Trilobiten.de

[Jens]

Euan N. K. Clarkson & Per Ahlberg (2002): Ontogeny and Structure of a New, Miniaturised and Spiny Olenid Trilobite from Southern Sweden. - Palaeontology, Volume 45 (1): 1-22.

Several hundred specimens of a tiny olenid trilobite, Ctenopyge ceciliae sp. nov., have been found in stinkstone nodules in the upper Cambrian Peltura scarabaeoides Zone in southern Sweden. This exceptionally spinose form is known only from disarticulated specimens, but is quite well preserved, and all growth stages are represented. The early ontogenetic stages are exceptionally small, the protaspis being only half the size of that of the associated Peltura species. There may have been no more than three thoracic segments. Thus the whole ontogeny was compressed, and this together with the very small size of the adult indicates a true miniaturisation. Whereas the likely control of the origin of the tiny C. ceciliae was basically progenesis, the extreme spinosity had a different origin; allometric growth or possibly peramorphosis. C. ceciliae is small enough for the spines to have appreciably retarded sinking through frictional effects, and this small trilobite is interpreted as a free-swimming or floating form.

[Jens]

Trevor J. Cotton (2001): The Phylogeny and Systematics of Blind Cambrian Ptychoparioid Trilobites. - Palaeontology, Volume 44, Issue 1 Page 167.

The paraphyletic trilobite suborder Ptychopariina includes a large proportion of Cambrian trilobite diversity and is probably ancestral to most groups of post-Cambrian trilobites. Resolution of the phylogenetic relationships within the group is therefore crucial to a better understanding of the initial radiation of trilobites. The recognition of approaches that can successfully resolve the relationships of ptychoparioid taxa is an important first step towards this aim. Cladistic analysis was used to determine relationships within the Cambrian ptychoparioid trilobite family Conocoryphidae, and to test claims that the family is polyphyletic. Ninety-seven characters were coded for 40 conocoryphid species and nine non-conocoryphids. The results indicate that the family consists of four distantly related clades. Three are recognized here as distinct families, including an extensively revised Conocoryphidae, and the families Holocephalidae and Atopidae. The fourth clade is referred to the subfamily Acontheinae (Corynexochida) as the new Tribe Hartshillini. Analysis of the disparity of these four clades shows that they are significantly less morphologically variable than the original polyphyletic taxon, demonstrating the possible effects of taxonomic error on macroevolutionary studies of morphological disparity.

[Jens]

Nigel C. Hughes,a,* Ralph E. Chapman and Jonathan M. Adrainc (1999): The stability of thoracic segmentation in trilobites: a case study in developmental and ecological constraints. - Evolution & Development, Volume 1, Issue 1, Page 24.


The decline in origination rate of new metazoan body plans following the Cambrian radiation has been suggested to reflect developmental canalization in derived taxa, limiting their ability to evolve forms with radically different morphotypes. Segmentation is a fundamental aspect of arthropod body plan, and here we show that a derived trilobite that secondarily converged on a morphotype characteristic of basal members of the clade also reverted to a pattern of segmental variability common among basal trilobites. Hence a secular trend in loss of variability of the trilobite thorax was not due to the evolution of an inviolable developmental constraint. This result challenges the notion of developmental canalization in phylogenetically derived taxa. Rather, early variability in trilobites may be the result of ecological factors that promoted segment-rich thoracic morphotypes during Cambrian time.

[Jens]

Euan N. K Clarkson, John Ahlgren, Cecilia M Taylor (2003): Structure, ontogeny, and moulting of the olenid trilobite Ctenopyge (Eoctenopyge) angusta Westergård, 1922 from the upper Cambrian of Västergötland, Sweden. - Palaeontology, Volume 46, Issue 1, Page 1-27.

