共查询到20条相似文献,搜索用时 15 毫秒
1.
Størmer L 《Science (New York, N.Y.)》1977,197(4311):1362-1364
Fossil floras and faunas of a Lower Devonian black shale from Alken, Germany, include aquatic, amphibious, and terrestrial forms. The presence of these forms suggests conditions in favor of an invasion of the land. Various arthropod adaptations to terrestrial life are present, including the development of a preoral cavity. 相似文献
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Shear WA Bonamo PM Grierson JD Rolfe WD Smith EL Norton RA 《Science (New York, N.Y.)》1984,224(4648):492-494
A new fossil site near Gilboa, New York, is one of only three where fossils of terrestrial arthropods of Devonian age have been found. The new Gilboan fauna is younger than the other two but richer in taxa. Fragmentary remains and nearly whole specimens assigned to Eurypterida, Arachnida (Trigonotarbida, Araneae, Amblypygi, and Acari), Chilopoda [Craterostigmatomorpha(?) and Scuterigeromorpha(?)], and tentatively to Insecta (Archaeognatha) have been found. The centipedes and possible insects may represent the earliest records known for these groups. 相似文献
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Oldroyd DR 《Science (New York, N.Y.)》1985,230(4724):432-433
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Middle Devonian articulate brachiopods (Ludlowville and Moscow Formations, Hamilton Group, New York) have external tapered holes with a central boss that are indistinguishable from drillholes of naticid gastropods that are known from the Triassic and later. Drillholes are specific to prey (ribbed shells were avoided) and specific to sites on prey. Healed drillholes suggest penetration of live prey. As many as 44 percent of the preferred prey are drilled, indicating a level of predation that has been reported only from post-Paleozoic strata. 相似文献
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A diverse assemblage of algal stromatolites occurs in Devonian reef complexes of the Canning Basin, Western Australia. Some forms grew on fore-reef depositional slopes down to at least 45 meters below sea level and are believed to be products of deepwater nonskeletal algae. It is concluded that algal stromatolites in the stratigraphic record are not to be regarded as diagnostic evidence for deposition in very shallow water. 相似文献
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A nearly complete spider spinneret was found in Middle Devonian rocks (about 385 to 380 million years old) near Gilboa, New York. This is the earliest evidence yet discovered for silk production from opisthosomal spigots, and therefore for spiders. Two previously known Devonian fossils described as spiders lack any apomorphies of the order Araneae and are probably not spiders. The spigots of the Devonian spinneret resemble those of members of the living suborder Mesothelae, but the number of spigots and their distribution are like those of members of the suborder Opisthothelae, infraorder Mygalomorphae. The Devonian spider belonged to a clade that may be the sister group of all other spiders, of Mesothelae, or of Opisthothelae. 相似文献
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Thousands of specimens of the enigmatic fossil Gluteus minimus (new genus, newt species) occur in a 5-centimeter-thick interval within the Maple Mill Shale and in equivalent deposits of the Devonian of eastern Iowa. They are roughly lenticular. bilobed fossils up to 11 millimeters in diamiter and 8 milllimeters thic. These objects consistently asymmetrical in the same direction. defy placement in any known higher taxon when their morphology. histology, and apatitic composition considered. 相似文献
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Sack FD 《Science (New York, N.Y.)》2004,304(5676):1461-1462
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运用灰色关联分析法评价建三江垦区地下水水质的研究 总被引:5,自引:0,他引:5
地下水是自然环境的组成部分,人类活动会导致地下水质的变化。文章收集了建三江垦区地下水监测数据,采用灰色关联分析法评价其地下水水质。评价结果符合该地区地下水实际情况,并为井灌区地下水质的评价提供了依据。 相似文献
