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11.
本文对扁头中国短头鲵(新属新种) (Sinobrachyops placenticephalus gen. et sp. nov.) 的形态特征和分类位置进行简述.标本得自著名的恐龙化石产地——自贡大山铺,产出时代为中侏罗世.中国短头鲵是目前迷齿类中在地史上最年轻的一个属.它的发现使迷齿类在地球上生存时代的上限推移到中侏罗世. 相似文献
12.
内蒙阿左旗乌兰塔塔尔中渐新世的梳趾鼠类 总被引:2,自引:1,他引:1
本文描述和比较了发现在我国内蒙古阿左旗乌兰塔塔尔地区中渐新统的三属七种啮齿类梳趾鼠科化石,其中包括三个新种.并对某些种类的归属和性质做了初步的讨论. 相似文献
13.
宁夏同心中新世铲齿象化石 总被引:8,自引:6,他引:2
本文记述了宁夏同心地区中中新世哺乳动物群中铲齿象化石——同心铲齿象 (Platybelodon tongxinensis) (原定为同心嵌齿象 (Gomphotherium tongxinensis). 通过与国内外已现的有关铲齿象对比,确认其与国内已发现的葛氏种关系最近,可能属同一枝系.同心种与葛氏种相比,是性质相对原始分布层位较低的我国第二个铲齿象种.文章初步讨论了其 M_3 的某些变异性状.并结合现有的其它标本初步阐述了铲齿象类下门齿的两种结构类型,原始型的同心层状结构和衍生型的齿质柱状结构.建议根据这两种结构仍将铲齿象类划分为 Platybelodontinae 和 Amebelodontinae. 相似文献
14.
STEPHEN R. WESTROP 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1983,16(1):15-24
The Ordovician illaenine Bumastoides exhibits a distinctive effaced and strongly convex morphology. Orientation of the visual field, the extreme convexity of the cephalon and the nature of the thoracic articulation support an interpretation of Bumastoides as an infaunal trilobite that was poorly suited to epifaunal crawling. The genus may have been sedentary; spending most of its post-larval life cycle within a burrow. Suspension feeding would be a viable existence for a sedentary trilobite such as Bumastoides. Maintenance of a burrow is essential for respiration and would require a firm, cohesive substrate. The infaunal niche had become occupied by trilobites by at least the Late Cambrian and continued to be exploited through the Ordovician, Silurian and. possibly, into the Devonian. Convergence has led to the appearance of the effaced, strongly convex morphotype in a number of unrelated families, including the Illaenidae, Asaphidac, Aulacopleuridae, Plethopeltidae and Scutelluidae. A high numerical abundance of illaenid trilobites, such as Illaenus and Bumastoides , is characteristic of the illaenid–chcirurid association, which persisted from the early Ordovician until at least the Late Silurian. This association has been recorded from shelf-edge and on-shelf carbonate buildups and shallow subtidal level bottom environments. It appears to be confined to firm substrates. 相似文献
15.
长江中游鱼类寄生棘头虫区系的研究 总被引:13,自引:1,他引:12
经过3年10次调查,剖检湖北省宜都、黄冈两处江段所产72种鱼类,共计766尾。收集棘头虫10种,其中包括2新种和1新组合,即蛇鮈新棘吻虫(新种)Neoechinorhynchus saurogobi sp.nov.,长江丽棘虫(新种)Brentisentis yangtzensis sp.nov.(Illiosontidae),鲤丽棘虫(新组合)B.cyprini comb.nov.。对长江中游鱼类寄生棘头虫区系的特点进行了分析和探讨。 相似文献
16.
Nieper(1969)依据澳大利亚 Queenslaad 西部 Nora 组(下奥陶统)的标本以 Trigonodus triangularius Nieper 1969 为模式种,建立了牙形刺新属 Trigonodus. Cooper(1981)将 Nieper 的形式属 Trigonodus 修正为器官属,包括 PM Sa Sb Sc Sd 分子,并将此属的模式种改为 Trigonodus larapintinensis (Crespin, 1943). Cooper 的观点被很多牙形刺专家接受, Trigonodus 属名也被广泛引用在牙形刺文献中 (Stauge, 1984;安泰庠、郑昭昌,1990), 相似文献
17.
Summary Late Arenigian biohermal reef mounds and biostromes within the shallow-marine platform facies of the upper San Juan Formation
of the Precordillera (Western Argentina) represent a new Early Ordovician reef type. The meter-sized reefs are dominated byZondarella communis n.g. n. sp. The new taxon is characterized by domical, bulbous and laminar morphotypes exhibiting growth layers and thin
horizontal and vertical as well as intermingled skeletal elements included within different sets. The fossil maybe compared
with stromatolites and stromatoporoids but an interpretation as primitive stromatoporoids is favoured. 相似文献
18.
