Calymenesun granulosa Lu的背壳及接合构造*

描述了Ｃａｌｙｍｅｎｅｓｕｎ ｇｒａｎｕｌｏｓａ Ｌｕ的腹边缘及结合构造,并讨论了此种三叶虫的卷曲机制。认为当其卷曲完善时,尾“边缘“及部分胸肋纳入头颊下,以往描述了尾边缘的部分实际上是尾背结合沟所在位置。卷曲形式为半螺旋卷曲。     

Abnormalities in early Paleozoic trilobites from central and eastern China

Malformations are common in trilobites, but the majority of described specimens are from Europe and North America. Only a few abnormal trilobites have been reported from China. Ten abnormal trilobites from Cambrian, Ordovician and Silurian strata in central and eastern China are documented. The abnormal Ordovician trilobites are found for the first time in China. All malformations occur in the thoraxes and pygidia, and were caused by a sub-lethal predatory attack, genetic or embryological malfunction, or injury sustained during molting. It is difficult to identify the predators of the six injured trilobites, but potential predators include Cambrian non-trilobite arthropods, Ordovician cephalopods, and Silurian eurypterids, chondrichthyes or cephalopods, even cannibalistic trilobites. Abnormal specimens caused by sub-lethal predatory attacks mainly occur in Cambrian strata in China and other areas in the world, and are rare in post-Cambrian strata. This pattern may reflect the rise of predators and increased predation in the post-Cambrian, which led to an increased trilobite fatality rate, thus reducing the probability that injured specimens would become fossilized.     

Rusophycus carleyi (James, 1885), Trace Fossils from the Lower Ordovician of Southern Morocco,and the Trilobites that Made Them

Thin-bedded, pyrite-rich, fine sandstones and mudstones of the Floian-Dapingian Upper Fezouata Formation contain abundant trace fossils Rusophycus carleyi in close association with a species of the asaphid trilobite Asaphellus. The sizes and shapes of this trilobite and the traces match closely. Five specimens have even been found where an articulated specimen of Asaphellus appears to be directly located over a specimen of Rusophycus carleyi within a thin bed of sandstone, suggesting that the trilobite animal may have been trapped on top of a trace that it had just made. Such intimate associations between a putative tracemaker and a trace are rare in the fossil record and particularly rare for Trilobita. The number of coxal impressions that form part of R. carleyi, eleven, matches the number expected for an asaphid trilobite (one for each of eight thoracic segments and one for each of three post-oral cephalic appendages). Impressions of the hypostome, thoracic tip impressions, cephalic margin, and pygidial margin in a few of the traces also match those of this asaphid trilobite. R. carleyi has been found in Ordovician strata of other parts of the world in association with asaphid trilobites.     

Heterochrony in the Silurian radiation of encrinurine trilobites

Divergence of Silurian encrinurine trilobite clades from common ancestry may be modelled as hetero-chronic pattern. Comparing ontogenies of ancestral late Ordovician Encrinuroides and the descendant punctarus and uariolaris plexi of Silurian Encrinurus provides a test of this hypothesis. Heterochrony in the punctarus plexus is dissociated with respect to entire organisms, but regionally global throughout cranidia (paedomorphic states) and pygidia (peramorphic states). Regulatory dissociation may explain the apomorphous enrollment strategy of this group. The uariolaris plexus, for which a growth series of Balizoma dimitroui (Perry & Chatterton) provides ontogenetic data, shows a complex of peramorphic cephalic character states. Changes in developmental timing thus provide a mechanism by which morphologic and ecologic divergence of closely-related clades was catalyzed in the Llandovery encrinurine radiation. Paedomorphic and dissociated Lineages of the odontopleurid Leonaspis provide a comparable example of divergent heterochronic pattern associated with coexisting (in the same biofacies) species of comparatively recent common ancestry.     

