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1.
Hardy, Peter G. & Broadhurst, Frederick M. 1978 04 IS: Refugee communities ofCarbonirola
Sparse elongate forms of the non-marine bivalve Carbonirola are associated with an abundance of trace fossils comprising resting traces (Cubichnia) referable to Lockeia , trails (Repichnia) and escape shafts (Fugichnia), all in arenaceous sediments of the Upper Carboniferous. Associated organic-rich argillaceous sediments contain the well-known, abundant and highly variable Carbonirola body fossil faunas. The latter we interpret (in common with other workers) as the remains of shells preserved in what was the typical life environment (characterized by muddy sediments and slow rates of sedimentation). The elongate shells associated with escape shafts we interpret as the only form of Carbonicola capable of escape upwards from burial by rapid sedimentation. For such fugitives from preexisting 'established communities' we propose the term 'refugee community'.  相似文献   

2.
New outcrops discovered in detrital ante-Stephanian sequences of the Southwestern Pyrenean Axial Zone (Béarn and Basque Country), yield abundant and varied faunas and floras. Among these the goniatite faunas are of particular interest. In a detailed palaeontological study, 9 species of Namurian age are recognized characterizing 3 levels of different age: the levels R1a2 (Reticuloceras circumplicatile Subzone) and R1a3 (Reticuloceras todmordenense Subzone) belong in the lower R1 Zone (Kinderscoutian, Reticuliceras inconstants Zone), Namurian B; the third level is Upper Namurian in age (Yeadonian, lower Gastrioceras Zone), Namurian C. These goniatite associations are palaeogeographically linked with those of the rest of Europe and North Africa, but their stratigraphical succession is not continuous.  相似文献   

3.
Fossil bivalves bearing oblique ribs first appeared in the Mid Ordovician but their diversity remained low during the Palaeozoic. The diversity soon increased after the Early Triassic, peaking in the Early Cretaceous. The Palaeozoic–Mesozoic record is dominated by burrowing bivalves (mainly pholadomyoids and trigonioids), which developed oblique ribs with symmetric profiles, probably adapted for shell reinforcement, although there are indications that the ribs of trigonioids also enhanced burrowing efficiency. After the Paleocene, the main groups of burrowing bivalves were veneroids (primarily tellinoideans and lucinoideans) and nuculoids, which generated oblique ribs of the shingled type, adapted to increase burrowing efficiency. The inferred change in function at the Mesozoic/Cenozoic boundary can be correlated with an increase in mean mobility of the bivalve faunas bearing oblique ribs through time. This implies a major ecological cause for the observed temporal patterns, which forced bivalve faunas to burrow more rapidly and efficiently. In particular, either the Phanerozoic increase in the diversity of durophagous predators or the accelerating rate of sediment reworking (both being a consequence of the Mesozoic Marine Revolution), or both, could have provided the necessary evolutionary force.  相似文献   

4.
许寿永 《古生物学报》1993,32(2):188-195
研究了广西马平灰岩的标准地点柳州楼梯山剖面的地层及其珊瑚,描述皱纹珊瑚7属10种,其中5新种,并系统地阐述了马平组的沿革.  相似文献   

5.
The North American Upper Ordovician reference standard, the Cincinnatian Series, contains rich shelly microfossil faunas in its type area in the Cincinnati Region but graptolites are uncommon in most of its shallow-water calcareous sediments. Consequently, the graptolite correlation of this key sequence has remained uncertain, in part, even controversial. A review of both previously published recently discovered graptolite Occurrences in the type Cincinnatian, combined with data from the important graptolite successions in Oklahoma New York-Quebec, has not only clarified the graptolite correlation of the Cincinnatian but also added new data on the morphology taxonomy, the vertical horizontal distribution, of several taxa. The information now at hand indicates that the Edenian Stage correlates with the C. spiniferus Zone, the Maysvillian Stage with the C. pygmaeus lower middle P. manitoulinensis Zone, the Richmondian Stage with the upper P. manitoulinensis , the D. complanatus , possibly part of the C. inuiti Zone. Comparison between graptolite conodont biostratigraphic evidence reveals no apparent conflict. Correlations are proposed between Upper Ordovician North American stages, graptolite conodont zones, successions in Texas, Oklahoma, Sweden, European graptolite zones, British series.  相似文献   

