Silurian Trilobites Research Articles

Late Ordovician and early Silurian trilobites from Tasmania

Late Ordovician and early Silurian trilobites from Tasmania

Examining abnormal Silurian trilobites from the Llandovery of Australia.

Abnormal trilobites present insight into how arthropods with fully biomineralised exoskeletons recovered from injuries, genetic malfunctions, and pathologies. Records of abnormal Silurian trilobites in particular show an abundance of specimens with teratologies and a limited record of injuries. Here we expand the record of abnormal Silurian trilobites by presenting seven new abnormal specimens of Odontopleura (Sinespinaspis) markhami from the early Silurian (Llandovery, Telychian) Cotton Formation, New South Wales. We use these specimens to illustrate novel evidence for asymmetric distribution of pleural thoracic spine bases. These abnormal bases likely reflect genetic complications, resulting in morphologies that would unlikely have aided the fitness of abnormal individuals. In considering records of malformed Silurian trilobites more broadly, we propose that the largest trilobites may have been prey at this time. This indicates a possible change in the trophic position of trilobites when compared to Cambrian and Ordovician palaeoecosystems.

Primitivo Hernández-Sampelayo (1880−1959): Paleozoic ironstones and fossils

The mining engineer Primitivo Hernández-Sampelayo was one of the most relevant figures in the study of the Spanish Paleozoic since Lucas Mallada’s time. After a few years working in mining companies, he entered the Geological and Mining Institute of Spain in 1914, where he worked until his retirement in 1950. The results of his studies are the large monographs on Paleozoic sedimentary ironstones (the one devoted to Galicia, 1922–1935, was published in four volumes with a total of 1,813 pp.), or the explanations to the geological map of Spain at a 1:1,000,000 scale (Cambrian System, 1934, 240 pp.; Silurian System –Ordovician included–, 1942, 848 pp.). In addition to other contributions on mineral raw materials, his papers include numerous Paleozoic regional studies, maps for the first cartographic series at a 1:50,000 scale and, above all, regional and systematic paleontological works. The latter were dedicated to Cambrian, Ordovician and Silurian trilobites, graptolites, cephalopods, archaeocyathids and ichnofossils, as well as to Carboniferous mollusks. His interest in the Paleozoic and the geology of northwestern Spain were the main subjects of his reception at the Royal Academy of Sciences of Spain (1934: Geology of Galicia) and of the inaugural address of the 1953/54 course at the same institution (Paleozoic marine life. Fossil remains). A monograph on Spanish graptolites was published in 1960 as a posthumous paper of the author. To the research work of Hernández-Sampelayo we must add his personal interest to form a museum to exhibit the mineralogical, paleontological and petrological diversity of Spain. As a result of his know-how, he established the current Geominero Museum in the great hall of the headquarters of the Geological and Mining Institute of Spain, where it was held the XIV International Geological Congress of 1926.

PROFESOR VALERIAN MYKOLAYOVYCH WEBER — OUTSTANDING GEOLOGIST-SURVEYER AND EXPERT IN TRILOBITES (to the 150th Аnniversary of his birth)

Valerian Мykolayovych Weber (1871—1940) entered the history of geological science of the former USSR and the world as an outstanding geologist-surveyor, a prominent paleontologist, a specialist in trilobite fauna and Paleozoic stratigraphy, a teacher and organizer of science, an active member of scientific geological societies. He was the discoverer of a number of deposits of iron and copper-arsenic-lead ores, coal, and oil. The scientist studied the classical sections and fauna of the Paleozoic of Western Europe, carried out geological surveys in sultry Turkestan. As a geologist, Valerian Mykolayovych traveled and studied regions of Central Asia, Urals, Crimea, Caucasus, Pamirs, Novaya Zemlya, Svalbard, the Timan Ridge and the Far East. Of particular importance for him were the unique Paleozoic sections of the Donetsk folded structure. The scientist is the author of the monographs “Field Geology”, “Mineral Resources of Turkestan” and the geology of the Cheleken Peninsula, he is also known as a seismologist — he studied the Andijan, Akhalkalaki and Shemakha earthquakes. However, paleontological studies of trilobites brought world fame to the scientist. In total, for Permian, Devonian, Ordovician, and Silurian trilobites, V.M. Weber wrote six original monographs and more than ten articles. The first large monograph by V.M. Weber was the book “Trilobites of Turkestan”, then “Trilobites of Donbass” and a series of consolidated monographs on the Carboniferous trilobites of the USSR. The monograph by V.M. Weber “Trilobites of Donbass” contains material on trilobites collected by scientists from continuous, “reference” sections of marine carboniferous deposits of the Donets Basin. Paleontological works by V.M. Weber cover a wide range of geological time — from the Ordovician to the Permian inclusive. They are important for the stratigraphy of the sedimentary strata of the Carboniferous Donbas of Central Asia, Urals, Caucasus, Crimea and other geological regions of the USSR.

