Trilobite Species Research Articles

Trilobites from the mid-Darriwilian (Middle Ordovician) of the Amadeus Basin, central Australia

Sixteen species of trilobites are described from the Middle Ordovician (mid-Darriwilian, Da2) Stairway Sandstone and Stokes Siltstone at multiple spot localities from the Amadeus Basin, Northern Territory, central Australia. New trilobite taxa described include two new genera: Ghanaspis gen. nov. and Iridis gen. nov.; as well as five new species; Eisarkaspis jonesi sp. nov., Ghanaspis ritchiei gen. et sp. nov., Iridis schoonorum gen. et sp. nov., Lycophron titan sp. nov., and Norasaphus (Norasaphus) patersoni sp. nov. Of these, Lycophron titan sp. nov. is the largest species of trilobite so far documented from Australia and possibly the third largest in the world. Also redescribed is Basilicus thorntoni [=Asaphus (Megalaspis?) thorntoni] based on the recently rediscovered type material and additional specimens from elsewhere in the basin. *P.M. Smith [Patrick.Smith@austmus.gov.au], Palaeontology Department, Australian Museum Research Institute, Sydney, New South Wales, 2010, Australia and, Department of Biological Sciences, Macquarie University, Sydney, New South Wales, 2109, Australia; J.R. Laurie [john.r.laurie@gmail.com], Department of Biological Sciences, Macquarie University, Sydney, New South Wales, 2109, Australia.

Earth science collections of the Centre Grégoire Fournier (Maredsous) with comments on Middle Devonian–Carboniferous brachiopods and trilobites from southern Belgium

Although the Centre Grégoire Fournier of the Maredsous Abbey is especially famous for the fossils and minerals from the Carboniferous (Viséan) ‘black marble’ of Denée, a marine conservation-Lagerstätte, its palaeontological collections likewise include some types and illustrated specimens of invertebrates (cystoids, goniatites, ostracods, trilobites) and fishes from the Ordovician, Devonian and Carboniferous of Belgium. These specimens are discussed and/or illustrated as is the case of the fragments of two Belgian meteorites (Lesves and Tourinnes-la-Grosse chondrites) that are part of the CGF mineralogical and petrological collections. Moreover, the type material of 30 species and subspecies of Upper Devonian–Pennsylvanian linguliformean and rhynchonelliformean brachiopods (described by de Koninck (1847), J. Fraipont (1888a), Ch. Fraipont (1908), Demanet (1923, 1934), Demanet (in Demanet & Van Straelen, 1938), and Grimm (1998)) and that of two Middle–Upper Devonian species of trilobites (Stainier, 1887; Richter & Richter, 1933), almost all from the Namur–Dinant Basin (southern Belgium), are re-investigated and/or fully figured for the first time in order to facilitate future taxonomic revision. The obscure Tournaisian genus Anomianella de Ryckholt (1851) is rejected from the bivalves and transferred to the brachiopods (Craniida). It is probably related to Petrocrania Raymond, 1911. The lectotype (hereby selected) of Orthis latissima M‘Coy, 1844 and that of Producta corrugata M‘Coy, 1844, both from the Viséan of Ireland, are photographically illustrated (for the first time for the former). The lectotype of Productus murchisonianus de Koninck, 1847 from the Upper Palaeozoic of Tasmania (Australia) is also designated.

Moulting in the Cambrian oryctocephalid trilobiteArthricocephalites xinzhaiheensisfrom Guizhou Province, South China

