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991.
A New Marine Reptile (Sauropterygia) from New Zealand: Further Evidence for A Late Cretaceous Austral Radiation of Cryptoclidid Plesiosaurs 总被引:1,自引:0,他引:1
Kaiwhekea katiki gen. et sp. nov. represents the first described cryptoclidid plesiosaurian from New Zealand. It is one of the largest cryptoclidids known, at a length of over 6.5 m, and represents the third reported genus of austral Late Cretaceous cryptoclidids. Kaiwhekea katiki is from siltstones of the Katiki Formation, upper Haumurian Stage (Cenomanian–Maastrichtian; c. 69–70 Ma) of coastal Otago, South Island, New Zealand. In the Late Cretaceous, the locality lay close to the polar circle. The holotype and only known specimen is an articulated skeleton with skull, preserved mostly as natural molds, but which lacks the forelimbs and pectoral girdle. The skull is relatively large and possesses several distinct characters, including a substantial, deep, jugal. There are about 43 upper and 42 lower teeth in each jaw quadrant; all are homodont, slim, and slightly recurved, lacking prominent ornament. Kaiwhekea probably took single soft-bodied prey. Based on cranial structure, it clearly belongs with the Cryptoclididae, but is not certainly close to the southern Late Cretaceous cryptoclidids Morturneria (Seymour Island, Antarctica) and Aristonectes (Chile, Argentina). 相似文献
992.
David R. Vann Amishi Joshi Cecilia Pérez Arthur H. Johnson J. Frizano Daniel J. Zarin Juan J. Armesto 《Biogeochemistry》2002,60(1):25-47
We assessed a number of biomass and soil parameters in order to examinerelationships among nutrient availability, forest productivity and vegetationpatterns in two old-growth forested watersheds in a pristine montane landscapeon Isla de Chiloé, Chile. We selected watersheds in both gymnosperm- andangiosperm-dominated forests and determined tree species, d.b.h. and health forall trees < 2 cm d.b.h. in plots established at 50m intervals. Soils were sampled at two depths in each plot andanalyzed for total C and N, and for exchangeable Ca, K, Mg andresin-extractableP. Allometric relationships and vegetation nutrient concentrations were used todetermine above-ground pools from the vegetation survey data. Growth rates werederived from increment core measures. Soil pools of most elements measuredappear adequate to support forest growth indefinitely. Mineralized nitrogen,which is similar in quantity to the annual demand for nitrogen from the soil isthe exception, consistent with the possibility of N limitation in two of theforest types studied. A third type, an evergreen broadleaved forest, appears torequire substantially more nitrogen than would appear to be available from netmineralization measurements. Productivity per unit of nitrogen required fromthesoil is quite high, largely as a consequence of the evergreen habit of thespecies in these forests. Compared to other temperate montane forests in theNorthern Hemisphere, nutrient pools and cycling characteristics were found tobemostly similar across forest types, in spite of considerable variation invegetation and soils. 相似文献
993.
Evidence is presented for the first time that chemolithoautotrophic ammonia oxidizers (CAO) and chemolithoautotrophic nitrite oxidizers (CNO) colonize in appreciable cell numbers the phyllosphere of spruce trees in a forest ecosystem exposed for decades to high levels of atmospheric nitrogen (The Höglwald Forest, Bavaria, Germany). The results strongly indicate that both, CAO and CNO are predominantely located inside the spruce needles, most likely within the stomatal cavity. These results are further supported by field experiments of NH3 uptake into twigs on intact spruce trees in the presence and absence of 10 Pa acetylene, an inhibitor of the ammonia monooxygenase of CAO. It is clearly demonstrated for the first time that in situ uptake of NH3 from the atmosphere into spruce needles exposed to high levels of atmospheric N is not catalyzed exclusively by the tree, but is the result of combined activities of both, the spruce trees and the chemolithoautotrophic nitrifiers colonizing the needles. 相似文献
994.
Abstract. Using the unusually well-documented butterfly fauna of Davis, Yolo County, California, it is shown that the mainly native species commonly observed in gardens breed mostly or entirely on alien plants, especially naturalized weeds. Over 40% of the fauna has no known native hosts in the urban–suburban environment. Were certain alien weeds to be eradicated or their abundance greatly reduced, the urban-suburban butterfly fauna would disappear. This might be regarded as an unfortunate, and perhaps intolerable, side-effect of such programs. 相似文献
995.