The first Silurian trilobite with three‐dimensionally preserved soft parts reveals novel appendage morphology

AbstractThe first Silurian trilobite known with soft parts preserved, a Dalmanites species, is described from the Herefordshire Lagerstätte. Biramous appendages and much of the alimentary system are evident. High‐fidelity three‐dimensional preservation reveals a novel arrangement of the exopod, in which successive filaments are connected by a presumed membrane. This morphology explains a misinterpretation of the exopod as supporting spiral structures, originally reported nearly 150 years ago. Comparison with other trilobite limbs indicates that the exopod morphology of Dalmanites is present in other members of Phacopida. The function of the exopod is considered to be primarily respiratory.

Insights into a 429-million-year-old compound eye

In all arthropods the plesiomorphic (ancestral character state) kind of visual system commonly is considered to be the compound eye. Here we are able to show the excellently preserved internal structures of the compound eye of a 429 Mya old Silurian trilobite, Aulacopleura koninckii (Barrande, 1846). It shows the characteristic elements of a modern apposition eye, consisting of 8 (visible) receptor cells, a rhabdom, a thick lens, screening pigment (cells), and in contrast to a modern type, putatively just a very thin crystalline cone. Functionally the latter underlines the idea of a primarily calcitic character of the lens because of its high refractive properties. Perhaps the trilobite was translucent. We show that this Palaeozoic trilobite in principle was equipped with a fully modern type of visual system, a compound eye comparable to that of living bees, dragonflies and many diurnal crustaceans. It is an example of excellent preservation, and we hope that this manuscript will be a starting point for more research work on fossil evidence, and to develop a deeper understanding of the evolution of vision.

Ontogeny of the trilobite Elrathia kingii (Meek) and comparison of growth rates between Elrathia kingii and Aulacopleura koninckii (Barrande)

AbstractTrilobites offer almost unparalleled insight into the growth and development of fossil ecdysozoans. Here I use newly collected material of Elrathia kingii (Meek) to estimate growth rates and describe shape change over the ontogeny of E. kingii. Well‐preserved, articulated specimens from all post‐embryonic stages were collected from a 1.5 m interval of the upper Wheeler Formation (Miaolingian Series, Cambrian) in western Utah (USA), and size and landmark‐based shape data were digitized from photographs. Growth rates were estimated and compared with previously published data on the Silurian trilobite, Aulacopleura koninckii (Barrande). Like A. koninckii, the cephalic growth rate in E. kingii was constant and of similar magnitude to the minimum growth rate along the trunk, and growth rates in the trunk were lower during the holaspid (‘adult’) period than during the meraspid (‘juvenile’) period. However, body length at the onset of meraspis was smaller, the growth gradient along the trunk during meraspis was shallower, and the terminal number of thoracic tergites was smaller in E. kingii than in A. koninckii. Despite these differences, these two species had similar maximum body lengths, because higher overall growth rates in E. kingii compensated for other differences. The rate of cephalic shape change in E. kingii decreased at the transition from meraspis to holaspis, while the pygidium became more morphologically distinct from the thorax during holaspis. I also provide an emended diagnosis for E. kingii, descriptions of the ontogeny and ventral morphology, and evidence that E. kingii holaspids had an invariant number of tergites.

Early Silurian (Llandovery) Trilobite fauna from

The aim of this study is to analyze the assemblage of trilobites in the Silurian sequences of Iran by exploring stratigraphic section of the Silurian Niur Formation (Asadli section). Based on comprehensive field studies and laboratory investigations three Trilobite genera were identified in the study area including Calymene blumenbachii, Gravicalymene convolva, Dalmanites brevigladiolus and Calymene sp. according to this trilobite assemblage a Rhuddanian to Telychian stages (Llandovery) is suggested for deposition of the study strata. The recognized trilobite fauna will be used as a base for future geological studies on the Silurian strata in Kopeh-Dagh Basin. This is the first report of trilobites from the Silurian (Llandovery) Niur Formation in Asadli section, north- east, Iran.

