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1
Babcock, Loren E. "Trilobite malformations and the fossil record of behavioral asymmetry". Journal of Paleontology 67, n.º 2 (março de 1993): 217–29. http://dx.doi.org/10.1017/s0022336000032145.
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Malformations of trilobites are classified as healed injuries, teratological conditions, and pathological conditions. An improved method of recognizing such malformations combines information about the conditions under which cell injury can occur, the processes by which animal tissues react to injury, and trilobite morphology.Study of healed injuries of polymeroid trilobites shows that injuries attributed to sublethal predation tend to be most commonly preserved on the pleural lobes, the posterior half of the body, and the right side. Statistically significant differences in the number of predation scars between the right and left sides is interpreted as evidence of right-left behavioral asymmetry in some predators of trilobites or the trilobites themselves. Asymmetrical, or lateralized, behavior in present-day animals is one manifestation of handedness, and is usually related to a functional lateralization of the nervous system. Evidence of behavioral lateralization in some Paleozoic predators or prey suggests that those organisms also possessed lateralized nervous systems. Right-left differences in preserved predation scars on trilobites date from the Early Cambrian (Olenellus Zone), and are the oldest known evidence of behavioral asymmetry in the fossil record.Other examples of structural or behavioral asymmetry from the fossil record of animals are cited. Lateralization is recognized in representatives of the Arthropoda, Annelida, Bryozoa, Echinodermata, Cnidaria, Mollusca, Chordata, and Conodonta, and in trace fossils.
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Servais, Thomas, Alain Blieck, Martial Caridroit, Xu Chen, Florentin Paris e M. Franco Tortello. "The importance of plankton and nekton distributions in Ordovician palaeogeographical reconstructions". Bulletin de la Société Géologique de France 176, n.º 6 (1 de novembro de 2005): 531–43. http://dx.doi.org/10.2113/176.6.531.
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Abstract Trilobites and brachiopods are the two main fossil groups that allowed construction of the first palaeogeographical maps for the early Palaeozoic. Together with the bivalves and ostracodes, the benthic elements of these fossil groups have proved to be of great palaeobiogeographical importance. For this reason, these groups are usually considered to be ‘better’ fossils for inferring Ordovician palaeogeography. The present study indicates that planktic and nektic fossil groups should not be neglected in such palaeobiogeographical studies. The plotting on a palaeogeographical reconstruction for the Arenig (Lower Ordovician, – 480 Ma) of some planktic (acritarchs, chitinozoans) and nektic (vertebrates, pelagic trilobites) fossil groups indicates that their distribution appears in part surprisingly similar to that of the benthic trilobite faunas that are considered to display the greatest provincialism. For example, the distribution of the ‘peri-Gondwanan’ acritarch province including Arbusculidium filamentosum, Coryphidium and Striatotheca, and the distribution of the Eremochitina brevis chitinozoan assemblage are almost identical to the palaeogeographical distribution of the Calymenacean-Dalmanitacean trilobite fauna. A review of the different planktic and nektic fossil groups also indicates that it is very important to carefully select ‘good’ palaeogeographical indicators, in most cases from a large number of taxa. It appears that almost all fossil groups include some ‘good’ palaeobiogeographical ‘markers’. Therefore it is important to search for ‘better’ taxa within each fossil group, instead of looking only for the ‘better’ fossil groups as a whole.
3
ZENG, HAN, FANGCHEN ZHAO, ZONGJUN YIN e MAOYAN ZHU. "Appendages of an early Cambrian metadoxidid trilobite from Yunnan, SW China support mandibulate affinities of trilobites and artiopods". Geological Magazine 154, n.º 6 (5 de abril de 2017): 1306–28. http://dx.doi.org/10.1017/s0016756817000279.
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AbstractAppendage anatomy contributes crucial data for understanding the evolution and ecology of Euarthropoda. The Palaeozoic trilobites show a great diversity of exoskeletons in the fossil record. However, soft parts, especially appendages, have only been discovered from a few trilobite species. Here we report extraordinarily preserved appendages in the trilobite species Hongshiyanaspis yiliangensis Zhang & Lin in Zhang et al. 1980 (Redlichiida, Metadoxididae) from a single mudstone layer of the Xiazhuang fossil assemblage within the Hongjingshao Formation (Cambrian Series 2, Stage 3) near Kunming, Yunnan, SW China. The appendages exhibit the common architecture revealed by other trilobites and artiopods by consisting of a pair of uniramous antennae followed by a series of paired homonomous biramous limbs. The antennae in holaspid individuals comprise up to 27 spinous podomeres and their ontogeny occurs by lengthening of the podomeres. The post-antennal biramous limbs are similar to those in other polymerid trilobites and artiopods by having a single-segmented protopodite and an endopodite comprising seven segments, but possess a unique wide tripartite exopodite with long setae. Sophisticated appendage anatomy, including the body–limb junction, fine setae, putative muscle bundles and duct-type tissues, are also revealed. Appendages of trilobites, artiopods and other upper stem-group euarthropods are compared and summarized. The H. yiliangensis appendages highlight the high morphological disparity of exopodites and the conservativeness of endopodites in trilobites and artiopods. This morphological pattern, together with similar body patterning seen in crustaceans but not in chelicerates, supports the mandibulate affinities of trilobites and at least some artiopods.
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Stilwell, Jeffrey D. "Trilobites and Linnaeus: the first fossil reconstruction from 1759". Archives of Natural History 33, n.º 1 (abril de 2006): 101–8. http://dx.doi.org/10.3366/anh.2006.33.1.101.
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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.
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Valentine, James W. "Molecules and the Early Fossil Record". Paleobiology 16, n.º 1 (1990): 94–95. http://dx.doi.org/10.1017/s0094837300009751.
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The earliest fossil record of animals has long been an enigma. For nearly a century after the appearance of The Origin of Species, mineralized trilobites were thought to be among the first organisms to appear as fossils, and as they were considered to be complex life forms, a long previous episode of animal evolution seemed to be indicated. Discovery and description of Tommotian and Vendian faunas, with their small shelly and Ediacaran fossils respectively, provided us with an idea of the nature of organisms in strata that are progressively older than the trilobite-bearing beds. Yet in these older assemblages we do not find the sorts of organisms that might be expected to be precursors to the well-known Phanerozoic clades. The puzzle remains.
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Gunderson, Gerald O. "New genus of Late Cambrian gastropod". Journal of Paleontology 67, n.º 6 (novembro de 1993): 1083–84. http://dx.doi.org/10.1017/s0022336000025440.
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Gastropods are rare fossils in the Cambrian of Wisconsin. They are usually small and flattened. During the summer of 1978, while collecting trilobites along the western side of the state, I discovered a new gastropod in the Crepicephalus zone (as defined by Twenhofel, Raasch, and Thwaites, 1935; Nelson, 1951). It is a three-dimensional fossil represented by external mold and steinkern. This was the only gastropod uncovered during the splitting of over 200 kilograms of sandstone, which also yielded hundreds of trilobite cranidia and pygidia.
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Kim, Dong Hee, Stephen R. Westrop e Ed Landing. "Middle Cambrian (Acadian Series) conocoryphid and paradoxidid trilobites from the Upper Chamberlain's Brook Formation, Newfoundland and New Brunswick". Journal of Paleontology 76, n.º 5 (setembro de 2002): 822–42. http://dx.doi.org/10.1017/s0022336000037501.
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The Fossil Brook Member of the upper Chamberlain's Brook Formation is a thin (up to 14 m) but distinctive, unconformity-bound depositional sequence recognizable from Rhode Island to eastern Newfoundland in Avalonian North America. Its diverse trilobite fauna was first described more than century ago from the limestone-rich facies of the member in southern New Brunswick. However, the systematics, stratigraphic context, and biostratigraphic significance of these trilobites have remained poorly known. A revision of the conocoryphid and paradoxidid trilobites has been completed, and the taxa set into their stratigraphic context within the middle Middle Cambrian. The faunas of the Fossil Brook are assigned to the Eccaparadoxides eteminicus Zone of Avalon. Although biogeographic barriers between Avalon and Gondwana remained strong in the Middle Cambrian and few shared trilobite species are present, a generalized correlation of the E. eteminicus Zone into Gondwana is with the Badulesia tenera Zone of the Toushamian Stage in Morocco and the Badulesia Zone of the Caesaraugustian Stage in Spain.
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Fortey, Richard A., e Nigel C. Hughes. "Brood pouches in trilobites". Journal of Paleontology 72, n.º 4 (julho de 1998): 638–49. http://dx.doi.org/10.1017/s0022336000040361.
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During the Cambrian and Ordovician trilobites belonging to a variety of clades developed distinctive inflated bulbs on the preglabellar field. We make the case that these bulbs were brood pouches, which were employed for retaining and protecting larval trilobites in order to ensure a higher rate of survivorship. Living arthropods of several classes develop comparable spherical structures—for example the domicilium of certain ostracodes. Living limuloids, likely the trilobites' closest living relatives, carry large and yolky eggs in an homologous, prelabral site. There are some trilobite examples where “species pairs” found in the same fossil sites appear to differ only in the presence or absence of the preglabellar bulb. These may represent the female and male of a single species, respectively. If so, this is the first well-supported case of sexual dimorphism in trilobites. Some more problematic examples are discussed, where alleged dimorphism would have to be more extreme.
