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1.
Abstract Fossil otariid pinnipeds of the extinct genera Prototaria Takeyama and Ozawa, 1984, and Neotherium Kellogg, 1931, known from Middle Miocene deposits bordering the North Pacific Ocean, are small, primitive pinnipeds in the subfamily Imagotariinae. They have a small supraorbital process of the frontal or have lost it entirely, a three-rooted first molar, small paroccipital process, and ear morphology indicating that they belong in the subfamily Imagotariinae. Their unique derived characters include extreme intertemporal constriction and highly modified cheek teeth, the premolars having become molarized by the addition of protocones and lingual cingula. Prototaria Takeyama and Ozawa, 1984, the most primitive known imagotariine genus, contains two species, P. primigena Takeyama and Ozawa, 1984, and P. planicephala Kohno, 1994, both of early Middle Miocene age from Japan. Prototaria has a few derived characters, including a large antorbital process, narrow intertemporal region, and large orbit, but its primitive characters apparently were inherited from enaliarctine ancestors. The long enigmatic Neotherium mirum Kellogg, 1931, of Middle Miocene age from California, USA, is related to Prototaria, but differs by having an elongate skull, very slender zygomatic arch, ventrally exposed median lacerate foramen, and smaller but more molarized premolars. A more primitive new genus and species, Proneotherium repenningi Barnes, related to N. mirum, is from the early Middle Miocene Astoria Formation, coastal Oregon, USA. It shares some derived characters with Prototaria, and shares many other important derived characters with N. mirum. Imagotariines probably arose from some species of Early Miocene enaliarctines, became diverse in Middle and Late Miocene time, and are only known from the North Pacific realm. Although they might include the ancestors of true walruses of the subfamily Odobeninae, no known imagotariines appear to have been adapted for mollusk feeding as are the highly evolved modern walruses. Instead, imagotariines appear to have retained a primitive piscivorous diet, as did the fur seals and sea lions of the subfamily Otariinae.  相似文献   

2.
Hiroto  Ichishima 《Island Arc》1994,3(4):473-485
Abstract Kentriodon hobetsu , a new species, is described from a partial skull from the Middle Miocene Takinoue Formation, in Hokkaido, Japan. The holotype skull includes the base of the rostrum and a fairly well preserved braincase. The new species is distinguished clearly from previously described species of Kentriodon Kellogg, 1927, by the shape of the anterior margin of the pterygoid sinus fossa, the large premaxilla, rounded facial margin, and lesser development of rugosities and processes. This new record of Kentriodon , the first named kentriodontid dolphin from the western North Pacific, extends the geographic range of the genus significantly.  相似文献   

3.
Abstract Fossil pinnipeds in the extinct otariid subfamily Allodesminae are large, relatively highly evolved marine carnivores that became abundant and diverse in Middle Miocene time and were restricted to the North Pacific Ocean. Their record extends from early Middle Miocene through Late Miocene, with records from California, Oregon, Washington, Baja California and Japan. Allodesmines are characterized by extreme sexual dimorphism, a large orbit, retracted orbital margin of the zygomatic arch, a deeply mortised jugal-squamosal junction, wide palate, bulbous cheek tooth crowns, nearly flat tympanic bulla with wrinkled ventral surface, a large tympanohyal fossa, large ear ossicles and deep mandible. Eleven allodesmine species are known (eight of which are named), in at least four genera, and most belong to the typical genus Allodesmus Kellogg, 1922. The earliest and most generalized allodesmine known is from the early Middle Miocene (ca 16 Ma) Astoria Formation in coastal Oregon. The last known records are from Late Miocene rocks (ca 10 Ma) in California and Washington. New taxa proposed here are: the genus Brachyallodesmus Barnes and Hirota, to contain Allodesmus packardi Barnes, 1972; the genus Megagomphos Hirota and Barnes, to contain Allodesmus sinanoensis (Nagao, 1941); the species Allodesmus sadoensis Hirota, (Middle Miocene, Japan); the species Allodesmus megallos Hirota (Middle Miocene, Japan); and the species Allodesmus gracilis Barnes (Middle Miocene, California). Additionally, the genus Atopotarus Downs, 1956, and the species Allodesmus kelloggi Mitchell, 1966, are resurrected. Allodesmines were apparently a rapidly evolving group, and most appear to have been adapted to roles later filled by otariine, dusignathine and imagotariine otariids, and the Phocidae (true seals). They became extinct in Late Miocene time and left no living descendants. Although some of their characters evolved convergently with various living species of the pinniped family Phocidae, Allodesminae are an otariid group and not part of the evolutionary history of Phocidae.  相似文献   

