The upper cambrian of the chopko river section,norilsk region,northwestern siberian platform: Stratigraphy and trilobites

The section that serves as a reference section for the upper Middle-Upper Cambrian in the Norilsk Region is studied; regularities in the distribution and succession of lithological varieties of rocks and facial types are established; and intervals representing settings at the base of the outer shelf slope, on the upper shelf slope, and on the shallow-water carbonate platform are recognized. Based on the study of trilobites, ten biostratigraphic units are recognized. Thirty-seven trilobite species are described. The biostratigraphic scheme developed by the authors is correlated with the main world sections.     

Trilobites of the suborder Eodiscina from the Lower Cambrian of the northeastern Siberian platform (Khorbosuonka River section)

Trilobites of the suborder Eodiscina from the Lower Cambrian section of the Khorbosuonka River (Siberian Platform, Olenek Uplift) are studied. The stratigraphic distribution of these forms in the section is shown Two new species, Hebediscus sublongus sp. nov. and Korobovia khorbosuonica sp. nov., are described. This is the first occurrence of the genus Korobovia on the Siberian Platform. The new record provides additional data on morphology and expands the paleogeographic range of the genera represented by the newly described species.     

The biostratigraphic and palaeoenvironmental significance of Lower Cambrian (Botomian) trilobites from the Ak-Kaya section of the Altai Mountains (southern Siberia,Russia)

The presence of one of the oldest records of polycystine Radiolaria in the Lower Cambrian sedimentary sequence of the Ak-Kaya section (Gorny Altai) requires a biostratigraphic dating. The trilobites found recently a few tens of meters below the radiolarian-bearing level belong to Calodiscus resimus Repina, Serrodiscus fossuliferus Repina and Alacephalus aff. contortus Repina; they suggest that this part of the Shashkunar Formation can be correlated with the lower part of the Botomian stage. The absence of eyes in the two former species suggests a mode of life buried in the fine pelagic sediments. Indications of the presence of a strongly developed musculature on the third species point to a palaeoenvironment characterized by a relatively high hydrodynamic regime.     

Early and Mid Cambrian trilobites from the outer-shelf deposits of Nevada and California, USA

A latest Early Cambrian and earliest Mid Cambrian polymeroid trilobite fauna, consisting of 16 genera and 25 species, is reported from the peritidal deposits of the Mule Spring Limestone and outer-shelf deposits of the Emigrant and Monola formations of Nevada and California. The Mid Cambrian fauna includes a new genus, Tonopahella , and four new species, T. goldfieldensis , Oryctocephalus americanus , Onchocephalites claytonensis , and Syspacephalus variosus . The peri-Gondwana species Oryctocephalus orientalis , Oryctocephalites runcinatus , and Paraantagmus latus are recorded in Laurentia for the first time.     

New Cambrian lobopods and chaetognaths of the Siberian Platform

The association of isolated remains of lobopods with a netlike structure, including plates of Microdictyon rozanovi sp. nov. and sclerites with spinelike process of Onychomicrodictyon spiniferum gen. et sp. nov., as well as saberlike sclerites of Protohertzina yudomica sp. nov. interpreted as grasping spines of chaetognaths, is described from the middle part of the Inikan Formation of the Toyonian Stage of the Lower Cambrian (Lermontovia dzevanovskii Zone). The diagnoses and species composition of the genera Microdictyon and Protohertzina are refined.     

Two middle Cambrian diceratocephalid trilobites, Cyclolorenzella convexa and Diceratocephalus cornutus, from Korea: development and functional morphology

Park, T.-Y. & Choi, D.K. 2010: Two middle Cambrian diceratocephalid trilobites, Cyclolorenzella convexa and Diceratocephalus cornutus , from Korea: development and functional morphology. Lethaia , Vol. 43, pp. 73–87.
Silicified sclerites of the latest middle Cambrian trilobites, Cyclolorenzella convexa and Diceratocephalus cornutus , have been recovered from the Sesong Formation, Korea. Their morphological similarity and stratigraphic occurrences suggest that D. cornutus is a descendant of C. convexa . The ontogenies of both trilobites demonstrate that a pair of long frontal horns in the cephalon of D. cornutus is an evolutionarily novel structure. It is inferred that redeployment of some pre-existing regulatory gene played a significant role in constructing the frontal horns of D. cornutus . The frontal horns may have been a defensive structure to deter predators. The facial suture of D. cornutus , which extends onto the frontal horns and splits them into the dorsal and ventral halves, was a solution to enable easier forward egression during ecdysis. □ Functional morphology, Korea, Middle Cambrian, ontogeny, trilobites .     