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Ortega-Hernández, Javier, Jorge Esteve e Nicholas J. Butterfield. "Humble origins for a successful strategy: complete enrolment in early Cambrian olenellid trilobites". Biology Letters 9, n.º 5 (23 de outubro de 2013): 20130679. http://dx.doi.org/10.1098/rsbl.2013.0679.
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Trilobites are typified by the behavioural and morphological ability to enrol their bodies, most probably as a defence mechanism against adverse environmental conditions or predators. Although most trilobites could enrol at least partially, there is uncertainty about whether olenellids—among the most phylogenetically and stratigraphically basal representatives—could perform this behaviour because of their poorly caudalized trunk and scarcity of coaptative devices. Here, we report complete—but not encapsulating—enrolment for the olenellid genus Mummaspis from the early Cambrian Mural Formation in Alberta, the earliest direct evidence of this strategy in the fossil record of polymerid trilobites. Complete enrolment in olenellids was achieved through a combination of ancestral morphological features, and thus provides new information on the character polarity associated with this key trilobite adaptation.
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Chen, Zhengpeng, Yuanlong Zhao, Xinglian Yang, Jorge Esteve, Xiong Liu e Shengguang Chen. "Life cycle evolution in the trilobites Balangia and Duyunaspis from the Cambrian Series 2 (Stage 4) of South China". PeerJ 11 (10 de abril de 2023): e15068. http://dx.doi.org/10.7717/peerj.15068.
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The evolution process can be reconstructed by tracking the changes in the dynamic characters of life cycles. A number of related trilobites from the Cambrian of South China provide additional information for the study of trilobite evolutionary patterns, which has been hampered by previous incomplete fossil record though. Here, Balangia and Duyunaspis represent related Cambrian oryctocephalid trilobites from South China, are comprehensively discussed over the ontogeny, and the results show that, from B. balangensis via D. duyunensis to D. jianheensis, their exoskeletal morphology shows a directional evolution. Based on the direction of evolutionary changes in the development of Balangia and Duyunaspis, we speculate that Duyunaspis likely evolved from Balangia instead of Balangia evolved from Duyunaspis, as was previously assumed. This inference is also supported by the phylogenetic tree. This research provides not only a better understanding of the mechanisms of evolution in trilobites, but also new insights for the relationship between developmental evolutionary changes and phylogeny in trilobites.
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Briggs, Derek E. G. "Arthropod paleobiology". Paleobiology 11, n.º 4 (1985): 361–67. http://dx.doi.org/10.1017/s0094837300011672.
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An international conference on “Fossil Arthropods as Living Animals” was held at the Royal Society of Edinburgh on October 25–27, 1984. Major international conferences devoted to fossil arthropods are rare events. The previous one, which was held in Oslo in July 1973 as a NATO Advanced Study Institute, resulted in a volume on “Evolution and Morphology of the Trilobita, Trilobitoidea and Merostomata” (Martinsson 1975). Participants in the Edinburgh meeting heard 28 contributions covering all aspects of arthropod paleobiology. Most are published as a special issue of the Transactions of the Royal Society of Edinburgh: Earth Sciences (Waterston 1985). All four major arthropod groups are treated (trilobites, crustaceans, chelicerates, and uniramians), as well as trace fossils and some groups of problematic status.
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Connolly, Sean R., e Arnold I. Miller. "Global Ordovician faunal transitions in the marine benthos: proximate causes". Paleobiology 27, n.º 4 (2001): 779–95. http://dx.doi.org/10.1666/0094-8373(2001)027<0779:goftit>2.0.co;2.
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During the Ordovician Radiation, domination of benthic marine communities shifted away from trilobites, toward articulate brachiopods, and, to a lesser degree, toward bivalves and gastropods. In this paper, we identify the patterns in origination and extinction probabilities that gave rise to these transitions. Using methods adapted from capture-mark-recapture (CMR) population studies, we estimate origination, extinction, and sampling probabilities jointly to avoid confounding patterns in turnover rates with temporal variation in the quality of the fossil record. Not surprisingly, higher extinction probabilities in trilobites relative to articulate brachiopods, bivalves, and gastropods were partly responsible for relative decreases in trilobite diversity. However, articulate brachiopods also had higher origination probabilities than trilobites, indicating that relative increases in articulate brachiopod diversity would have occurred even in the absence of between-class differences in extinction probabilities. This contrasts with inferences based on earlier Phanerozoic-scale, long-term averages of turnover probabilities, and it indicates that a major cause of this faunal transition has been overlooked.
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Finnegan, Seth, e Mary L. Droser. "Body size, energetics, and the Ordovician restructuring of marine ecosystems". Paleobiology 34, n.º 3 (2008): 342–59. http://dx.doi.org/10.1666/07074.1.
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Major shifts in ecological dominance are one of the most conspicuous but poorly understood features of the fossil record. Here we examine one of the most prominent such shifts, the Ordovician shift from trilobite to brachiopod dominance of benthic ecosystems. Using an integrated database of high-resolution paleoecological samples and body size data, we show that while the average local richness and relative abundance of trilobites declined significantly through the Ordovician, the estimated standing biomass of trilobites, and by implication the amount of energy that they used, remained relatively invariant. This is attributable to an increase in the average body size of trilobite species in our data set, and especially to the widespread occurrence of the exceptionally large Middle-Late Ordovician trilobite genus Isotelus. Brachiopods increase in both mean body size and relative abundance throughout the Ordovician, so that estimates of brachiopod biomass and energetic use increase substantially between the Early and Late Ordovician. Although the data set includes a range of depositional environments, similar trends are observed in both shallow subtidal and deep subtidal settings. These results suggest that diversification of the Paleozoic Fauna did not come at the energetic expense of the Cambrian Fauna. The declining relative abundance of trilobites may reflect a combination of numerical dilution and the necessary energetic trade-offs between body size and abundance.
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Mángano, M. Gabriela, Luis A. Buatois, Beatriz G. Waisfeld, Diego F. Muñoz, N. Emilio Vaccari e Ricardo A. Astini. "Were all trilobites fully marine? Trilobite expansion into brackish water during the early Palaeozoic". Proceedings of the Royal Society B: Biological Sciences 288, n.º 1944 (3 de fevereiro de 2021): 20202263. http://dx.doi.org/10.1098/rspb.2020.2263.
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Trilobites, key components of early Palaeozoic communities, are considered to have been invariably fully marine. Through the integration of ichnological, palaeobiological, and sedimentological datasets within a sequence-stratigraphical framework, we challenge this assumption. Here, we report uncontroversial trace and body fossil evidence of their presence in brackish-water settings. Our approach allows tracking of some trilobite groups foraying into tide-dominated estuaries. These trilobites were tolerant to salinity stress and able to make use of the ecological advantages offered by marginal-marine environments migrating up-estuary, following salt wedges either reflecting amphidromy or as euryhaline marine wanderers. Our data indicate two attempts of landward exploration via brackish water: phase 1 in which the outer portion of estuaries were colonized by olenids (Furongian–early late Tremadocian) and phase 2 involving exploration of the inner to middle estuarine zones by asaphids (Dapingian–Darriwilian). This study indicates that tolerance to salinity stress arose independently among different trilobite groups.
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Schoenemann, Brigitte. "Evolution of Eye Reduction and Loss in Trilobites and Some Related Fossil Arthropods". Emerging Science Journal 2, n.º 5 (4 de novembro de 2018): 272. http://dx.doi.org/10.28991/esj-2018-01151.
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The fossil record of arthropod compound eyes reflects different modes and occasions of eye reduction and blindness. In the best-studied fossil examples, the trilobites [trilobites: extinct arthropods, dominant during the Palaeozoic], which have an excellent geological record, eyes are primary structures, and in all known genera which lack them, eye-loss is always secondary. Once the eyes were lost, they never were never re-established. The most striking examples occur in the Upper Devonian, when two unrelated major groups of trilobites, with different kinds of eyes, underwent eye reduction and even total loss of the eyes over the same time period, undoubtedly due to long-term environmental change. One reason is that a mud blanket spread over a vast area, there was no firm substrate, and many trilobites became small and many became endobenthic, reducing or losing their eyes in the process. Toxic environmental conditions may also have had an effect. Certain coeval forms remained, however, which still possess perfectly good compound eyes. Either they found vacant refuges where they could survive, or alternatively their visual systems were elaborate enough to adapt to the changing conditions. Another inducement for evolving small, reduced compound eyes is to become a tiny organism oneself, with simply not enough space to establish a regular and functional compound eye, and in such minaturised eyes special adaptations for capturing enough photons are necessary. Thus very small compound eyes often establish wide acceptance angles of their ommatidia, collecting light over large angular ranges of space and it is beneficial to have a wide rhabdom provided that it is short, has a wide lens diameter, and perhaps even possess highly sensitive receptor cells. We find such a miniaturised system in the first recorded planktonic trilobite. Another kind of reduction of a compound eye, or parts of it, also occurs, if selective pressure claims for a high specialisation of eyes that results in several facets fusing into a single functional unit. This probably can be found in phacopid trilobites, ~400 million years old. Here the enlarged aperture of a resulting large lens may allow vision under dim light conditions such as at greater depth. The fossil record gives relatively little evidence about parasites, which often have reduced eyes. Agnostida are blind relatives of trilobites which lived during the Cambrian and Ordovician. An early suggestion was that some of these were parasitic, but this was never commonly adopted. Finally penstastomids (Crustacea), worm-like parasitic organisms, already have been blind from the Cambrian (~487Ma).
