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41.
The exceptionally preserved Early Cambrian stem rhynchonelliform brachiopod Longtancunella and its implications 总被引:1,自引:0,他引:1
ZHIFEI ZHANG LARS E. HOLMER QIANG OU JIAN HAN DEGAN SHU 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2011,44(4):490-495
Zhang, Z., Holmer, L. E., Ou, Q., Han, J. & Shu, D. 2011: The exceptionally preserved Early Cambrian stem rhynchonelliform brachiopod Longtancunella and its implications. Lethaia, Vol. 44, pp. 490–495. The extraordinary Longtancunella chengjiangensis is one of the rarest and most problematic brachiopods from the Early Cambrian Chengjiang Lagerstätte, where it occurs in unique gregarious clusters with up to ten individuals attached by their stout pedicles to a single hard exoskeleton. Although the general morphology and soft anatomy of Longtancunella is available, its taxonomy and systematic placement within the Brachiopoda remains problematic. New exceptionally preserved specimens show that the pedicle of Longtancunella cannot be considered homologous with the pedicles in crown Rhynchonelliformea or Linguliformea. The pedicle of Longtancunella emerges from a ventral umbonal foramen with a rounded plate that must have been secreted by specialized ventral mantle epithelium. The rounded plate is proposed to be a homologue to the colleplax – a plate covering the umbonal foramen, which is otherwise known from the extinct rhynchonelliform chileates. Longtancunella is proposed to represent a soft‐shelled stem rhynchonelliform brachiopod with chileate features, thus demonstrating for the first time that the chileate‐like umbonal perforation functions as a pedicle opening. The unusual preservation of the annulated chileate‐like holdfast supports the view that it may have been secreted as stacks of chitinous or even mineralized ‘attachment pads’. Together with having a spirolophous lophophore and U‐shaped gut, Longtancunella displays a unique mixture of linguliform and rhynchonelliform characters that throw new light on an early stage of rhynchonelliform diversification. □Brachiopods, Cambrian, Chengjiang Lagerstätte, Chileata, colleplax, pedicle. 相似文献
42.
CHRISTIAN B. SKOVSTED GLENN A. BROCK TIMOTHY P. TOPPER JOHN R. PATERSON LARS E. HOLMER 《Palaeontology》2011,54(2):253-286
Abstract: Large collections of Eccentrotheca helenia sp. nov. from the lower Cambrian Wilkawillina and Ajax limestones in the Arrowie Basin, South Australia, contain abundant low, cap‐shaped and high, laterally compressed isolated sclerites in addition to partially articulated tubular specimens. The scleritome of Eccentrotheca helenia sp. nov. is fully described for the first time and shown to be formed by ontogenetic fusion of sclerites into successively stacked sclerite rings, forming a larger, tubular structure. The apical termination of the tube is highly variable, but is primarily constructed by low, cap‐shaped sclerites and characterised by a central aperture of variable inclination. The adapical portion of the tube is predominantly constructed by high, laterally compressed sclerites, but individual sclerite rings can contain both cap‐shaped and laterally compressed sclerites along with sclerites of intermediate morphology. The apical aperture presumably housed organic structures for attachment to a hard substrate, but the scleritome also occasionally preserves small lateral perforations between fused sclerites, which may have served to stabilise the scleritome by providing additional points of anchorage. In the Arrowie Basin, E. helenia is found in association with archaeocyath‐microbial‐spongiomorph‐dominated bioherms and most likely inhabited pendant or cryptic habitats within these bioherms. Eccentrotheca‐like sclerites form an integral part of the scleritomes of many tommotiids which may confuse taxonomic analysis. Sclerites previously assigned to ‘E.’guano, consistently occur together with sclerites of Kulparina rostrata in stratigraphic intervals consistently older than strata hosting E. helenia. Rare fused specimens indicate that the sclerites of K. rostrata and ‘E.’guano belong to the same scleritome. 相似文献
43.
LEONID E. POPOV EVA EGERQUIST LARS E. HOLMER 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2007,40(1):85-96
New data on the earliest ontogeny of Mid-Ordovician Baltoscandian clitambonitoid ( Apomatella , Neumania and Oslogonites ) and polytoechioid ( Antigonambonites and Raunites ) brachiopods reveal significant differences in the life history of the taxa belonging to these two superfamilies. The Polytoechioidea and probably other members of the Billingsellida had planktotrophic larvae, in which the dorsal and ventral mantle lobes formed separately and without reversion. The 'pedicle sheath' in Antigonambonites is secreted by a section of modified ventral mantle and thus this 'pedicle' is not homologous within the pedicle of rhynchonellate brachiopods. It is likely that polytoechioids and other members of the strophomenate clade had the same type of ontogeny and mode of attachment. In contrast, the ontogeny and mode of attachment of clitambonitoids are similar to that of recent rhynchonellates: their mantle lobes and both valves formed simultaneously, and the pedicle most likely formed from the larval pedicle lobe. Evidence for the lecithotrophic nature of clitambonitoid larva is discussed. This confirms that the Clitambonitoidea, unlike the Polytoechioidea, represents an ingroup within the Rhynchonellata. 相似文献
44.
