Taphonomic versus ecologic controls on taxonomic relative abundance patterns in tempestites

Evaluation of taphonomic sample bias in tempestites is an important prerequisite for paleoecologic analysis in storm-dominated shelf settings. Data from tempestites in the Upper Cambrian Bison Creek Formation of southern Alberta indicate that size, sorting greatly influences trilobite relative abundance patterns. Shifts in relative abundances of taxa both within and between beds are matched by changes in trilobite size. That is, collections fall into two intergrading types of assemblage which are dominated by taxa which reach large and small adult sizes, respectively. These shifts in dominance are interpreted as taphonomic variability within a single trilobite biofacies. Biofacies differentiation is expressed as abrupt changes in relative abundance patterns that are independent of trilobite size. Qualitative general models for size-sorting in tempestites are developed. Size-sorting in graded tempestites produces vertical shifts in relative abundances of taxa that mimic those expected in short-term autogenic ecologic succession. Size-sorting between beds in a single section could lead to an overestimation of the number of biofacies present. Size-sorting between proximal and distal portions of a depth gradient might generate abundance patterns that mimic those expected for 'depth-related communities', even in the complete absence of any underlying ecologic differentiation. The models represent taphonomic null hypotheses which must be rejected prior to making paleoecologic inferences in storm-dominated shelf environments. 0 Taphonomy, tempestites, Trilobita, Upper Cambrian, paleoecology.     

Relative abundances of living and dead molluscs in two Californian lagoons

Assemblages of living benthic invertebrates (predominantly bivalve molluscs) from the sand-channel habitat of two Southern California (U.S.A.) lagoons were sampled on ten occasions over a 37-month period. A one-time sampling of the corresponding assemblages of accumulating dead remains made possible a contrast of living and dead assemblages designed to assess the biasing effects of post-mortem transportation, shell dissolution, and time-averaging. Species-by-species comparisons of the living and dead molluscs found together in the same samples strongly suggested that post-mortem transportation is insignificant within this high-energy habitat. A similar conclusion arose from contrasting the pattern of spatial heterogeneity of the living community with that of the dead assemblage. Species presence-and-absence comparisons were generally more reliable than comparisons of relative abundances. Adjustments for experimentally determined rates of post-mortem shell dissolution proved significant and further decreased the correspondence in relative abundances between living and dead assemblages. Greater temporal variability of living populations at Mugu Lagoon, probably caused by a more harsh physical environment, increased the differences in composition between living and dead assemblages, which suggests that correspondence in relative abundances between living and dead assemblages generally should be expected to decrease as the life environment becomes more harsh.     

Hosts as habitats: faunal similarity of phytophagous insects between host plants

1. Published lists on the phytophages recorded on 86 cabbage plant species (Brassicaceae) and 30 thistle species (Cynaroideae) were used to investigate patterns in the faunal similarity of phytophages. This was done by calculating the Jaccard index and a standardised index of similarity between pairs of host species using presence/absence data. 2. The faunal similarity measured as Jaccard indices indicated that pairs of cabbage hosts share on average 36% of phytophagous species whereas pairs of thistle hosts share only 10%. 3. The faunal similarity between two host species increased with the taxonomic affinity of hosts. This increase was more pronounced in thistles than in cabbage plants. 4. Irrespective of the taxonomic affinity of hosts, in the cabbage plants the faunal similarity of endophages was lower than in ectophages. In contrast, in the thistles faunal similarity differed only between endophages and ectophages for hosts of the same genera. 5. Differences in the patterns of faunal similarity between the two host taxa may be due to idiosyncratic characteristics of the plant taxa, e.g. the unique chemical properties of the cabbage plants and the resource‐rich flower heads of thistles.     