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Crônier, Catherine, e Allart van Viersen. "The ‘Mur des douaniers’, an exceptionally well-preserved Early Eifelian fossil site". Bulletin de la Société Géologique de France 179, n.º 1 (1 de janeiro de 2008): 89–95. http://dx.doi.org/10.2113/gssgfbull.179.1.89.
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Abstract The ‘Mur des douaniers’ biota at the former French/Belgian border contains a rich and diversified Lower Eifelian benthic fauna, and especially trilobites. Palaeobiodiversity and sedimentological analyses have led to the interpretation of the general palaeoenvironmental/palaeoecological context. This trilobite-rich locality is an exceptionally well-preserved Early Eifelian fossil site with regard to the regional scale. Unfortunately, its growing reputation led to fossil pillage and now this palaeontological site is protected as a Nature Reserve. From now on, no complementary observation of the palaeontological data, the taphonomic analysis, the ichnological, sedimentological and geochemical record can be made to provide a better palaeoecological synthesis.
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Anfimova, Galina. "The ‘historical’ collection of fossil invertebrates from Lower Palaeozoic deposits of the Bohemian Massif (Czeсh Republic) as an object of scientific and cultural heritage". GEO&BIO 2022, n.º 22 (30 de junho de 2022): 3–28. http://dx.doi.org/10.15407/gb2303.
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The years 2022 marks the 95th anniversary of the foundation of the Geological Museum, the predecessor of the Department of Geology of the National Museum of Natural History NAS of Ukraine. However, the origins of its collections date back to the 19th century. The aim of the article is the ancient regional paleontological collection, which consists of fossil remains of various systematic groups of fauna and flora from the Lower Palaeozoic of the Bohemian Massif (Czech Republic) and is stored under #582. Various aspects of its value, primarily scientific and historical, were identified and characterised. The territory from which the collection originates is recognised as key in the knowledge of stratigraphy and palaeontology of the Lower Palaeozoic. The temporal range of fossils in the collection is Middle Cambrian to Middle Devonian. Fossil remains were collected from 45 localities, of which 2 are Cambrian, 15 are Ordovician, 16 are Silurian, and 12 are Devonian. The collection consists of two parts. The first contains 545 specimens of trilobite fossil remains. Trilobites in the collection are represented by all (11) currently known orders, 29 families, 105 genera, and 140 species (138 species according to the modern classification). The second part of the collection consists of 325 specimens of representatives of other characteristic faunal groups of the Lower Palaeozoic of the Bohemian Massif. This fauna associated with trilobites is represented in the collection by eight phyla (cnidarians, arthropods, molluscs, bryozoans, brachiopods, echinoderms, semichordates, and chordates) and 23 classes. The systematic composition of the second (non-trilobite) part of the collection includes more than 100 (!) species. A systematic catalogue of the collection, demonstrating its significant taxonomic diversity, has been compiled. The owner of the collection was the Mineralogical Cabinet of St. Volodymyr Imperial University of Kyiv, to which ‘the collection of Bohemian Silurian fossils’ in the amount of 1051 specimens arrived in 1874 ‘from the Bohemian Museum with the help of Prof. Jan Krejčí’ by purchase. The collection has an important scientific, educational, exhibitional, and historical value. Individual groups of the fauna of the collection are subject to revision and may become the object of research in numerous scientific works.
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Anfimova, Galina. "The ‘historical’ collection of fossil invertebrates from Lower Palaeozoic deposits of the Bohemian Massif (Czeсh Republic) as an object of scientific and cultural heritage". GEO&BIO 2022, n.º 22 (30 de junho de 2022): 3–28. http://dx.doi.org/10.15407/gb2203.
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The years 2022 marks the 95th anniversary of the foundation of the Geological Museum, the predecessor of the Department of Geology of the National Museum of Natural History NAS of Ukraine. However, the origins of its collections date back to the 19th century. The aim of the article is the ancient regional paleontological collection, which consists of fossil remains of various systematic groups of fauna and flora from the Lower Palaeozoic of the Bohemian Massif (Czech Republic) and is stored under #582. Various aspects of its value, primarily scientific and historical, were identified and characterised. The territory from which the collection originates is recognised as key in the knowledge of stratigraphy and palaeontology of the Lower Palaeozoic. The temporal range of fossils in the collection is Middle Cambrian to Middle Devonian. Fossil remains were collected from 45 localities, of which 2 are Cambrian, 15 are Ordovician, 16 are Silurian, and 12 are Devonian. The collection consists of two parts. The first contains 545 specimens of trilobite fossil remains. Trilobites in the collection are represented by all (11) currently known orders, 29 families, 105 genera, and 140 species (138 species according to the modern classification). The second part of the collection consists of 325 specimens of representatives of other characteristic faunal groups of the Lower Palaeozoic of the Bohemian Massif. This fauna associated with trilobites is represented in the collection by eight phyla (cnidarians, arthropods, molluscs, bryozoans, brachiopods, echinoderms, semichordates, and chordates) and 23 classes. The systematic composition of the second (non-trilobite) part of the collection includes more than 100 (!) species. A systematic catalogue of the collection, demonstrating its significant taxonomic diversity, has been compiled. The owner of the collection was the Mineralogical Cabinet of St. Volodymyr Imperial University of Kyiv, to which ‘the collection of Bohemian Silurian fossils’ in the amount of 1051 specimens arrived in 1874 ‘from the Bohemian Museum with the help of Prof. Jan Krejčí’ by purchase. The collection has an important scientific, educational, exhibitional, and historical value. Individual groups of the fauna of the collection are subject to revision and may become the object of research in numerous scientific works.
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Lieberman, Bruce S., e Joseph G. Meert. "Biogeography and the nature and timing of the Cambrian radiation". Paleontological Society Papers 10 (novembro de 2004): 79–92. http://dx.doi.org/10.1017/s1089332600002357.
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Biogeographic patterns from early Cambrian trilobites are used to evaluate the nature and timing of the Cambrian radiation. Results from a phylogenetic biogeographic analysis reveal that patterns of vicariance are compatible with a vicariant distribution of trilobites across what were originally joined elements of the supercontinent Pannotia; further, there is limited evidence for coordinated range expansion or geo-dispersal by these trilobites. As Pannotia had split apart sometime between 550-600 Ma this suggests that trilobites, and by extension several other metazoan taxa, had begun to diversify by this interval. This result suggests that there may have been some period of cryptic diversification by metazoans prior to the Cambrian radiation, though the inferred length of this interval is not as long as that invoked by some molecular studies. Perhaps trilobites existed at low population densities in marginal environments before they became paleontologically emergent. Even though the results suggest some apparent gap in the fossil record, the evolutionary signature of this gap is still preserved in the paleobiological patterns from the fossil record, indicating that the fossil record is still the one best source of data on the nature of key episodes in the history of life, like the Cambrian radiation.
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Schwimmer, David R. "Taxonomy and biostratigraphic significance of some Middle Cambrian trilobites from the Conasauga Formation in western Georgia". Journal of Paleontology 63, n.º 4 (julho de 1989): 484–94. http://dx.doi.org/10.1017/s0022336000019703.
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Biostratigraphic correlations of the Conasauga Formation in the southern Appalachians have been hindered by unreliable trilobite taxonomy. New fossil collections and re-examination of type specimens allow revision or confirmation of assignments for several Middle Cambrian trilobite taxa. These revisions reveal sufficient relationships with trilobites outside the region to place fossiliferous strata in Floyd County, Georgia, into the Oryctocephalus and Bolaspidella assemblage zones of the Middle Cambrian section defined for the Great Basin.Trilobite taxa considered are: (Agnostida) Baltagnostus centerensis (Resser, 1938) and Peronopsis cf. P. cuneifera (Barrande, 1846); (Ptychopariida) Alokistocare americanum (Walcott, 1916), Elrathia antiquata (Salter, 1859), Asaphiscus gregarius Walcott, 1916, and Glyphaspis cf. G. capella (Walcott, 1916).
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Sennikov, Nikolay V., Igor’ V. Korovnikov, Olga T. Obut, Dmitry A. Tokarev, Natalya V. Novozhilova e Taniel Danelian. "The Lower Cambrian of the Salair and Gorny Altai (Siberia) revisited". Bulletin de la Société géologique de France 188, n.º 1-2 (2017): 1. http://dx.doi.org/10.1051/bsgf/2017002.