6.
Commelina communis stomata closed within 1 h of transferring intact plants from 27 degrees C to 7 degrees C, whereas tobacco (Nicotiana rustica) stomata did not until the leaves wilted. Abscisic acid (ABA) did not mediate cold-induced C. communis stomatal closure: At low temperatures, bulk leaf ABA did not increase; ABA did not preferentially accumulate in the epidermis; its flux into detached leaves was lower; its release from isolated epidermis was not greater; and stomata in epidermal strips were less sensitive to exogenous ABA. Stomata of both species in epidermal strips on large volumes of cold KCl failed to close unless calcium was supplied. Therefore, the following cannot be triggers for cold-induced stomatal closure in C. communis: direct effects of temperature on guard or epidermal cells, long-distance signals, and effects of temperature on photosynthesis. Low temperature increased stomatal sensitivity to external CaCl(2) by 50% in C. communis but only by 20% in tobacco. C. communis stomata were 300- to 1,000-fold more sensitive to calcium at low temperature than tobacco stomata, but tobacco epidermis only released 13.6-fold more calcium into bathing solutions than C. communis. Stomata in C. communis epidermis incubated on ever-decreasing volumes of cold calcium-free KCl closed on the lowest volume (0.2 cm(3)) because the epidermal apoplast contained enough calcium to mediate closure if this was not over diluted. We propose that the basis of cold-induced stomatal closure exhibited by intact C. communis leaves is increased apoplastic calcium uptake by guard cells. Such responses do not occur in chill-sensitive tobacco leaves.  相似文献   

7.
笔者对东北地区12个样点的芦苇叶片的植硅体进行了分析,探讨了芦苇植硅体在空间上的分布规律,揭示芦苇植硅体的环境指示意义,为定量恢复古环境提供参考。实验结果表明:12个样点中芦苇植硅体基本类型相同,共有5种主要植硅体类型,即中鞍型、帽型、芦苇扇型、尖型和棒型;但芦苇植硅体的浓度随着纬度的变化而相应的发生变化。总体来说,纬度较低的样点芦苇植硅体的浓度较大,而纬度较高的样点芦苇植硅体的浓度相对较小;随着纬度的变化,芦苇的特征植硅体中鞍型的浓度也呈现波状变化,牡丹江以南的几个样点中鞍型植硅体浓度相对较大,9、10两个月牡丹江以北的几个样点中鞍型植硅体浓度迅速减少。芦苇扇型植硅体则呈现出纬度较高的样点植硅体浓度较大,纬度较低的样点植硅体浓度较小的特点,芦苇扇型植硅体的空间变化规律与扇型植硅体的不同。  相似文献   

8.
Several trace fossils of burrowing ophiuroids, Asteriacites lumbricalis von Schlotheim 1820, occur on slabs of thinly‐bedded silty limestone in the lower Spathian part of the Lower Triassic Thaynes Formation in central Utah. This is the first record of Asteriacites in the Lower Triassic of North America. Their occurrence adds information to studies of the recovery of marine faunas following the Permian extinctions, including the oxygénation of benthic sediments.  相似文献   

9.
The mid-Pliocene warming episode is well established along the margins of the North Atlantic and probably affected areas as far north as Iceland. Rich marine mollusc faunas have been described from the 500 m of Pliocene siliciclastic deposits on the Tjörnes Peninsula in northeast Iceland. The faunal compositions indicate a development from warm-water to arcto–boreal conditions. We have analysed the oxygen isotope composition of 96 well-preserved specimens of the bivalves Arctica islandica and Pygocardia rustica and interpreted the data as palaeotemperatures. After corrections for the isotopic composition of Pliocene seawater, the temperatures are in accordance with other palaeotemperature proxies. We interpret our data as reflecting a gradual change from warm-water conditions (summer temperatures between 10 and 15°C) during the deposition of the lower part of the Tjörnes beds (Tapes Zone and lower part of Mactra Zone) to cold-water conditions (summer temperatures between 5 and 10°C) at the top (top of Mactra Zone and Serripes Zone). The coldest interval is found in the middle of the Serripes Zone, where summer temperatures (5–8°C) are comparable to those of the present environment off northern Iceland. The arrival to Tjörnes of cold-water molluscs of Pacific origin postdates the cooling of the seas around Iceland. We suggest that the cold interval in the Serripes Zone represents a cooling event prior to the final warm period (ca. 3.3–3.0 Ma [Dowsett et al. (1999) Middle Pliocene paleoenvironmental reconstruction: PRISM2. US Geol. Survey Open File Rep. 99–53]) of the mid-Pliocene warming.  相似文献   