Effects of plot size on the ordination of vegetation samples

Questions: Do ordination patterns differ when based on vegetation samples recorded in plots of different size? If so, how large is the effect of plot size relative to the effects of data set heterogeneity and of using presence/absence or cover‐abundance data? Can we combine plots of different size in a single ordination? Methods: Two homogeneous and two heterogeneous data sets were sampled in Czech forests and grasslands. Cover‐abundances of plant species were recorded in series of five or six nested quadrats of increasing size (forest 49‐961 m2; grassland 1‐49 m²). Separate ordinations were computed for plots of each size for each data set, using either species presences/absences or cover‐abundances recorded on an ordinal scale. Ordination patterns were compared with Procrustean analysis. Also, ordinations of data sets jointly containing plots of different size were calculated; effects of plot size were evaluated using a Monte Carlo test in constrained ordination. Results: The results were consistent between forest and grassland data sets. In homogeneous data sets, the effect of presence/absence vs. cover‐abundance was similar to, or larger than, the effect of plot size; for presence/absence data the differences between ordinations of differently sized plots were smaller than for cover‐abundance data. In heterogeneous data sets, the effect of plot size was larger than the effect of presence‐absence vs. cover‐abundance. The plots of smaller size (= 100 m2 in forests, = 4 m² in grasslands) yielded the most deviating ordination patterns. Joint ordinations of differently sized plots mostly did not yield patterns that would be artifacts of different plot size, except for plots from the homogeneous data sets that differed in size by a factor of four or higher. Conclusions: Variation in plot size does influence ordination patterns. Smaller plots tend to produce less stable ordination patterns, especially in data sets with low ß‐diversity and species cover‐abundances. Data sets containing samples from plots of different sizes can be used for ordination if they represent vegetation with large ß‐diversity. However, if data sets are homogeneous, i.e. with low ß‐diversity, the differences in plot sizes should not be very large, in order to avoid the danger of plot size differences distorting the real vegetation differentiation in ordination patterns.     

云南早寒武世澄江化石库中两种埋藏相的化石定量分析

通过昆明海口马房村同一个采坑的化石连续采集和统计,对澄江化石库中两种埋藏相(以事件层泥岩和背景层泥岩所代表)内化石保存和组合特征进行定量研究,结果表明:(1)事件层内化石量并不随单一事件层厚度变化而变化。物种在剖面上不同层位的事件层内分布不均匀,表现为单层富集现象;而背景层内的化石含量与背景层的沉积厚度有关,背景层的沉积厚度越厚,化石数量就越多。(2)事件层与背景层内化石组合和结构存在很大差异。事件层内化石组合与背景层内化石组合相比具有更多的物种组成和更复杂的古群落结构;而背景层内化石组合面貌单调,在剖面上保持稳定。(3)事件层内化石生物体腐烂发生在埋藏之后,绝大多数化石生物是被活埋后保存下来的;而背景层内化石主要表现为外壳和弱矿化有机质生物表皮在海床表面长时间停滞而堆积形成,明显受到时间均衡作用(time-average)的影响。(4)事件层内化石在埋藏前无搬运作用,或发生近原栖息地的快速搬运,埋藏后无生物扰动。背景层内大量壳体相连的双瓣壳节肢动物化石和完整海绵体化石的存在则表明,背景层代表一个低氧、低能并具有有限生物扰动的沉积环境。     

The large-mammal fauna from the Kibish Formation

The Kibish faunal remains are useful for reconstructing the habitat of the earliest documented Homo sapiens and for understanding the community within which early modern humans existed. A diverse assemblage of large mammals, including many species of bovids, suids, and equids, has been recovered from the Kibish Formation. There are no extinct large mammals represented in the fossil assemblage, and the overall taxonomic composition of the fossil fauna is similar to the modern-day wildlife community living near the Omo River. The fossil faunal assemblage shows a paucity of arboreal primates, and carnivore species are rare. However, the faunal sample includes possible Cephalophus (duiker) remains and Hylochoerus meinertzhageni (giant forest hog), taxa that are extremely rare in the African fossil record, and both indicate more closed habitats. Comparative analyses of the Kibish faunal remains using the ecological-diversity approach document close associations with edaphic grassland and woodland vegetation types. These vegetation forms are similar to current habitats surrounding the Omo River.     

Faunal change, environmental variability and late Pliocene hominin evolution

Global change during the late Pliocene was manifested in declining temperatures, increased amplitude of climate cycles, and shifts in the periodicity of orbital climate forcing. Linking these changes to the evolution of African continental faunas and to hominin evolution requires well-documented fossil evidence that can be examined through substantial periods of time. The Omo sequence of southern Ethiopia provides such a database, and we use it to analyze change in the abundances of mammal taxa at different levels of temporal and taxonomic resolution between 4 and 2 Ma. This study provides new evidence for shifts through time in the ecological dominance of suids, cercopithecids, and bovids, and for a trend from more forested to more open woodland habitats. Superimposed on these long-term trends are two episodes of faunal change, one involving a marked shift in the abundances of different taxa at about 2.8+/-0.1 Ma, and the second the transition at 2.5 Ma from a 200-ka interval of faunal stability to marked variability over intervals of about 100 ka. The first appearance of Homo, the earliest artefacts, and the extinction of non-robust Australopithecus in the Omo sequence coincide in time with the beginning of this period of high variability. We conclude that climate change caused significant shifts in vegetation in the Omo paleo-ecosystem and is a plausible explanation for the gradual ecological change from forest to open woodland between 3.4 and 2.0 Ma, the faunal shift at 2.8 +/-0.1 Ma, and the change in the tempo of faunal variability of 2.5 Ma. Climate forcing in the late Pliocene is more clearly indicated by population shifts within the Omo mammal community than by marked turnover at the species level.     