Pollination and phenology of flowers in the canopy of two contrasting rain forest types in Amazonia,Colombia 总被引:3,自引:0,他引:3
The main objective of this investigation was to study the pollination characteristics of two types of Amazonian rain forest at plant community level. Seasonally inundated forest was compared with upland (tierra firme) forest. The study focused on plant species in the canopy. The pollination spectra show that in both forests most canopy trees and lianas are pollinated by small bees, large bees, butterflies or by small, relatively unspecialized insects. In the upland forest small bees are the most important pollinators (32% of all species of trees and lianas are pollinated by them), whereas large bees are predominant in the floodplain (22%). Other pollinators, like hummingbirds, bats, moths, and beetles are less common (>10%), but always somewhat more important in the flood plain than in the upland forest. Bees are the most common pollinators of epiphytes. In the flood plain forest, flies are also important as epiphyte pollinators (19%), whereas in the upland forest hummingbirds pollinate more epiphytes. The phenological patterns are quite similar in both the upland and the flood plain. We found a peak in flowering in the transition period between the wet and the dry season. Flowering activity was lowest during the wet season. Differentiation in sexual systems was correlated with life form. Dioecy and monoecy were found mostly among tree species. Most species of all life forms though were hermaphroditic. No difference with respect to the relative importance of sexual systems was found between the two forest types. 相似文献
996.
Differences in Composition and Mucosal Adhesion of Bifidobacteria Isolated from Healthy Adults and Healthy Seniors 总被引:8,自引:0,他引:8
Fang He Arthur C. Ouwehand Erika Isolauri Masataka Hosoda Yoshimi Benno Seppo Salminen 《Current microbiology》2001,43(5):351-354
Fifty-one Bifidobacterium strains were isolated from the feces of healthy adults (30–40 years old) and seniors (older than 70 years of age). B. adolescentis, B. breve, B. infantis, and B. longum were isolated from the healthy adults and B. adolescentis and B. longum from elderly subjects. The tested bacteria bound, in vitro, to intestinal mucus in a strain dependent manner. The strains
isolated from healthy adults, and especially B. adolescentis, bound better to intestinal mucus than those isolated from seniors. These results indicate that the mucosal adhesive properties
of the human Bifidobacterium flora were reduced with the aging of the host. This shift to a Bifidobacterium flora with reduced adhesive abilities may explain the decrease in bifidobacteria levels in the intestinal microflora of aging
people.
Received: 7 February 2001 / Accepted: 3 April 2001 相似文献
997.
CYP2E1-dependent toxicity and oxidative stress in HepG2 cells 总被引:11,自引:0,他引:11
Arthur I. Cederbaum Defeng Wu Montserrat Mari Jingxiang Bai 《Free radical biology & medicine》2001,31(12):80-1543
998.
Arthur Bob Karnuah Hirohide Uenishi Sachiko Kiuchi Misaki Kojima Akira Onishi Hiroshi Yasue Tadayoshi Mitsuhashi 《Mammalian genome》2001,12(7):518-523
A swine resource family was constructed at the National Institute of Animal Industry, Japan, in order to determine the genetic
regions responsible for economically important traits, including fetus development. To identify genes expressed in the early
stage of embryo development, we cataloged and mapped genes expressed in a 28-day-old normal pig embryo. In this effort, we
have mapped 64 genes, which have map information in human genome onto a swine radiation hybrid (RH) map, IMpRH. These mappings
provided additional chromosomal homologies between swine and human to improve the comparative map between the two species.
The distribution of the genes assigned to swine chromosomes are as follows: 9 genes were assigned on SSC6; 6 genes each assigned
on SSC5 and SSC14; 5 genes each assigned on SSC3, SSC4, and SSC8; 4 genes each assigned on SSC1, SSC7, SSC9, and SSC15; 3
genes each assigned on SSC2, SSC13 and SSCX; and 1 gene each assigned on SSC10, SSC11, and SSC16. Moreover, the present findings
revealed 18 new chromosomal homologies between pig and human. Briefly, SSC3 regions were indicated to correspond with HSA1
and HSA10; SSC4 with HSA6; SSC5 with HSA2, HSA15, and HSA16; SSC6 with HSA3, HSA6, and HSA20; SSC7 with HSA11; SSC8 with HSA3,
HSA6, and HSA7; SSC9 with HSA8; SSC13 with HSA1; SSC14 with HSA13; SSC15 with HSA19; SSC16 with HSA9.
Received: 19 December 2000 / Accepted: 13 March 2001 相似文献
999.
Lead poisoning was produced in suckling rats by lead fed to lactating mother rats being transmitted to newborns maternal milk. The brain of 25 day old lead poisoned rats contained 6.0 to 12.5 ppm lead. Zinc was depressed 56% (cerebral cortex), 45% in cerebellum and 43% (caudate nucleus) whereas copper was depressed 52% in the cerebellum. Inhibition of monoamine oxidase (pargyline) or partial depletion of serotonin and norepinephrine did not alter the concentration of Fe, Cu, Zn, or Mn in brain. 相似文献
1000.