with the Falkland Islands Development Corporation and Department of Mineral Resources. Ho- malonotids and calmoniids were collected from classic Lower Devonian exposures of the Fox Bay Formation in West Falkland (e.g., Fox Bay, Pebble Island), as well as from many new localities in both East and West Falk- land. We recovered the first calmoniid trilobites from East Falkland, including Bainella nilesi, Bainella sp. nov?, and Metacryphaeus sp. Our findings confirm the Malvinokaffric affinities of the Falkland trilobite faunas.

Growth stages of Acadoparadoxides harlani. 1 2 Terence P. Fletcher and George Theokritoff 1 Dunbar, East Lothian, UK 2 Rutgers University, New Jersey Acadoparadoxides harlani is one of the earliest paradoxidids and was described from Cambrian clastic rocks of the Braintree region in Massachusetts. It is a species known to reach over 0.5m in length. The problems of trilobite taxonomy are no more emphasised than those encountered in dealing with the paradoxidids. The system whereby a holotype is expected to represent a typical specimen of a genus or species is clearly unsatisfactory when one considers the number of gradually changing growth stages in forms that reach relatively enormous sizes. Although that specimen may act as a reliable standard of reference for similarly sized material, the absence of such a growth stage in other collections may result in possible consanguinity being unrecognised and unnecessary synonymy. A sequence of photographs representing intraspecific variation of holaspid growth stages is displayed to emphasise the difficulty of presenting a conventional description of a type specimen. Comment is also made on contemporaneous material from Newfoundland, Morocco, Spain, and England, where the species has been considered a possible end- member of an earliest paradoxidid morphocline – nobilis, mureroensis, briareus, and harlani.

Calcite ‘bifocals’ enabled a trilobite to see simultaneously both near and far. 1 1 2 1 Jozsef Gal , Gabor Horvath , Euan N. K. Clarkson and Otto Haiman 1 Department of Biology, Eotvos University, Budapest, Hungary 2 Department of Geology and Geophysics, University of Edinburgh, UK Bifocal eyeglasses were invented by Benjamin Franklin in 1784. Though several kinds of man-made optical imaging systems have been developed to provide for human needs, mimicking to some degree the effective visual systems engineered by animal evolution, it is not until now that bifocal imaging lenses are reported. In the Ordovician (Caradoc) phacopid Dalmanitina socialis, however, the calcite lenses were used bifocally, and as far as we are aware this is the only known instance in the animal kingdom. We propose that the function of these bifocal lenses was to enable the trilobite to focus simultaneously on both very near objects (e.g. floating food particles and tiny prey) and more distant objects (the sea floor, conspecifics, or approaching enemies). This was achieved through the central and peripheral lens regions respectively, without requiring any capacity for accommodation within the eye. Using a large-scale optical model of these bifocal lenses, we have been able to demonstrate that if Dalmaniti- na had possessed small sublensar retinae appropriately positioned, the trilobite could sharply see both near and far objects. We show that the apparent resemblance between the erroneous correcting lens surface designed by Rene Descartes in 1637 and the correcting interface in the compound bifocal Dalmanitina lens is actually accidental and hence misleading. This is probably the reason why earlier students of Dalmanitina lenses did not recognise its bi- focality.

Taphonomy of the Devonian trilobites (Paraná Basin, Brazil) in a sequence stratigraphy framework: some preliminary observations. Renato Pirani Ghilardi and Marcello Guimarães Simões Departamento de Zoologica, Universidade Estadual Paulista, Botucatu, Brazil Taphonomic data available for trilobites were integrated with the Bergamaschi’s sequence stratigraphy model for the Ponta Grossa Formation (?Lochkovian to Frasnian), Parana Basin. According to the model, the deposits (storm-dominated shoreface and shallow-marine) of this unit, in the Jaguariaiva region, Parana State, encompass the Sequence rd B, a 3 order depositional sequence (165m thick), constituting four small-scale parasequences. Although thick and laterally persistent, beds containing exclusively trilobite remains are unknown; homalonotid and calmoniid remains are non-randomly distributed in the sequence. Homalonotids (Burmeisteria notica), for example, dominate the deposits near the MFS (Maximum Flooding Surface) and are represented by moult remains (sclerites, thoracic segments, thoracopygidium, pygidia, and cephala; 98.3%, n=59) and an enrolled specimen (1.7%, n=1). Calmoniid (Paracalmonia, Calmonia) moult remains (93.1%, n=27) are distributed throughout the sequence, but complete specimens (6.9%, n=2) are preferentially preserved in less bioturbated sediments of the basal portion of TST (Trans- gressive System Tracts). Differences in trilobite behaviour, environmental parameters and the intensity of bioturbation in distinct parts (e.g., TST, MFS) of the sequence could explain the observed pattern. In fact, trilobites are virtually absent in obrution deposits near the MFS where epifaunal and sessile invertebrates (brachiopods, conulariids) commonly are preserved in life position.