The genus Ctenopyge is known mainly from disarticulated sclerites and from rare complete specimens flattened in shales. Hitherto, very few specimens have been found preserved intact and in three dimensions. In a recently discovered fauna, however, in the Peltura minor Subzone in Västergötland, central Sweden, there occur several species of Ctenopyge, of which many are complete and superbly preserved; moreover they occur at all stages of growth. Of these the abundant Ctenopyge (Eoctenopyge) angusta Westergård, 1922 is described and reconstructed here as an adult, and the entire ontogeny is documented for all post-protaspid growth stages. Many characters typical of the adult, such as the long genal spines and the caudal spine, develop very early in ontogeny, and the relative dimensions of the cranidium do not greatly change during growth. Macropleural spines, however, develop later. The transitory pygidium, relatively large and shield-shaped in the early meraspid, later becomes very small as the ten thoracic segments are liberated; a median spine develops on the last thoracic segment only at the holaspid stage. Instar groupings can be clearly distinguished for the early stages. Recurrent associations of sclerites are interpreted as moulting configurations. As reconstructed, the genal spines are horizontal and parallel with the extended thorax; an adaptation which presumably allowed the trilobite to rest on the sea floor.

[Jens]

J. Javier Álvaro, Daniel Vizcaïno, Vratislav Kordule, Oldrich Fatka and Gian Luigi Pillola (2004): Some solenopleurine trilobites from the Languedocian (Late Mid Cambrian) of Western Europe. - Geobios, Volume 37 (2): 135-147

Abstract
The solenopleurine trilobite genera Jincella and Liosolenopleura are revised herein. The species Jincella prantli, Jincella convexa nov. sp. and Liosolenopleura serventi occur in Languedocian (upper Middle Cambrian) rocks of the southern Montagne Noire (France), southwestern Sardinia (Italy), and the Píbram-Jince and Skryje areas (Czech Republic). The correlation of their first appearances permits us to improve the Middle Cambrian biostratigraphic correlations in western and central Europe. At least 17 Middle Cambrian Bohemian species are already reported outside the Czech Republic, whose outcrops can be considered as a hinge in the correlations between southwestern Europe, Saxo-Thuringia, Avalonia and Baltica.

[Jens]

David J. Holloway (2004): The Trilobite Subfamily Monorakinae (Pterygometopidae). - Palaeontology, Volume 47 (4): Page 1015.

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 probably derived from the Pterygometopinae, and includes the genera and subgenera Monorakos, Carinopyge, Ceratevenkaspis, Elasmaspis, Evenkaspis (Evenkaspis) and E. (Parevenkaspis), of which Carinopyge, Elasmaspis and Evenkaspis (Parevenkaspis) are known only from limited parts of the exoskeleton. Monorakines have a stratigraphical range of Caradoc-Ashgill. Their known geographical distribution in the Siberian Platform, Taimyr, the Russian Far East, and the Seward Peninsula of Alaska is restricted to areas that in the Ordovician were part of the palaeocontinents of Siberia and Arctida, which must have been connected or situated close together at that time. The occurrence of monorakines in the Taimyr Peninsula but their absence from Baltica does not support the suggestion of some workers that Taimyr was part of Baltica in the Ordovician.

[Jens]

Jan Ove R Ebbestad, Graham E Budd (2002): Burlingiid trilobites from Norway, with a discussion of their affinities and relationships. -Palaeontology, Volume 45 (6), 1171-1195.

Four Middle and Upper Cambrian burlingiid trilobites from the Oslo Region, Norway, are described including Burlingia angusta sp. nov. from the Ptychagnostus punctuosus Zone and Schmalenseeia athrotryphe sp. nov. from the lower part of the Lejopyge laevigata Zone. New complete material previously attributed to Schmalenseeia jagoi Whittington is assigned to Burlingia. Cladistic analysis supports the genera Burlingia and Schmalenseeia as currently understood, including the placement of the controversial middle Middle Cambrian Schmalenseeia acutangula Westergård in Schmalenseeia, even though it lacks typical characters of the genus such as the median ridge on the preglabellar field. The analysis also supports burlingiid monophyly, and suggests that Schmalenseeia was derived from a broadly Burlingia-like ancestor, with S. acutangula displaying how the transition may have occurred. The broader relationships of Burlingia remain obscure, although similarities between burlingiids and the arthropod Kleptothule from the Early Cambrian Sirius Passet fauna are discussed: these include overall form, lack of functional hinges in the thorax, and details of the cephalic region. It is unclear whether these similarities represent general progenetic features, are functional convergences or, less likely, represent a genuine relationship.

[Jens]

R. M Owens (2002): Cyclopygid Trilobites from the Ordovician Builth-Llandrindod Inlier, Central Wales. - Palaeontology, 45 (3), 469-485.

