共查询到20条相似文献,搜索用时 15 毫秒
1.
The diagnoses of the conchostracan genera Cratostracus and Porostracus are revised following a re-examination of their type species under a scanning electron microscope. In Cratostracus each growth line has a serrated lower margin. Radial lirae branch into smaller ridges that merge with each other to give the upper part of each growth band in the ventral region of the carapace a slightly undulating surface. Cross-bars are present between these lirae. In Porostracus the radial lirae on the growth bands near the umbo are long and relatively widely spaced. There is a fine reticulum between them in the umbonal part of the carapace and cross-bars on the ventral surface. The ornament of Porostracus indicates that it can be assigned to the family Halysestheriidae rather than to the Afrograptidae, in which it has been placed previously. Morphological analysis of most of the species of the two genera and closely related Orthestheria (Migransia) under the scanning electron microscope is required before their stratigraphic potential can be fully realized. 相似文献
2.
The spinicaudatan Neodiestheria Chen is an important component of the diverse Early Cretaceous Yanjiestheria fauna in eastern Asia. Examination under a scanning electron microscope of newly collected and well-preserved specimens of Neodiestheria dalaziensis Chen from the Albian Dalazi Formation of Zhixin, Jilin Province, north-eastern China, has revealed morphological features of the carapace not recognized previously, namely that puncta are not only evenly distributed on growth bands near the umbo and gradually merge into a punctate fine reticulation and dense radial lirae on each growth band in the upper-middle part of the carapace, but also occur on growth lines and within the lumina of a fine reticulum, and between radial lirae on growth bands in the middle and lower parts of the carapace. Growth bands in anteroventral, ventral and posteroventral parts of the carapace are also ornamented with transversely elongate large pits (depressions) surrounded by swellings, appearing as a large reticulum superimposed over fine reticulation and radial lirae. These ontogenetically developing morphological patterns on the growth bands of the juvenile stage of the carapace indicate that Neodiestheria is closely related phylogenetically to Triglypta Wang. 相似文献
3.
Shreerup Goswami Kamal Jeet Singh Shaila Chandra 《Journal of Asian Earth Sciences》2006,28(4-6):218-233
Gondwana basins of Orissa State constitute a major part of the Mahanadi Master Basin. These Gondwana sediments, ranging from Asselian to Albian in age, contain remnants of three basic floral assemblages i.e. Glossopteris Assemblage, Dicroidium Assemblage and Ptilophyllum Assemblage which can be recognized through the Permian, Triassic and Early Cretaceous, respectively. The megafloral assemblages of different basins of this state are discussed briefly. This report mainly deals with the plant species diversification in different lithological formations and the development of flora in the Gondwana basins of Orissa. A number of successive megafloras are recognized. Among those, leaves are the dominant part of the preserved flora, followed by fruits and roots. No wood parts are preserved in the major basins. These pre-angiospermic floras have been systematically analyzed to depict the evolutionary trends, and palaeofloristics of these basins. The distribution of plant fossils in different formations of these basins depicts provincialism in Gondwana flora within the Orissa. 相似文献
4.
5.
6.
Chen Jin-Hua Toshifumi Komatsu Cao Mei-Zhen Frank Stiller 《Journal of Asian Earth Sciences》2006,27(6):943-951
The non-marine bivalve species Trigonioides (Kumamotoa) quadratus Gu and Ma is described from the Fourth Member of the Hekou Formation in western Fujian, southeastern China. This species previously was regarded to belong to the subgenus Trigonioides (s.s.), which is restricted to the Early Cretaceous. Herein, it is included into the subgenus Kumamotoa. It is compared to Cenomanian (early Late Cretaceous) species from Japan and Korea such as Trigonioides (Kumamotoa) mifunensis Tamura, Trigonioides (Kumamotoa) matsumotoi Kobayashi and Suzuki and Trigonioides (Kumamotoa) paucisulcatus Suzuki. The age of the Fourth Member of the Hekou Formation is discussed. 相似文献
7.
The fossil clam shrimp genus Xibeiestheria Wang in Shen et al., 1982, a component of the well-known Early Cretaceous Yanjiestheria fauna, was originally described from the lower Aptian Jingchuan Formation of Yanchi County, Ningxia Hui Autonomous Region of northwestern China. The morphological re-examination under an SEM of the holotype of the type species Xibeiestheria pora Wang in Shen et al., 1982 has revealed new taxonomic features not previously recognized. These include: (1) growth lines with serrated lower margins, having a row of small pores; (2) widely spaced radial lirae intercalated cross bars on growth bands in the dorsal part of the carapace; (3) fine reticulum occurring within coarse reticulation on growth bands in the middle part of the carapace; (4) puncta radially aligned along the widely spaced radial lirae on growth bands in the lower part of the carapace. 相似文献
8.