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This paper discusses the fossil record, stratigraphy and sedimentary environments of lower Cambrian sequences that crop out in the Salair and Gorny Altai, southern part of western Siberia (Russia). Numerous and well-preserved archaeocyaths and a few small shelly fossils (SSF) have been discovered in carbonate sequences that crop out nearby the Gavrilovka village, Salair. The presence of the Gordonicyathus howelliarchaeocyath Zone is established for the first time in this thick sequence of biogenic carbonates, in addition to the Nochoroicyathus mariinskii Zone, which was known previously from the Gavrilovka Formation. Both of these zones are Atdabanian in age. It is likely that accumulation of the Gavrilovka Formation took place in relatively shallow waters, along reef buildups surrounded by lagoons with archaeocyaths. In the Ak-Kaya section of the Gorny Altai, the trilobite species Alacephalus contortus and Poliellaspis rotundata, known previously from the upper Atdabanian, were discovered, only a few meters above horizons bearing lower Botoman trilobites. We may consider that the previously known age range of these two species is slightly longer and should be extended up to the lower Botoman. Alternatively, on the basis of their paleoecological affinity for agitated waters, these trilobites may be interpreted as reworked in lower Botoman strata.
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Valencia Giraldo, Yenny Paola, Luis Carlos Escobar Arenas, Juliana Mendoza Ramirez, Daniel Delgado Sierra e Andrés Leonardo Cárdenas Rozo. "Review of fossiliferous localities at Antioquia department, Colombia". Boletín de Ciencias de la Tierra, n.º 40 (1 de julho de 2016): 46–54. http://dx.doi.org/10.15446/rbct.n40.53748.
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Even though only 11.5% of Antioquia’s area has outcrops of sedimentary rocks, a review of the literature and the development of a digital map of fossil localities (27), allows us to conclude that the region has a great palaeontological potential. The data show that Antioquia’s fossil occurrences date from Ordovician (~ 485.4 to ~ 443.8Ma) to Quaternary (~ 2.6Ma to the Present). Moreover, there are macro-fossils belonging to different phyla (i.e. Chordata, Echinodermata, Hemichordata, Mollusca and Trachaeophyta). The oldest paleofauna in the area, consists of graptolites and trilobites recorded in Paleozoic metasedimentary rocks, whereas marine mollusks and echinoderms compose the major fossil assemblages of the Cretaceous. The paleoflora (i.e. fossil leaves and petrified wood) in the area is associated with to the Amagá Formation (Oligocene - Miocene). Finally, fossils of terrestrial vertebrates (i.e. mastodons and horses) are recorded in Quaternary deposits.
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Landing, Ed, Gerd Geyer e Kenneth E. Bartowski. "Latest Early Cambrian small shelly fossils, trilobites, and Hatch Hill dysaerobic interval on the Québec continental slope". Journal of Paleontology 76, n.º 2 (março de 2002): 287–305. http://dx.doi.org/10.1017/s0022336000041718.
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Latest Early Cambrian continental slope deposition of the early Hatch Hill dysaerobic interval (new name, latest Early Cambrian—earliest Ordovician) is recorded by dark grey shales and turbidite limestones in the Bacchus slice at Ville Guay, Québec. Platform-derived microfaunas of the Bicella bicensis trilobite assemblage were transported into a dysoxic environment of the upper “Anse Maranda Formation,” and many organisms were buried alive. Phosphatization preserved a diverse skeletal fossil assemblage that includes four agnostid trilobites, echinoderm debris, and twenty small shelly fossil taxa. The latter include five helcionellids; Pelagiella Matthew, 1895b, classified herein as a gastropod; a bivalve (Fordilla Barrande, 1881); the brachiopod Linnarssonia taconica Walcott, 1887; two conodontomorphs; four hyoliths; and such phosphatic and calcareous problematica as Coleoloides Walcott, 1889, emend. Most small shelly fossil taxa, including Discinella micans Billings, 1872, range through much of the Olenellus Zone and Elliptocephala asaphoides assemblage interval. Trilobites allow a more resolved correlation into the uppermost Olenellus Zone. A comparable stratigraphy occurs in Cambrian—Ordovician slope facies of the Bacchus slice and the Giddings Brook slice in eastern New York. The “Anse Maranda Formation” correlates with the West Granville—Browns Pond—lower Hatch Hill formations in eastern New York and brackets two dysaerobic intervals (Browns Pond and early Hatch Hill). Sea-level change associated with the Hawke Bay regression between the Browns Pond and Hatch Hill onlap/dysaerobic intervals led to the longest period of oxygenated green shale and sandstone deposition on the east Laurentian slope in the late Early Cambrian-earliest Ordovician.
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Geyer, Gerd, e John S. Peel. "Middle Cambrian trilobites from the Ekspedition Bræ Formation of North Greenland, with a reappraisal of the genusElrathina". Journal of Paleontology 91, n.º 2 (20 de dezembro de 2016): 265–93. http://dx.doi.org/10.1017/jpa.2016.152.
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AbstractThe richly fossiliferous Ekspedition Bræ Formation of North Greenland yields a typical oligospecific fossil assemblage with well-preserved trilobites, helcionelloids, and lingulate brachiopods. The trilobites includeItagnostus subhastatusnew species,Itagnostussp. cf.I.gaspensis(Rasetti, 1948),Elrathina aphroditenew species,Elrathina athenanew species,Elrathina heranew species, andElrathia groenlandicanew species—a fossil assemblage typical of theBathyuriscus-ElrathinaZone as known from the Cordilleran regions of Laurentia. Excellent preservation allows a detailed assessment of the prosopon and elucidates aspects of the ontogenetic development ofElrathinaandElrathia. An evaluation ofElrathinaincludes a redescription of its type species,E.cordillerae(Rominger, 1887), based on the type material, and indicates that most specimens collected from the Burgess Shale and previously dealt with asE.cordilleraerepresent a new species.
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Geyer, Gerd, Miguel Caldeira Pais e Thomas Wotte. "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". PalZ 94, n.º 4 (25 de fevereiro de 2020): 645–60. http://dx.doi.org/10.1007/s12542-020-00514-x.
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Abstract 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.
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AXHEIMER, NIKLAS, MATS E. ERIKSSON, PER AHLBERG e ANDERS BENGTSSON. "The middle Cambrian cosmopolitan key species Lejopyge laevigata and its biozone: new data from Sweden". Geological Magazine 143, n.º 4 (23 de maio de 2006): 447–55. http://dx.doi.org/10.1017/s0016756806002007.
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The middle Cambrian Lejopyge laevigata Zone is poorly exposed in Scandinavia. Both this zone, however, and the succeeding Agnostus pisiformis Zone are well exposed at a classic locality at Gudhem, Västergötland, south-central Sweden. The sequences consist of finely laminated alum shale with scattered stinkstone (orsten) lenses. Three measured and sampled sections yielded a diverse fossil fauna, dominated by trilobites, in particular agnostoids, and the bradoriid Anabarochilina primordialis. Fossils are excellently preserved but restricted to the stinkstones. The L. laevigata Zone at Gudhem includes several geographically widespread key agnostoid species, notably Tomagnostella sulcifera, Clavagnostus spinosus, Glaberagnostus altaicus, Lejopyge laevigata and L. armata. The L. laevigata Zone in Scandinavia is here extended to include the traditional Solenopleura? brachymetopa Zone, and its lower boundary is defined by the FAD of L. laevigata. Trilobite evidence shows that the upper part of the Scandinavian L. laevigata Zone approximately correlates with the Proagnostus bulbus Zone of China and elsewhere.
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Paterson, John R., Gregory D. Edgecombe e Michael S. Y. Lee. "Trilobite evolutionary rates constrain the duration of the Cambrian explosion". Proceedings of the National Academy of Sciences 116, n.º 10 (19 de fevereiro de 2019): 4394–99. http://dx.doi.org/10.1073/pnas.1819366116.
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Trilobites are often considered exemplary for understanding the Cambrian explosion of animal life, due to their unsurpassed diversity and abundance. These biomineralized arthropods appear abruptly in the fossil record with an established diversity, phylogenetic disparity, and provincialism at the beginning of Cambrian Series 2 (∼521 Ma), suggesting a protracted but cryptic earlier history that possibly extends into the Precambrian. However, recent analyses indicate elevated rates of phenotypic and genomic evolution for arthropods during the early Cambrian, thereby shortening the phylogenetic fuse. Furthermore, comparatively little research has been devoted to understanding the duration of the Cambrian explosion, after which normal Phanerozoic evolutionary rates were established. We test these hypotheses by applying Bayesian tip-dating methods to a comprehensive dataset of Cambrian trilobites. We show that trilobites have a Cambrian origin, as supported by the trace fossil record and molecular clocks. Surprisingly, they exhibit constant evolutionary rates across the entire Cambrian, for all aspects of the preserved phenotype: discrete, meristic, and continuous morphological traits. Our data therefore provide robust, quantitative evidence that by the time the typical Cambrian fossil record begins (∼521 Ma), the Cambrian explosion had already largely concluded. This suggests that a modern-style marine biosphere had rapidly emerged during the latest Ediacaran and earliest Cambrian (∼20 million years), followed by broad-scale evolutionary stasis throughout the remainder of the Cambrian.
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Dzik, Jerzy, e Nguyen Duc Phong. "Dating of Cambrian-Ordovician boundary strata in northernmost Vietnam and methodological aspects of evolutionary biostratigraphic inference". Stratigraphy 13, n.º 2 (2016): 83–93. http://dx.doi.org/10.29041/strat.13.2.01.