Cyclopygids are a minor element in the abundant trilobite fauna of the Ordovician Llanfawr Mudstones Formation (teretiusculus-gracilis biozones) of the Builth-Llandrindod inlier. The rarity of these trilobites may be due to the accumulation of these sediments close to the shoreward limit of their depth range, and if this is the case, their presence, together with sedimentological evidence, can be used to infer the bathymetric limits within which the Llanfawr Mudstones Formation might have been deposited. Species of Degamella, Microparia (Microparia), Microparia (Heterocyclopyge), Sagavia and Emmrichops are described; some are common to the Dobrotivá Formation in Bohemia, whilst others have affinities with species from approximately coeval strata in Kazakhstan and north-west China.

[Jens]

R. M. Owens 2004: Late Ordovician and early Silurian Proetida (Trilobita) from north-western and central Europe. - Palaeontology, 47 (3),557-578.

Species belonging to genera of three families of the Proetida (Proetidae, Rorringtoniidae and Toernquistiidae) are described from the upper Ashgill of southern Sweden, and the same or related species noted from the adjacent parts of northern and central Europe. Proetidae are represented by Paraproetus brevifrons (Angelin), Ogmocnemis irregularis Kielan, Ogmocnemis jaanussoni sp. nov. and Parvigena putealis sp. nov.; it is argued that all belong to the Cornuproetinae, not Tropidocoryphinae where they were previously classified. Ogmocnemis is resurrected for some Upper Ordovician species included previously in Decoroproetus. The rorringtoniid genera Rorringtonia and Madygenia are recognised for the first time in southern Sweden, and it is argued that these are probably closely related, and both are included in the same family; both are recorded for the first time from Silurian (Llandovery) strata. Zetaproetus is claimed to be a junior subjective synonym of Rorringtonia. Solariproetus, first described from north-west China, is assigned to the Toernquistiidae as a late, derived member, and S. prosthemesos sp. nov. is described from late Rawtheyan strata in the Holy Cross Mountains, Skåne and the English Lake District. Comments are given on the stratigraphical and palaeogeographical distribution of these taxa.

[Jens]

H. B. Whittington (2003): The trilobite family Nileidae: morphology and classification. - Palaeontology, 46 (4), 635-646.

Species of genera currently referred to Nileidae are reviewed, and those of Hemibarrandia, Lakaspis, Peraspis and Symphysurina are excluded from the family. Nileidae are united in having a distinctive form of the hypostome, the glabellar organ, in the shallowness or absence of external furrows on the axial and pleural regions, and in the development of strong ventral ridges on the axial region. It is contended that the glabellar organ of nileids and illaenids may not be homologous with the glabellar tubercle of asaphids, that the median ventral suture is not exclusively a character of Asaphina, and doubt is cast on the identification of an asaphoid protaspis as being that of Nileus. These arguments provide a case for allying Nileidae with the Illaenidae, rather than with the Asaphina.

[Jens]

J. O. R. Ebbestad, P. Ahlberg, M. Høyberget (2003): Redescription of Holmia inusitata (Trilobita) from the Lower Cambrian of Scandinavia. -Palaeontology, 46 (5), 1039-1054.

Well-preserved topotype material of Holmia inusitata Ahlberg and Bergstro¨m, in Ahlberg et al., from the Lower Cambrian of Lauselva, southern Norway, allows a redescription of the species. Intraspecific variation of characters, such as the expansion and relative length (sagittal) of the anterior glabellar lobe and the curvature and length of the ocular lobes, is shown. The species is, however, considered a typical member of Holmia. A discussion of character variation and distribution within species of Holmia further demonstrates a great degree of intrageneric variation. Thus, the newly erected Baltobergstroemia Lieberman is regarded as a subjective synonym of Holmia, since the differences between the two genera can only effectively be applied to the type species. The age of the succession with H. inusitata is not well constrained by regional lithological correlations or by an acritarch assemblage, and lacks the well-differentiated faunas of the uppermost zones in the Lower Cambrian of Scandinavia. It is obvious that it must be older than the Holmia kjerulfi-group Zone, and strata with H. inusitata are, therefore, maintained as a discrete zone underlying that zone.

[Jens]

Alison Bowdler-Hicks, J. Keith Ingham, Alan W Owen (2002): The taxonomy and stratigraphical significance of the Anglo-Welsh Cryptolithinae (Trinucleidae, Trilobita). - Palaeontology, 45 (6), 1075-1105.