Dimorphism in the evolutionary trends of paradoxidids from Murero (Spain). 1 2 2 R. Gozalo , E. Liñán and M.E. Dies 1 Departamento de Geologia, University of Valencia, Spain 2 Departamento de Ciencias de la Terre, University of Zarazoga, Spain The study of the succession of paradoxidids in several sections in the Murero area (Iberian Chains) allows recognition of dimorphism in Acadoparadoxides and Eccaparadoxides which is interpreted herein as of a sexual origin. In chronological order, the species studied are Acadoparadoxides mureroensis, Eccaparadoxides rouvillei, E. sequeiro- si and E. brachyrachys from Early Middle Cambrian to Late Middle Cambrian (Leonian to Caesaraugustan ages). Two morphotypes, A and B, are recognised on the basis of the pygidial length and also, in the youngest species, of the thoracic characters. Morphotype A is more abundant. The dimorphism in A. mureroensis (early Leonian) appears only in the relative lengths of the pygidia. As this species is considered the ancestor of the Spanish Eccapar- adoxides species (Caesaraugustan), it can be suggested that the thoracic dimorphism began later in evolution. Ecca- paradoxides rouvillei (Leonian to Caesaraugustan transition) has macropleural first and second segments. In E. se- queirosi and E. brachyrachys, morphotype A has a relatively short pygidium and a more homogeneous thorax that progressively widens backwards from the third thoracic segment which is micropleural. Morphotype B has a relatively long pygidium and a thorax with three or more micropleural segments depending on the species.

A review of the Cambrian trilobites of southern Norway. Ole A. Hoel Institut för Geovetenskaper avd för Historisk Geologi och Paleontologi, Uppsala, Sweden Cambrian rocks of Norway are preserved at scattered localities largely in two areas; the autochthonous Oslo graben, and the lower allochthonous Caledonide nappes, which were deposited about 450km northwest of their present location. The fossils are almost exclusively trilobites, but lingulate and ‘articulate’ brachiopods, early molluscs and hyoliths occur at some levels. The Lower Cambrian of southern Norway crops out exclusively along the Caledonide front. Only twelve trilobite species are found, half of which are olenellids. In the Middle Cambrian, the number of both outcrops and species increase dramatically. The lowermost Middle Cambrian is only found in the northern part of the Basin, but subsequent transgression meant that most zones of the Middle and Upper Cambrian are present throughout the basin. The succession seems to be more complete in some areas (Oslo, Eiker, Ringerike, Northern Mjøsa), but that may depend on more extensive outcrops and/or sampling. The Middle Cambrian agnostid diversity is comparable to that of Sweden, but non-agnostids are rare in most of Norway. The olenid diversity of the Upper Cambrian is the same in both countries, but agnostids and non-olenids are more diverse in Sweden.

The trilobite subfamily Monorakinae (Pterygometopidae). David J. Holloway Museum Victoria, Melbourne, Australia The Monorakinae is a subfamily of the Pterygometopidae characterised by the fusion of L2 and L3 in the glabella. The resulting bicomposite lobe is expanded backwards to reach the occipital furrow, displacing L1 from contact with the axial furrow and causing the realignment of S1 to a markedly oblique orientation. The bicomposite lobe is commonly bounded adaxially by a longitudinal furrow containing three pairs of apodemal pits. The Monorakinae was possibly derived from the Pterygometopinae, and includes the genera Monorakos, Carinopyge, Ceratevenkas- pis, Elasmaspis, Evenkaspis and Parevenkaspis, some of which are incompletely known. Monorakines have a stratigraphical range of Caradoc to Ashgill and are largely confined to the Siberian Platform and the Russian Far East. The subfamily is known elsewhere only from the Seward Peninsula of Alaska, which may have been part of the Siberian continent during the Ordovician.