This paper deals with the taxonomic revision of the Early Cretaceous large, many-chambered planispiral planktonic foraminifera, historically assigned to the genus Globigerinelloides or alternatively assigned in the 1990s to the genera Globigerinelloides Cushman and ten Dam, Biglobigerinella Lalicker, Blowiella Krechmar and Gorbachik and Alanlordella BouDagher-Fadel. In a previous paper we demonstrated that the morphological and microstructural features used in the literature for distinguishing Blowiella from Globigerinelloides have value only at species level, and the former genus was thus invalidated (being the junior synonym). Moreover, the Late Aptian specimens assigned to Biglobigerinella by some authors, based on the presence of twin last chamber(s), are also included in Globigerinelloides because individuals sharing the same features (number of chambers, growth rate, size of umbilicus, and a finely perforate wall) may or may not possess twin last chamber(s). Meanwhile, Moullade et al. questioned the taxonomic value of Alanlordella, erected by BouDagher-Fadel to accommodate planispiral taxa possessing a macroperforate wall. All the species analysed here possess a finely perforate wall and consequently cannot be assigned to this taxon.The large species of Globigerinelloides retained here, with six or more chambers in the outer whorl, are G. algerianus Cushman and ten Dam, G. aptiensis Longoria, G. barri (Bolli, Loeblich and Tappan) and G. ferreolensis (Moullade).In the sections studied, Globigerinelloides aptiensis was first found close to the Barremian/Aptian boundary, even though this species was recorded in Spain (Rio Argos) in the mid Upper Barremian; very rare, small, seven-chambered individuals here assigned to Globigerinelloides ferreolensis are recorded in the Lower Aptian (just below and within the Selli Level, OAE1a), while a few specimens belonging to Globigerinelloides barri occur in the Globigerinelloides ferreolensis Zone (Upper Aptian). Globigerinelloides aptiensis and G. ferreolensis range up to the Ticinella bejaouaensis Zone while Globigerinelloides barri disappears at the top of the Globigerinelloides algerianus Zone; finally, Globigerinelloides algerianus obviously spans the eponymous total range zone.From an evolutionary point of view, two lineages within the many-chambered Globigerinelloides have been recognized. In the first, already known in the literature, Globigerinelloides aptiensis gave rise to G. ferreolensis, which evolved into G. algerianus; the latter in turn gave rise to Pseudoplanomalina cheniourensis as the final evolutionary member. In the second lineage Globigerinelloides barri originated from G. blowi. 相似文献
9.
内蒙古包头达尔罕茂明安联合旗发现了保存完整的白垩纪大型本内苏铁目拟苏铁科拟苏铁属(Cycadeoidea)茎干化石。茎干化石呈椭球形,保存完好,高56cm,最大直径48cm,化石表面密布的菱形叶柄基呈螺旋状排列,从基部至顶端叶柄基逐渐变小,球果不均匀散生于叶柄基之间。茎干化石从内到外包括中央的髓部、外围的木质部圆筒、叶柄基、球果等。这是国内首次发现保存比较完整的本内苏铁目拟苏铁科茎干化石。同时,在茎干化石产地附近还发现有裸子植物宽孔异木(Xenoxylon latiporosum(Cramer)Gothan)木化石。本内苏铁茎干及宽孔异木化石对于研究本内苏铁目的演化历史和当时的植物群组成特点具有重要的科学意义。 相似文献
10.
云南禄丰县川街盆地中侏罗统产出弓鲛鱼类化石后甸弓鲛(Hybodus houtienensis Young)、新庄弓鲛(新种)(Hybodus xinzhuangensis Sun)、川街弓鲛(新种)(Hybodus chuanjieensis Sun)。后甸弓鲛(Hybodus houtienensis Young)是中国发现最早的弓鲛鱼类之一,正型标本为破碎的鳍棘,副型标本为一枚牙齿齿冠。依据在川街盆地相同层位发现的新化石材料,对后甸弓鲛副型标本进行了增补,补充了描述,建立了2个弓鲛新种:新庄弓鲛与川街弓鲛,丰富了"后甸弓鲛带"弓鲛类群,并讨论了弓鲛属的生物地层、生活的古环境和地理分布特征。 相似文献
11.
