共查询到20条相似文献，搜索用时 31 毫秒
1.
Alexander RM 《Science (New York, N.Y.)》2003,301(5640):1678-1679
The largest living rodent is the South American capybara, a creature the size of a sheep that unlike smaller rodents stands on relatively straight legs. However, as Alexander explains in his Perspective, a new fossil find in Venezuela (Sánchez-Villagra et al.) reveals that the capybara would be dwarfed by Phoberomys, a giant rodent the size of a buffalo that lived during the Miocene Epoch. 相似文献
2.
A double mass extinction at the end of the paleozoic era 总被引：4，自引：0，他引：4
Three tests based on fossil data indicate that high rates of extinction recorded in the penultimate (Guadalupian) stage of the Paleozoic era are not artifacts of a poor fossil record. Instead, they represent an abrupt mass extinction that was one of the largest to occur in the past half billion years. The final mass extinction of the era, which took place about 5 million years after the Guadalupian event, remains the most severe biotic crisis of all time. Taxonomic losses in the Late Permian were partitioned among the two crises and the intervening interval, however, and the terminal Permian crisis eliminated only about 80 percent of marine species, not 95 or 96 percent as earlier estimates have suggested. 相似文献
3.
Jurassic fossil vertebrates collected from the Falla Formation in the Central Transantarctic Mountains included a partial skull and postcranial elements of a crested theropod, Cryolophosaurus ellioti gen. nov. sp. nov. The theropod bears some resemblance to the large tetanurans of the Middle to Late Jurassic but also has primitive ceratosaurian features. Elements from a prosauropod, teeth from scavenging theropods, a pterosaur humerus, and a tritylodont molar were also recovered. The presence of this fauna suggests that a mild climate existed at high paleolatitude in this area of Gondwana during the Early Jurassic. 相似文献
4.
Asfaw B White T Lovejoy O Latimer B Simpson S Suwa G 《Science (New York, N.Y.)》1999,284(5414):629-635
The lack of an adequate hominid fossil record in eastern Africa between 2 and 3 million years ago (Ma) has hampered investigations of early hominid phylogeny. Discovery of 2.5 Ma hominid cranial and dental remains from the Hata beds of Ethiopia's Middle Awash allows recognition of a new species of Australopithecus. This species is descended from Australopithecus afarensis and is a candidate ancestor for early Homo. Contemporary postcranial remains feature a derived humanlike humeral/femoral ratio and an apelike upper arm-to-lower arm ratio. 相似文献
5.
Fossils of a giant sauropod dinosaur, Turiasaurus riodevensis, have been recovered from terrestrial deposits of the Villar del Arzobispo Formation (Jurassic-Cretaceous boundary) of Riodeva (Teruel Province, Spain). Its humerus length (1790 millimeters) and estimated mass (40 to 48 metric tons) indicate that it may have been the most massive terrestrial animal in Europe and one of the largest in the world. Phylogenetic analysis indicates that the fossil represents a member of a hitherto unrecognized group of primitive European eusauropods that evolved in the Jurassic. 相似文献
6.
利用中国畜牧业统计资料,结合全国草地覆盖遥感数据,采用生态能学方法,分析了2000—2010年中国草地鼠害发生的空间分布特征与变化趋势,评估了鼠害对草地生态系统生物量的危害损失。结果表明:2000—2010年,中国草地鼠害的发生面积、发生程度和造成的损失总体呈上升趋势;11年间全国由于鼠害造成草地生物量的损失年均约1.181 54×10~7 t,年份间鼠害差异大,2006年草地生物量损失最大,为2.537 23×10~7 t;区域草地鼠害损失大小排序为西南、西北、华北、东北,西藏自治区鼠害最严重,年均草地生物量损失占全国总量的38.09%。 相似文献
7.
8.
Coprinites dominicana gen.nov., spec.nov. (Coprinaceae) found in amber from the Dominican Republic is the earliest known gilled mushroom, the first fossil fleshy agaric determinable, and the only kiiown fossil "mushroom" (Agaricales) from the tropics. This find is of significance with respect to the evolutionary development of the Basidiomycetes. Because the appearance of this fossil is quite modern, it suggests that mushrooms as a group probably arose much earlier than the early to mid-Tertiary. 相似文献
9.