Ordovizium und Silur. Überschwemmungen,eine Eiszeit und die Eroberung des Festlandes

Ordovician and Silurian sediments are predominantly black shales formed from anoxic pelagic environments. Adjacent shallow marine areas are represented by reefs and well‐sorted sands deposited worldwide on continental shelves. Pelagic realms hosted a great variety of graptolite colonies which due to their rapid evolution are excellent index fossils besides a multitude of new species of trilobites and brachiopods. Reef builders were mainly bryozoans and tabulate corals. During the Ordovician, the earliest spores mark the beginning conquest of land by plants. A mass extinction at the end of the Ordovician was probably caused by a worldwide climatic change which is also evident from traces of a contemporaneous glaciation.     

Biostratinomy and functional morphology of enrollment in two Middle Devonian trilobites

Although it is common knowledge that many trilobites enrolled, behavioral and functional aspects of enrollment are not at all well understood. Taphonomic details portrayed by enrolled trilobites in the Middle Devonian Hamilton Group (New York State) indicate that enrollment was a complex and morphologically constrained behavior. The trilobites Phacops rana (Green) and Greenops boothi (Green) are frequently enrolled in Hamilton strata; biostratinomic data indicate two very different enrollment postures. Interlocking morphologies (coaptative devices) and apodeme structure and disposition indicate that these postures reflect specific behaviors which involved interaction between tergal structures, inferred musculature, and the substratum. Phacops enrolled by burrowing forward and down into the sediment; dorsal muscles, attached to prominent articulating half-rings, imbricated the thorax such that each lappet overlapped the next posterior segment and locked into a posterior pleural facet. The pygidium was brought into place as the posterior segments of the thorax were placed into vincular notches along the lateral margin of the ventral cephalon. The pygidium locked with the cephalic vincular furrow to complete ‘perfect sphaeroidal’ closure. Greenops enrolled with the cephalon in an upright position at the sediment surface; a submarginal furrow on the ventral surface of the pygidium received the anterior rim of the cephalon. Relatively narrow articulating half-rings limited pleural rotation. Segments were loosely locked into narrow facets at the anterior margin of the next posterior lappet. In spite of rudimentary lappet and half-ring structures, Greenops displays an elaborate system of thoracopygidial muscles which involved dorsoventral and longitudinal attachments along the thorax and into the pygidium. Phacops, in contrast, displays very poorly developed apodemes which occur in the thorax only. Longitudinal muscle strength was likely less important during Phacops enrollment than is evident for the Greenops enrollment procedure. Conversely, Phacops clearly relied to a great degree upon competent closure devices which are poorly developed in Greenops. Biostratinomic data reveal different enrollment behaviors which reflect the function of different enrollment-related morphologies present in each species.     

Phylogenetic and biogeographic analysis of sphaerexochine trilobites

Background

Sphaerexochinae is a speciose and widely distributed group of cheirurid trilobites. Their temporal range extends from the earliest Ordovician through the Silurian, and they survived the end Ordovician mass extinction event (the second largest mass extinction in Earth history). Prior to this study, the individual evolutionary relationships within the group had yet to be determined utilizing rigorous phylogenetic methods. Understanding these evolutionary relationships is important for producing a stable classification of the group, and will be useful in elucidating the effects the end Ordovician mass extinction had on the evolutionary and biogeographic history of the group.

Methodology/Principal Findings

Cladistic parsimony analysis of cheirurid trilobites assigned to the subfamily Sphaerexochinae was conducted to evaluate phylogenetic patterns and produce a hypothesis of relationship for the group. This study utilized the program TNT, and the analysis included thirty-one taxa and thirty-nine characters. The results of this analysis were then used in a Lieberman-modified Brooks Parsimony Analysis to analyze biogeographic patterns during the Ordovician-Silurian.

Conclusions/Significance

The genus Sphaerexochus was found to be monophyletic, consisting of two smaller clades (one composed entirely of Ordovician species and another composed of Silurian and Ordovician species). By contrast, the genus Kawina was found to be paraphyletic. It is a basal grade that also contains taxa formerly assigned to Cydonocephalus. Phylogenetic patterns suggest Sphaerexochinae is a relatively distinctive trilobite clade because it appears to have been largely unaffected by the end Ordovician mass extinction. Finally, the biogeographic analysis yields two major conclusions about Sphaerexochus biogeography: Bohemia and Avalonia were close enough during the Silurian to exchange taxa; and during the Ordovician there was dispersal between Eastern Laurentia and the Yangtze block (South China) and between Eastern Laurentia and Avalonia.     