Littoral benthos of a Victorian lake and its outlet stream: Spatial and temporal variation

Abstract There have been few comparative studies of the fauna in the two major types of freshwater systems, lakes and streams, in the one locality. This study compared the faunal assemblages at two times of the year (summer and winter) on stones in three locations: the littoral zone of two shores in Lake Purrumbete (one wave-exposed and one sheltered) and riffles in the Curdies River, which flows out of the lake. The lake fauna was dominated by crustaceans, gastropods and planarians, whereas the stream fauna was dominated by insects. The most abundant lake taxa were also present, but much less abundant, in the stream. The total number of species and individuals and densities of some common species varied between the three locations and between seasons. However, no consistent pattern reflecting a difference between the two lake shores was evident. Interpretation of MDS ordinations of the lake fauna was dependent on the data standardizations applied, with increased separation of the season-location combinations when species were standardized to equal total abundances; the seasonal difference was always greatest for the exposed (cliff) shore. In contrast, MDS on the stream fauna showed seasonal differences under all standardizations. This was consistent with the high seasonal turnover of species in the stream compared with the lake. These results demonstrate that, even within a local area with similar geology and connected water bodies, lake and stream fauna from the same substratum (stones) can be markedly different. Taxa that occurred in both were more abundant in the lake, whereas seasonal differences in abundance were much greater in the stream.     

The assessment of arboreal insect fauna: comparisons of knockdown sampling and faunal lists

Abstract. 1. A comparison is made between the fauna of six British tree species sampled by pyrethrum knockdown and the faunal lists in the literature for the same tree species.
2. Conspecific trees vary both in abundance of arthropods and their proportional distribution across taxa, but there are important overriding differences between tree species.
3. The percentage similarity in faunal composition between tree species reflects the ecological specificity of the arthropod groups used for the comparison.
4. The similarity in species composition between tree species is least for phytophages, the guild most closely associated with particular tree species, The two species of Salix are most similar in their fauna for most guilds.
5. About 40% of the entirely phytophagous species in the faunal lists for native trees were found in the knockdown samples.
6. The proportion of individuals of predominantly phytophagous taxa collected that belong to the relevant faunal lists ranges from 0.39 to 0.99.
7. Those species found in the knockdown samples which are not included in faunal lists none the less contribute to the trophic web of the tree.
8. The relative species richness of arboreal faunas assessed from knockdown samples parallels that derived from faunal lists.
9. The two approaches to the categorization of arboreal faunas, knockdown sampling and faunal lists, provide comparable data.     

Coral assemblages, biofacies, and ecological zones in the mid-Holocene reef deDosits of the Enriquillo Valley, Dominican Republic

Stemann, T. A. & Johnson, K. G. 1992 07 15: Coral assemblages, biofacies. and ecological zones in the mid-Holocene reef deposits of the Enriquillo Valley, Dominican Republic. A large, subaerially exposed mid-Holocene reef in the Enriquillo Valley (southwest Dominican Republic) provides an excellent opportunity to examine the relationship between reefal ecology and reefal deposits. Coral species richness and diversity in the Enriquillo reef are comparable to that found in the recent of the Caribbean, and ecological zonation comprised of a shallow-water branching coral zone and a deeper water mixed-coral zone is apparent. Similar zonation and diversity patterns have been recognized on living Caribbcan reefs with moderate wave exposure. Three statistically discrete biopdcies can be discriminated in the Enriquillo deposits using quadrat point-counting techniques commonly used to census modern reefs. They include a facies dominated by Acropora cervicornis, a low diversity assemblage with abundant, large colonies of Siderastrea siderea and Stephanocoenia intersepta, and a higher diversity assembbdge composed of various taxa including Montastraea spp., Colpophyllia spp., and Agaricia spp. Each facies can be recognized at scales of 1–3 m², though in some cases they extend for more than 20 m². In general, the A. cervicornis facies is spatially segregated from the other two biofacies. although neither the shallow nor the deep-water ecological zone is comprised of a single reef biofacies. Rather, the biofacies described here appear to represent distinct micro-environments resulting from ecological variation at a subzonal scale. Micro-environments of similar scale are most likely preserved in other reef deposits. Recognition of these subzonal biofacies may have important consequences for the stratigraphical and paleoccological interpretation of fossil reefs. Corals, biofacies, reef zonation, coral communities, fossil reefs.     