It is important to understand moulting behaviours in trilobites through different growth stages. Most studies have focused on patterns of moulting in trilobites based on a few exuviae. The present study is based on 177 disarticulated specimens of Arthricocephalites xinzhaiheensis from the Balang Formation (Cambrian Series 2, Stage 4, Guizhou Province, South China). The abundance of disarticulated assemblages allows the distinction between carcasses and exuviae to be made with confidence and enables a detailed exploration of moulting behaviours. About 96.6% of exuviae of both meraspides and holaspides of Ar. xinzhaiheensis show a disarticulated cranidium characterizing Henningsmoen's configuration. The trilobites commonly used the cephalic sutures and cephalothoracic joint for moulting, involving lateral rotation or inversion of the cranidium to create a wide exuvial gape. Only one specimen displays the Somersault configuration characterized by an overturned lower cephalic unit and the data also show that trilobites employing the cephalic sutures to create an anterior exuvial gape are rare in holaspides. Though some specimens are similar to Salter's configuration with an inverted cephalon with respect to the thoracopygon, the specimens show closed cephalic sutures and thus dissociated or inverted cephala are likely to represent disturbed carcasses. Several other species of oryctocephalid trilobites display Henningsmoen's configuration indicating that exuviation by disarticulated cranidium to enlarge the exuvial gape was prevalent in the family from Cambrian Series 2 Stage 4 to the succeeding Wuliuan Stage of the Miaolingian Series.

Systematic and biostratigraphy of the genera Parasolenopleura, Badulesia, and Pardailhania in the Iberian Chains: a useful zonation for the Miaolingian Series (former middle Cambrian) in the Mediterranean region

The trilobite species of three genera included in the Family Solenopleuridae: Parasolenopleura, Badulesia, and Pardailhania are revised. These genera have a great biostratigraphic interest due to their broad distribution in the Miaolingian Series (former middle Cambrian) of the Mediterranean Subprovince and because they constitute an evolutionary lineage, that facilitates an accurate regional correlation. Two of these genera (Pardailhania and Badulesia) have been used to define middle Cambrian zones in Spain (lower and middle Caesaraugustan, equivalent to the uppermost Wuliuan and the lower Drumian stages). Although, all authors have been using the same species to establish the Mediterranean biozonation of this interval time, the zone concept has been modified since Sdzuy’s original idea. A thorough study of three localities from the Iberian Chains (Murero, Jarque, and Villafeliche) have allowed us to revise the lower and middle Caesaraugustan zonation in the Iberian Chains and for extension, in the Mediterranean region by comparison with the other localities where those genera are recorded. We propose now a review zonation based on trilobite phylozones, including new stratigraphic and systematic data from the Iberian Chains in order to clarify the intercontinental correlation of this time interval

The post‐embryonic ontogeny of the early Cambrian trilobite Estaingia bilobata from South Australia: trunk development and phylogenetic implications

AbstractTrilobites are one of the most diverse and abundant fossil groups from the early Palaeozoic, and as such are useful for answering important questions about early animal evolution, including developmental processes. Ontogenetic information for a large number of trilobite species has been published, but cases where multiple articulated specimens are known across the full range of developmental stages are rare. The early Cambrian (Series 2, Stage 4) Emu Bay Shale biota from Kangaroo Island (South Australia) is numerically dominated by trilobites, particularly articulated specimens of the ellipsocephaloid Estaingia bilobata, which are present in densities of >600 individuals per square metre on certain bedding planes. Here we describe the essentially complete post‐embryonic ontogenetic series of E. bilobata from the Emu Bay Shale, and investigate patterns of growth relating to articulation and segmentation in this early Cambrian arthropod. Estaingia bilobata exhibits the hypoprotomeric mode of growth, with the epimorphic phase (the cessation of trunk segment generation) reached prior to the onset of the holaspid period. The meraspid pygidium had an extended equilibrium period in which anterior segment release into the thorax was matched by subterminal segment generation. Previously undocumented morphological features of E. bilobata, including the hypostome and bispinose pleural tips in holaspides, are also described. The growth characteristics and morphological features of E. bilobata documented herein strengthen close phylogenetic relationships between the Estaingiidae, Ellipsocephalidae and Xystriduridae.

Elrathia hensonensis nomen novum, new replacement name for Elrathia groenlandica Geyer and Peel, 2017 (Trilobita, Ptychopariacea)

In an article by Geyer and Peel (2017, p. 288), we inadvertently coined a species-group name, Elrathia groenlandica Geyer and Peel, 2017 for a trilobite species of the superfamily Ptychopariacea. This name is a junior homonym of Elrathia? groenlandica Poulsen, 1927 and is thus invalid (ICZN Article 57.2; see International Commission on Zoological Nomenclature, 1999). We therefore propose Elrathia hensonensis new name as the replacement name for E. groenlandica Geyer and Peel, 2017. The new species name is derived from the Henson Gletscher area, North Greenland, the region where the type locality of this species is located.