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Unrepeatability of evolution and the correspondence of the fossil record to ancestor-descendant successions of species are the unavoidable, although usually hidden, assumptions in any reliable age determination based on fossils. We expose these assumptions while dating early Paleozoic carbonate rock deposits in the Lung Cu section at the Vietnamese/Chinese border. The best-preserved and most abundant fossils in this section are shumardiid trilobites. The succession of shumardiid species, based on data from elsewhere, provides an evolutionary reference standard. The shumardiid record is not sufficiently complete to verify hypotheses of ancestor-descendant relationships but enables estimation of the "degree of evolutionary advancement" of the Vietnamese species. This suggests an age close to the Cambrian/Ordovician boundary. Although considered non-scientific by cladists, such inferences are testable. Support for a late Furongian or early Tremadocian age is provided by the occurrence of Cordylodus conodonts in strata above the trilobite-bearing bed. The conodont evolution has a good fossil record interpreted in population terms in the Baltic region and Australia, including the lineage represented in Vietnam. Age determination based on such evolutionary reasoning is reliable but of a relatively low resolution, because the rate of morphological evolution is generally low. Generally, more precise dating is offered by distribution of fossils controlled by ecological factors, which are repeatable and mostly diachronous over large geographic distances, but they may have happened relatively rapidly. The appearance of the Iapetognathus-Chosonodina-bearing conodont assemblage in the Lung Cu area, as suggested by its occurrences elsewhere, was probably due to abrupt faunal migration into the region.
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LIÑÁN, ELADIO, JOSÉ ANTONIO GÁMEZ VINTANED e RODOLFO GOZALO. "The middle lower Cambrian (Ovetian)Lunagraulosn. gen. from Spain and the oldest trilobite records". Geological Magazine 152, n.º 6 (10 de junho de 2015): 1123–36. http://dx.doi.org/10.1017/s0016756815000084.
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AbstractThe type material ofAgraulos antiquusSdzuy, 1961 from the La Herrería Formation, northern Spain, is revised together with additional material and included in the new genusLunagraulos. The stratigraphical range ofLunagraulos antiquus(Sdzuy, 1961) – occurring below that of the trilobite species of the generaLunolenus,MetadoxidesandDolerolenusin the type locality of Los Barrios de Luna in the province of León, northern Spain – and the accompanying ichnofossil assemblage demonstrate an Ovetian age (lower part of Cambrian Stage 3, currently being discussed by the International Subcommission on Cambrian Stratigraphy) for this species. Moreover, the trilobiteLunagraulos tamamensisn. gen. n. sp. is found in the Tamames Sandstone near the village of La Rinconada in the province of Salamanca, central Spain. The biostratigraphical position of this new taxon and its accompanying ichnoassemblage is also analysed and assigned to the lowermost Ovetian Stage. The genusLunagraulosis therefore the oldest agraulid found in the fossil record. The exceptional presence ofLunagraulosin a marine coarse siliciclastic succession – a facies rather typical for the ichnofossilsCruzianaandRusophycus, some of the oldest signs of trilobite activity – suggests that first trilobite representatives may have inhabited high- to middle-energy, marine environments. This hypothesis may also explain both the taxonomic and biostratigraphic heterogeneity of the first trilobite genera appearing across the world, due to preservation problems in this type of facies. Comparison of theLunagraulos biostratigraphy with other coeval Spanish fossil assemblages allows us to propose its intercontinental correlation with the oldest records of currently known trilobites.
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Hughes, Nigel C., Alessandro Minelli e Giuseppe Fusco. "The ontogeny of trilobite segmentation: a comparative approach". Paleobiology 32, n.º 4 (2006): 602–27. http://dx.doi.org/10.1666/06017.1.
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Ontogenetic stages of trilobites have traditionally been recognized on the basis of the development of exoskeletal segmentation. The established protaspid, meraspid, and holaspid phases relate specifically to the development of articulated joints between exoskeletal elements. Transitions between these phases were marked by the first and last appearances of new trunk segment articulations. Here we propose an additional and complementary ontogenetic scheme based on the generation of new trunk segments. It includes an anamorphic phase during which new trunk segments appeared, and an epimorphic phase during which the number of segments in the trunk remained constant. In some trilobites an ontogenetic boundary can also be recognized at the first appearance of morphologically distinct posterior trunk segments. Comparison of the phase boundaries of these different aspects of segment ontogeny highlights rich variation in the segmentation process among Trilobita. Cases in which the onset of the holaspid phase preceded onset of the epimorphic phase are here termed protarthrous, synchronous onset of both phases is termed synarthromeric, and onset of the epimorphic phase before onset of the holaspid phase is termed protomeric. Although these conditions varied among close relatives and perhaps even intraspecifically in some cases, particular conditions may have been prevalent within some clades.Trilobites displayed hemianamorphic development that was accomplished over an extended series of juvenile and mature free-living instars. Although developmental schedules varied markedly among species, morphological transitions during trilobite development were generally regular, limited in scope, and extended over a large number of instars when compared with those of many living arthropods. Hemianamorphic, direct development with modest change between instars is also seen among basal members of the Crustacea, basal myriapods, pycnogonids, and in some fossil chelicerates. This mode may represent the ancestral condition of euarthropod development.
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Madsen, Vivianne Berg. "A review of the Andrarum Limestone and the upper alum shale (Middle Cambrian) of Bornholm, Denmark". Bulletin of the Geological Society of Denmark 34 (19 de dezembro de 1985): 133–43. http://dx.doi.org/10.37570/bgsd-1985-34-12.
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The lithology and fossil content of the Middle Cambrian Andrarum Limestone on Bornholm is briefly reviewed. Trilobites, brachiopods and hyolithids are common, acid residues contain a rich fauna of pelagiellaceans, rostroconchs and echinoderm fragments. Most of these are phosphatized with well preserved mi- cro- and ultrastructures. A revised list of trilobites is presented. New finds of trilobites in the lowermost upper alum shale show the lower part of the Lejopyge laevigata Zone to be no more than 10 cm thick. The occurrence of the Upper Cambrian conodont Westergaardodina tricuspidata permits a more exact placement of the Middle-Upper Cambrian boundary. The Middle Cambrian deposits are shown to be 3 m ± 10 cm in total thickness in the two localities known on Bornholm.
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Landing, Ed, Susan C. Johnson e Gerd Geyer. "Faunas and Cambrian volcanism on the Avalonian marginal platform, southern New Brunswick". Journal of Paleontology 82, n.º 5 (setembro de 2008): 884–905. http://dx.doi.org/10.1666/07-007.1.
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The Cambrian inlier at Beaver Harbour, southern New Brunswick, is now confidently referred to the marginal platform of the late Proterozoic–Early Paleozoic Avalon microcontinent. The sub-trilobitic Lower Cambrian Chapel Island and Random Formations are unconformably overlain by the mafic volcanic-dominated Wade's Lane Formation (new). Late Early Cambrian trilobites and small shelly taxa in the lowest Wade's Lane demonstrate a long Random–Wade's Lane hiatus (middle Terreneuvian–early Branchian). Latest Early–middle Middle Cambrian pyroclastic volcanism produced a volcanic edifice at Beaver Harbour that is one of three known volcanic centers that extended 550 km along the northwest margin of Avalon. Middle Middle Cambrian sea-level rise, probably in theParadoxides eteminicusChron, mantled the extinct volcanics with gray-green mudstone and limestone of the Fossil Brook Member. Black, dysoxic mudstone of the upper Manuels River Formation (upper Middle Cambrian,P. davidisZone) is the youngest Cambrian unit in the Beaver Harbour inlier.Lapworthella cornu(Wiman, 1903) emend., a senior synonym of the genotypeL. nigra(Cobbold, 1921),Hyolithellus sinuosusCobbold, 1921, and probablyAcrothyra seraMatthew, 1902a, range through the ca. 8 m.y. of the trilobite-bearing upper Lower Cambrian, andH. sinuosusandA. serapersist into the middle Middle Cambrian.Lapworthella cornuandH. sinuosusreplaced the tropical taxaL. schodackensis(Lochman, 1956) andH. micansBillings, 1872, in cool-water Avalon.
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Webster, Mark, e Steven J. Hageman. "Buenellus chilhoweensisn. sp. from the Murray Shale (lower Cambrian Chilhowee Group) of Tennessee, the oldest known trilobite from the Iapetan margin of Laurentia". Journal of Paleontology 92, n.º 3 (26 de março de 2018): 442–58. http://dx.doi.org/10.1017/jpa.2017.155.