10.
The rice paddy eel, Pisodonophis boro (P. boro), is of special interest because of its peculiar burrowing habits. P. boro penetrates the substrate tail-first, a technique common for ophichthids, but it is able to burrow head-first as well. P. boro exhibits three feeding modes: inertial feeding, grasping, and spinning. Rotational feeding is a highly specialized feeding mode, adopted by several elongate, aquatic vertebrates and it is likely that some morphological modifications are related to this feeding mode. The detailed morphology of the head and tail of P. boro is examined with the goal to apportion the anatomical specializations among head-first burrowing, tail-first burrowing, and rotational feeding. The reduced eyes, covered with thick corneas may be beneficial for protection during head-first burrowing, but at the same time decreased visual acuity may have an impact on other sensory systems (e.g. cephalic lateral line system). The elongated and pointed shape of the skull is beneficial for substrate penetration. The cranial bones and their joints, which are fortified, are advantageous for resisting high mechanical loads during head-first burrowing. The aponeurotic connection between epaxial and jaw muscles is considered beneficial for transferring these forces from the body to the head during rotational feeding. Hypertrophied jaw muscles facilitate a powerful bite, which is required to hold prey during spinning movements and variability in the fiber angles of subdivisions of jaw muscles may be beneficial for preventing the lower jaw from being dislodged or opened. Furthermore, firm upper (premaxillo-ethmovomerine complex) and lower jaws (with robust coronoid processes) and high neurocranial rigidity are advantageous for a solid grip to hold prey during rotational feeding. The pointed shape of the tail and the consolidated caudal skeleton are beneficial for their tail-first burrowing habits. It is quite likely that the reduction of the caudal musculature is related to the tail-first burrowing behavior because the subtle movements of the caudal fin rays are no longer required.  相似文献   

11.
本文报道了采自贵州沿河土地坳下奥陶统的牙形石,计有25属39种,根据牙形石组合特片分析,认为其与黔北其它地区下奥陶统牙形石组合面貌基本一致,属北大西洋牙形石动物地理区。  相似文献   

12.
The graptolite faunal succession of the late Tremadoc to early Arenig in southern Bolivia is established from the Cieneguillas and Culpina sections and compared with faunas from other regions. The succession yields important data for the discussion on the proposed GSSP at the base of the Tetragraptus approximatus Zone and the completeness of the successions in eastern North America and Scandinavia. The graptolite faunas of the Aorograptus victoriae, Kiaerograptus supremus, Araneograptus murrayi, Hunnegraptus copiosus and Tetragraptus phyllograptoides zones are reviewed and the faunal associations discussed. The Kiaerograptus supremus Zone is regarded as a local Scandinavian biozone.  相似文献   