The Problematic Fossil Mobergella radiolata as an Index Species of the Lower Cambrian Stages

The biostratigraphy of the lower boundaries of the Atdabanian Stage of the General Stratigraphic Scale of Russia and Stage 3 of the International Chronostratigraphic Chart is discussed. It is generally accepted that the first appearance of trilobites is the main characteristic of these stages. The difficulties in selecting the correlation level for the lower boundary of Stage 3 on the basis of trilobites are explained by the different taxonomic compositions of the assemblages of the most ancient representatives of this arthropod group on different paleocontinents and evident diachronism of the levels of their first appearance. For these purposes, it is proposed to use the species Mobergella radiolata Bengtson, 1968, the geographical distribution of which is wider than that of any species of ancient trilobites. It was shown that in the stratotype region of the Lower Cambrian stages in the Siberian Platform (the interfluve between the Lena and Aldan rivers), M. radiolata appears in sections at the same level as the first Atdabanian archaeocyaths of the Retecoscinus zegebarti Zone. This allows M. radiolata to be used as an index species for the base of the Atdabanian. Finds of M. radiolata in other regions of the Siberian Platform (west, north, and southeast, interior areas of the platform) make this microfossil an extremely valuable tool for biostratigraphy of the Lower Cambrian, with a much higher correlation potential than locally common early Atdabanian archaeocyaths or trilobites.

Unexpectedly curved spines in a Cambrian trilobite: considerations on the spinosity in Kingaspidoides spinirecurvatus sp. nov. from the Anti-Atlas, Morocco, and related Cambrian ellipsocephaloids

The new ellipsocephaloid trilobite species Kingaspidoides spinirecurvatus has a spectacular morphology because of a unique set of two long and anteriorly recurved spines on the occipital ring and the axial ring of thoracic segment 8. Together with the long genal spines this whimsical dorsally directed spine arrangement is thought to act as a non-standard protective device against predators. This is illustrated by the body posture during different stages of enrolment, contrasting with the more sophisticated spinosities seen in later trilobites, which are discussed in brief. Kingaspidoides spinirecurvatus from the lower–middle Cambrian boundary interval of the eastern Anti-Atlas in Morocco has been known for about two decades, with specimens handled as precious objects on the fossil market. Similar, but far less spectacular, spine arrangements on the thoracic axial rings are known from other ellipsocephaloid trilobites from the Anti-Atlas of Morocco and the Franconian Forest region of Germany. This suggests that an experimental phase of spine development took place within the Kingaspidoides clade during the early–middle Cambrian boundary interval.

Cambrian deposition in northwestern Africa: Relationship of Tamlelt massif (Moroccan‒Algerian border region) succession to the Moroccan Meseta

The Tamlelt massif is physiographically grouped as a continuation of the easternmost High Atlas. However, re-examination of the Tamlelt's Cambrian litho- and biostratigraphy shows a depositional history that differs from that of the Souss Basin to the southwest (i.e., west-central High Atlas and eastern Anti-Atlas of Morocco). Our re-examination leads to recommendations on the local stratigraphic succession and nomenclature. Trilobites from the Al Hamrat Formation in the Tamlelt massif indicate late early Cambrian (upper Epoch 2) siliciclastics overlying shallow marine, carbonate-rich deposits (Jbel Menhouhou Formation) similar to and coeval with those of the distant western Anti-Atlas region but older than and lithologically distinct from fluviatile siliciclastics (Epoch 3) in the nearby eastern Anti-Atlas. The Jbel Menhouhou carbonates unconformably overlie probable terminal Proterozoic volcanics and clastics of the Bou Kaïs Formation (new) and are overlain by shales and arenites of the upper Kheneg El Kahal Group, which features a Cambrian Stage 4 regressive half-cycle. Regional differences in lithofacies disappear in the early Miaolingian with relatively monotonous, mudstone-rich facies in the Tamlelt massif area (Batene El Jdari Formation) comparable to those of the Jbel Wawrmast Formation of the west-central High Atlas and central‒eastern Anti-Atlas. Probable early late Cambrian brachiopods from siliciclastic rocks of the Tamlelt area indicate a later Cambrian depositional history similar to that of the Anti-Atlas and perhaps Moroccan Meseta. The distinctiveness of the upper lower Cambrian deposits of the Souss Basin from those of the Tamlelt massif apparently reflects a depositional framework independent from other regions of the Atlas ranges, and suggests the Tamlelt region was confluent with the Meseta basin to the northwest. Known trilobites permit precise age assignments through the Tamlelt succession and include species (or forms) which contribute to a refined correlation within West Gondwana and improve West Gondwana‒Baltica correlation. The new trilobite species Saukianda? (Saukianda?) dresnayi is proposed.