Taxonomic and Numerical Resolutions of Nepomorpha (Insecta: Heteroptera) in Cerrado Streams

Transformations of natural landscapes and their biodiversity have become increasingly dramatic and intense, creating a demand for rapid and inexpensive methods to assess and monitor ecosystems, especially the most vulnerable ones, such as aquatic systems. The speed with which surveys can collect, identify, and describe ecological patterns is much slower than that of the loss of biodiversity. Thus, there is a tendency for higher-level taxonomic identification to be used, a practice that is justified by factors such as the cost-benefit ratio, and the lack of taxonomists and reliable information on species distributions and diversity. However, most of these studies do not evaluate the degree of representativeness obtained by different taxonomic resolutions. Given this demand, the present study aims to investigate the congruence between species-level and genus-level data for the infraorder Nepomorpha, based on taxonomic and numerical resolutions. We collected specimens of aquatic Nepomorpha from five streams of first to fourth order of magnitude in the Pindaíba River Basin in the Cerrado of the state of Mato Grosso, Brazil, totaling 20 sites. A principal coordinates analysis (PCoA) applied to the data indicated that species-level and genus-level abundances were relatively similar (>80% similarity), although this similarity was reduced when compared with the presence/absence of genera (R = 0.77). The presence/absence ordinations of species and genera were similar to those recorded for their abundances (R = 0.95 and R = 0.74, respectively). The results indicate that analyses at the genus level may be used instead of species, given a loss of information of 11 to 19%, although congruence is higher when using abundance data instead of presence/absence. This analysis confirms that the use of the genus level data is a safe shortcut for environmental monitoring studies, although this approach must be treated with caution when the objectives include conservation actions, and faunal complementarity and/or inventories.     

An 11400 year paleoecological history of a British chalk grassland

The first broad-based, paleoecological analysis of a sedimentary sequence on the British chalk, dating to the terminal Pleistocene, reveals a history of climatic, vegetational and faunal change. The past co-occurrence of currently allopatric species among molluscs, beetles and plants supports hypotheses of the impermanence of communities. Modern pollen rain data are utilized to refine the ecological interpretation of the fossil pollen data. The presence of the Windermere Interstadial (Allerod) and the Loch Lomond re-advance (Younger Dryas) are represented by decreased abundances of arboreal taxa and increased representation of cold grassland elements. Open grassland habitats appear to have been a continuous landscape element, at least locally, since the late-glacial period on the northern British chal Mands, although their species composition has changed greatly in the last 11400 yr.     

Floristic turnover in Iceland from 15 to 6 Ma – extracting biogeographical signals from fossil floral assemblages

Aim This study aims to document the floristic changes that occurred in Iceland between 15 and 6 Ma and to establish the dispersal mechanisms for the plant taxa encountered. Using changing patterns of dispersal, two factors controlling floristic changes are tested. Possible factors are (1) climate change, and (2) the changing biogeography of Iceland over the time interval studied; that is, the presence or absence of a Miocene North Atlantic Land Bridge. Location The North Atlantic. Methods Species lists of fossil plants from Iceland in the time period 15 to 6 Ma were compiled using published data and new data. Closest living analogues were used to establish dispersal properties for the fossil taxa. Dispersal mechanisms of fossil plants were then used to reconstruct how Iceland was colonized during various periods. Results Miocene floras of Iceland (15–6 Ma) show relatively high floristic turnover from the oldest floras towards the youngest; and few taxa from the oldest floras persist in the younger floras. The frequencies of the various dispersal mechanisms seen in the 15‐Ma floras are quite different from those recorded in the 6‐Ma floras, and there is a gradual change in the prevailing mode of dispersal from short‐distance anemochory and dyschory to long‐distance anemochory. Two mechanisms can be used to explain changing floral composition: (1) climate change, and (2) the interaction between the dispersal mechanisms of plants and the increasing isolation of proto‐Iceland during the Miocene. Main conclusions Dispersal mechanisms can be used to extract palaeogeographic signals from fossil floras. The composition of floras and dispersal mechanisms indicate that Iceland was connected both to Greenland and to Europe in the early Middle Miocene, allowing transcontinental migration. The change in prevalence of dispersal modes from 15 to 6 Ma appears to reflect the break‐up of a land bridge and the increasing isolation of Iceland after 12 Ma. Concurrent gradual cooling and isolation caused changes in species composition. Specifically, the widening of the North Atlantic Ocean prevented taxa with limited dispersal capability from colonizing Iceland, while climate cooling led to the extinction of thermophilous taxa.     