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AbstractThe Ediacaran to lower Cambrian Chilhowee Group of the southern and central Appalachians records the rift-to-drift transition of the newly formed Iapetan margin of Laurentia. Body fossils are rare within the Chilhowee Group, and correlations are based almost exclusively on lithological similarities. A critical review of previous work highlights the relatively weak biostratigraphic and radiometric age constraints on the various units within the succession. Herein, we document a newly discovered fossil-bearing locality within the Murray Shale (upper Chilhowee Group) on Chilhowee Mountain, eastern Tennessee, and formally describe a nevadioid trilobite,Buenellus chilhoweensisn. sp., from that site. This trilobite indicates that the Murray Shale is of Montezuman age (provisional Cambrian Stage 3), which is older than the Dyeran (provisional late Stage 3 to early Stage 4) age suggested by the historical (mis)identification of “Olenellussp.” from within the unit as reported by workers more than a century ago.Buenellus chilhoweensisn. sp. represents only the second known species ofBuenellus, and demonstrates that the genus occupied both the Innuitian and Iapetan margins of Laurentia during the Montezuman. It is the oldest known trilobite from the Iapetan margin, and proves that the hitherto apparent absence of trilobites from that margin during the Montezuman was an artifact of inadequate sampling rather than a paleobiogeographic curiosity. The species offers a valuable biostratigraphic calibration point within a rock succession that has otherwise proven recalcitrant to refined dating.UUID:http://zoobank.org/30af790b-e7b1-44c3-b1d5-55cdf579bde2
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Luo, Mei, Fan Liu, Yue Liang, Luke C. Strotz, Jiayue Wang, Yazhou Hu, Baopeng Song, Lars E. Holmer e Zhifei Zhang. "First Report of Small Skeletal Fossils from the Upper Guojiaba Formation (Series 2, Cambrian), Southern Shaanxi, South China". Biology 12, n.º 7 (24 de junho de 2023): 902. http://dx.doi.org/10.3390/biology12070902.
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A small skeletal fossil assemblage is described for the first time from the bioclastic limestone interbeds of the siltstone-dominated Guojiaba Formation, southern Shaanxi, China. The carbonate-hosted fossils include brachiopods (Eohadrotreta zhujiahensis, Eohadrotreta zhenbaensis, Spinobolus sp., Kuangshanotreta malungensis, Kyrshabaktella sp., Lingulellotreta yuanshanensis, Eoobolus incipiens, and Eoobolus sp.), sphenothallids (Sphenothallus sp.), archaeocyaths (Robustocyathus sp. and Yukonocyathus sp.), bradoriids (Kunmingella douvillei), chancelloriids sclerites (Onychia sp., Allonnia sp., Diminia sp., Archiasterella pentactina, and Chancelloria cf. eros), echinoderm plates, fragments of trilobites (Eoredlichia sp.), and hyolithelminths. The discovery of archaeocyaths in the Guojiaba Formation significantly extends their stratigraphic range in South China from the early Tsanglangpuian at least to the late Chiungchussuan. Thus, the Guojiaba Formation now represents the lowest known stratigraphic horizon where archaeocyath fossils have been found in the southern Shaanxi area. The overall assemblage is most comparable, in terms of composition, to Small skeletal fossil (SSF) assemblages from the early Cambrian Chengjiang fauna recovered from the Yu’anshan Formation in eastern Yunnan Province. The existing position that the Guojiaba Formation is correlated with Stage 3 in Cambrian Series 2 is strongly upheld based on the fossil assemblage recovered in this study.
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Zhao, Yuanlong, Mingkun Wang, Steven T. LoDuca, Xinglian Yang, Yuning Yang, Yujuan Liu e Xin Cheng. "Paleoecological Significance of Complex Fossil Associations of the Eldonioid Pararotadiscus guizhouensis with other Faunal Members of the Kaili Biota (Stage 5, Cambrian, South China)". Journal of Paleontology 92, n.º 6 (30 de abril de 2018): 972–81. http://dx.doi.org/10.1017/jpa.2018.41.
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AbstractThe planktonic medusiform taxon Pararotadiscus guizhouensis (Zhao and Zhu, 1994) is one of the most abundant components of the Kaili Biota. Many specimens are in direct association with other taxa, including trilobites, brachiopods, hyolithids, echinoderms, and algae, as well as the trace fossil Gordia. Four types of interrelationships between P. guizhouensis and associated fossils are recognized: symbiosis, co-burial, attachment of benthic taxa on P. guizhouensis carcasses, and scavenging of P. guizhouensis carcasses. These associations of P. guizhouensis within the Kaili Biota are unique among occurrences of medusiform fossils in Burgess Shale-type biotas worldwide and provide important insights concerning ecological complexity in the Kaili Biota and in Cambrian marine communities in general.
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Kluessendorf, Joanne, e Donald G. Mikulic. "Temporal Patterns in the Arthropod Trace-Fossil Record". Short Courses in Paleontology 3 (1990): 66–98. http://dx.doi.org/10.1017/s2475263000001744.
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Arthropods are currently abundant and diverse in many environments, with terrestrial insects alone accounting for at least 70% of all extant animal species (Barnes, 1980). The fossilization potential of arthropods, however, is low. With the exception of trilobites, ostracods, and decapods, most arthropod exoskeletons are weakly mineralized and contain abundant organic material. Multielement construction and ecdysis (shedding of exoskeleton during life) introduces the problem of disarticulation and transportation. Therefore, preservation of most arthropods as body fossils requires exceptional circumstances such as rapid burial or anoxic conditions.
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Landing, Ed, e Stephen R. Westrop. "Upper Lower Cambrian depositional sequence in Avalonian New Brunswick". Canadian Journal of Earth Sciences 33, n.º 3 (1 de março de 1996): 404–17. http://dx.doi.org/10.1139/e96-030.
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The Hanford Brook Formation (emended) is a thin (up to 42+ m), upper Lower Cambrian depositional sequence that is unconformably bounded by the lower Lower Cambrian (Random Formation) and the middle Middle Cambrian (Fossil Brook Member of the Chamberlain's Brook Formation). These stratigraphic relationships of the trilobite-bearing Hanford Brook Formation indicate deposition on the Avalonian marginal platform in the Saint John, New Brunswick, region and provide more evidence for a uniform, latest Precambrian–Cambrian epeirogenic history and cover sequence in Avalon. The Hanford Brook Formation is a deepening–shoaling sequence with (i) lower, transgressive sandstone deposited in episodically high-energy environments (St. Martins Member, new); (ii) highstand–regressive, dysaerobic mudstone – fine-grained sandstone with volcanic ashes (Somerset Street Member, new); and (iii) upper, regressive, planar and hummocky cross-stratified sandstone (Long Island Member, new). Trilobites are common in the distal Somerset Street Member, and ostracodes and brachiopods dominate the St. Martins and Long Island members. Condensation of the St. Martins Member and absence of the Long Island Member where the Random Formation and Fossil Brook Member are thinnest suggest onlap of the Hanford Brook and pronounced, sub-Middle Cambrian erosion across epeirogenically active blocks in southern New Brunswick.
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Li, Xing, e Mary Droser. "The development of Early Paleozoic shell concentrations: evidence from the Cambrian and Ordovician of the Great Basin". Paleontological Society Special Publications 6 (1992): 183. http://dx.doi.org/10.1017/s2475262200007437.
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Shell concentrations have constituted an important and conspicuous part of the stratigraphic record since the Early Cambrian. The paleontological and stratigraphic significance of shell beds is well understood, primarily from Mesozoic and Cenozoic examples. Lower Paleozoic fossil concentrations, however, have not received much attention. The Cambrian and Ordovician evolutionary radiations were two of the most significant events in the history of life and established the Cambrian and Paleozoic faunas respectively. In order to determine the effect of these radiations on the development of fossil accumulations, a systematic study of early Paleozoic shell beds was conducted in the Great Basin areas of California, Nevada, and Utah.In order to minimize taphonomic variations in original chemical and physical conditions, shell beds were compared from strata deposited in similar depositional environments from similar tectonic settings. Preliminary analysis of the shell beds from relatively pure carbonate facies and mixed carbonate and siliciclastic facies shows: 1) that shell concentrations became a significant stratigraphic feature in the later Early Cambrian; 2) the thickness and lateral extent of the shell beds increase from Early Cambrian to Middle Ordovician; 3) the abundance and internal complexity of the shell beds increase from Early Cambrian to Middle Ordovician; and 4) the Cambrian and Early Ordovician shell beds are primarily, if not exclusively, dominated by trilobites whereas the Middle Ordovician shell beds are dominated by brachiopods and ostracodes.These data show a temporal trend in the development of the early Paleozoic shell beds. The nature of the Cambrian and Ordovician shell beds differs qualitatively and quantitatively. There is an increase in physical scale, abundance, and internal complexity through time. The thickness and abundance of the trilobite beds increase through the Cambrian. Interestingly, although trilobites were still diverse and abundant, they did not commonly generate thick trilobite beds after the Late Cambrian. The early Middle Ordovician is a critical time in the development of early Paleozoic shell beds. A variety of monotaxic and polytaxic shell beds, including 6m thick composite beds, first appeared at this time. While the brachiopods and ostracodes generate laterally extensive, commonly monotaxic, shell beds, the gastropods and bryozoans only formed lenticular concentrations.
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Schoenemann, Brigitte, e Euan N. K. Clarkson. "Vision in fossilised eyes". Earth and Environmental Science Transactions of the Royal Society of Edinburgh 106, n.º 4 (dezembro de 2015): 209–20. http://dx.doi.org/10.1017/s1755691016000232.