Proetid trilobites from the middle Telychian (Llandovery, Silurian) Ningqiang Formation, Shaanxi, China

Four proetid trilobite species, Chuanqianoproetus guizhouensis Yin in Yin and Li, 1978, C. shuangheensis Wu, 1977, C. sp., and Latiproetus guizhouensis Yin in Yin and Li, 1978, are described from the Ningqiang Formation in Ningqiang County, Shaanxi, China. They are middle Telychian (Llandovery, Silurian) in age. Chuanqianoproetus and Latiproetus are both regarded as members of the subfamily Warburgellinae; the former has been considered to be a junior subjective synonym of Astroproetus, but on the basis of its morphology we argue here that they represent two independent genera. The poorly sorted bioclastic grainstones containing trilobite sclerites may indicate their deposition in turbulent conditions on an open marine platform.

Edrioasteroids on corals: Taphonomic feedback and sedimentary processes control the ecology of a Late Ordovician (Katian: Cincinnatian, Richmondian) community in central Kentucky, USA

Communities of organisms that encrusted hardgrounds and skeletal material developed and became widespread during the Great Ordovician Biodiversification Event, and this community structure was a well-established part of the marine ecosystem by the Late Ordovician. Here we describe and investigate an example of skeletal encrustation from the Bardstown Member of the Drakes Formation (Upper Ordovician, Katian, Richmondian) near Mount Washington, Kentucky. This occurrence exhibits three dense coral beds near its base which primarily contain the problematic colonial organism Tetradium, the colonial rugose coral Cyathophylloides, and the solitary rugose corals Grewingkia and Streptelasma, as well as several species of stromatoporoids, bryozoans, brachiopods, cephalopods, and trilobites. In one locality, the corals in the uppermost bed are fragmented, reoriented, and encrusted, demonstrating reworking and taphonomic feedback of the skeletons. Tetradium skeletons created hard-substrate clasts that were exploited by a community of sclerobionts including stromatoporoids, bryozoans, and edrioasteroid echinoderms. The skeletons of Cyathophylloides, abundant in the underlying coral beds, are in life orientation and host a lower diversity of encrusters. Corals at other exposures of the Bardstown Member are not significantly reworked and do not host encrusters, suggesting localization of submarine erosion. Here, we describe the stratigraphy, paleoecology, and comparative taphonomy of the Bardstown coral beds at two localities to assess: 1) the burial and taphonomic feedback of the coral skeletons; 2) the community structure and evolution, attachment strategies, and substrate preferences of the encrusting community; and 3) the spatial patterns of submarine erosion and disturbance at the Bardstown coral bed horizons.

Trilobite compound eyes with crystalline cones and rhabdoms show mandibulate affinities

Most knowledge about the structure, function, and evolution of early compound eyes is based on investigations in trilobites. However, these studies dealt mainly with the cuticular lenses and little was known about internal anatomy. Only recently some data on crystalline cones and retinula cells were reported for a Cambrian trilobite species. Here, we describe internal eye structures of two other trilobite genera. The Ordovician Asaphus sp. reveals preserved crystalline cones situated underneath the cuticular lenses. The same is true for the Devonian species Archegonus (Waribole) warsteinensis, which in addition shows the fine structure of the rhabdom in the retinula cells. These results suggest that an apposition eye with a crystalline cone is ancestral for Trilobita. The overall similarity of trilobite eyes to those of myriapods, crustaceans, and hexapods corroborates views of a phylogenetic position of trilobites in the stem lineage of Mandibulata.