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

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

The peri-Gondwanian Early Silurian trilobites from Kopeh Dagh, Iran

ABSTRACT Silurian trilobites of the Niur Formation in the Robat-e-Gharebil area are described and illustrated. Three genera and five species are identified, including: Calymene dastanpouri sp. nov. Calymene sp., Flexicalymene meeki, Gravicalymene hagani and Dalmanites ypacarayensis. The palaeogeographic relationships of the Eastern Alborz Range with the Northern Gondwana supercontinent during the Late Palaeozoic are also considered. The Early Silurian trilobites of lower part of the Niur Formation were comparable with those of other parts of Iran, Southern Europe, Northern Africa, Middle East and South of China. This similarity suggests that the Robat-e-Gharebil area (Kopeh Dagh region) was part of the peri- Gondwana supercontinent during the Early Silurian.

The Development of the Silurian Trilobite Aulacopleura koninckii Reconstructed by Applying Inferred Growth and Segmentation Dynamics: A Case Study in Paleo-Evo-Devo

Fossilized growth series provide rare glimpses into the development of ancient organisms, illustrating descriptively how size and shape changed through ontogeny. Occasionally fossil preservation is such that it is feasible to test alternative possibilities about how ancient development was regulated. Here we apply inferred developmental parameters pertaining to size, shape, and segmentation in the abundant and well-preserved 429 Myr old trilobite Aulacopleura koninckii that we have investigated previously to reconstruct the post-embryonic ontogeny of this ancient arthropod. Our published morphometric analyses associated with model testing have shown that: specification of the adult number of trunk segments (polymorphic in this species) was determined precociously in ontogeny; that growth regulation was targeted (i.e., compensatory), such that each developmental stage exhibited comparable variance in size and shape; and that growth gradients operating along the main body axis, both during juvenile and adult ontogeny, resulted from a form of growth control based on positional specification. While such developmental features are common among extant organisms, our results represent the oldest evidence for them within Metazoa. Herein, the novel reconstruction of the development of A. koninckii permits visualization of patterns of relative and absolute growth and segmentation as never before possible for a fossilized arthropod ontogeny. By conducting morphometric analysis of appropriate data sets it is thus possible to move beyond descriptive ontogenetic studies and to address questions of high interest for evolutionary developmental biology using data from fossils, which can help elucidate both how developmental processes themselves evolve and how they affect the evolution of organismal body patterning. By extending similar analyses to other cases of exceptional preservation of fossilized ontogeny, we can anticipate beginning to realize the research program of “paleo-evo-devo”.

Size, shape, and systematics of the Silurian trilobite Aulacopleura koninckii

A new dataset of the highest quality specimens of fully articulated, juvenile and mature exoskeletons of the Czech middle Silurian trilobite Aulacopleura koninckii offers improved resolution of original morphology by all measures considered. The degree of variation in both size and shape among later meraspid instars was constant, and suggesting targeted growth in both attributes. Size-related changes in the shape of the dorsal exoskeleton and of the segment-invariant cephalon were detected in the meraspid stage, but in the holaspid phase marked allometry was detected only in the trunk region, with the pygidium showing notable expansion in relative size. Meraspid cranidial allometry was subtle, with significant changes in instar form detectable only after several molts. This trilobite developed gradually throughout meraspid and holaspid ontogeny, with the synchronous cessation of trunk segment appearance and release at the onset of the holaspid phase. Precise development of shape and size occurs in the context of marked variability in the number of trunk segments at maturity, illustrating complex patterns of character variation within a species. A new systematic description establishes the synonymy of several subspecies with A. koninckii.

Vanishing ocean: how tethys reshaped the world by Dorrik Stow. Oxford University Press, Oxford, 2010. No. of pages: xii + 300. Price: UK£16.99. ISBN 978-0-19-921428-0 (hardback).