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ABSTRACTThis paper presents a review of recent developments in the study of vision in fossil arthropods, beginning with a discussion of the origin of visual systems. A report of the eyes of Cambrian arthropods from different Lagerstätten, especially the compound and median arthropod eyes from the Chengjiang fauna of China, is given. Reference is made also to compound eyes from the lower Cambrian Emu Bay Shale fauna of Australia and the Sirius Passet fauna of Greenland; also to the three-dimensionally preserved ‘Orsten’ fauna of Sweden. An understanding of how these eyes functioned is possible by reference to living arthropods and by using physical tools developed by physiologists. The eyes of trilobites (lower Cambrian to Upper Permian) are often very well preserved, and the structure and physiology of their calcite lenses, and the eye as a whole, are summarised here, based upon recent literature. Two main kinds of trilobite eyes have been long known. Firstly, there is the holochroal type, in which the lenses are usually numerous, small and closely packed together; this represents the ancestral kind, first found in lowermost Cambrian trilobites. The second type is the schizochroal eye, in which the lenses are relatively much larger and each is separated from its neighbours. Such eyes are confined to the single suborder Phacopina (Lower Ordovician to Upper Devonian). This visual system has no real equivalents in the animal kingdom. In this present paper, the origin of schizochroal eyes, by paedomorphosis from holochroal precursors, is reviewed, together with subsequent evolutionary transitions in the Early Ordovician. A summary of new work on the structure and mineralogy of phacopid lenses is presented, as is a discussion of the recent discovery of sublensar sensory structures in Devonian phacopids, which has opened up new dimensions in the study of trilobite vision.
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Daley, Allison C., Jonathan B. Antcliffe, Harriet B. Drage e Stephen Pates. "Early fossil record of Euarthropoda and the Cambrian Explosion". Proceedings of the National Academy of Sciences 115, n.º 21 (21 de maio de 2018): 5323–31. http://dx.doi.org/10.1073/pnas.1719962115.
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Euarthropoda is one of the best-preserved fossil animal groups and has been the most diverse animal phylum for over 500 million years. Fossil Konservat-Lagerstätten, such as Burgess Shale-type deposits (BSTs), show the evolution of the euarthropod stem lineage during the Cambrian from 518 million years ago (Ma). The stem lineage includes nonbiomineralized groups, such as Radiodonta (e.g., Anomalocaris) that provide insight into the step-by-step construction of euarthropod morphology, including the exoskeleton, biramous limbs, segmentation, and cephalic structures. Trilobites are crown group euarthropods that appear in the fossil record at 521 Ma, before the stem lineage fossils, implying a ghost lineage that needs to be constrained. These constraints come from the trace fossil record, which show the first evidence for total group Euarthropoda (e.g., Cruziana, Rusophycus) at around 537 Ma. A deep Precambrian root to the euarthropod evolutionary lineage is disproven by a comparison of Ediacaran and Cambrian lagerstätten. BSTs from the latest Ediacaran Period (e.g., Miaohe biota, 550 Ma) are abundantly fossiliferous with algae but completely lack animals, which are also missing from other Ediacaran windows, such as phosphate deposits (e.g., Doushantuo, 560 Ma). This constrains the appearance of the euarthropod stem lineage to no older than 550 Ma. While each of the major types of fossil evidence (BSTs, trace fossils, and biomineralized preservation) have their limitations and are incomplete in different ways, when taken together they allow a coherent picture to emerge of the origin and subsequent radiation of total group Euarthropoda during the Cambrian.
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Foote, Mike, e David M. Raup. "Fossil preservation and the stratigraphic ranges of taxa". Paleobiology 22, n.º 2 (1996): 121–40. http://dx.doi.org/10.1017/s0094837300016134.
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The incompleteness of the fossil record hinders the inference of evolutionary rates and patterns. Here, we derive relationships among true taxonomic durations, preservation probability, and observed taxonomic ranges. We use these relationships to estimate original distributions of taxonomic durations, preservation probability, and completeness (proportion of taxa preserved), given only the observed ranges. No data on occurrences within the ranges of taxa are required. When preservation is random and the original distribution of durations is exponential, the inference of durations, preservability, and completeness is exact. However, reasonable approximations are possible given non-exponential duration distributions and temporal and taxonomic variation in preservability. Thus, the approaches we describe have great potential in studies of taphonomy, evolutionary rates and patterns, and genealogy.Analyses of Upper Cambrian-Lower Ordovician trilobite species, Paleozoic crinoid genera, Jurassic bivalve species, and Cenozoic mammal species yield the following results: (1) The preservation probability inferred from stratigraphic ranges alone agrees with that inferred from the analysis of stratigraphic gaps when data on the latter are available. (2) Whereas median durations based on simple tabulations of observed ranges are biased by stratigraphic resolution, our estimates of median duration, extinction rate, and completeness are not biased. (3) The shorter geologic ranges of mammalian species relative to those of bivalves cannot be attributed to a difference in preservation potential. However, we cannot rule out the contribution of taxonomic practice to this difference. (4) In the groups studied, completeness (proportion of species [trilobites, bivalves, mammals] or genera [crinoids] preserved) ranges from 60% to 90%. The higher estimates of completeness at smaller geographic scales support previous suggestions that the incompleteness of the fossil record reflects loss of fossiliferous rock more than failure of species to enter the fossil record in the first place.
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Edgecombe, Gregory D. "Arthropod Origins: Integrating Paleontological and Molecular Evidence". Annual Review of Ecology, Evolution, and Systematics 51, n.º 1 (2 de novembro de 2020): 1–25. http://dx.doi.org/10.1146/annurev-ecolsys-011720-124437.
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Phylogenomics underpins a stable and mostly well-resolved hypothesis for the interrelationships of extant arthropods. Exceptionally preserved fossils are integrated into this framework by coding their morphological characters, as exemplified by total-evidence dating approaches that treat fossils as dated tips in analyses numerically dominated by molecular data. Cambrian fossils inform on the sequence of character acquisition in the arthropod stem group and in the stems of its main extant clades. The arthropod head problem incorporates unique appendage combinations and remains of the nervous system in fossils into a scheme mostly based on neuroanatomy and Hox expression domains for extant forms. Molecular estimates of arthropod origins in the Cryogenian or Ediacaran predate a coherent picture from the arthropod fossil record, which commences as trace fossils in the earliest Cambrian. Probabilistic morphological clock analysis of trilobites, which exemplify the earliest arthropod body fossils, supports a Cambrian origin, without the need to posit an unfossilized Ediacaran history.
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Fletcher, Terence P., e Desmond H. Collins. "The Burgess Shale and associated Cambrian formations west of the Fossil Gully Fault Zone on Mount Stephen, British Columbia". Canadian Journal of Earth Sciences 40, n.º 12 (1 de dezembro de 2003): 1823–38. http://dx.doi.org/10.1139/e03-057.
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West of the Fossil Gully Fault Zone on Mount Stephen, the three lowest members only of the Burgess Shale Formation are preserved: the Kicking Horse Shale, the Yoho River Limestone, and the Campsite Cliff Shale. The formation rests unconformably upon the Takakkaw Tongue Formation, whose dark basinal limestones conformably overlie paler shelf-like limestones of the Mount Whyte Formation. Mapping has resolved a long-standing problem and shown that the stratigraphical position of the famous Mount Stephen Trilobite Beds lies within the Campsite Cliff Shale. It has also revealed some of the complexities of the Fossil Gully Fault Zone, among which different periods and directions of component fault movements are indicated. Faunal evidence shows that the PlagiuraKochaspis to Albertella and Albertella to Glossopleura zonal boundaries lie within the Takakkaw Tongue sequence. Within the Burgess Shale, three distinct soft-bodied communities occur at different stratigraphical levels on this mountain slope. The oldest, characterized by the arthropod Alalcomenaeus and chelicerate Sanctacaris, occurs low in the Kicking Horse Shale Member and is best known from Collins Quarry. The others lie within the Campsite Cliff Shale Member. The Trilobite Beds, characterized by claws of the dinocarid Anomalocaris and moults of the trilobite Ogygopsis klotzi, onlap the sloping top of a proximal bench facies of the Yoho River Limestone Member close to the Cathedral Escarpment. Slightly older and farther out in the basin are beds characterized by the dinocarid Laggania and a tulip-like animal related to Dinomischus, excavated about 12 m above the top of a thin distal wedge facies of the Yoho River Limestone at the S7 site. Among the illustrated trilobites, a new corynexochine from the Campsite Cliff Shale Member is figured.
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McKinney, Frank K. "The Age of Things Found in the Earth". Paleontological Society Special Publications 11 (2002): 31–46. http://dx.doi.org/10.1017/s2475262200009801.
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One of my favorite places to collect fossils is a steep, high railway cut in a rural part of southern Kentucky, where a ridge made of limestone sat right across the most efficient route the railway could take. When that cut was first made, professional paleontologists and amateur fossil collectors came by to have a look at the newly exposed rock; but although the fossils could be seen, we could get hardly anything out because they were almost all too firmly locked within the rock. Within just a couple of years, weathering had caused some of the weaker, clay-rich layers to break down a little, yielding loads of fossils. The rock around the fossils broke apart into small grains, and the fossils themselves, skeletal remains of marine animals, could be picked up by the hundreds of thousands: crinoids, blastoids, brachiopods, screw-shaped parts of bryozoans, trilobites, individual cone-shaped corals, strange conical snails, even rare starfish.
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McKinney, Frank K. "The Age of Things Found in the Earth". Paleontological Society Special Publications 9 (1999): 39–58. http://dx.doi.org/10.1017/s2475262200014003.