13.
  • 1 The review is mainly concerned with Carboniferous non-marine Anthracosiidae and Myalinidae, of which only the shells are known, and with certain unspecialized non-byssate suspension-feeding bivalves which had smooth shells and burrowed shallowly.
  • 2 Limited experimental evidence and observation of living bivalves suggest that in certain Recent siphonate species and in some members of the non-siphonate Anthracosiidae the shape of the shell was functionally related to movement through the sediment in the same way. Predicted optimum shapes of shells for downward burrowing and for upward near-vertical movement in sands and silts were apparently realized in the Anthracosiidae, which constituted a series of highly variable opportunistic assemblages. It is stressed, however, that the shape of the shell always appears to be a compromise between several functional requirements.
  • 3 In both the early Anthracosiidae and in several analogous Recent marine genera, orientation of the long axis of the shell was the same for downward burrowing and for upward pushing, that is near the vertical, with posterior end upward.
  • 4 Invasion of the Pennine late-Namurian delta took place when marine bivalves pushed upward, thereby avoiding sedimentation from delta lobes moving seaward relatively swiftly. The evolution of Carbonicola occurred at about this time (the Marsdenian Age) when the bivalves acquired a smooth elongate shell of ‘streamlined’ form, having a hinge plate with swellings and depressions on it (later to evolve into teeth). All these features tend to characterize the active shallow burrowers of today.
  • 5 Entry into soft-bottom eutrophic conditions of fresh water is characterized in several unionids by increase in height/length (H/L or w/m) ratio of shell, in anterior end/length (A/L) and in obesity (T/L) (see Fig. 2, centre). These changes also took place in established faunas of Carbonicola characteristic of richly carbonaceous shales, in faunas of supposed Anthraconaia in more carbonaceous sediments of mid-and late-Carboniferous times in the U.S.A. and in Anthraconauta of the British late Carboniferous (Westphalian C and D). The genus Anthracosphaerium epitomizes the culmination of these trends in the Anthracosiidae, and species of the genus were probably epifaunal or shallowly infaunal active burrowers on soft bottoms in Westphalian upper A and B time.
  • 6 Two contrasting patterns of growth characterize the shells of the widely variable unionid Margaritifera margaritifera. In the first, dorsal arching of the shell, with straightening and reflexion of the ventral margin, provides increased weight but decreased ligamental strength. In the second, in which the ‘hinge line’ tends to remain straight while the dorsal margin becomes more rounded and obesity increases, there is increased metabolic efficiency for active surface movement. The maintenance of these trends within the species, which may be regarded as secondarily opportunistic, affords a means of insurance for survival within the highly variable environments of fresh water. The same trends are recognizable in established faunas of Carbonicola, where it is likely that they performed the same function, as well as in Mesozoic and Cenozoic Unionidae.
  • 7 The functional explanation outlined in paragraph (6) may be extended to provide an ecological meaning for Ortmann's ‘Law of Stream Distribution’, which states that obesity of unionid shells increases downstream. This applies broadly, within a fairly wide range of variation, a fact which again suggests ‘insurance’ of faunas against the variable hazards of fresh-water habitats.
  • 8 In bivalves having considerable thickness of shell in relation to their size, and having strong umbonal development, specific gravity of the living bivalve is correlated with H/L and T/L ratios of the shell, as in the venerid Venerupis rhomboides. In this species, differences in the specific gravities of the bivalves, as well as their shape, appear to be functionally related to shallowly infaunal burrowing in different substrates.
  • 9 The conclusions of paragraphs 6 and 8 provide a functional explanation, in terms of selection, for the palaeoecological ‘law’ of Eagar (1973), which is applicable to established faunas of Carbonicola in mid-Carboniferous time, and relates variational trends in two main groups of shells primarily to increases in the relative water velocities of the palaeoenvironments.
  • 10 Where the growth of relatively unspecialized bivalve shells has been measured, allometric relationships have usually been found in H-L and T-L scatters. Logarithmic lines have two inflexions and linear scatters a sigmoidal form. A similar pattern of allometric growth has been found in both Carbonicola (H-L) and Anthraconauta (m-w). These patterns appear to be related to the optimum requirements of water-borne larvae, the initial byssal phase of settlement, when ability to burrow quickly is essential, and the main period of growth and activity. It is herein suggested that the final second inflexion, which indicates a falling off of gain in H/L and T/L ratios, may be a genetically controlled modification of the growth pattern which counteracts the operation of the ‘cube-square rule’ (of Thompson, 1942) and prolongs productive life.
  • 11 Patterns of relative growth of the shell may be significantly modified by conditions of the habitat; both T/L and H/L ratios may be increased, with general reduction in size, in the less ‘favourable’ habitats. Both these ratios have been similarly modified, the one in the ‘natural laboratory’ of a lake formed by the damming up of streams, and the other in transplant experiments with living Venerupis. In both these latter cases, phenotypic changes took place in the same direction as those expected on the basis of natural selection. Direct response to environmental factors cannot therefore be ruled out as an agent in similar changes noted in Carbonicola and supposed Anthraconaia in paragraphs (5) and (9) and may have been operative in those of paragraphs (7) and (8).
  相似文献   