Dorrik Stow has written an unusual book, the ‘biography’ of an ocean and one that no longer exists, at that. Geologists and non-geologists alike will enjoy this CSI-type exposition of what is no longer there based on the evidence, sometimes rich, more commonly slender, always fascinating, and found here and there in various corners of the globe. What is there is good. Stow writes well and engages the reader by blending his own field experiences into a story that is wide ranging. Indeed, this is the sort of clear text that would form an appropriate basis for a graduate seminar course, provided the students also read the primary references. Maps are well drawn and essential to the story, showing the changing geometry of Tethys with time. Other figures and photographs are fine, but I would like to have seen more of them. The quality of the paper is inadequate for good reproduction of images; I craved a section of high-quality art paper with well-produced photographs of key sites in colour. The author is, of course, a master at compiling compelling images from the field (Stow, 2005). And, while discussing illustrations, why is the Late Devonian mass extinction ignored in figure 7? I do have two quibbles with Vanishing Ocean, one minor and the other more major. My minor complaint is that Stow has failed to have his palaeontological facts checked, so he blunders more than once. For example, he states that the arthropod exoskeleton is composed of chiton (p. 63), and figures a Jurassic crinoid and Silurian trilobites which are ‘… typical of the Late Permian Tethys Ocean’ (p. 73). More annoyingly, Stow labours over ‘disproving’ that the end Cretaceous mass extinction was not the product of a bolide impact. I think the true fruit of extinction studies over the past 30+ years has been to show that major events commonly coincide with more than one environmental perturbation (postulated at least as long ago as Hoffman, 1989). Stow is willing to recognise ‘… a combination of environmental drivers’ (p. 185), but does not favour an impact as one of them. Discussions of mass extinctions have moved on from the ‘I'm right’ ‘No. I'm right’ state of argument, thank goodness. Rather, constructive debate of diverse and multiple lines of evidence, supported by increasingly sophisticated laboratory data and field observations, is the route to confident consensus. But, overall, my criticisms are minor. Vanishing Ocean is readable and informative, and is ably written to interest and entertain a wide audience. I enjoyed reading it and recommend it to you.

Late Silurian trilobites from the Nuratau and Turkestan ranges, Uzbekistan and Tajikistan

Silurian trilobites of Ludlow and Přídolí age are described from sections in southern Uzbekistan and from adjacent parts of Tajikistan. They belong to 22 species (10 named and 12 under open nomenclature) distributed among 13 genera belonging to the families Proetidae, Tropidocoryphidae, Aulacopleuridae, Scharyiidae, Cheiruridae, Encrinuridae and Odontopleuridae. The following new species are described: Interproetus pentaxus, Paleodechenella turkestanica, P. zaaminicus, Cromus tamchii and Leonaspis nuratensis. The generic associations from the mid Ludlow bear a striking resemblance to coeval ones from Bohemia, and include genera otherwise known only from that region or from adjacent parts of central Europe. The trilobite faunas from the late Ludlow and Přídolí series are much less diverse and are dominated by genera of the Warburgellinae (Tropidocoryphidae), which include one species common to Vaigatch Island in the Russian Arctic, and Podolia, Ukraine. The closest links of the diverse central Asian mid Ludlow faunas are therefore to central Europe, whilst the sparser younger Ludlow and Přídolí faunas, such as they are, suggest closer links to Baltica.

Odontopleura generalandersi – a new Silurian trilobite species of the Odontopleura genus occurring in the north Poland

Until now, only one representative of the trilobite Odontopleura ovata Emmrich, 1839, belonging to the Odontopleura Emmrich, 1839 genus and classified into the Odontopleuridae Burmeister, 1843 family, has been known. The paper presents a new Silurian trilobite species classified into the Odontopleura genus. Trilobites of the Odontopleurida Whittington, 1959 order lived within a time period from the Middle Cambrian to the Upper Devonian. At present, their fossilised remnants can be found on every continent.

Trilobites and Linnaeus: the first fossil reconstruction from 1759

A paper by renowned eighteenth century Swedish naturalist, Carl Linnaeus, published in 1759, contained the first fossil reconstruction of what was later called a trilobite and was an early milestone in invertebrate palaeontology. The earliest work devoted solely to Palaeozoic trilobites (Arthropoda), Linnaeus' “Petrificatet Entomolithus paradoxus …” delved, in great detail, into the classification of this genus intermedium between known marine crustaceans. Linnaeus depicted on two folding, copper-engraved plates the fossil animal (comprising the cephalon, thorax and pygidium with pleural spines and furrows) from the best-preserved material in limestone thus far recovered, including an erroneous interpretation of antennae in relation to this Swedish material – however, confirmed in the latter part of the nineteenth century with well-preserved Silurian trilobites.