Evolution of Irvingella from the Machari Formation, Korea. 1 2 1 Paul Hong , Jeong Gu Lee and Duck K. Choi 1 School of Earth and Environmental Sciences, Seoul National University, Korea 2 Department of Natural History, National Science Museum, Taejon, Korea Irvingella is a Late Cambrian trilobite with a wide geographic distribution over formerly separated Palaeozoic continents. The evolutionary lineage of Irvingella was first explored by Palmer (1965) based on material from the Great Basin of the United States, in that the most noticeable morphologic change is the progressive reduction of preglabellar field in descendant species. A similar phenomenon has also been observed from the Machari Forma- tion of Korea, where four species of Irvingella occur successively: from oldest to youngest, I. prisca from the Eugo- nocare longifrons Zone, I. megalops from the Eochuangia hana Zone, and I. sp. nov. A and I. major from the Ag- nostotes orientalis Zone. I. prisca and I. megalops have relatively long preglabellar fields comparable to I. angusti- limbata from North America and I. tropica from Australia, whereas the younger forms, such as Irvingella sp. nov. A and I. major are characterised by lack of preglabellar field. This evolutionary series appears to provide a better stratigraphic resolution for intercontinental correlation.

Revision of Viaphacops species from the Devonian of Bolivia. Yumiko Iwasaki American Museum of Natural History, New York Although abundant research has been done on the Devonian calmoniids of Bolivia during the past century, the pha- copids have been neglected. The purpose of this study was to revise the phacopid Viaphacops from Bolivian localities. This genus, which has been characterised by a much reduced occipital furrow and glabellar lobe 1L, was originally proposed as a subgenus of Paciphacops by Maximova (1972), and has since been alternatively described as either a subgenus or a genus by various authors. The specimens of Viaphacops were collected from such classic localities as Belen, Pujravi, and Padilla. In addition, material from Totora-Aiquile and Tarija is reported here for the first time. Based on this newly collected material five new species are proposed for Viaphacops, one of which is from Tarija that co-occurs with a Paciphacops species. This is the first instance in which the species are reported to be coeval.

Agnostoids from the uppermost Middle and Upper Cambrian of the Khos-Nelege River reference section (northeastern flank of the Siberian Platform). 1 2 Nadezhda P. Lazarenko and Tatyana V. Pegel 1 All-Russian Research Institute of Ocean Geology and Mineral Resources, St. Petersburg, Russia 2 Siberian Research Institute of Geology, Geophysics and Mineral Resources, Novosibirsk, Russia The Khos-Nelege River reference section has a continuous Middle-Upper Cambrian succession perfectly characterised by trilobite, brachiopod and conodont assemblages with abundant cosmopolitan genera and species. It is represented by cyclic alternation of argillaceous and carbonate rocks of the Ogon'or Formation deposited on a carbonate slope into a deep-water open basin. The traditional Middle-Upper Cambrian boundary and several well correlatable global horizons are determined here (the bases of the Glyptagnostus stolidotus, G. reticulatus zones, Irvingella in association with Agnostotes). Upper Cambrian strata are subdivided into seven trilobite zones, and the following agnostoids, amongst others, are very important in the trilobite assemblages: Lejopyge armata, L. laevigata, Goniagnos- tus spiniger, Ptychagnostus aculeatus, Clavagnostus bisectus, C. spinosus, Oidalagnostus changi, O. trispinifer, Peronopsis insignis, Goniagnostus nathorsti, Nahannagnostus nganasanicus, Oedorhachis typicalis, Proagnostus bulbus, Aspidagnostus laevis, Glyptagnostus stolidotus, G. angelini, G. reticulatus, Aspidagnostus lunulosus, A. ru- gosus, Agnostus inexpectans, A (Homagnostus) obesus, Pseudagnostus idalis, P. rotundatus, P. communis, Agnos- totes (Pseudoglyptagnostus) elegans, Peratagnostus orientalis, Rhaptagnostus cf. R. obsoletus, Neoagnostus quad- ratus, Agnostus hedini, Lotagnostus asiaticus, L. trisectus, and Geragnostus sp.