Ordovician trilobites from the lower part of the Dawan Formation (Floian–Dapingian) at Huanghuachang, Yichang, Hubei, southern China

Twelve trilobite species assigned to 11 genera are described from the Lower Unit of the Dawan Formation at the Huanghuachang section of Yichang, Hubei, southern China, which has been ratified by the International Union of Geological Sciences (IUGS) as the Global Stratotype Section and Point (GSSP) for the base of the Middle Ordovician Series and the Third Stage (Dapingian) of the Ordovician System. Of these trilobites, five species, i.e., Carolinites genacinaca genacinaca, Ovalocephalus eoprimitivus, Rhombampyx chinensis, Taihungshania tachengssuensis, and Niobe (Niobella) obscura n. sp., occur in the lowermost part of the Dawan Formation, and are restricted to the upper part of the Oepikodus communis conodont biozone to the lower part of the Oepikodus evae Biozone. Two species, Liomegalaspides taningensis and Pseudocalymene transversa, are distributed almost throughout the Lower Unit of the Dawan Formation; two taxa, Annamitella sp. and Mioptychopyge sp., are recorded from the middle part and upper part of the Oepikodus evae Biozone, respectively; and two other species, Rhombampyx yii and Aulacopleura (Paraaulacopleura) dawanensis, appear in the upper part of the Lower Unit of the Dawan Formation, which is referred to the Middle Ordovician Microzarkodina flabellum-Baltoniodus triangularis Biozone. Agerina parva has a shorter range, across the Lower–Middle Ordovician boundary. The fauna is dominated by Liomegalaspides taningensis, which is assigned to the Liomegalaspides Biofacies, and indicates an inner-shelf environment.For regional chronostratigraphic correlation, the occurrence of the middle–late Floian (approximately Corymbograptus deflexus Zone) forms Carolinites genacinaca genacinaca and Taihungshania tachengssuensis in the fauna is of great significance: the former, a pelagic trilobite species, occurs extensively in North America, East Siberia, Novaya Zemlya, and Spitsbergen; the latter is widely distributed in the Yangtze Region, occurring in Sichuan, Guizhou, Yunnan, southern Shaanxi, and eastern Anhui as well as in Hubei.The trilobites of the fauna are mostly typical of the South China Plate and eastern Peri-Gondwana, but the presence of Agerina and Niobe (Niobella) suggests faunal links with coeval Baltoscandian assemblages, and the occurrence of Rhombampyx is indicative of a Laurentian affinity.

A new trilobite species from the upper Rhuddanian (lower Silurian) of South China, and its biogeographical implications

Wei, X. & Zhan, R. B., 20 September 2018. A new trilobite species from the upper Rhuddanian (lower Silurian) of South China, and its biogeographical implications. Alcheringa 43, 33–42. ISSN 0311-5518.Xin Wei [xwei@nigpas.ac.cn]. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, 210008, PR China; University of Science and Technology of China, Hefei, 230026, PR China; Renbin Zhan [rbzhan@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, 210008, PR China; University of Chinese Academy of Science, Beijing, 100049, PR China.Anacaenaspis yanpingensis sp. nov., from the lower Niuchang Formation (upper Rhuddanian, lower Llandovery, lower Silurian), is the first record of this genus from South China. The biogeographical distribution of Anacaenaspis and some other trilobite genera from South China (e.g., Gaotania, Hyrokybe, Aulacopleura and Raphiophorus) in the Llandovery evidences faunal exchanges between Avalonia–Baltica, Laurentia, Australia and South China. We attribute these dispersals to prevailing ocean currents, and especially equatorial countercurrents, which would have propagated dispersals during the Rhuddanian, shortly after the end-Ordovician mass extinction.