Sphaeroidal enrolment in middle Cambrian solenopleuropsine trilobites

Esteve, J., Zamora, S., Gozalo, R. & Liñán, E. 2010: Sphaeroidal enrolment in middle Cambrian solenopleuropsine trilobites. Lethaia, 10.1111/j.1502‐3931.2009.00205.x Fifty specimens belonging to species of Solenopleuropsis and Pardailhania from Spain and France demonstrate sphaeroidal enrolment in Cambrian trilobites for the first time. These solenopleuropsines show novel coaptative structures in different regions of the exoskeleton: in the cephalon there are vincular furrows and notches; in the thorax an articulating facet is developed at the pleural margins, with a ball and socket connection on the adaxial most portion, and an articulating half‐ring axially; the pygidium possesses an articulating facet. The interaction of these coaptative structures resulted in a sphaeroidal enrolment that was a progressive act from the first articulation between the occipital ring and the first segment to the pygidial articulating facet. A similar type of sphaeroidal enrolment is observed in the Devonian trilobite Phacops. Both Cambrian and Devonian trilobites developed a vincular furrow in the ventral surface of the cephalon to close their bodies tightly. In both cases, this is probably a convergent adaptation to protect against predators and obrution. Indeed, the enrolled trilobites are very common in obrution deposits restricted to shallow and soft muddy substrates. □Coaptative structures, convergence, Murero Formation, Pardailhania, Solenopleuropsinae, Solenopleuropsis.     

The life habits of the Ordovician illaenine trilobite Bumastoides

The Ordovician illaenine Bumastoides exhibits a distinctive effaced and strongly convex morphology. Orientation of the visual field, the extreme convexity of the cephalon and the nature of the thoracic articulation support an interpretation of Bumastoides as an infaunal trilobite that was poorly suited to epifaunal crawling. The genus may have been sedentary; spending most of its post-larval life cycle within a burrow. Suspension feeding would be a viable existence for a sedentary trilobite such as Bumastoides. Maintenance of a burrow is essential for respiration and would require a firm, cohesive substrate. The infaunal niche had become occupied by trilobites by at least the Late Cambrian and continued to be exploited through the Ordovician, Silurian and. possibly, into the Devonian. Convergence has led to the appearance of the effaced, strongly convex morphotype in a number of unrelated families, including the Illaenidae, Asaphidac, Aulacopleuridae, Plethopeltidae and Scutelluidae. A high numerical abundance of illaenid trilobites, such as Illaenus and Bumastoides , is characteristic of the illaenid–chcirurid association, which persisted from the early Ordovician until at least the Late Silurian. This association has been recorded from shelf-edge and on-shelf carbonate buildups and shallow subtidal level bottom environments. It appears to be confined to firm substrates.     

A tiny eye indicating a planktonic trilobite

Abstract: Cambrian trilobites mainly lived on the sea floor, and up till now few, if any, unequivocally planktonic trilobites have been reported from earlier than the Ordovician. The late Cambrian (Furongian) to late Ordovician olenids are a distinctive group of benthic (sea‐floor dwelling) or nekto‐benthic trilobites. Here we show, however, that one recently described, miniaturized and very spiny olenid species, Ctenopyge ceciliae must have been planktonic (passively drifting or feebly swimming in the upper waters of the sea). This interpretation is based not only upon body form but also on the analysis of its visual system and may be one of the earliest records of the planktonic realm being invaded by trilobites.     

Structure, patterns and function of cuticular terraces in trilobites

Schmalfuss, Helmut 1981 12 15: Structure, patterns and function of cuticular terraces in trilobites [Konstruktionsmorphologie Nr. 1331. Lethaia . Vol. 14, pp. 331–341. Oslo. ISSN 0024–1164.
Cuticular terrace systems are widespread in trilobites. Two different patterns, occurring independently of each other, are recognized: transverse dorsal terraces with the scarp facing backwards, and concentric ventral terraces on the doublures with the scarp facing outwards. Ontogenetically, there is a secondary increase of terrace number, so distances between single terraces remain constant. The dorsal terraces functioned to provide unidirectional friction facilitating the burrowing process. The ventral terraces on the doublures were used to consolidate the walls of a filter chamber underneath the animal. * Trilobita, cuticular terraces, functionol morphology .     