Protaspides of Cambrian trilobites. Dong-Chan Lee and Brian D. E. Chatterton Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada Chung-Hung Hu reported protaspides of many Cambrian trilobite species during the 1960s to the 1980s. These protaspid specimens are re-examined and re-analysed in comparison with Cambrian protaspides described by other workers. The protaspides are clustered into five morphotypes, which would indicate the existence of five new super- familial groupings within the suborder Ptychopariina. Each morphotype, and the families assigned to it, are as fol- lows: morphotype A - Kingstoniidae (Komaspidella), Lonchocephalidae, Menomoniidae, and Catellicephalidae; morphotype B - Cedariidae, Anomocaridae, Crepicephalidae, Marjumiidae, and Llanoaspididae; morphotype C - Housiinae, Phylacteridae, and Norwoodiidae; morphotype D - Parabolinoididae; and morphotype E - Aphelaspidi- nae and Elviniidae. Protaspides of the superfamily Dikelocephalacea (the Ptychaspididae) are distinguishable from these five protaspid morphotypes of the Ptychopariina. Protaspides of the suborder Olenina exhibit a wider range of morphologic variation than expected from the relatively robust monophyletic status of the group, based on holaspid morphologies. Of these Cambrian ptychopariide protaspides, crepicephalid protaspides display the closest morphologies to metaprotaspides of the Proetida, implying close relationship to, and possible ancestry of the post-Cambrian Proetida. Protaspid similarities of Leiostegium and Ptarmigania support the inclusion of the Leiostegiina within the Corynexochida. Missisquoiidae and Kingstoniidae (Blountia) also have protaspides similar to those of the Corynex- ochida.

Occurrence of Yosimuraspis (Trilobita, Early Ordovician) in the Taebaek Group of Korea: biostratigraphic and palaeogeographic significance. Seung-Bae Lee and Duck K. Choi School of Earth and Environmental Sciences, Seoul National University, Korea The Cambro-Ordovician sedimentary rocks in Korea (the Choson Supergroup), have been differentiated into five groups based on distinct lithological succession, faunal contents, and geographic distribution; they are the Taebaek, Yongwol, Chongson, Pyongchang, and Mungyong groups. Of these, the Taebaek and Yongwol groups are region- ally extensive and stratigraphically well understood owing to the prolific occurrence of trilobites and conodonts. The contrasting faunas of the Taebaek and Yongwol groups resulted in two separate biostratigraphical schemes for the Lower Palaeozoic of Korea; this on the other hand hampers precise correlation between the two groups and thus detailed palaeogeographical reconstruction of the Korean Peninsula. Yosimuraspis is an earliest Ordovician trilobite endemic to Korea and China. It was originally erected from the Yongwol Group, but little attention has been paid to the genus until its occurrence was known in China in the 1980s. Yosimuraspis is extremely abundant, constituting 75-95% of the collections; it is associated with Jujuyaspis, a guide fossil indicating the Cambrian-Ordovician boundary. The Cambrian-Ordovician boundary in the Taebaek Group has hitherto been obscured due to the paucity of fossils across the putative Cambrian-Ordovician boundary interval. The recent discovery of Yosimuraspis from the Taebaek Group not only helps clarify the Cambrian-Ordovician boundary in the region, but also supports the palaeogeographical model that during the Palaeozoic most of the Korean Peninsula was connected through contiguous shallow waters to North China.