4.
Abstract A nearly complete skeleton of a fossil sperm whale from the Middle Miocene age Bessho Formation at Shiga-mura, Nagano Prefecture, the most complete fossil physeterid skeleton found in Japan, is here named Scaldicetus shigensis, new species. Its abruptly tapered rostrum, deep supracranial basin, and high occipital crest are typical of physeterids. Large teeth with crenulate enamel on conical crowns, present in both the palate and mandible, are consistent with the genus Scaldicetus du Bus, 1867, a genus originally based on fossils discovered in the Antwerp Basin, Belgium. Scaldicetus shigensis is relatively primitive, having a relatively long, slender rostrum, large zygomatic arches, large tympanic bullae, prominent occipital condyles, low tooth count and a sloping occipital shield that is deeply emarginated laterally by large temporal fossae. The probable mandibular tooth count is 12, only one more than the primitive eutherian mammalian dentition. Despite its abundant primitive characters, Scaldicetus shigensis has very asymmetrical external nares, comparable to the living sperm whale, Physeter catodon, and is in this way more derived than most of the contemporaneous fossil physeterids. At a time when other sperm whales were more highly evolved, Scaldicetus shigensis retained a primitive occipital shield, large tympanic bullae, and low tooth count, as in primitive Oligocene odontocetes such as Agorophiidae. It was a relict form in Middle Miocene time, and provides an indication of a primitive stage of sperm whale evolution heretofore undocumented. Fossils from elsewhere previously referred to as Scaldicetus, largely on the basis of tooth characters, range in age from Early Miocene to Plio-Pleistocene time. Cranial material that would clarify relationships is lacking for most of these, and this time range seems too long for a cetacean genus. Because of this simplistic approach to identifications, Scaldicetus is probably a grade taxon, not a natural biological grouping. However, the tooth morphology of Scaldicetus shigensis is correct for the genus Scaldicetus, so we provisionally assign it to this genus. Redefinition of the genus Scaldicetus and revision of the Physeteridae are beyond the scope of the present study.  相似文献   

5.
Abundant palynological fossils are found from the drill core in the west slope of Songliao Basin, the first full coring borehole that drilled throughout the Neogene. Two Palynological assemblages are recognized according to their vertical distributions, i.e., the late early Miocene–middle Miocene assemblage from the Da'an Formation named as Caryapollenites simplex-Momipites coryloides-Celtispollenites sp.-Tsugaepollenites igniculus, and the late Miocene-early Pliocene assemblage from the Taikang Formation named as Artemisiaepollenites minor-Betulaceoipollenites sp.-Carpinipites sp.-Polypodiaceaesporites sp. On the basis of the composition of each assemblage, we infer that the climate was warm-temperate to sub-tropic during the late early Miocene–middle Miocene and the vegetation was mainly deciduous broadleaved forest and subordinate coniferous and broad-leaved mixed forest with few understory ferns, and probably some shallow fresh water wetlands. The climate then turned cooler and drier in the late Miocene–early Pliocene, represented by the development of xerophytic herbs and temperate plants, although the canopy of the forest remained relatively stable. The results significantly improve the understanding of the Cenozoic palynostratigraphy in the Songliao Basin, and provide new data for both stratigraphical correlation and paleovegetational and paleoclimatical analysis in adjacent area.  相似文献   

6.
The skull and mandible of a Late Miocene fossil pig,Chleuastochoerus,are compared morphologically with those of extant pigs and peccaries,and subjected to a functional analysis.The presence of a rostral bone in the skull and relatively strong rostral muscles indicates that Chleuastochoerus possessed considerable digging ability,though the relatively narrow occipital surface and the shortness of the skull would have restricted the range of motion through which the skull could be swung.The distinctive pre-zygomatic plate and over-canine arch-niche may have played a role in protecting the skull and canines during digging.The massive masticatory muscles,reconstructed based on well-developed parietal and zygomatic crests,would have enabled the mouth to close quickly and contributed to moving the mandible both longitudinally and laterally.The configuration of the cranio-mandibular joint and its relatively high position show clearly that Chleuastochoerus was capable of both crushing and grinding movements during mastication.The comparatively simple structure of the crown surfaces of the cheek teeth suggests that the food of Chleuastochoerus may have been softer than that of extant suids.The diet of Chleuastochoerus is postulated to fall between those of true forest pigs and open habitat pigs,and the habitat of Chleuastochoerus to be relatively humid forest edge or nearby areas of open steppe.  相似文献   