Comment on the paper written by Gutiérrez-Marco et al. (2017)

Recently, in an article written by Gutiérrez-Marco et al. and published in Annals of Geophysics [60, Fast Track 7, 2017], there are some incorrect affirmations written against my work in the paleontological field that I have been carried out for more than 10 years on new species of trilobites from the Ordovician of Morocco. They have questioned the quality of my work but also that of my collaborators and the institutions with which I am collaborating, particularly the Geological Museum of the Seminario of Barcelona (Spain), an institution that has been doing geological research since 1874. For this reason, I will present here some evidences that show the incorrectness of such statements reported in the paper by Gutiérrez-Marco et al. [2017]

Trilobites from the Gzhelian (Pennsylvanian) of the Moscow Region

A new trilobite species, Ditomopyge (Carniphillipsia) mosquensis sp. nov., from the Gzhelian of the Moscow Region (Rusavkino, Gzhel, and Shchelkovo localities) is described. Its members have previously been assigned to Ditomopyge (Carniphillipsia) planiloba (Weber, 1933). The establishment of Griffithides gruenewaldti var. ivanovi Ivanov et Weber in Weber, 1937, which has previously been regarded as a synonym of Kaskia gruenewaldti (von Moller, 1868) (Hanh and Hahn, 1970), as a valid species, Kaskia ivanovi (Ivanov et Weber in Weber, 1937), is confirmed.

Some middle and late Cambrian trilobites and brachiopods from the Adamsfield Trough, Tasmania

Jago, J.B., Bentley, C.J., Laurie, J.R. & Corbett, K.B., 26 June 2018. Some middle and late Cambrian trilobites and brachiopods from the Adamsfield Trough, Tasmania. Alcheringa 43, 1-17. ISSN 0311-5518.Cambrian Series 3 and Furongian trilobites and brachiopods are described from the Adamsfield Trough in southwestern Tasmania. The oldest fossils are very poorly preserved trilobites, assigned to Asaphiscidae gen. et sp. indet. from within the Island Road Formation a short distance above the unconformity with the underlying Proterozoic Wedge River Beds. A trilobite species from within the isolated Boyd River Formation is referred to Lioparia sp. The Island Road Formation and the Boyd River Formation are stratigraphically equivalent to the Trial Ridge Beds which have previously been dated as belonging to the Lejopyge laevigata Zone. The Trial Ridge Beds are overlain unconformably by the Singing Creek Formation. In the Adamsfield, Clear Hill and Stepped Hills areas, stratigraphic equivalents of the Singing Creek Formation collectively contain the trilobites Pseudaphelaspis sp., Pseudaphelaspis? sp., Prochuangia sp., Mindycrusta sp., Nepeidae gen. et sp. indet., and Olenidae gen. et sp. indet. plus the brachiopods described herein as Billingsella sp. aff. costata, Billingsella sp. A, Billingsella sp. B and a possible member of the Billingselloidea. The Singing Creek Formation has been previously correlated with the Stigmatoa diloma Zone. The genus Lotosoides Shergold 1975 is placed in synonymy with Prochuangia Kobayashi 1935.James B. Jago* [jim.jago@unisa.edu.au] University of South Australia, School of Natural and Built Environment, Mawson Lakes, SA 5095, Australia; Christopher J. Bentley [bigfossil@bigpond.com] 30 Albert Street, Clare, SA 5453, Australia; John R. Laurie [john.r.laurie@gmail.com] Department of Biological Sciences, Macquarie University, NSW 2109, Australia; Keith D. Corbett [keith.corbett@bigpond.com] 35 Pillinger Drive, Fern Tree, Tas 7054, Australia.

The Furongian break-up (rift/drift) unconformity in the central Anti-Atlas, Morocco