Trilobite associations from the Middle and Upper Ordovician Anderson Shale Formation in Jämtland, central Sweden. Kristina Mansson Department of Geology, University of Lund, Sweden The Anderson Shale Formation of Jämtland is situated within the Caledonian Front and belongs to the Lower Al- lochthon. The lower part of the formation is assigned to the Hustedograptus teretiusculus Zone, whereas the upper part extends from the basal Nemagraptus gracilis Zone well into Diplograptus multidens Zone. The Anderson Shale is generally richly fossiliferous, having both benthic and pelagic elements, and is a variable unit both faunally and lithologically. The trilobite faunas of the Anderson Shale include distinctive associations of taxa at the genus level. Trilobite associations have been studied from three localities in the Storsjon district in central Jämtland (Ander- son, Marielund, and the northwest shore of Froson). Two clearly disinguishable associations are found: a) a raphiophorid and, b) an olenid association. The trilobite fauna on Froson is generally dominated by species of the olenid Triarthrus; remopleuridids (Robergia) are also common in some beds. On Anderson the most common are species of Ogygiocaris; in some limestone beds they comprise c.50% of the trilobite specimens. Nileids are fairly common in limestones from the lower part of the Anderson Shale. The trilobite faunas at Marielund are dominated by raphio- phorids, trinucleids and dionidids. These faunas are here regarded as raphiophorid associations. Similar associations occur on Anderson in the shaly mudstones, but no species of the Dionididae are found at this locality. The composition of the trilobite faunas from the Anderson Shale in Jämtland suggests deposition in fairly deep-water environments, probably on the outer shelf.

A revision of Nephranomma (Phacopidae), with new species from Victoria, Australia. Andrew C. Sandford School of Earth Sciences, University of Melbourne and Museum of Victoria, Melbourne, Australia Phacopidella (Nephranomma) Erben, 1952 was erected to embrace a number of phacopid taxa of Emsian to Eifelian age. The genus is problematic however as the type species, P. (N.) drepanomma was described from only limited material. Consequently, the affinities of Nephranomma have been variously interpreted. Richter, Richter and Struve (1959) recognised Nephranomma as a genus but reiterated its close relationship with Phacopidella. However, Alber- ti (1965), and Chlupác (1975) concluded that Nephranomma was a junior synonym of Reedops. This assignment broadens the concept of Reedops towards an unacceptable generalisation of Reedops-group morphologies. Strict ad- herence to the concept of Reedops excludes taxa attributable to Nephranomma and supports the generic status of the latter, in accord with Flick and Struve (1984), Pribyl and Vanek (1970), and Pek and Vanek (1986). Phacops sweeti Etheridge and Mitchell, 1895, from the Emsian of central Victoria is close to the type species of Nephranom- ma. Three new phacopid species from the Lochkovian to Pragian of central Victoria can be similarly assigned to Nephranomma; these are the earliest representatives of the genus. Pribyl and Vanek (1970) suggested derivation of Nephranomma from Reedops in the Emsian, but the age and transitional morphologies of these new species suggest derivation from Lochkovella in the early Lochkovian.

Pellets associated with Bohemian Ordovician trilobites: preliminary report. 1* 2 Jana Slavícková and Petr Kraft 1 Paleontological Department, National Museum, Prague, Czech Republic 2 Institute of Geology and Palaeontology, Charles University, Prague, Czech Republic Clusters of small cylindrical pellets c.1mm long and 0.3mm in diameter occur sporadically in Ordovician strata in Bohemia. They are commonly assigned to the ichnogenus Tomaculum and occur in sphaerical, lenticular, or aligned accumulations, and can be associated with body fossils. In the course of our investigation they have been studied inside the shells of hyoliths, bellerophontids and in echinoderm tests. Several clusters have been observed inside the cephala of trilobites. Until now, only examples associated with the Middle Ordovician trilobite species Ormathops atavus, Pricyclopyge binodosa and Parabarrandia crassa are at our disposal. The positions of the clusters are not fixed in these species but they are commonly situated under the glabella and in the anterior parts of the cephalon. The origin of the pellets is unknown but two main preliminary suggestions may be considered: pellets are faeces of carcass-feeders which are feeding on soft parts, and/or are using cephalic shields as hiding places. Interpretation of these pellets as trilobite eggs is very improbable.