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Heckman DS Geiser DM Eidell BR Stauffer RL Kardos NL Hedges SB 《Science (New York, N.Y.)》2001,293(5532):1129-1133
The colonization of land by eukaryotes probably was facilitated by a partnership (symbiosis) between a photosynthesizing organism (phototroph) and a fungus. However, the time when colonization occurred remains speculative. The first fossil land plants and fungi appeared 480 to 460 million years ago (Ma), whereas molecular clock estimates suggest an earlier colonization of land, about 600 Ma. Our protein sequence analyses indicate that green algae and major lineages of fungi were present 1000 Ma and that land plants appeared by 700 Ma, possibly affecting Earth's atmosphere, climate, and evolution of animals in the Precambrian. 相似文献
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以内蒙古自治区正蓝旗沙地区为区域,研究浑善达克沙地植物适宜性。借助TWINSPAN数量分类法将浑善达克沙地79个样方进行植物群落类型划分,并依据浑善达克沙地342个植物分布点(79个样方点加资料整理的263个植物分布数据)和29个与沙地植物适宜性相关的环境因子(14个气象因子、12个土壤因子和3个地形因子)数据,运用最大熵模型在30m的空间尺度上分别模拟该地区流动沙地、半流动沙地、半固定沙地、固定沙地、河泛地和林地植物群落的潜在分布,并获取各类植物的适宜地块。结果表明:1)根据潜在环境因子和分布点建立的各类生境植物群落适宜性分布模型,评判模型精准度的AUC值均0.883,达到了好的模拟效果,故此模型在此区域的研究是合理的。2)在29个环境因子中,对植物适宜性贡献量较大的是年均降水量、积温、高程和地表土壤pH(KCl)、大气干燥度、大气气压以及地表土壤粘土含量。3)在流动沙地向固定沙地的正向演替中,土壤粘土含量和土壤pH(KCl)逐渐减少,土壤阳离子交换量逐渐增加,对应生境植物对降水量的需求量不断增加,对积温要求逐渐降低。4)沙米(Agriophyllum squarrosum)、猪毛菜(Salsola collina)作为流动沙地的先锋植物以及其他生境的伴生种,适生于正蓝旗沙地区大部分地区,面积为9 463.53km2;刺蓬(Salsola ruthenica)和糙隐子草(Cleistogenes squarrosa)群落等半流动沙地植物群落分布在除流动沙地之外的沙地,适宜区面积为8 551.13km2。地榆(Sanguisorba officinalis)和水麦冬(Triglochin palustre)多分布于正蓝旗中部到西北部区域的河泛地,面积为761.17 km2;黄柳(Salix gordejevii)、柠条(Caragana korshinskii)、杨柴(Hedysarum mongolicum)和沙打旺(Astragalus adsurgens)群丛分布于半固定沙地背风坡以及固定沙地阴坡,面积为3 387.56km2;榆树(Ulmus pumila)和杨树(Populus)等乔木受大兴安岭南段山地和燕山北部山地区系的影响,多适宜于东部区域。 相似文献
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Molluscan phylogeny: the paleontological viewpoint 总被引:1,自引:0,他引:1
Stasek (1) theorized that the extant mollusks are the progeny of three separate lineages that separated before the phylum was well established. He wrote that no known intermediate forms, fossil or living, bridge the "enormous gaps between any two of the three lineages," and therefore treated each as a separate subphylum. These subphyla are (i) the subphylum Aculifera Hatscheck 1891, containing only the class Aplacophora, derived from the most primitive ancestors of the Mollusca; (ii) the subphylum Placophora von Jhering 1876, containing only the class Polyplacophora, and emphasizing the pseudometamerism of its more advanced premollusk ancestor; and (iii) the subphylum Conchifera Gegenbaur 1878, containing the Monoplacophora and the other classes derived from it. We point out that the Polyplacophora may be derived from the Monoplacophora instead of a more primitive ancestral stock. We also suggest that the Conchifera can be separated into two major lineages, each worthy of the rank of subphylum. The fossil record indicates that the Monoplacophora gave rise to the Gastropoda, Cephalopoda, Rostroconchia, and possibly Polyplacophora, and that the Pelecypoda and Scaphopoda are derived from the Rostroconchia. These last three classes thus form a lineage that diverged from the Monoplacophora in the Early Cambrian. They emphasized a shell form that in all groups is primitively open at both ends, allowing the gut to remain relatively straight, with an anterior mouth and posterior anus. They became burrowing (infaunal) deposit or filter feeders. We coin the term Diasoma (through-body) for the subphylum containing these three classes (Rostroconchia, Pelecypoda, and Scaphopoda). The remaining three classes (Monoplacophora, Gastropoda, and Cephalopoda) emphasize a conical univalved shell, usually twisted into a spiral. The relatively small single aperture forces the anus to lie close to the mouth, and the gut is bent into a "U." Most are surface-dwelling (epifaunal) grazers or carnivores. We coin the name Cyrtosoma (hunchback-body) for the subphylum containing these three classes. Strictly speaking, the cyrtosomes are the ancestors of the diasomes but, in fact, both subphyla appeared and began to diversify within a few million years in the Early Cambrian. Note added in proof: After proofs were corrected we were informed that the new genus Opikella (40) is preoccupied by (Opikella = Oepikella) Thorslund 1940, an Ordovican ostracod. We rename the mollusk genus Oepikila. 相似文献