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One of my favorite places from which to collect fossils is a steep, high railway cut in a rural part of southern Kentucky, where a ridge made of limestone sat right across the most efficient route the railway could take. When that cut was first made, professional paleontologists and amateur fossil collectors came by to have a look at the newly exposed rock; but although the fossils could be seen, we could hardly get anything out because they were almost all too firmly locked within the rock. Within just a couple of years, weathering had caused some of the weaker, clay-rich layers to break down a little, yielding loads of fossils. The rock around the fossils broke apart into small grains, and the fossils themselves, skeletal remains of marine animals, could be picked up by the hundreds of thousands: crinoids, blastoids, brachiopods, screw-shaped parts of bryozoans, trilobites, individual cone-shaped corals, strange conical snails, even rare starfish.
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HUGHES, NIGEL C., SHANCHI PENG, O. N. BHARGAVA, A. D. AHLUWALIA, SANDEEP WALIA, PAUL M. MYROW e S. K. PARCHA. "Cambrian biostratigraphy of the Tal Group, Lesser Himalaya, India, and early Tsanglangpuan (late early Cambrian) trilobites from the Nigali Dhar syncline". Geological Magazine 142, n.º 1 (janeiro de 2005): 57–80. http://dx.doi.org/10.1017/s0016756804000366.
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Precise biostratigraphic constraints on the age of the Tal Group are restricted to (1) a basal level correlative with the Anabarites trisulcatus–Protohertzina anabarica Assemblage Zone of southwest China, (2) a level near the boundary of the lower and upper parts of the Tal Group correlative with the early Tsanglangpuan Stage (Drepanuroides Zone), and (3) an interval low in the upper part of the Tal Group correlative with later in the Tsanglangpuan Stage (Palaeolenus Zone). These correlations are based on small shelly fossil and trilobite taxa. Other chronostratigraphic constraints include the marked negative δ13C isotopic excursion coincident with the transition from the Krol Group to the Tal Group. This excursion is used as a proxy for the Precambrian–Cambrian boundary in several sections worldwide and, if applied to the Lesser Himalaya, indicates that the boundary is at or just above the base of the Tal Group. The upper parts of the Tal Group may be of middle or late Cambrian age and might form proximal equivalents of sections in the Zanskar–Spiti region of the Tethyan Himalaya. Both faunal content and lithological succession are comparable to southwest China, furthering recent arguments for close geographic proximity between the Himalaya and the Yangtze block during late Neoproterozoic and early Cambrian time. Trilobites from the uppermost parts of the Sankholi Formation from the Nigali Dhar syncline are described and referred to three taxa, one of which, Drepanopyge gopeni, is a new species. They are the oldest trilobites yet described from the Himalaya.
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Abe, Francine R., e Bruce S. Lieberman. "Quantifying morphological change during an evolutionary radiation of Devonian trilobites". Paleobiology 38, n.º 2 (2012): 292–307. http://dx.doi.org/10.1666/10047.1.
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The fossil record provides an important source of data on adaptive radiations, and indeed some of the earliest theoretical insights on the nature of these radiations were made by paleontologists. Here we focus on the diverse DevonianMetacryphaeusgroup calmoniid trilobites, known from the Malvinokaffric Realm, which have been considered a classic example of an adaptive radiation preserved in the fossil record. We use a geometric morphometric analysis in conjunction with phylogenetic and biogeographic patterns and data on speciation rates. Using ancestral character state reconstruction during speciation events, we quantify patterns of morphological change in order to assess the role ecological and geographical factors may have played in mediating this radiation. We found no significant differences between the amount of morphological change that occurred during speciation events when ancestors and descendants were in the same area as opposed to when they occupied different areas. Further, the magnitude of morphological divergence did not change through time or with cladogenetic rank. These patterns, in conjunction with the fact that the radiation occurs in a geographically heterogeneous region subjected to repeated episodes of sea-level rise and fall, suggest that at the macroevolutionary scale this radiation may have been motivated more by phenomena that facilitated geographic isolation than by competition.
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Crimes, T. P., e Jiang Zhiwen. "Trace fossils from the Precambrian–Cambrian boundary candidate at Meishucun, Jinning, Yunnan, China". Geological Magazine 123, n.º 6 (novembro de 1986): 641–49. http://dx.doi.org/10.1017/s0016756800024158.
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AbstractThe Precambrian–Cambrian boundary candidate section at Meishucun, China, has yielded trace fossils which are abundant at some horizons. The earliest occur in Unit 3 of the Zhongyicun Member approximately 8 m above the lower selected stratotype reference point for the boundary and includeArenicolitessp.,Asteriacitessp.,Neonereites biserialis, N. uniserialisandSellaulichnus meishacunensis. The next trace-fossil-bearing horizon is in Unit 6 of the Zhongyicun Member whereCochlichnussp.,Monomorphichnussp.,Neonereites biserialisandN. uniserialisoccur. Immediately above, in Unit 7, areCruzianasp.,Didymaulichnus miettensis, Monomorphichnussp. andRusophycussp. In the Badaowan Member at the top of the section there areDidymaulichnussp. andTaphrhelminthopsis circularisin Unit 9,Arenicolitessp.,Diplocraterionsp.,Gordia molassica, Skolithossp. andT. circularisin Unit 11, andGordia meandria, ?Plagiogmussp.,Skolithossp. andT. circularisin Unit 12.Comparison of this trace-fossil distribution with that in key Precambrian–Cambrian boundary sections in other countries indicates that the ranges of a few trace fossils cross the boundary (e.g.Didymaulichnus, Neonereites, Planolites) but most appear only in the Cambrian. Different ichnogenera seem to appear at various levels above the boundary.ArenicolitesandAsteriacitesare among the first, whileTaphrhelminthopsis circularisis only encountered higher in all sequences. Some have only been recorded at much higher levels and relatively close to the first appearance of trilobites (e.g.Cruziana, Diplocraterion, Rusophycus). This suggests that the first appearance of specific trace fossils or groups of trace fossils may be valuable for locating the boundary in some sections and for correlating late Precambrian and early Cambrian strata.
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Webster, Mark, e Nigel C. Hughes. "Compaction-related deformation in Cambrian olenelloid trilobites and its implications for fossil morphometry". Journal of Paleontology 73, n.º 2 (março de 1999): 355–71. http://dx.doi.org/10.1017/s0022336000027827.
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Morphometric analyses of silicified and nonsilicified (preserved in shale) specimens of the olenelloid trilobites Olenellus (Olenellus) gilberti Meek (in White, 1874) and Nephrolenellus geniculatus Palmer, 1998, from the Lower Cambrian C-Shale Member of the Pioche Formation show that even well-preserved specimens in shales have undergone significant changes in lateral as well as vertical dimensions as a result of compaction. Analyses of cephalic landmarks show that in both species compaction causes posteriordirected collapse of the anterior lobe of the glabella, adaxial deformation of the ocular lobes, and abaxial and anterior splaying of genal regions. These shape changes are explicable in terms of observed exoskeletal fracture patterns. Landmarks show an increase in scatter around their ontogenetic trajectories that is generally proportional to the degree of lateral shift each landmark has undergone. Interspecific differences in compactional response may depend on the relative convexity of the cephalon. Olenellus (Olenellus) gilberti is a low-convexity species and shows marked lateral shape change, particularly in the genal region. Nephrolenellus geniculatus is more convex and shows less severe lateral shape change. Landmarks of both species exhibit an average trebling of the degree of scatter around their average ontogenetic trajectories in compacted samples. Because even well-preserved specimens in shales differ in shape from their precompactional appearance, results of morphometric studies utilizing metric distances between landmarks in trilobites where compaction can be detected must be interpreted with caution.
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Brasier, Martin D., Mordeckai Magaritz, Richard Corfield, Luo Huilin, Wu Xiche, Ouyang Lin, Jiang Zhiwen, B. Hamdi, He Tinggui e A. G. Fraser. "The carbon- and oxygen-isotope record of the Precambrian–Cambrian boundary interval in China and Iran and their correlation". Geological Magazine 127, n.º 4 (julho de 1990): 319–32. http://dx.doi.org/10.1017/s0016756800014886.
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AbstractThe fossiliferous section at Meishucun of Yunnan, China, is a candidate stratotype section for the Precambrian–Cambrian boundary. Early diagenetic dolomites and phosphorites have been sampled across the boundary interval here, and in the correlated section at Maidiping in Sichuanand Valiabad in Iran, for comparison of their carbon and oxygen isotopes. This is the first such study that is calibrated by biostratigraphy in the interval from the earliest (pre-Tommotian) skeletal fossils to trilobites. Although negative oxygen isotopes indicate a diagenetic signal in the Zhongyicun Member and basal Badaowan Member phosphorites, two carbon-isotope cycles are clearly present and can be correlated in dolomitic rocks between the two sections. The first appearance datum (FAD) of the earliest skeletal assemblage (zone I, Marker A), FAD of diverse micromolluscs (zone II, Marker B) and FAD of Chinese trilobites (zones IV, V) and Marker C appear at similar points on the carbon-isotope curve in the two Chinese sections. Integrated carbon-isotope and early skeletal fossil biostratigraphy is shown to have the potential to correlate further afield, with sections in Iran, as well as with India, Siberia, Morocco and Australia. We suggest that a distinctive positive excursion provides a global marker for the interval between Marker B and C in China and just below the Tommotian Stage of Siberia.