The taxonomic status of the stratigraphically-important Caradoc genera Salterolithus Bancroft, 1929, Broeggerolithus Lamont, 1935 and Smeathenia Dean, 1960 and the species therein is critically reviewed. The radial alignment patterns of the fringe pits within the E arcs are used to distinguish Salterolithus from Broeggerolithus; fringe morphology and pit counts are used to distinguish species within these genera. 'Broeggerolithus' harnagensis is reassigned to Salterolithus and S. praecursor, S. caractaci paucus and Smeathenia smeathenensis are all regarded as junior synonyms of Salterolithus harnagensis. This revision of the Anglo-Welsh Cryptolithinae reveals the evolution of morphologically very variable populations and environmentally constrained morphotypes and species. Eight species and subspecies of Salterolithus and Broeggerolithus are retained and redescribed and their stratigraphical distribution in the Caradoc of Britain, Ireland, Belgium and Scandinavia is clarified.

[Jens]

J. Javier Álvaro, Olaf Elicki, Gerd Geyer, Adrian W. A. Rushton and John H. Shergold (2003): Palaeogeographical controls on the Cambrian trilobite immigration and evolutionary patterns reported in the western Gondwana margin. - Palaeogeography, Palaeoclimatology, Palaeoecology, 195 (1-2), 5-35.

Abstract
Southward drifting of the western Gondwanan margin during the Cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate (such as carbonates and evaporites). Recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of Cambrian benthic communities. Palaeogeographical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration, speciation and extinction rates. The variability of the documented biogeographical patterns is directly related to species diversity, in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms. Early Cambrian trilobite faunas show a high degree of both substrate control and endemicity, although transgressions led to parallel shifts in faunal compositions. By contrast, Mid-Cambrian trilobite faunas are relatively uniform across western Gondwana, and latest Mid- and Late Cambrian associations document influence of an increased similarity with Asian trilobite faunas.

[Jens]

Cronier C, Bartzsch K, Weyer D, Feist R (1999): Larval morphology and ontogeny of a late Devonian Phacopid with reduced sight from Thuringia, Germany. - JOURNAL OF PALEONTOLOGY, 73 (2): 240-255.

Abstract:
Exceptionally rich and well-preserved silicified exuviae comprising numerous immature growth stages allow the tracing of detailed morphological and morphogenetical features of the reduced-eyed phacopid species Cryphops? ensae (Richter and Richter, 1926) from the latest Famennian of Thuringia (Central Germany). Ontogenetic features of this species are more similar to those of Phacops than to Trimerocephalus.

[Jens]

Bird C, Clarkson E. (2003): Observations on the ontogeny of the upper Cambrian trilobite Peltura scarabaeoides westergaardi Henningsmoen, 1957. -GFF, 125: 177-190 Part 4,

Abstract: A partial ontogeny (meraspides 1-6, 10, 11, and holaspid) is described for P. scarabaeoides westergaardi, based upon intact and exceptionally well preserved specimens from Vastergotland, Sweden. Previous studies of the ontogeny of Peltura have been based upon disarticulated sclerites only. Close comparisons are made with the known early stages of P. scarabaeoides scarabaeoides. During ontogeny the glabella first lengthens and then becomes considerably wider during late ontogeny, the visual surface becomes distinct only in later stages, and the eye becomes increasingly close to the glabella. The body remains very spiny until relatively late in ontogeny, though the hook-shaped pleural spines typical of the adult have developed by meraspid degree 10. Axial nodes, prominent in the early stages disappear after meraspid 6, and no trace of the tuberculate sculpture of the meraspid stages is present in the adult. A triangular gap between the anterior edge of the first thoracic pleura and the rear margin of the cephalon has developed by degree 10; this presumably facilitated enrolment. A note is appended on the visual surface of P. scarabaeoides scarabaeoides, previously known only from internal moulds.

Addresses: Bird C (reprint author), Univ Edinburgh, Dept Geol & Geophys, Kings Bldgs,W Mains Rd, Edinburgh, Midlothian EH9 3JW Scotland
Univ Edinburgh, Dept Geol & Geophys, Edinburgh, Midlothian EH9 3JW Scotland
E-mail Addresses: euan.clarkson@ed.ac.uk