This paper presents a stratigraphic, sedimentological and palaeontological study of the Cambrian–Ordovician transition in the central Anti-Atlas in order to characterize the rift-drift transition of the Cambrian Atlas Rift. The event stratigraphy and sedimentology of the Cambrian–Ordovician transition in the central Anti-Atlas, and the endemic character of the latest shelly faunas from the Cambrian Atlas Rift have been reviewed, the latter by sampling the Bailiella Formation and the base of the Jbel Lmgaysmat Formation. In the vicinity of Foum Zguid, central Anti-Atlas, several unconformities (joined laterally into one single angular discordance or paraconformity) can be recognized across the Cambrian–Ordovician transition: (i) a ravinement surface capped by lenses of polymictic conglomerates marking the top of the Azlag Formation and reflecting reworking of the substrate under sharp transgressive conditions; (ii) a skeletal calcareous siltstone bed at the base of the Jbel Lmgaysmat Formation preserving surficial silicification (silcretization related to broad uplift, denudation and weathering of an exposed landscape dominated by silica-rich rocks), postdated by fissuring associated with hydrothermal mineralization of Fe (Ba-Mn-Pb) ore deposits, linked to the opening of the so-called El Graara graben; (iii) generalized uplift and denudation, followed by sedimentation of alluvial-to-fluvial and proximal coastal-plain deposits (lower member of the Lower Fezouata Formation); and (iv) a final drowning and shaly blanketing of the inherited palaeorelief by the upper member of the same formation, which marks the beginning of passive-margin conditions. The Bailiella Formation has yielded the trilobite species Planolimbus hessikouanus, Maladioidella? destombesi n.sp. and Bailiella sepulcra n.sp., and the Jbel Lmgaysmat Formation Bailiaspis? glabrata, which point to biogeographic connections with the neighbouring Avalonian and west-European margins of Northwest Gondwana and Baltica.

Trilobites and agnostids from the Goyder Formation (Cambrian Series 3, Guzhangian; Mindyallan), Amadeus Basin, central Australia.

A new assemblage containing twenty-two species of trilobites and agnostids is described from the Goyder Formation (Cambrian Series 3) in the Ross River Syncline and Gardiner Ranges of the Amadeus Basin, Northern Territory, central Australia. New trilobite taxa described include the genus, Trephina gen. nov., and four new species Adelogonus prichardi sp. nov., Hebeia stewarti sp. nov., Liostracina joyceae sp. nov., and Trephina ranfordi sp. nov. Two agnostid taxa previously known only from Antarctica, Ammagnostus antarcticus Bentley, Jago Cooper, 2009 and Hadragnostus helixensis Jago Cooper, 2005, are also documented. Of the two agnostid species, the latter is the most age diagnostic, previously reported from the Cambrian Series 3 (Guzhangian; late Mindyallan; Glyptagnostus stolidotus Zone) Spurs Formation in Northern Victoria Land. This age for the Goyder Formation assemblage is supported by the co-occurrence of the trilobites Biaverta reineri Öpik, 1967, Blackwelderia repanda Öpik, 1967, Henadoparia integra Öpik, 1967, Monkaspis cf. travesi (Öpik, 1967), Nomadinis pristinus Öpik, 1967, Paraacidaspis? priscilla (Öpik, 1967), and Polycyrtaspis cf. flexuosa Öpik, 1967, also known from the late Mindyallan (G. stolidotus Zone) successions of the neighbouring Georgina Basin (Northern Territory and Queensland). The generic assemblage of the Goyder Formation is also similar to those from the Guzhangian (Mindyallan) of other parts of Australia (New South Wales, South Australia, and Western Australia), in addition to East Antarctica and North and South China.

A new high-resolution 3-D quantitative method for analysing small morphological features: an example using a Cambrian trilobite

Taphonomic processes play an important role in the preservation of small morphological features such as granulation or pits. However, the assessment of these features may face the issue of the small size of the specimens and, sometimes, the destructiveness of these analyses, which makes impossible carrying them out in singular specimen, such as holotypes or lectotypes. This paper takes a new approach to analysing small-morphological features, by using an optical surface roughness (OSR) meter to create a high-resolution three-dimensional digital-elevation model (DEM). This non-destructive technique allows analysing quantitatively the DEM using geometric morphometric methods (GMM). We created a number of DEMs from three populations putatively belonging to the same species of trilobite (Oryctocephalus indicus) that present the same cranidial outline, but differ in the presence or absence of the second and third transglabellar furrows. Profile analysis of the DEMs demonstrate that all three populations show similar preservation variation in the glabellar furrows and lobes. The GMM shows that all populations exhibit the same range of variation. Differences in preservation are a consequence of different degrees of cementation and rates of dissolution. Fast cementation enhances the preservation of glabellar furrows and lobes, while fast dissolution hampers preservation of the same structures.