The eyes of trilobites: The oldest preserved visual system

The oldest preserved visual systems are to be found in the extinct trilobites, marine euarthropods which existed between about 520 and 250 million years ago. Because they possessed a calcified cuticle, they have a good fossil record, and commonly the lens-bearing surfaces of their paired compound eyes are well preserved. The sublensar structures, however, remain unknown. Three kinds of eyes have been distinguished. Holochroal eyes, apomorphic for trilobites, typically have many contiguous small lenses, set on a kidney-shaped visual surface. Lens optics, angular range of vision, and ontogeny have been established for many compound eyes. Some pelagic trilobites have enormous eyes, subtending a panoramic field of view. Schizochroal eyes are found only in one group, the phacopids (Ordovician to Devonian). These have large lenses, separated from each other by cuticular material, and the lenses have a complex doublet or triplet internal structure, which could focus light sharply. The optics of phacopid eyes are becoming increasingly well known despite the fact that there are no direct counterparts in any living arthropods today. Schizochroal eyes are apomorphic for phacopids and were derived by paedomorphosis from a holochroal precursor. Abathochroal eyes are confined to a short-lived Cambrian group, the eodiscids (of which most representatives were blind). Less is known about them than other trilobite eyes and their origins remain obscure. Some trilobite groups had no eyes, but had other kinds of sensory organs. In Upper Devonian times several groups of trilobites independently underwent progressive eye-reduction leading to blindness, related to prevailing environmental conditions of the time. The last trilobites (of Carboniferous and Permian age), however, had normal holochroal eyes, which persisted until the final extinction of trilobites at the end of the Permian.     

Trilobites within nautiloid cephalopods

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

Foliomena Fauna (Brachiopoda) from the Upper Ordovician of Sardinia

The late Ordovician brachiopod assemblage from Sardinia is one of the youngest members of the deep-water Foliomena fauna and is characterized by the following core taxa: Christiania , Cyclospira , Dedzetina and Foliomena . The fauna also contains Epitomyonia , Leangella , Glyptorthis and Skenidioides , which are more typical of shallower-water environments during the late Ordovician but occupied deeper-water niches during the Silurian following the termination of the Foliomena fauna. The suprafamilial placement of the family Chrustenoporidae is discussed and the new species Dedzetina serpaglii and Leangella ( Leangella ) fecunda are established. In common with many mid-Ashgill Foliomena faunas the Sardinian assemblage shows significant differences from other faunal developments of this type, reflecting its geographical position and shallower water conditions than those of the classic early Ashgill Foliomena faunas. The brachiopods occur with abundant trilobites belonging to a variant of the cyclopygid fauna. The faunas developed on part of a complex of microcontinents derived from peri-Gondwana during the Ordovician.     

粤西云开地区中奥陶世翼形类(双壳类)一新超科——郁南蛤超科 Yunannioidea superfam.nov.

本研究记述粤西云开地区中奥陶统东冲组一种奇异的翼形类(双壳类)化石,建立了郁南蛤超科(新超科)Yunannioidea superfam.nov.,郁南蛤科(新科)Yunanniidae fam.nov.,郁南蛤属(新属)Yunannia gen.nov.及2新种:干坑郁南蛤(新属新种)Yunannia gankeng...     