Trilobite faunas in Upper Cambrian peritidal bank facies in the Appalachians. 1 2 1 J. F. Taylor , D. K. Brezinski and B. K. Sell 1 Geoscience Department, Indiana University of Pennsylvania, USA 2 Maryland Geological Survey, Baltimore, Maryland, USA Alternation of microbial reef and tidal flat lithofacies in cyclic, outer shelf deposits in the Appalachians produces corresponding shifts in biofacies on a scale of meters and tens of meters. This requires cautious interpretation of range data, limiting the precision of correlation possible among sections. However, a homotaxial succession of four species of Plethopeltis from reefs through 350m of strata allows definition of a Plethopeltis Zone spanning most of the Sunwaptan Stage. A basal P. saratogensis Subzone is assigned to the Lower Sunwaptan Substage; the remaining subzones constitute the Upper Sunwaptan. Recovery of P. stitti expands the established geographic range of that species and confirms correlation with lowest Upper Sunwaptan strata in Oklahoma. Restriction of P. obtusus to material that includes the unusual pygidium associated with the type cranidium decreases its known geographic and stratigraphic range, allowing recognition of a short P. obtusus Subzone in the Upper Sunwaptan. Reefs higher in the zone yield a species similar to P. concavus, but it lacks the diagnostic concave frontal area. Saukiids dominate collections from grainstones throughout the Upper Sunwaptan, often occurring in dense concentrations. The limited ranges of some species (e.g. Prosaukia stosei and P. corrugata) render them useful for fairly precise correlation.

Lower Ordovician stratigraphy and trilobite faunas from the Southern Famatina Range, La Rioja, Argenti- na. M. Franco Tortello and Susana B. Esteban Departamento Paleontologica Invertebrados, Museo de La Plata, Argentina The Upper Member of the Volcancito Formation (Lower Ordovician) crops out at the Portezuelo de La Alumbrera Creek (southern part of the Famatina range, La Rioja Province, northwestern Argentina). The 160m thick section is composed mainly of outer-shelf thin-bedded fine-grained sandstone/siltstone couplets, massive silty sandstones, and massive to laminated clayey siltstones (‘Facies Assemblage 1’). Middle shelf massive to laminated clayey siltstones and hummocky cross-stratified calcareous sandstones and mudstones (‘Facies Assemblage 2’) are restricted to the lower and the uppermost part of the section. Trilobites from the middle part of the succession include both pelagic forms (Corrugatagnostus sp., Prospectatrix sp., and three representatives of a new cyclopygid genus), and benthic taxa (Hapalopleura aff. (H.) longicornis, H. sp. nov., Asaphellus? sp., Proteuloma sp. nov., Bienvillia sp., and ?Ole- nidae gen. et sp. nov.). Cyclopygids are the dominant element of the faunal assemblages. Precise international correlation is difficult because most of the studied species have not been described elsewhere, but generic occurrences and specific affinities suggest a Late Tremadoc age. Sedimentological and faunal analyses indicate low-oxygen water bottom conditions. Occurrences of Corrugatagnostus and Prospectatrix provide additional evidence for a largely peri-Gondwanan distribution of these genera.

Phylogeny and biogeography of the Reedocalymeninae. S. T. Turvey Department of Earth Sciences, University of Oxford, UK The phylogeny of the Reedocalymeninae, an Ordovician subfamily of the Calymenidae, is revised using cladistic analysis. Twenty species of the diverse shallow-water genus Neseuretus are included in the analysis because this genus has previously been regarded as representing the basal calymenid condition, and is an important biogeographic indicator taxon for many Gondwanan and peri-Gondwanan regions during the Lower Ordovician (Arenig to Llan- virn). The remainder of the subfamily is analysed at the generic level. Cladogram topology indicates that one species previously assigned to Neseuretus, N. intermedius, from South China, should be reassigned to a new genus, as it represents the sister taxon to the clade ([Neseuretinus + Vietnamia] + Sarrabesia) and is separated from other species of Neseuretus by the clade (Reedocalymene + Calymenesun). Pradoella and Calymenella are nested within Neseure- tus. Neseuretus consists of several clades each containing species from different geographical regions, which suggests that no significant environmental barrier existed between these regions in the Lower Ordovician. This expands the European-South Chinese biogeographic region to include South America, an idea supported by the results of recent fieldwork from inner shelf facies on the South China Plate, and by critical reassessment of existing taxonomic literature.