Middle Cambrian trilobites from the vicinity of Dolgii Mys Mountain (Khakassia,Batenevsky Ridge)

The trilobites Oryctocarella sibirica (Tomash.) and Lancastria plana (Tomash.) from the basal Middle Cambrian in the vicinity of Dolgii Mys Mountain (Batenevsky Ridge, Khakassia) are described. These trilobites were previously described by V.D. Tomashpolskaya, but the original collection was subsequently lost. Repeated finds allowed a detailed study of these species. It is established that relatively small specimens of Oryctocarella sibirica are more similar to Ovatoryctocara granulata. In addition, these species have much in common with the genus Arthricocephalus in morphological characters. New material of Lancastria plana is described in detail. These trilobites were originally assigned to the genus Paraoryctocephalops, although according to the data of Blacker and Peel (1997), they should be transfered to the genus Lancastria.     

Spinitheca gen. nov.—A new orthothecimorph hyolith genus from the Lower Cambrian of the Siberian platform

The study of the morphology of orthothecimorph hyoliths from the Atdabanian (Lower Cambrian) of the Siberian Platform allowed the recognition of the new genus and species Spinitheca sysoievi gen. and sp. nov.     

The Lower Cambrian trilobites from the Görlitz Synclinorium (Germany) — review and new results

PalZ - The present article reviews recent advances in the knowledge of the Lower Cambrian trilobite faunas of the Görlitz area, Saxonia, eastern Germany. New additions to the fauna...     

How species longevity, intraspecific morphological variation, and geographic range size are related: a comparison using late Cambrian trilobites

Phenotypic variation is fundamental to evolutionary change. Variation not only evinces the connectivity of populations but it is also associated with the adaptability and evolvability of taxa. Despite the potential importance of morphological variation in structuring evolutionary patterns, little is known about how relative differences in intraspecific morphological variation and its geographic structure are linked to differences in species longevity. This study offers a novel combination of analyses that reveal the quantitative relationships among intraspecific variation, geographic range size and duration in the fossil record using late Cambrian trilobites. Results show that geographic range size and duration are positively correlated. Surprisingly, longer lived species tend to have less intraspecific variation. Phylogenetic effects were also explored and found not to determine the association between these variables. However, the distribution of geographic range sizes shows strong phylogenetic signal. In light of previous work, one possible explanation for these results is that species with shorter durations have comparatively higher rates of morphological evolution, reflected in higher phenotypic variation overall.     

Vendian-Cambrian tidal and sabkha facies of the Siberian platform

Summary The Vendian-Cambrian interval on the Siberian Platform contains thick carbonate and evaporite sequences formed in extensive shallow-water basins. The carbonate sequences are characterized by a cyclic composition. Finegrained dolomites, undulated algal dolomites, flat pebble conglomerates, storm breccias and solution-collapse breccias form the base of each cycle. These rocks are characterized by an increased clay content which can be high enough to form argillites. Short sedimentation breaks reflected by mudcracks or silicification horizons are present as well as small cross-bedded tidal channels. Peloidal grainstones with algal overgrowth dominate in the central parts of the cycles. These members are often recrystallized and dolomitized. Micritic dolomites, undulous laminated dolomites, storm breccias and columnar stromatolites with abundant mud cracks form the upper members of the cycles. These sequences are free of clay but contain abundant anhydrite crystals and nodules. In the uppermost parts of some cycles massive layered anhydrite beds are present. The cycles vary in thickness, but usually they are between 15 and 20 m thick. The lower cycle member documents extreme shallow-water deposits. They formed in tidal and partially also supratidal zones not far from the mainland, from where fine clayey material was washed in. These parts of the sequence reflect a slow transgression. The central member of a cycle was deposited during the maximal transgression in a shallow basin with normal salinity and rather active hydrodynamics. Sedimentation of the upper part of the cycles reflects a regression stage (tidal and especially sabkha environments). The final layered anhydrite beds formed most probably in relict lakes on the sabkha plain. During sea-level falls some sequences of the central parts of the cycles were subaerially exposed and underwent partial dolomitization. The Vendian-Cambrian sabkhas are partly comparable with their recent counterparts.     

Trilobites from the lower and lowermost middle Cambrian of the Kiya River reference section (Kuznetsk Alatau)

The Kiya River reference section is characterized by trilohites confined to units X–XV of the Lower Cambrian Usa Formation and to the base of the lowermost Middle Cambrian Berikul Formation. Trilobites are represented by 130 species assigned to 77 genera. The given paper describes 38 species belonging to 27 genera. 16 species, 2 genera and one subfamily are new. All of them occur in the Usa Formation and in the Lower Cambrian pebbles of the Berikul Formation. Biostratigraphic analysis shows that the trilobite fauna contains characteristic trilobite assemblage elements of the Lower Cambrian regional stages in the Altay-Sayan Fold Belt, i.e. the Kiya and Kameshki regional stages (Atdabanian Stage), the Sanashtykgol regional stage (Botomian Stage), the Obruchev regional stage (Toyonian Stage). Table I shows trilobite species composition and vertical distribution in the reference section.     