7.
Ergasilidae are a globally distributed group of copepods parasitising fish. Despite their common occurrence in European freshwaters, there is relatively little molecular data available. In this study, we recorded three ergasilid copepod species parasitising six fish species (families Cyprinidae, Percidae, Centrarchidae) in lentic water bodies along the River Morava in the Czech Republic: Ergasilus sieboldi infecting fish gills, Paraergasilus longidigitus infecting nasal cavities and Neoergasilus japonicus infecting fins. This represents a further occurrence of N. japonicus as a non-native European species, and the first report of P. longidigitusis from Central Europe waters. While strong niche selection potentially offers a free niche for each of these ergasilids in all hosts, parasite co-infections were relatively rare, with species distribution among hosts reflecting host preference. This study provides the first molecular data for E. sieboldi and P. longidigitus as native European ergasilid copepods. Phylogenetic analysis based on combined 18S and 28S rDNA showed a close relationship between P. longidigitus with other Paraergasilus species, supporting a monophyletic origin of this genus. The phylogenetic position of E. sieboldi was not clearly resolved, highlighting the need for more data and further intensive genetic investigations of other ergasilid species.  相似文献   

8.
The genus Paliurus is characterized by its distinctive orbicular-winged fruits and a trilocular (or bilocular) ovary. Macrofossil records suggested this genus was distributed widely in North America, Europe, and Asia during the Paleogene and Neogene, before its present limitation to Eurasia. In this study, we describe some Paliurus fossil winged fruits from the lower part of Youganwo Formation (middle Eocene) and Huangniuling Formation (late Eocene) of the Maoming Basin, South China. These fruits are recognized as Paliurus favonii Unger based on a detailed study on the fossil morphology and cuticle characteristics. This represents the earliest occurrence of Paliurus fossil fruits in eastern Asia, and to date is the world’s lowest latitude appearance for this genus. The most ancient records of Paliurus throughout the world are from the middle Eocene of North America and the late Eocene of Japan, leading some researchers to conclude the Paliurus may have originated in North America. Molecular data, however, do not support this hypothesis. The present Paliurus fossil fruits provide new evidence for the origin and phytogeographic history of this genus.  相似文献   

9.
We report a fossil specimen referable to Sinomastodontinae gen. et sp. indet. from the Neogene strata at Yanghecun locality, Xihe County, Gansu Province, China. The specimen is characterized by a brevirostrine mandible, complete pretrite trefoils, and relatively simple posttrite half lophids, showing typical features of Sinomastodon. It differs from the other known species of Sinomastodon by the following features: relatively short and wide m3 due to fewer lophid numbers, less inflated pretrite accessory central conules, poorly developed secondary trefoils and cementum, and relatively strong cingulid. All of these features indicate a bias towards pleisiomorphies of Sinomastodon, implying that this specimen is more ancestral than any known species of Sinomastodon. The symphysis of the new specimen is relatively long, which differs from the typical brevirostrine Sinomastodon, and thus we consider it a gen. et sp. indet. in the Subfamily Sinomastodontinae. In addition, the horizon in which the present specimen was found probably represents the Upper Miocene because it is lower than Pliocene strata yielding Hipparion (Proboscidipparon) pater. Generally, Sinomastodon is considered to have migrated from North America at about the time of the Miocene/Pliocene boundary, and to have been derived from a certain clade of American gomphotheres. However, the discovery of the Yanghecun specimen verifies that Sinomastodon lived in East Asia during the Late Miocene, and probably derived from Old World gomphotheres (e.g., G. wimani). The similarity between the members of the Subfamilies Sinomastodontinae and those of Cuvieroniinae is suggested to have been the result of parallel evolution.  相似文献   