C. S. Degoute C. Dubreuil M. J. Ray J. Guitton M. Manchon V. Banssillon J. L. Saumet 《European journal of applied physiology and occupational physiology》1994,69(5):414-420
Studies by laser-Doppler flowmetry of middle ear microcirculation changes induced by physical and chemical stimuli in the animal have only recently been made. This prospective study, performed in humans, was designed to compare the effects of a postural manoeuvre (headup tilt 30°), hypotension and locally applied vasoconstriction on middle ear blood flow during anaesthesia. Circulatory changes provoked by a headup tilt of 30°, and successive intravenous boluses of potent vasodilators, were compared with circulatory changes provoked by locally applied adrenaline, in ten healthy patients in good physical states undergoing middle ear surgical repair. Heart rate and direct arterial pressure were continuously recorded via a radial artery cannula. Middle ear blood flow was continuously recorded via a laser-Doppler probe placed on the promontorium cavi tympani. Metabolic parameters (partial pressure of O2 and CO2 in arterial blood, pH, arterial lactate concentrations) and arterial concentrations of propofol were measured just before and just after the experiment. Headup tilt did not modify heart rate, mean arterial pressure or middle ear blood flow. Vasodilators (nicardipine, nitroprusside, nitroglycerin) provoked a fall in arterial pressure (P<0.0001,P<0.0001,P<0.019, respectively), but did not induce any significant variations in heart rate; variations occurred in middle ear blood flow (P>0.05, not significant) which were different according to patients and agents. Locally applied adrenaline provoked a fall in the middle ear blood flow (P<0.0012), with no effect on heart rate and arterial pressure. There were no significant changes in metabolic values, or propofol serum concentrations. The behaviour of the middle ear blood flow submitted to hypotension, posture, or to vasoconstriction could be related to counteracting regulatory responses and/or to direct vascular effects. 相似文献
19.
D. E. Doan Y. E. Cohen J. C. Saunders 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1994,174(1):103-110
Laser interferometry was used to measure umbo velocity in the developing BALB/c mouse middle ear at 133 pure-tone frequencies between 2.0 kHz and 40.0 kHz, all at a constant 100 dB sound pressure level. Umbo velocities increased with age across the entire frequency range, and reached adult-like levels by about 19 days between 2.0 and 22.0 kHz. Velocities at 28.0 and 34.0 kHz took 27 and 52 days respectively to reach adult-like levels.A simple middle-ear model utilizing compliance, resistance, and inertia elements matched the general trends of our velocity results and provided an indication of the anatomical basis for the growth in umbo velocity. The model suggested that velocity development at the lowest frequencies may be attributed to increases in tympanic membrane compliance. The model also indicated that both the frictional resistance of the middle ear and the inertia of the tympanic membrane and ossicles decreased during the growth period.At frequencies below 20.0 kHz, age-related increases in umbo velocity coincided with improvements in Nj1 thresholds recorded from the round window and evoked potential thresholds obtained from the cochlear nucleus. These results indicated that the functional development of the middle-ear plays a major role in the development of hearing in the mouse.Portions of this work were presented at the Fifteenth Meeting of the Association for Research in Otolaryngology 相似文献
20.
Dr. Andrei V. Dronov 《Facies》1993,28(1):169-180
Summary Several Waulsortian-type mud mounds nearly 500 m thick and about 5 km long occur in the Middle Paleozoic carbonate section
of the Aktur nappe in the mountains on the right bank of Isfara river. These buildups form a well developed barrier system
that stretches along the South Ferganian carbonate platform margin and divides the carbonate complex into a fore-reef and
a back-reef part. The time of the mounds' most active growth was from the Late Silurian (Ludlow) to the Middle Devonian (Eifel).
Three main facies types can be recognized in the mud mounds: 1. micritic core facies, 2. sparitic flank facies and 3. loferitic
capping facies. The central massive or crudely bedded part of the mounds consists of white or light grey clotted micrite.
Macrofossils are rare. The sparitic flank facies in contrast consists of coarse and densely packed crinoidal wackestone-floatstones
with some brachiopod shell debris. Solitary rugose corals, tabulate corals, stromato-poroids and fragments of mollusks are
also abundant. The tops of the mounds are usually covered with loferitic pelmicrites or oolitic grainstone caps. Stromatactis-like
structures are very rare and poorly developed in the South Ferganian mud mounds. However, almostin all such mounds horizons
of calcitic breccias can be found.
In order to explain all the features found in the Fergana mounds an ‘atoll-like’ model has been proposed which starts the
evolution of the mud mounds with a small nucleus bioherm. The main stage of the evolution corresponds to an atoll-like structure
developing on the surface of shallow water platforms. White clotted micrite of the mound core facies is interpreted as a accumulation
of fine-grained sediment in an inner lagoon flanked by crinoidal bar deposits. The mound flank facies represents the atoll
rim deposits from where the carbonate mud is derived. The capping loferitic facies is considered as tidal flat deposit that
developed on top of the buildups during the last stage of its evolution. The knoll shape of the mounds is explained by the
retreat of the atoll flanking crinoidal bars back into the inner lagoon during the rise in sea level. Stromatactis-like structures
of small cavities filled with sparry calcite owe their existence to burrowing organisms. Calcitic breccias are interpreted
as paleokarst collapse breccias. They indicate that the tops of the mud mound became subaerially exposed. Other evidence for
a subaerial exposure can be seen in the occurrence of Variscian ‘black and white’ limestone gravel on the tops of some mud
mounds. According toWard et al. (1970) these sediments were produced above the sea level at the edge of hypersaline lakes situated on islands. 相似文献