Trilobites and sedimentary structures from the Kermeur Formation (Caradoc; Crozon Peninsula, France) : a protected marine environment. 1 2 M. Vidal and A. Loi 1 Université de Bretagne Occidentale, Brest, France 2 Università degli Studi di Cagliari, Italy The Kermeur Formation, of Caradoc age, is very well exposed at Veryac'h beach in the Crozon Peninsula, western Armorican Massif, France. Sedimentological study provides evidence that these terrigenous facies are deposits of open platform and of protected environment. The base of the Kermeur Formation, composed of argillaceous sandy facies, shows very abundant bioturbation and absence of any laminae or bedding structures. This protected marine facies yielded trilobites and less common echinoderms (Calix) always scattered through the sediments. Colpocory- phe grandis, accounting for more than 50% of the trilobite fauna, is most probably preserved in situ, as indicated by the very high proportion of articulated specimens, some representing moulting arrangements of parts. Despite of this very low energy environment, other trilobite taxa such as the relatively abundant Onnia, dalmanitids or scarce taxa such as Eccoptochile, are always disarticulated specimens. As indicated by the composition of the benthic fauna, usually found in an open platform environment, the determining factors would be energy level and bottom substrate rather than depth. Indeed, this peculiar environment was closed to the coastline and probably shallower than an open platform. Eastwards, in the Raguenez section, further studies on the same stratigraphic levels in the open marine environment, would precisely identify the distinctive features of this Caradoc protected fauna.

Early Ordovician sedimentary rocks and trilobite diversity patterns in the southern Montagne Noire (Lan- guedoc, France). 1 2 Daniel Vizcaïno and J. Javier Álvaro 1 Carcassone, France Université de Lille, France 2 CNRS, Université de Lille, France The Tremadoc to ‘Arenig’ rocks of the southern Montagne Noire (France) have been classically subdivided into six formations (Darneyre or La Dentelle, Saint-Chinian, La Maurerie, La Cluse de l’Orb, le Foulon and Landeyran) and 13 palaeontological levels or zones (from A to M), based on assemblages of trilobites, echinoderms, graptolites and trace fossils. However, a certain ambiguity is indicated by comparison of litho- and biostratigraphical units due to the coincidence of lithological and ‘supposed’ biostratigraphical boundaries. A new revision of this stratigraphical framework permits a better understanding of the facies control on trilobite diversification processes. The apparent ‘endemic’ character of some trilobite assemblages could be a consequence of taxonomic criteria, and a systematic revision is necessary in order to establish better biogeographical and biostratigraphical implications for this rich fauna.

Trilobites alive! The art of scientifically accurate reconstructions of fossils and palaeoenvironments. Anthony B. Windberg Karawara, Perth, Australia The art of reconstructing organisms in palaeo-art has predominately understated the crucial role of the palaeoenvir- onment. A thorough research of the important link between organisms and their environment must be the focus of any complete reconstruction. These serve to illustrate as accurately as possible past life and environments to a scientific and general audience. Taphonomic implications and modern ecological analogies are used in my work to reconstruct behavioural aspects such as an organism’s interaction within a population and with other species. While there is a tendency for palaeo-artists to overcrowd scenes with a wide array of organisms, convincing reconstructions will emphasise realism and naturalism. A sole reliance on prior reconstructions should be avoided and emphasis placed on researching specimens. The reconstruction of an early Cambrian scene, depicting trilobites from the Transantarc- tic Mountains within an archaeocyathan reef system, involved extensive research into numerous aspects of trilobite behaviour and morphology. This investigation involved correspondence with palaeontologists, and reference to rele- vant scientific literature, photographs and specimens. For example, the examination of a late Palaeozoic trilobite specimen provided insight into patterning and colour markings. Taphonomic studies inferred details on the ecology of the trilobite environment and informed the surrounding habitat. Palaeo-art is increased in significance with adher- ence to scientific principles and a complete investigation of palaeoenvironments.