Attribution of burrows in the Wealden Group of southern England to Ophiomorpha is rejected. The burrows are essentially cylindrical, unlined and with a meniscate fill. Any outer knobbly appearance is due to diagenetic poikilotopic cementation or to differential weathering of a mudchip-sand fill. The variable nature of meniscate fill reflects passage of the producer through the thin-bedded, alternating sand-mud sediments or along sand-mud interfaces. The burrows are assigned to Beaconites, though, since the identity of this ichnotaxon has been questioned, reference is also made to Taenidium. Two ichnoassociations are recognized: (1) a Beaconites antarcticus-Scoyenia (or Taenidium-Scoyenia) association (Weald Clay) of marginal lacustrine situation with fluvial input, and (2) a Beaconites barretti-Planolites (or Taenidium-Planolites ) association of the fluvial (lacustrine delta) of the Lee Ness Sandstone (Ashdown Formation). The Wealden burrows offer no inherent indications of palaeosalinity, and inferences made on supposed occurrences of Ophiomorpha in the Wealden Group must be reassessed. Other occurrences of Ophiomorpha in non-marine facies are questioned. 相似文献
12.
This contribution is a short history of the Zambian copper flower, Becium homblei (recently renamed B. centraliafricanum that has attracted attention as a plant associated with Cu-rich soils. It has a peculiar discontinuous distribution in Central Africa which has been explained in terms of biotype depletion. A field investigation into the ecology of the species shows that it is able to tolerate soil Cu concentrations of up to 15,000 μg/g (ppm), and soil nickel concentrations of nearly 5000 μg/g. B. homblei is also found on areas where soil metals are in trace quantities, and where soil bases, particularly Ca, are low. In spite of its tolerance to a wide range of edaphic conditions, the distribution of the species is very restricted in Zimbabwe, and this is almost certainly due to severe interspecific competition with a closely related species, B. obovatum, which is common on soils not unusually enriched in heavy metals. Pioneering work on geobotanical prospecting by use of Becium homblei was carried out by the late G. Woodward and others in the 1950s and 1960s. This species was used successfully for geobotanical prospecting for Cu. This present report is a brief history of these pioneering studies 相似文献
13.
Guilian Sheng Lianjuan Wu Xindong Hou Junxia Yuan Shenghong Cheng Bojian Zhong Xulong Lai 《Frontiers of Earth Science》2009,3(1):100-106
The evolution of Elephantidae has been intensively studied in the past few years, especially after 2006. The molecular approaches
have made great contribution to the assumption that the extinct woolly mammoth has a close relationship with the Asian elephant
instead of the African elephant. In this study, partial ancient DNA sequences of cytochrome b (cyt b) gene in mitochondrial genome were successfully retrieved from Late Pleistocene Mammuthus primigenius bones collected from Heilongjiang Province in Northeast China. Both the partial and complete homologous cyt b gene sequences and the whole mitochondrial genome sequences extracted from GenBank were aligned and used as datasets for
phylogenetic analyses. All of the phylogenetic trees, based on either the partial or the complete cyt b gene, reject the relationship constructed by the whole mitochondrial genome, showing the occurrence of an effect of sequence
length of cyt b gene on mammoth phylogenetic analyses. 相似文献
14.
15.
Simon F. Mitchell 《Cretaceous Research》2005,26(6):895-897
Four new specimens of Euscalpellum? coatesi Donovan and Davis-Strickland from the Maastrichtian of Jamaica are described; two of these occur in association with the right valve of the rudistid bivalve Chiapasella radiolitiformis (Trechmann). This demonstrates that E.? coatesi is not a barnacle, but rather represents an unusual preservational state of the left valve of C. radiolitiformis retaining only the cellular inner part of the shell. 相似文献
16.
Analyses of a sediment core from Little Pond, located in the town of Bolton, Massachusetts, provide new insights into the history of environmental and ecological changes in southern New England during the late Holocene. Declines in organic content and peaks in the abundance of Isoetes spores indicate reduced water depth at 2900–2600, 2200–1800, and 1200–800 calibrated years before present (cal yr BP), generally consistent with the timing of dry conditions in records from elsewhere in the northeastern United States. The Little Pond pollen record features little change over the last 3000 yr, indicating that the surrounding vegetation was relatively insensitive to these periods of drought. The 1200–800 cal yr BP dry interval, however, coincides with increased abundance of Castanea pollen, suggesting that the expansion of Castanea in southern New England may have been influenced by late-Holocene climatic variability. 相似文献
17.
Gui Zhen Men 《Mathematical Geology》1991,23(1):71-76
Hundreds of samples and 17 variables collected from coalfields of major coal-bearing strata over China except for Tibet and Taiwan, were used in this study. The dry, ash-free basis volatile matter (V
r) and caking index (G
(RI)) were chosen by means of correlation analysis and stepwise discriminatory analysis as major indices of a new classification. By means of the optimum section, the boundary value of the axis of ordinate (G
(RI)) and axis of abscissas (V
r) can be determined in the classification system. Thus, aV
r –G
(RI) classification scheme diagram was formed and bituminous coal was divided into nine classes. Use of correspondence analysis reduced dimensions of sample-expressive space without losing initial information. The trend on the factor surface of samples shows that the classification obtained from correspondence analysis conforms to theV
r –G
(RI) classification result and further verified the dependability of classification by two indices. At the same time, a certain relationship between the properties of a great variety of coal and their attributes can be explained. Hence, bituminous coal classification becomes more scientific, reasonable, and practical than before. 相似文献
18.