10.
Superposition of paleomagnetic polarity logs of seven chronologically overlapping piston cores from the central equatorial Pacific, using the established tropical radiolarian zonation as a stratigraphic reference, produced a nearly continuous correlation of magnetic and radiolarian events ranging from late Pleistocene to earliest Miocene. Twenty magnetic polarity epochs, and possibly as many as 30 polarity events, occur during this time span. Epoch 16 (reversed polarity) appears to be the longest interval (～ 14.8–17.6m.y. B.P.) among these Neogene magnetostratigraphic units. The middle/late Miocene boundary is shown to fall within latest Epoch 11 (normal) and its approximate age is between 10.5 and 11 m.y. B.P. The early/middle Miocene boundary occurs within the top of Epoch 16 at a suggested age of about 15 m.y. B.P.  相似文献   

11.
Larvae of the lotic caddisfly genus Hydropsyche may occur in densities of thousands to several tens of thousands of individuals/m2 across continents and running water types. Therefore, stream ecologists frequently face the task of identifying larvae of this genus. Early keys to larval Hydropsyche of Asia, Europe and North America often used the relatively complicated frontoclypeal colour pattern for species discrimination, whereas equivocal views about the variation of this pattern limited its use in recent keys. Has each species of a given species group a different (although intraspecifically variable) basic pattern of lighter spots on the darker frontoclypeus, or have all species of a group the same basic colour pattern that varies more or less intraspecifically? An answer to this question has obvious implications for the identification of the species as well as for the phylogeny of the genus, so we examined the variation of this colour pattern across ∼11,000 specimens of 10 Hydropsyche species from the Loire River (France).All 10 species had the same basic colour pattern on the frontoclypeus (six contrasting light patches on a dark background) that varied intraspecifically across a certain range of colour contrasts. Comparing other sources illustrating the frontoclypeus of Hydropsyche larvae provided more support for the idea that six contrasting light patches on the frontoclypeus is the typical basic colour pattern that varies within almost all European species; males of these species have a simple phallus form. Two European and many North American species of the genus (from the Ceratopsyche group) have a different basic colour pattern of seven light patches on the frontoclypeus that varies also intraspecifically; males of these species have a complicated phallus form.If the variation of such colour patterns in co-existing populations of several species is known, the relative contrast differences among the individual patches on the frontoclypeus and the form of the individual patches can provide valuable information for rapid species identification. Analysis of this variation may also contribute to phylogenetic studies of the genus Hydropsyche and other hydropsychids.  相似文献   

12.
Abstract The Upper Cenozoic sedimentary sequences drilled at Sites 1150 and 1151, Ocean Drilling Program Leg 186, enabled establishment of radiolarian zonation and calibration of the age of bioevents in the forearc area of the northern Japan Islands. The sequences were divided into nine zones from the Pleistocene Botryostrobus aquilonaris Zone to the Upper Miocene Lipmanella redondoensis Zone at Site 1150, and 11 zones from the Pleistocene Stylatractus universus Zone to the Middle Miocene Dendrospyris? sakaii Zone at Site 1151. These zones correlate successfully with the studied sequences of many of deep‐sea cores in the Northwest Pacific Ocean and with some sections of onshore Japan. Of 67 important radiolarian bioevents recognized during the study, 29 Pleistocene to Upper Miocene events were directly tied to the geomagnetic polarity time scale through the well‐defined paleomagnetic polarity records, and 21 Upper Miocene events were calibrated based on the diatom biostratigraphy. Of these events, 24 geographically widespread events were selected to test synchroneity and usefulness as time‐horizons within the mid‐to‐high latitude of the Northwest Pacific, involving eight other offshore and onshore sections. Examination showed that most of the zonal boundary events are synchronous within the considered region, and that many diachronous events, most of which are eliminated from the zonal scheme, are unreliable events linked to rare and sporadic occurrences of the species. Radiolarian biostratigraphy of the studied cores clearly indicates three major hiatuses in the Middle Pleistocene, Late Miocene and late Middle Miocene. The latter two hiatuses can be correlated to two global oceanic hiatuses, NH6 and NH3, respectively.  相似文献   

13.
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14.
The extension of the magnetic reversal record back to the early Miocene is presented. This record is pieced together with the aid of microfloral analysis from three low sedimentation rate siliceous deep sea cores from the Equatorial Pacific.Nineteen Magnetic Epochs are now recognized from the earliest Miocene to the Present. By correlating the micropaleontological data in our cores with selected foraminiferal datums from DSDP Leg IX we correlate these datums with the following magnetic epochs: the Pulleniatina Datum occurs in the lower part of Epoch 5, the G. acostaensis Datum occurs in Epoch 11, the G. nepenthes Datum occurs in Epoch 12, the Orbulina Datum at the Epoch 15/16 boundary and the G. dissimilis Datum in the lower part of Epoch 16. The Early/Middle Miocene boundary (Orbulina Datum) is tentatively placed at the top of Epoch 16.  相似文献   