14.
Information from lizard lineages that have evolved a highly elongate (snake‐like) body form may clarify the selective forces important in the early evolution of snakes. Lizards have evolved bodily elongation via two distinct routes: as an adaptation to burrowing underground or to rapid locomotion above ground. These two routes involve diametrically opposite modifications to the body plan. Burrowing lizards have elongate trunks, small heads, short tails, and relatively constant body widths, whereas surface‐active taxa typically have shorter trunks, wider heads, longer tails, and more variable body widths. Snakes resemble burrowing rather than surface‐active (or aquatic) lizards in these respects, suggesting that snakes evolved from burrowing lizards. The trunk elongation of burrowing lizards increases the volume of the alimentary tract, so that an ability to ingest large meals (albeit consisting of small individual prey items) was present in the earliest snakes. Subsequent shifts to ingestion of wide‐bodied prey came later, after selection dismantled other gape‐constraining morphological attributes, some of which may also have arisen as adaptations to burrowing through hard soil (e.g. relatively small heads, rigid skulls). Adaptations of snake skulls to facilitate ingestion of large prey have evolved to compensate for the reduction of relative head size accompanying bodily elongation; relative to predator body mass, maximum sizes of prey taken by snakes may not be much larger than those of many lizards. This adaptive scenario suggests novel functional links between traits, and a series of testable predictions about the relationships between squamate morphology, habitat, and trophic ecology. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 293–304.  相似文献   

15.
The affinities of three problematic groups of elongate, burrowing reptiles (amphisbaenians, dibamids and snakes) are reassessed through a phylogenetic analysis of all the major groups of squamates, including the important fossil taxa Sineoamphisbaena, mosasauroids and Pachyrhachis; 230 phylogenetically informative osteological characters were evaluated in 22 taxa. Snakes (including Pachyrhachis) are anguimorphs, being related firstly to large marine mosasauroids, and secondly to monitor lizards (varanids). Scincids and cordylids are not related to lacertiforms as previously thought, but to anguimorphs. Amphisbaenians and dibamids are closely related, and Sineoamphisbaena is the sister group to this clade. The amphisbaenian-dibamid-Sineoamphisbaena clade, in turn, is related to gekkotans and xantusiids. When the fossil taxa are ignored, snakes, amphisbaenians and dibamids form an apparently well-corroborated clade nested within anguimorphs. However, nearly all of the characters supporting this arrangement are correlated with head-first burrowing (miniaturization, cranial consolidation, body elongation, limb reduction), and invariably co-occur in other tetrapods with similar habits. These characters are potentially very misleading because of their sheer number and because they largely represent reductions or losses. It takes very drastic downweighting of these linked characters to alter tree topology: if fossils are excluded from the analysis, a (probably spurious) clade consisting of elongate, fossorial taxa almost always results. These results underscore the importance of including all relevant taxa in phylogenetic analyses. Inferring squamate phylogeny depends critically on the inclusion of certain (fossil) taxa with combinations of character states that demonstrate convergent evolution of the elongate, fossorial ecomorph in amphisbaenians and dibamids, and in snakes. In the all-taxon analysis, the position of snakes within anguimorphs is more strongly-corroborated than the association of amphisbaenians and dibamids with gekkotans. When the critical fossil taxa are deleted, snakes ‘attract’ the amphisbaenian-dibamid clade on the basis of a suite of correlated characters. While snakes remain anchored in anguimorphs, the amphisbaenian-dibamid clade moves away from gekkotans to join them. Regardless of the varying positions of the three elongate burrowing taxa, the interrelationships between the remaining limbed squamates (‘lizards’) are constant; thus, the heterodox affinities of scincids, cordylids, and xantusiids identified in this analysis appear to be robust. Finally, the position of Pachyrhachis as a basal snake rather than (as recently suggested) a derived snake is supported on both phylogenetic and evolutionary grounds.  相似文献   

16.
Conodont data have been utilized to identify the Silurian/Devonian boundary within the Camelford Limestone near Wellington, NSW. Conodont faunas are documented from the eosteinhornensis Zone to early delta Zone with one new species of Walliserodus ( W. multistriatus ) and two new species of Ozarkodina ( O. brocki and O. camelfordensis ) described. An apparatus reconstruction of Belodella anomalis is also presented.  相似文献   