Reproductive pentoxylalean material from the Albian Triton Point Formation, Fossil Bluff Group of Alexander Island, Antarctica is the youngest record of this group globally. Leaves are referred to Taeniopteris daintreei McCoy, ovulate reproductive organs to Carnoconites cranwelli Harris, and stem material to Pentoxylon sp. Occurring in leaf litter layers on palaeosol surfaces the sedimentology suggests that pentoxylalean plants grew upon areas of the floodplain distal to the river channel, where they covered the forest floor in a similar habit to modern brambles. The forest floor was shared with Equisetales and liverworts, an abundance of ferns [Cladophlebis Brongniart, Gleichenites Goeppert, Phyllopteroides Medwell, Sphenopteris (Brongniart) Sternberg], as well as angiosperms. Bennettitales, Ginkgoites Seward and Nilssonia Brongniart were rare within these communities, as were coniferous trees. 相似文献
19.
Occurrence of Cordaitales from lower Gondwana sediments of Ib-River Coalfield, Orissa, India: An Indian scenario 总被引:1,自引:0,他引:1
Kamal Jeet Singh Shreerup Goswami Shaila Chandra 《Journal of Asian Earth Sciences》2007,29(5-6):666-684
The Ib-River Coalfield in Orissa State is a part of Mahanadi Master Basin. Recent extensive investigations were conducted in this Coalfield to locate fossiliferous beds in the Lower Gondwana deposits and as a result a large cache of plant fossils were recovered from Lower Permian sediments (Barakar Formation) exposed in Jurabaga and Lajkura Collieries. The complete flora includes 23 genera representing nine orders viz., Lycopodiales, Equisetales, Sphenophyllales, Filicales, Cordaitales, Coniferales, Ginkgoales, Cycadales and Glossopteridales. Only the Cordaitales, represented by four genera i.e., Noeggerathiopsis, Cordaites, Euryphyllum and Kawizophyllum are discussed in this paper. Cordaitalean leaves are described for the first time from this coalfield; the remaining plant groups will be considered in a subsequent publication. Cordaitalean leaves attributable to Noeggerathiopsis hislopii, Noeggerathiopsis minor, Euryphyllum whittianum, Euryphyllum maithyi, Kawizophyllum dunpathriensis and Cordaites sp. constitute about 13.90% (111 specimens) of the total plant assemblage collected from this Coalfield. Of the cordaitaleans, N. hislopii is most abundant (47.75%; 53 specimens) followed by E. whittianum (40.54%; 45 specimens). A summary of the distribution of Cordaitales throughout the Indian Gondwana is also presented. Floristic composition varies stratigraphically at the two Barakar exposures (Lajkura and Jurabaga Collieries). Cordaitales are preserved only in the lowermost (4th) horizon (lower floral zone). Strata in these collieries have been assigned to the lower and upper Barakar Formation based on floristic content and an Early Permian (Artinskian) age is assigned. 相似文献
20.
During the late Pleistocene and early Holocene, Bison was widely dispersed across North America and occupied most regions not covered by ice sheets. A dietary study on Bison paleopopulations from Alaska, New Mexico, Florida, and Texas was performed using two methods that relate dental wear patterns to diet, mesowear analysis and microwear analysis. These data were compared to a mixed sample of extant Bison from the North American central plains, extant wood Bison from Alberta (Canada) and a variety of other modern ungulates. Mesowear relates macroscopic molar facet shape to levels of dietary abrasion. The mesowear signature observed on fossil Bison differs significantly from the hyper-abrasive grazing diet of extant Bison. Tooth microwear examines wear on the surface of enamel at a microscopic scale. The microwear signal of fossil samples resembles to modern Bison, but the fossil samples show a greater diversity of features, suggesting that fossil Bison populations regularly consumed food items that are texturally inconsistent with the short-grass diet typical of modern plains Bison. Mesowear and microwear signals of fossil Bison samples most closely resemble a variety of typical mixed feeding ungulates, all with diets that are substantially less abrasive than what is typical for modern plains Bison. Furthermore, statistical tests suggest significant differences between the microwear signatures of the fossil samples, thus revealing geographic variability in Pleistocene Bison diets. This study reveals that fossils are of value in developing an understanding of the dietary breadth and ecological versatility of species that, in recent times, are rare, endangered, and occupy only a small remnant of their former ranges. 相似文献