CHRISTIAN WILLE LARS KUTZBACH TORSTEN SACHS† DIRK WAGNER† EVA-MARIA PFEIFFER‡ 《Global Change Biology》2008,14(6):1395-1408
Eddy covariance measurements of methane flux were carried out in an arctic tundra landscape in the central Lena River Delta at 72°N. The measurements covered the seasonal course of mid‐summer to early winter in 2003 and early spring to mid‐summer in 2004, including the periods of spring thaw and autumnal freeze back. The study site is characterized by very cold and deep permafrost and a continental climate with a mean annual air temperature of ?14.7 °C. The surface is characterized by wet polygonal tundra, with a micro‐relief consisting of raised moderately dry sites, depressed wet sites, polygonal ponds, and lakes. We found relatively low fluxes of typically 30 mg CH4 m?2 day?1 during mid‐summer and identified soil temperature and near‐surface atmospheric turbulence as the factors controlling methane emission. The influence of atmospheric turbulence was attributed to the high coverage of open water surfaces in the tundra. The soil thaw depth and water table position were found to have no clear effect on methane fluxes. The excess emission during spring thaw was estimated to be about 3% of the total flux measured during June–October. Winter emissions were modeled based on the functional relationships found in the measured data. The annual methane emission was estimated to be 3.15 g m?2. This is low compared with values reported for similar ecosystems. Reason for this were thought to be the very low permafrost temperature in the study region, the sandy soil texture and low bio‐availability of nutrients in the soils, and the high surface coverage of moist to dry micro‐sites. The methane emission accounted for about 14% of the annual ecosystem carbon balance. Considering the global warming potential of methane, the methane emission turned the tundra into an effective greenhouse gas source. 相似文献
45.
Phylogenetic analysis of Magnoliales and Myristicaceae based on multiple data sets: implications for character evolution 总被引:4,自引:1,他引:4
HERVÉ SAUQUET JAMES A. DOYLE TANYA SCHARASCHKIN THOMAS BORSCH KHIDIR W. HILU LARS W. CHATROU ANNICK LE THOMAS 《Botanical journal of the Linnean Society. Linnean Society of London》2003,142(2):125-186
Magnoliales, consisting of six families of tropical to warm-temperate woody angiosperms, were long considered the most archaic order of flowering plants, but molecular analyses nest them among other eumagnoliids. Based on separate and combined analyses of a morphological matrix (115 characters) and multiple molecular data sets (seven variable chloroplast loci and five more conserved genes; 14 536 aligned nucleotides), phylogenetic relationships were investigated simultaneously within Magnoliales and Myristicaceae, using Laurales, Winterales, and Piperales as outgroups. Despite apparent conflicts among data sets, parsimony and maximum likelihood analyses of combined data converged towards a fully resolved and well-supported topology, consistent with higher-level molecular analyses except for the position of Magnoliaceae: Myristicaceae + (Magnoliaceae + (( Degeneria + Galbulimima ) + ( Eupomatia + Annonaceae))). Based on these results, we discuss morphological evolution in Magnoliales and show that several supposedly plesiomorphic traits are synapomorphies of Magnoliineae, the sister group of Myristicaceae (e.g. laminar stamens). Relationships within Annonaceae are also resolved with strong support ( Anaxagorea basal, then ambavioids). In contrast, resolution of relationships within Myristicaceae is difficult and still incomplete, due to a very low level of molecular divergence within the family and a long stem lineage. However, our data provide good evidence that Mauloutchia is nested among other Afro-Malagasy genera, contradicting the view that its androecium and pollen are plesiomorphic © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 125–186. 相似文献
46.
GRAVEN THOMAS NIELSEN LINDA SLOT FENGER GRON PETER SVENSSON STEENGAARD PEDERSEN LARS ARENDT NIELSEN TROELS STAEHELIN JENSEN 《Somatosensory & motor research》2013,30(1):46-53
The aim of the present study was to study the sensibility in the area of saline-induced muscle pain. In three experiments, ten subjects were exposed to computer-controlled infusion of 0.5 ml isotonic (0.9%) or hypertonic (9%) saline into the anterior tibial muscle. The pain intensity was assessed on a visual analogue scale (VAS). The pain threshold (PT) to pressure and electrical stimulation in muscle and subcutaneous tissues was determined. Three experiments were performed in which infusion of hypertonic saline produced significantly higher VAS scores than isotonic saline. In all three experiments, there was no significant difference in PT obtained after infusion of isotonic saline compared with infusion of hypertonic saline. In experiment 1, the PT was determined at the infusion site and 4 cm from the infusion site. At the infusion site, the pressure PT decreased (- 19 2%) 1, 3, 5, 7 and 9 min after infusion of isotonic and hypertonic saline, but remained unchanged 4 cm from the infusion site. The intramuscular electrical PT at the infusion site and 4 cm from the infusion site increased significantly (29 6%) 5, 7 and 9 min after saline infusion. In experiment 2, the pressure PT and the intramuscular electrical PT were recorded after two infusions of saline separated by 1 day. The day after the first infusion, the pressure PT was decreased compared with the PT before the first infusion, but the electrical PT was not affected. Moreover, the hypertonic saline infusion given on the second day produced significantly higher (130 50%) VAS scores than the infusion given on the first day. In experiment 3, the PT was determined in the subcutaneous tissue, but no significant effects of saline infusion were found. The present placebo-controlled experiments failed to show muscular or subcutaneous hyperalgesia after saline-induced muscle pain per se. 相似文献
47.