17.
The dawning of the Late Palaeozoic glaciations affected faunas of Gondwana and induced endemism. Deposits of that epoch occur in Argentina and Australia, and they yield the oldest record of some endemic taxa. The new bivalve genusAmosius n. gen. described here comes from the lower strata of theLevipustula levis Zone (Serpukhovian) of central Patagonia, where it is associated with the oldest Carboniferous glacial deposits.   相似文献   

18.
《Palaeoworld》2021,30(4):677-688
The Hongguleleng Formation, the highest and most important Devonian marine carbonate horizon in western Junggar, contains an endemic shallow-water IcriodusPolygnathus conodont fauna with rare palmatolepids and other genera. The conodont faunas from the Bulongguoer and the Wulankeshun sections are similar, with high abundance (about 40%) of endemic taxa (13 taxa), indicating isolation of the Junggar Basin during early Famennian. Non-endemic species in the faunas suggest that the Lower Member of the Hongguleleng Formation is assignable to the Pa. rhomboidea Zone to the Pa. marginifera marginifera Zone of early Famennian, not including the Frasnian–Famennian boundary. The Upper Member may be of late Famennian–early Tournaisian in age on the basis of our preliminary faunal analysis.  相似文献   

19.
盐胁迫对扁桃光合特性和叶绿体超微结构的影响   总被引:14,自引:0,他引:14  
温室条件下,分别用浓度为150、300、350 mmol/L的NaCl和Na2SO4处理‘石头扁桃’和‘桃扁桃’实生苗植株,处理10 d后分别测定其叶片叶绿素含量、净光合速率、气孔导度、细胞间隙CO2浓度,并观察叶绿体超微结构的变化。研究发现:(1)盐胁迫下,‘石头扁桃’和‘桃扁桃’chl a、chl b均在低浓度盐区含量最高,而在高浓度盐区含量最低,Na2SO4处理区chl a、chl b含量均低于NaCl处理区;(2)‘石头扁桃’和‘桃扁桃’叶片净光合速率随盐浓度的增加而下降,‘石头扁桃’下降的幅度较大;(3)‘桃扁桃’叶片细胞间隙CO2浓度随盐浓度的增加而升高,但‘石头扁桃’叶片细胞间隙的CO2浓度变化没有稳定的规律;(4)2个品种的叶片气孔导度均随盐浓度的增加而降低;(5)盐胁迫后,叶绿体基粒、基质片层扭曲,类囊体肿胀;随盐浓度的增加,形变加剧,叶绿体由椭圆形肿胀成圆形,叶绿体膜解体,且‘石头扁桃’叶绿体对盐胁迫比较敏感。综合分析发现,2种盐胁迫对植物造成伤害的机理不同,‘石头扁桃’的耐盐能力较差。  相似文献   

20.
《Palaeoworld》2022,31(1):69-85
The Devonian/Carboniferous (D/C) transition is characterized by a major transgressive/regressive cycle which led to a widespread ocean anoxia known as the Hangenberg Black Shale Event (HBSE), as well to a major sea-level fall (Hangenberg Sandstone Event, HSSE), recognized around the world. Both events are known as the Hangenberg Crisis. In order to examine the D/C transition in shallow water environment, the Mighan section in eastern Alborz was studied in terms of conodont biostratigraphy and stable isotope geochemistry. Twenty-five conodont species belonging to seven genera were identified and 5 conodont zones discriminated; namely, the Bispathodus aculeatus aculeatus Zone, Bispathodus costatus Zone, Bispathodus ultimus Zone, Siphonodella praesulcata Zone, costatus-kockeli Interregnum, and the sulcata Zone. Below the Devonian–Carboniferous boundary (DCB), the Hangenberg Black Shale and Hangenberg Sandstone equivalents were recognized, representing the Hangenberg Crisis that highly affected trilobite, ammonoid, brachiopod and conodont faunas at Mighan and worldwide. The kockeli Zone of the latest Famennian is missing at Mighan due to the lack of conodonts, probably related with the major environmental changes linked with the Hangenberg Crisis recognizable worldwide. Carbon isotopes measured of micrites from Mighan indicate a proximal depositional environment of a shallow shelf with terrestrial input and the oxygen isotope values from conodont apatite suggest warm seawater temperatures of tropical and subtropical setting in the study area.  相似文献   

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