15.
The East Asian monsoons have fluctuated in concert with high-latitude warmth during the past several hundred thousand years, with humid summer monsoon-dominant climates characterizing warm intervals, including interglacials and interstadials, and arid winter monsoon-dominant climates characterizing cool intervals, including glacials and stadials. Of the states comprising the mid-Pleistocene to recent climatic regime, interglacials are most similar in terms of high latitude ice volumes and temperatures to those extant during the late Miocene and early Pliocene. Thus, an important question is whether Mio-Pliocene climates in northern China were analogous to a hypothetical ‘prolonged interglacial state,’ with increased summer monsoon precipitation and expansion of forest and steppe environments at the expense of desert environments.We utilize new and previously published carbon isotopic data from fossil teeth and soil carbonates to place constraints on paleovegetation distributions and to help infer the behavior of the monsoon system between ～ 7 and 4 Ma. We find that plants using the C4 photosynthetic pathway—which today are largely grasses found in regions with warm season precipitation—were present in northern China by late Miocene time, demonstrating that the C4 expansion in China was not significantly delayed compared to the global C4 event. During the late Miocene–early Pliocene interval, soil carbonate and tooth enamel δ13C data indicate: 1) that nearly pure C3-plant ecosystems existed in the southern Chinese Loess Plateau (CLP), and therefore ecosystems there were dominated by woody dicot, herbaceous dicot, or cool-season grass vegetation (or a combination of these), and 2) that the CLP was characterized by a pattern of northward-increasing C4 vegetation and aridity. Utilizing a broadened conceptual model for interpreting δ13C data, and citing independent faunal, floral, and lithostratgraphic data, we suggest that these patterns reflect northward expansion of forest and steppe ecosystems and relatively humid monsoon climates during the late Miocene and early Pliocene. An important implication of this interpretation is that the forcing mechanism illuminated by the temporal correlation during the Pleistocene between warm high latitudes and strong East Asian summer monsoons is a robust feature of the Eurasian tectonic–climatic system that predates the Plio-Pleistocene climatic reorganization.  相似文献   

16.
Four araphid diatom taxa were collected from Florida streams and studied with both light microscopy (LM) and scanning electron microscopy (SEM). Three taxa, formerly in the genus Fragilaria Lyngbye, are here placed in the genus Pseudostaurosira Williams et Round. On the basis of ultrastructure observed by SEM, the remaining taxon is placed in a new genus, Sarcophagodes. At least two of the species referred to Pseudostaurosira may have been confused with species of the genus Opephora Petit, which may have led to misinterpretation of the ecological characteristics of the latter genus.All the taxa treated here belong to the Family Fragilariaceae Greville as delimited in current classification schemes. Two new combinations Pseudostaurosiropsis geocollegarum (=Fragilaria geocollegarum Witkowski et Lange-Bertalot), Pseudostaurosira neoelliptica (=Fragilaria neoelliptica Witkowski) and the new species Pseudostaurosira clavatum are presented herein. Additionally, a new genus, Sarcophagodes, is erected to accommodate the new species S. delicatula. LM and SEM details, as well as criteria delimiting these taxa are discussed. More collections and further analyses are needed to assess the distribution of both Opephora and Sarcophagodes.  相似文献   

17.
马尼拉俯冲带北段增生楔前缘构造变形和精细结构   总被引：1，自引：0，他引：1       下载免费PDF全文
马尼拉俯冲带是南海的东部边界,记录了南海形成演化的关键信息,同时也是地震和海啸多发区域.本文利用过马尼拉俯冲带北段的高分辨率多道地震剖面,分析了研究区内海盆和海沟的沉积特征,精细刻画了区内增生楔前缘的构造变形、结构以及岩浆活动特征.研究区内增生楔下陆坡部分由盲冲断层、构造楔和叠瓦逆冲断层构成,逆冲断层归并于一条位于下中新统的滑脱面上,滑脱面向海方向的展布明显受到增生楔之下埋藏海山和基底隆起的影响;上陆坡的反射特征则因变形强烈和岩浆作用而难以识别;岩浆活动开始于晚中新世末期并持续至第四纪.马尼拉俯冲带北段增生楔的形成时间早于16.5 Ma,并通过前展式逆冲向南海方向扩展;马尼拉俯冲带的初始形成时间可能在晚渐新世,而此时南海海盆扩张仍在持续.南海东北缘19°N-21°N区域为南海北部陆坡向海盆的延伸,高度减薄的陆壳的俯冲造成马尼拉海沟北段几何形态明显地向东凹进.  相似文献   