Herring Gull Larus argentatus eggs from a study colony in the Baltic showed a slight but significant variation in egg size within the laying sequence. Last-laid eggs were only about 5% smaller by volume than first eggs. There was no significant difference in dry yolk weight or dry albumen weight, although possible differences were evident. The chicks had nearly equal hatching weights and equally long tarsi. There was no differential mortality in the third chick in the study colony, and there were no indications of egg-size-mediated mortality. The birds in the colony produced an average of 1.45 fledglings per pair. Compared with several other studied colonies, the difference in egg size within a clutch was low, and a comparison of colonies from northwestern Europe suggests that variance within the clutch is negatively correlated with fledging success, so that a large difference in size between first and last eggs is associated with low fledging success. We suggest that the size of the last egg in the clutch reflects the feeding potential in the environment and is mainly a nonadaptive response to poor feeding conditions during laying. 相似文献
48.
LARS-ANDERS HANSSON & LARS TRANVIK 《The Plant journal : for cell and molecular biology》2004,37(1):45-53
1. To test the response of algal communities to altered grazer abundance in lakes lacking efficient predators on herbivores, we performed field and experimental studies in two sub-Antarctic lakes (South Georgia).
2. The number of algal species in these high latitude lakes is low, and all dominant species have grazer-resistant adaptations, including spines in three dimensions ( Staurastrum sp.), large size ( Tribonema sp.), a mucus sheet allowing viable passage through the gut ( Chlamydocapsa sp., Elakatothrix sp.) or ability to recruit individuals from the sediment surface ( Mallomonas sp.).
3. Algal community composition was only slightly changed by experimentally altered grazer abundance, indicating that it was already adapted for a high grazing pressure. Hence, the diets of herbivores were restricted to vulnerable food organisms such as Mallomonas sp. and heterotrophic flagellates in the water column, and to benthic food sources.
4. At high grazer abundance, the concentration of available phosphorus (PO4 -P) in the water was lower than at low grazer abundances, due to inefficient nutrient regeneration by the copepod herbivores. Hence, in lakes where copepods are dominant grazers, algae suffer both directly from grazing and indirectly from reduced nutrient availability. 相似文献
2. The number of algal species in these high latitude lakes is low, and all dominant species have grazer-resistant adaptations, including spines in three dimensions ( Staurastrum sp.), large size ( Tribonema sp.), a mucus sheet allowing viable passage through the gut ( Chlamydocapsa sp., Elakatothrix sp.) or ability to recruit individuals from the sediment surface ( Mallomonas sp.).
3. Algal community composition was only slightly changed by experimentally altered grazer abundance, indicating that it was already adapted for a high grazing pressure. Hence, the diets of herbivores were restricted to vulnerable food organisms such as Mallomonas sp. and heterotrophic flagellates in the water column, and to benthic food sources.
4. At high grazer abundance, the concentration of available phosphorus (PO
49.
The Transpiration Rate of Unhardened, Hardened, and Dehardened Seedlings of Spruce and Pine 总被引:1,自引:0,他引:1
LARS CHRISTERSSON 《Physiologia plantarum》1972,26(2):258-263
Tissue injuries in winter are sometimes interpreted as caused by drought damages. The possibility that the tolerance of conifers of winter and spring conditions is increased through decrease in transpiration rate has been little investigated. The transpiration rate of 3 or 6 months old unhardened, hardened, and dehardened seedlings of Pinns silvestris L. and Picea abies (L.) Karst. was assessed gravimetrically, at 20°C. The transpiration rates of seedlings of spruce and pine which had been hardened for 3 months were about 1/2 the rates of dehardened seedlings. Transpiration during a dehardening period increased at different rates in pine and spruce. After a dehardening period of 3–5 days the transpiration rate of spruce reached a maximum, whereas pine reached the maximum transpiration rate after a dehardening period of 10–14 days. Transpiration of seedlings of spruce and pine hardened for 3 months showed only a very slight reaction to light and darkness. This indicated that stomata of hardened seedlings remained closed. The results are discussed in connection with frost and drought injuries in pine and spruce during early spring. 相似文献
50.