Systematics, palaeoenvironments and stratigraphy of the Silurian trilobite Dalmanites wandongensis Gill, 1948 and its bearing on the structural geology of the Kilmore area, Victoria

One of the most prolific trilobites in the mid-Palaeozoic of central Victoria is the dalmanitid Dalmanites wandongensis Gill, 1948. Extensive museum collections permit a revised diagnosis and a redescription of the species, and an interpretation of its distribution. The affinities of D. wandongensis lie with South American species assigned to Dalmanites and the closely related Kasachstania rather than northern hemisphere taxa including the D. caudata group. It occurs between Heathcote and Yan Yean in central Victoria, in late Wenlock and early Ludlow (Silurian) strata of the Dargile Group, on the eastern margins of the Melbourne Zone; its greatest abundance is between Kilmore and Wandong, where it is documented from over fifty localities, occurring rarely with other trilobite taxa. At Heathcote, Upper Plenty, Yan Yean and Kilmore East D. wandongensis stratigraphically underlies a more diverse trilobite fauna dominated by the encrinurid Cromus simpliciculus. This trilobite faunal succession defines a significant macrofaunal biostratigraphic datum in the sequence, complementing brachiopod and graptolite zonations. This datum is coincident with a subtle but widespread change in lithology that defines the lithostratigraphic boundary between the Yan Yean Formation and the Melbourne Formation. In the structurally complex and poorly exposed sequences of the Kilmore East area the distribution of D. wandongensis is used as a primary tool in mapping the distribution of these units. Outcrop patterns reveal the presence of two large scale east-northeast-oriented faults traversing the area that support a model of deformation for the Melbourne Zone in which transverse shearing is significant. Taphofacies and biofacies distribution in the Yan Yean Formation indicate a deep-water shelf depositional environment, at depths below maximum storm-wave base in the Kilmore-Wandong area, deepening eastwards, with outer shelf environments between Yan Yean and Christmas Hills.

Early Silurian (Llandovery) trilobites from the Cotton Formation, near Forbes, New South Wales, Australia

A trilobite fauna from the upper part of the Cotton Formation (late Llandovery, Spirograptus turriculatus Zone) in central west New South Wales includes the new species Raphiophorus sandfordi, Odontopleura (Sinespinaspis) markhami and Aulacopleura pogsoni. Species of Odontopleura and Aulacopleura have not previously been documented in Australasia. The association of these genera is observed in offshore biofacies in the Llandovery/Wenlock on several palaeocontinents. Affinities of the species are with congeners from Bohemia and northwestern Canada (Odontopleura, Aulacopleura) and Tarim and South China (Aulacopleura, Raphiophorus).

Silurian trilobite alpha diversity and the end-Ordovician mass extinction

Following the end-Ordovician extinction, global clade diversity of Silurian trilobites dropped to about half of Ordovician levels. Although clade diversity failed to recover, this extinction had surprisingly little long-term impact on the number of trilobite species that occupied local habitats (alpha diversity). A new compilation of data from Laurentia and other continents indicates that Silurian trilobite alpha diversities in all major environments were comparable to those of the Late Cambrian and Ordovician; shallow subtidal diversity reached an all-time high during the Late Ordovician. The profound differences in patterns at local and global levels demonstrate the necessity for a hierarchical approach to analyses of diversity. Factors governing global clade diversity are lodged at hierarchical levels beyond those controlling local species richness and must be sought in studies of between-habitat (beta) or geographic (gamma) diversity.

Stasis and extinction of Silurian (Llandovery–Wenlock) trilobite associations related to oceanic cyclicity

Silurian trilobites of the central United States belong to a series of temporally-successive associations which appeared abruptly, maintained taxonomic stasis for a time, and then disappeared abruptly. Their disappearance resulted from global perturbations of short-term duration and moderate magnitude, which caused substantial taxonomic replacement but no reorganization of major ecosystems. The most significant extinction and replacement in Silurian trilobite associations in the study area occurs near the Llandovery–Wenlock boundary. This turnover in trilobite associations appears to correspond to Jeppsson's Ireviken Event in his model of oceanic and climatic cyclicity. Major sea-level changes earlier in the Llandovery did not have a similar impact on trilobite associations.