18.
Lithological and geochemical features of platformal carbonates record the signatures of the global climates and the regional environmental settings and also reconstruct the diagenetic history and porosity evolution, which are essential to evaluate the potential of hydrocarbon reservoirs. This study investigates the platformal carbonates of the Oligo‐Miocene Krunji Formation of North East Java Basin, which are potentially significant hydrocarbon reservoirs. The carbonate sequence in a 283 m thick section at Kranji in East Java is subdivided into three lithological units: limestone unit 1, dolostone unit 2, and limestone unit 3, in ascending order. The strontium‐isotope ratios of well‐preserved calcite samples indicate the depositional period from Chattian (late Oligocene) to Burdigalian (early Miocene), which is consistent with ages of the foraminifer assemblages. Unit 1 consists of low‐porosity limestone, in which two horizons of subaerial exposure are recognized by the occurrence of red‐colored matrix and lower δ13C values. Unit 2 consists of dolomitic rock and exhibits coarse‐grained calcitic grains and cross‐stratified structure. Considering that this unit has been subject to dolomitization, the sediment of unit 2 was initially permeable and was likely deposited in a shoal setting. The overlying unit 3 of Aquitanian–Burdigalian age is characterized by a highly granular texture. High porosity and uniformly low δ13C and δ18O values indicate that Unit 3 was subjected to more intense meteoric diagenesis than the Chattian unit 1. This was likely a consequence of the Antarctic ice‐sheet expansion during the Oligocene/Miocene transition, which amplified sea level change. The unit 2 dolomite has high δ13C and δ18O values and a high 87Sr/86Sr ratio which resulted from the reflux of seawater into permeable the sediment body in middle‐late Miocene (Burdigalian Tortonian) following the deposition of unit 3. The porosity and permeability of the Kujung Formation were initially controlled by sedimentological processes, but largely modified by later diagenetic processes.  相似文献   

19.
Paleomagnetic results from the northern arm of Sulawesi show that the arm has been subjected to a clockwise rotation of more than 90° and that its rotational motion began no later than the middle Miocene. The mean direction showing a normal polarity at the Eocene to the early Miocene isD = 98.0° andI = 6.9°. A declination value ofD = 50.1° obtained from Miocene rocks indicates a transition stage of the rotational motion. The datum from Plio-Pleistocene volcanics isD = ?4.6° andI = ?9.3°. This suggests that the rotational motion terminated before the initiation of volcanic activity during the Plio-Pleistocene.  相似文献   

20.
Calcareous nannoplankton experienced rapid diversification at the Jurassic/Cretaceous boundary, including the appearance of several highly successful and long-ranging Cretaceous genera. This study examines, at high-resolution, calcareous nannofossil assemblages and bulk-rock oxygen and carbon isotopes of lower Tithonian to lower Berriasian (∼ 151 to 142 Ma) sediments recovered in Deep Sea Drilling Project Hole 534A, central Atlantic Ocean. The results show major changes in assemblage composition and abundance of three genera (Conusphaera, Nannoconus, and Polycostella). Conusphaera dominates the nannolith assemblage in the late middle Tithonian (“Conusphaera world”), while the nannoconid dominance (“Nannoconus world”) began in the Berriasian. The acme peak of the genus Polycostella in the late Tithonian partially superimposes that of Conusphaera. Although these genera are indicators of warm, oligotrophic surface waters, stable isotope data suggest that the individual taxa may flourish in slightly different ecological regimes. Nannoconus flourished under warmer and possibly more nutrient-depleted surface waters than Polycostella, a genus that thrived in relatively cooler waters. These findings imply paleoceanographic changes across the J/K boundary interval with a cooling in the late Tithonian, followed by a temperature increase in the Berriasian. Because the transfer of these heavily calcified nannolith taxa to the seafloor is more efficient than that of average coccolithophorids, the J/K evolutionary event changed carbonate cycling and burial in the oceans.  相似文献   

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