Revision of the Early and Middle Cambrian Acrotretids (Brachiopoda,Linguliformea) from the Siberian Platform

Paleontological Journal - This paper continues our revision of Yu.L. Pelman’s collection of the linguliformean brachiopods and of our own material from the Early–Middle Cambrian of the...     

Probable predation on Upper Cambrian trilobites and its relevance for the extinction of soft-bodied Burgess Shale-type animals

The lower Rabbitkettle Formation of northwestern Canada is a monofacial Upper Cambrian unit of variably calcareous, argillaceous siltstone and fine-grained sandstone with rare bioclastic grainstone, deposited on a gentle slope below fair-weather wave base with no discernible fluctuation in water depth. The trilobite fauna is a mixture of pandemic agnostoids and Laurentian polymeroids, including protaspides and meraspides, and individuals are disarticulated, non-abraded and mostly oriented convex-upward. Bioclasts are interpreted as in situ elements affected only by weak bottom currents and storm-induced turbulence. A major proportion of the larger (≥5 mm across) polymeroid cranidia and pygidia in the lower part (Marjuman) of the formation are broken; large thoracic segments are often broken at the axial furrow and some broken free cheeks occur, but essentially no broken agnostoids or hypostomes were observed. Trilobites are not broken in upper beds (Steptoean), above the base of the Glyptagnostus retculatus Zone. Physical breakage cannot be dismissed entirely, but most damage is interpreted to be due to size-selective predation, possibly through lethal blows similar to those delivered by some extant stomatopod crustaceans. A possible culprit may be an animal akin to Yohoia , known from the Middle Cambrian Burgess Shale. The distribution of attacked trilobites serves as a proxy for the presence and disappearance of soft-bodied carnivores. In the Rabbitkettle Formation, it suggests that Burgess Shale-type animals may have persisted into the Late Cambrian but suffered extinction at the Marjuman-Steptoean 'biomere' event when most trilobite species vanished.     

Gut evolution in early Cambrian trilobites and the origin of predation on infaunal macroinvertebrates: evidence from muscle scars in Mesolenellus

Trilobites are particularly common Cambrian fossils, but their trophic impact on the rapidly evolving marine ecosystems of that time is difficult to assess, due to uncertainties on how diverse their feeding habits truly were. Gut anatomy might help to constrain inferences on trilobite feeding ecology, but preservation of digestive organs is exceedingly rare. Muscle scars on the glabella, known as ‘frontal auxiliary impressions’ (FAIs), have been interpreted as evidence of the evolution of a pouch‐like organ with powerful extrinsic muscles (i.e. a crop) in some trilobites. Here we describe FAIs in Mesolenellus hyperboreus from Cambrian Stage 4 strata of North Greenland, which represents the oldest example of such structures and their first report in the Suborder Olenellina. Mesolenellus FAIs suggest that the crop in trilobites was clearly differentiated from the rest of the digestive tract, and essentially located under a hypertrophied glabellar frontal lobe. Reviews of the digestive anatomy of trilobite sister‐taxa and the glabellar morphology of the oldest‐known trilobites suggest that the gut of the trilobite ancestor was an essentially simple tract (i.e. no well‐differentiated crop) flanked laterally by numerous midgut glands. A crop first evolved in the Cambrian in groups like olenelloids and (later) paradoxidoids. Using ichnological evidence, we hypothesize that the emergence of olenelloids yields evidence for the evolution of predatory inclinations in a group of arthropods originally dominated by surface‐deposit‐feeders. By allowing the exploitation of a rapidly developing food source, infaunal animals, the diversification of feeding strategies in trilobites might partially explain their unparalleled evolutionary success.     

Integrated biostratigraphy and carbon isotopes from the Cambrian Tangwangzhai section,North China

The Tangwangzhai section, western Shandong Province, North China, the type section for the Cambrian Kushan and Chaomitian formations, yielded a diverse and relatively well-preserved conodont fauna, in which we recognize the Westergaardodina orygma, Westergaardodina matsushitai, Muellerodus? erectus, and Westergaardodina aff. fossa–Prooneotodus rotundatus zones of the North China conodont zonation. The Tangwangzhai conodont succession can be correlated not only with the polymerid trilobites occurring in the section but also with the conodont zones established for South China. The first occurrence of Furnishina longibasis and Furnishina quadrata in the upper part of the Westergaardodina matsushitai Zone allows the recognition of the base of the Paibian Stage and Furongian Series in the upper part of the Kushan Formation. The base of the Jiangshanian Stage, in the uppermost Muellerodus? erectus Zone, can be recognized by the presence of Westergaardodina cf. calix close to the base of the Chaomitian Formation. Chemostratigraphic analyses of the Tangwangzhai section show the onset of a positive carbon isotope excursion, referred to the SPICE event, in the upper part of the Kushan Formation at a level corresponding to the first occurrence of F. longibasis and F. quadrata. The base of the Jiangshanian Stage in the section is close to the demise of the SPICE positive excursion.