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Two groups of extant plants, lycopsids and psilopsids, alternatively have been suggested to be the living representatives of the earliest diverging lineage in vascular plant evolution. The chloroplast DNA (cpDNA) gene order is known to contain an inversion in bryophytes and tracheophytes relative to one another. Characterization of tracheophyte cpDNAs shows that lycopsids share the gene order with bryophytes, whereas all other vascular plants share the inverted gene order. The distribution of this character provides strong support for the fundamental nature of the phylogenetic separation of lycopsids and marks the ancient evolutionary split in early vascular land plants. 相似文献
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Playford PE McLaren DJ Orth CJ Gilmore JS Goodfellow WD 《Science (New York, N.Y.)》1984,226(4673):437-439
A moderate iridium anomaly, about 20 times the local background, has been found in Upper Devonian rocks in the Canning Basin. It occurs at or near the Frasnian-Famennian boundary, which is known to be associated with a major massextinction event of global extent. The anomaly occurs in an extremely condensed limestone sequence laid down under quiet deepwater conditions. Its occurrence suggests a causal link with some form of meteoroid impact. Moreover, carbon isotope data indicate that a large reduction in biomass could have occurred at this level. However, the anomaly coincides with a stromatolite bed containing the fossil cyanobacterium Frutexites; iridium, platinum, iron, manganese, cobalt, arsenic, antimony, and cerium are preferentially concentrated in filaments of this organism, with concentrations ranging from two to five times that of the matrix. It is possible that Frutexites extracted these elements directly from seawater, without the need for their derivation from an extraterrestrial source. 相似文献
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Rensing SA Lang D Zimmer AD Terry A Salamov A Shapiro H Nishiyama T Perroud PF Lindquist EA Kamisugi Y Tanahashi T Sakakibara K Fujita T Oishi K Shin-I T Kuroki Y Toyoda A Suzuki Y Hashimoto S Yamaguchi K Sugano S Kohara Y Fujiyama A Anterola A Aoki S Ashton N Barbazuk WB Barker E Bennetzen JL Blankenship R Cho SH Dutcher SK Estelle M Fawcett JA Gundlach H Hanada K Heyl A Hicks KA Hughes J Lohr M Mayer K Melkozernov A Murata T Nelson DR Pils B Prigge M Reiss B Renner T Rombauts S Rushton PJ 《Science (New York, N.Y.)》2008,319(5859):64-69
We report the draft genome sequence of the model moss Physcomitrella patens and compare its features with those of flowering plants, from which it is separated by more than 400 million years, and unicellular aquatic algae. This comparison reveals genomic changes concomitant with the evolutionary movement to land, including a general increase in gene family complexity; loss of genes associated with aquatic environments (e.g., flagellar arms); acquisition of genes for tolerating terrestrial stresses (e.g., variation in temperature and water availability); and the development of the auxin and abscisic acid signaling pathways for coordinating multicellular growth and dehydration response. The Physcomitrella genome provides a resource for phylogenetic inferences about gene function and for experimental analysis of plant processes through this plant's unique facility for reverse genetics. 相似文献
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调查龙岩市新罗城区主要园林绿地中的地被植物,分析其种类组成、应用方式和特点,提出积极开发利用乡土地被植物、科学引进应用外来地被植物的建议。 相似文献
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Shapiro JA 《Science (New York, N.Y.)》1985,230(4730):1155-1156