Lipinsky ES 《Science (New York, N.Y.)》1981,212(4502):1465-1471
As a source of chemicals, biomass has several intrnsic advantages over fossil mass: it is renewable, flexible through crop switching, and adaptable through genetic manipulation. Inflexibility of the fossil mass resource is compensated for by highly effective technology for production of olefins and aromatics, economies of scale, and a highly developed system of conversion products with large markets. Direct and indirect strategies to substitute for petrochemicals are based on ecological succession concepts. A proliferation of lignocellulosic fractionation processes is arising from the need for inexpensive, homogeneous, chemically useful biomass feedstocks. 相似文献
10.
Reisz RR 《Science (New York, N.Y.)》1977,196(4294):1091-1093
Petrolacosaurus, an Upper Pennsylvanian reptile, presents a combination of features that place it within a distinct family of the Eosuchia while also evidencing strong relationships to the ancestral reptiles. It is therefore the earliest and most primitive representative of the largest assemblage of fossil and living reptiles, collectively called diapsids. 相似文献
11.
平顺县北社乡晚秋农田鼠类分布和数量配置 总被引：1，自引：1，他引：0
2011年11月中旬,以铗捕和笼捕捕获实物标本为依据,在长治市潞城、壶关、平顺3县交界的平顺县北社乡,对坡地和沟川地2种不同类型农田的鼠类分布和数量配置进行了调查。调查共捕获5种鼠类,隶属3科4属,其中,古北界的种类4种,占80%;东洋界的种类1种,占20%。松鼠科的岩松鼠和鼠科的大林姬鼠只分布于坡地类型区,且数量较少,只占总数的6.72%和10.28%;数量最多的鼠类是鼠科的社鼠,占总数的40.71%,多在坡地活动;仓鼠科的大仓鼠和鼠科的黑线姬鼠则多在沟川地活动,在坡地分布较少,这2种鼠分别占捕获鼠总数的23.72%和18.58%。坡地类型区鼠的种类和数量均多于沟川地。 相似文献
12.
The importance of trophic ecology in adaptation and evolution is well known, yet direct evidence that feeding controls microevolution over extended evolutionary time scales, available only from the fossil record, is conspicuously lacking. Through quantitative analysis of tooth microwear, we show that rapid evolutionary change in Miocene stickleback was associated with shifts in feeding, providing direct evidence from the fossil record for changes in trophic niche and resource exploitation driving directional, microevolutionary change over thousands of years. These results demonstrate the potential for tooth microwear analysis to provide powerful insights into trophic ecology during aquatic adaptive radiations. 相似文献
13.
Randall JE 《Science (New York, N.Y.)》1973,181(4095):169-170
The maximum length of 36.5 feet (11.1 meters) attributed to the white shark (Carcharodon carcharias) by Günther and others is a mistake. Examination of the jaws and teeth of the specimen referred to by Günther and comparison with the jaws of white sharks of known length revealed a length of about 17 feet ( approximately 5 meters). The largest white shark reliably measured was a 21-foot (6.4-meter) individual from Cuba. Bites on whale carcasses found off southern Australia suggest that white sharks as long as 25 or 26 feet (7 (1/2) or 8 meters) exist today. The size of extinct Carcharodon has also been grossly exaggerated. Based on a projection of a curve of tooth size of Recent Carcharodon carcharias, the largest fossil Carcharodon were about 43 feet ( approximately 13 meters) long. 相似文献
14.
Mass extinctions in the marine fossil record 总被引：3，自引：0，他引：3
A new compilation of fossil data on invertebrate and vertebrate families indicates that four mass extinctions in the marine realm are statistically distinct from background extinction levels. These four occurred late in the Ordovician, Permian, Triassic, and Cretaceous periods. A fifth extinction event in the Devonian stands out from the background but is not statistically significant in these data. Background extinction rates appear to have declined since Cambrian time, which is consistent with the prediction that optimization of fitness should increase through evolutionary time. 相似文献
15.