贵州湄潭志留纪初期三叶虫动物群及其意义*

志留纪兰多维列世(Llandovery)鲁丹期(Rhuddanian)是奥陶纪末生物大灭绝后的残存期和复苏期。志留纪初期冈瓦纳大陆边缘壳相地层稀少,多数地区为沉积间断或笔石相地层,研究底栖壳相生物残存-复苏期的宏演化普遍缺乏理想材料,而华南上扬子区贵州湄潭地区发育了志留纪早期的壳相地层,即五里坡层(鲁丹阶中部)和牛场组(鲁丹阶上部),为探索这一关键地史时期三叶虫动物群宏演化型式及其背景机制提供了依据。贵州湄潭岩坪剖面和高江剖面的五里坡层和牛场组共发现三叶虫7目11科15属(含亚属)17种(含1新种、3未定种),根据其属级分类单元的时空分布规律,将这些三叶虫识别为5种宏演化类型:即减缩幸存型、扩增幸存型、复活幸存型、新生型和死支漫步型。不同类型的属级分类单元在大灭绝中具有不同的宏演化型式,体现出其应对灾变而采取的不同的生存策略。减缩幸存型和复活幸存型是大灭绝后生态系统复苏和再次辐射的主要源泉,它们的发展在一定程度上影响着整个生态系统的宏演化进程;新生型的出现则标志着大灭绝后环境的实质性改善,三叶虫的全面复苏也随之到来。     

华北地台西缘两个奥陶纪三叶虫新属

Family Raphiophoridae Angelin,1854GenusAbulbaspisgen.nov.Type species Bulbaspis ordosensisLuin Luet al.1976,from the Kli moli Formation(Llanvirn)ofZhuozishan,Wuhai,Inner Mongolia.Diagnosis A raphiophorid genus si milar toAmpyxDal man,1827,but distinguishe…     

Predation in the Ordovician and Silurian of Baltica

Signs of predation appear in the Middle Ordovician of Baltica. Shell repair dominates over the predatory borings in the Ordovician and Silurian. Predators attacked molluscs, brachiopods and tentaculitoids in the Ordovician and molluscs, tentaculitoids, brachiopods and ostracods in the Silurian. There is an increase in the number of prey species in the Late Ordovician, which could be related to the Great Ordovician Biodiversification Event. Molluscs are the favourite prey taxon in the Ordovician, but in the Silurian, molluscs became less dominant as the prey. This is probably not an artefact of preservation as Ordovician and Silurian molluscs are equally well preserved.     

Trilobite size-frequency distributions, recognition of instars, and phyletic size changes

Size-frequency analysis of over 5,000 Ordovician trilobites from the Teretiusculus Shales of the Builth inlier, central Wales, has revealed size distributions with counter intuitive shapes. Not only do most species show normal or slightly skewed distributions, despite the preponderance of moults, but there is no evidence of instar peaks. Such features can, however, be explained by reference to steady-state population structures of Recent marine arthropods, in which small individuals often form only a minor proportion of the post-larval population structure. Trilobite steady-state population structures would have differed in detail from species to species, but certain distribution shapes may have been characteristic of particular environments. These findings necessitate a reappraisal of previous work on trilobite size-frequency distributions, survivorship and recognition of instars. The Builth data also show the first clear evidence of phyletic size increase and parallel size changes in trilobites. ▭ Trilobites, size-frequency distributions, steady-state populations, instars, phyletic size changes.     

ONTOGENY AND HETEROCHRONY IN THE EARLY CAMBRIAN ORYCTOCEPHALID TRILOBITES CHANGASPIS, DUYUNASPIS AND BALANGIA FROM CHINA

Abstract:  Ontogenies are described for the first time for three species of Early Cambrian oryctocephalid trilobites: the oryctocephaline Changaspis elongata Lee, in Chien and the oryctocarines Duyunaspis duyunensis Chang and Chien, in Zhou et al . and Balangia balangensis Chien from the Balang Formation in eastern Ghuizhou Province, south-west China. The complete protaspid to holaspid ontogeny for Duyunaspis duyunensis and incomplete meraspid to holaspid ontogenies for Changaspis elongata and Balangia balangensis are described. The relative degree of ontogenetic variation within the lineage Duyunaspis duyunensis – Balangia balangensis is analysed and indicates that Balangia may have evolved from Duyunaspis by paedomorphosis. Decrease in thoracic segment number and concomitant increase in pygidial segment number in the later genus mirrors the pattern seen in the evolution of another oryctocephalid genus, Arthricocephalus . In both cases, selection was probably targeting an increase in cephalic convexity. This resulted in the evolution of a larger pygidium due to increased elevation of the axis above the substrate. The ontogenetic development of Changaspis provides evidence supporting the view that the Oryctocarinae may be considered as paedomorphic descendants of the Oryctocephalinae.