Tuzzolino AJ Economou TE Clark BC Tsou P Brownlee DE Green SF McDonnell JA McBride N Colwell MT 《Science (New York, N.Y.)》2004,304(5678):1776-1780
We present measurements of the dust particle flux and mass distribution from the Stardust Dust Flux Monitor Instrument (DFMI) throughout the flyby of comet 81P/Wild 2. In the particle mass regime from 10(-14) to 10(-7) kilograms, the spacecraft encountered regions of intense swarms of particles, together with bursts of activity corresponding to clouds of particles only a few hundred meters across. This fine-scale structure can be explained by particle fragmentation. We estimate that 2800 +/- 500 particles of diameter 15 micrometers or larger impacted the aerogel collectors, the largest being approximately 6 x 10(-7) kilograms, which dominates the total collected mass. 相似文献
16.
Pyrolysis mass spectrometry of complex organic materials 总被引：2，自引：0，他引：2
H L Meuzelaar W Windig A M Harper S M Huff W H McClennen J M Richards 《Science (New York, N.Y.)》1984,226(4672):268-274
Pyrolysis mass spectrometry in combination with computerized multivariate statistical analysis enables qualitative and quantitative analysis of nonvolatile organic materials containing molecular assemblies of a complexity and size far beyond the capabilities of direct mass spectrometry. The state of the art in pyrolysis mass spectrometry techniques is illustrated through specific applications, including structural determination and quality control of synthetic polymers, quantitative analysis of polymer mixtures, classification and structural characterization of fossil organic matter, and nonsupervised numerical extraction of component patterns from complex biological samples. 相似文献
17.
Derived features of a new boreosphenidan mammal from the Lower Cretaceous Yixian Formation of China suggest that it has a closer relationship to metatherians (including extant marsupials) than to eutherians (including extant placentals). This fossil dates to 125 million years ago and extends the record of marsupial relatives with skeletal remains by 50 million years. It also has many foot structures known only from climbing and tree-living extant mammals, suggesting that early crown therians exploited diverse niches. New data from this fossil support the view that Asia was likely the center for the diversification of the earliest metatherians and eutherians during the Early Cretaceous. 相似文献
18.
Abundant extraterrestrial chromite grains from decomposed meteorites occur in middle Ordovician (480 million years ago) marine limestone over an area of approximately 250,000 square kilometers in southern Sweden. The chromite anomaly gives support for an increase of two orders of magnitude in the influx of meteorites to Earth during the mid-Ordovician, as previously indicated by fossil meteorites. Extraterrestrial chromite grains in mid-Ordovician limestone can be used to constrain in detail the temporal variations in flux of extraterrestrial matter after one of the largest asteroid disruption events in the asteroid belt in late solar-system history. 相似文献
19.
de Heinzelin J Clark JD White T Hart W Renne P WoldeGabriel G Beyene Y Vrba E 《Science (New York, N.Y.)》1999,284(5414):625-629
The Hata Member of the Bouri Formation is defined for Pliocene sedimentary outcrops in the Middle Awash Valley, Ethiopia. The Hata Member is dated to 2.5 million years ago and has produced a new species of Australopithecus and hominid postcranial remains not currently assigned to species. Spatially associated zooarchaeological remains show that hominids acquired meat and marrow by 2.5 million years ago and that they are the near contemporary of Oldowan artifacts at nearby Gona. The combined evidence suggests that behavioral changes associated with lithic technology and enhanced carnivory may have been coincident with the emergence of the Homo clade from Australopithecus afarensis in eastern Africa. 相似文献
20.
五台县农田害鼠的多样性及其季节变动规律 总被引：3，自引：3，他引：0
2012年3—11月,在山西省五台县农田调查了农田害鼠的多样性及其季节变动规律。结果表明,当地农田害鼠群落为长尾仓鼠(Apodemus peninsulae)+大林姬鼠(Cricetulus longicaudatus)群落,这可为当地在灭鼠工作中确定投饵量提供理论依据;另外,当地害鼠群落的多样性指数和均匀度指数也较低,而其优势度指数偏高,主要是由当地优势鼠种之一——长尾仓鼠所占比率过高(77.12%)所致。对农田害鼠季节变动规律的研究表明,五台县农田害鼠数量一年中有1个高峰(6月),这不仅与群落自身的生态学特征有关,而且与当地气候、各物种间的相互关系和人为干扰有一定的关联。 相似文献