Paranasal pneumatization in extant and fossil Cercopithecoidea

Unlike most primates, extant cercopithecoids lack maxillary sinuses, which are pneumatic spaces in the facial skeleton lateral of the nasal cavity proper. Character state analysis of living cercopithecoids across well-supported topologies suggests that the sinus was lost at the origin of the superfamily, only to have evolved again convergently in extant macaques. Recent work has shown that a) the 'early loss' hypothesis is supported by the lack of any pneumatization in Victoriapithecus, a stem cercopithecoid, b) like extant macaques, the fossil cercopithecine Paradolichopithecus shows evidence of presence of the maxillary sinus (MS), and c) unlike extant colobines, the fossil colobine Libypithecus also possesses a maxillary sinus. To more fully assess the pattern of cercopithecoid sinus evolution, fossil taxa from both subfamilies (Colobinae, Cercopithecinae) were examined both visually and by computed tomography (CT). The observations were evaluated according to standard anatomical criteria for defining sinus spaces, and compared with data from all extant Old World monkey genera. Most taxa examined conformed to the pattern already discerned from extant cercopithecoids. Maxillary sinus absence in Theropithecus oswaldi, Mesopithecus, and Rhinocolobus is typical for all extant cercopithecids except Macaca. The fossil macaque Macaca majori possesses a well-developed maxillary sinus, as do all living species of the genus. Cercopithecoides, on the other hand, differs from all extant colobines in possessing a maxillary sinus. Thus, paranasal pneumatization has reemerged a minimum of two and possibly three times in cercopithecoids. The results suggest that maxillary sinus absence in cercopithecoids is due to suppression, rather than complete loss.     

Late Miocene biota from the Abad Member of the Carboneras-Nijar Basin (Spain,Andalusia): A bathyal fossil assemblage pre-dating the Messinian salinity crisis

Marly sediments of the early Messinian Abad Member of the Turre Formation from the northeastern sector of the Carboneras-Nijar Basin (southern Spain) have yielded a rich fossil assemblage, of which 60 taxa are documented herein. Besides nannoflora and microfauna, this assemblage includes the first autochthonous macrofauna described from the Abad Member. Based on the calcareous nannofossil assemblage, in particular the occurrence of the zonal index taxon Amaurolithus primus, the sediments are assigned to the Mediterranean calcareous nannofossil zone CNM17, corresponding to the latest Tortonian to earliest Messinian interval. This matches the age range generally reported for the Abad Member. Palaeoecological evidence from calcareous nannofossils (20 autochthonous taxa), planktic and benthic foraminifera (12 taxa), Porifera (3 taxa), Octocorallia (Keratoisis), Serpulidae (4 taxa), Bivalvia (5 taxa), Gastropoda (2 taxa), Brachiopoda (7 taxa), Cirripedia (Faxelepas) and Vertebrata (5 taxa) indicates an upper bathyal environment with an influx of neritic elements for the Abad Member near Carboneras. Additionally, several faunal components may represent allochthonous/parautochthonous elements from adjacent habitats, which were transported into the deep marine setting by turbiditic mass flows. Although similarities exist, the fossil assemblage from the marls is compositionally significantly different from the biota previously documented from a nearby exposed olistostrome, the ‘red breccia’. Similar fossil assemblages from the Mediterranean have so far mainly been reported from the Pliocene-Pleistocene of southern Italy and Greece. The Carboneras fauna thus adds to our knowledge of the development of these habitats and their biota prior to the Messinian salinity crisis. Beyond the novel palaeoenvironmental data, the range of the dyscoliid brachiopod Ceramisia meneghiniana, previously known only from the Pliocene of Italy, is extended to the Miocene of Spain. The cirripede crustacean Pycnolepas paronai De Alessandri, 1895 is transferred to the hitherto monospecific genus Faxelepas Gale, 2015, whereby the range of the latter (previously Maastrichtian to Danian) is extended to the late Miocene.     

POTENTIAL PITFALLS OF RECONSTRUCTING DEEP TIME EVOLUTIONARY HISTORY WITH ONLY EXTANT DATA,A CASE STUDY USING THE CANIDAE (MAMMALIA,CARNIVORA)

Reconstructing evolutionary patterns and their underlying processes is a central goal in biology. Yet many analyses of deep evolutionary histories assume that data from the fossil record is too incomplete to include, and rely solely on databases of extant taxa. Excluding fossil taxa assumes that character state distributions across living taxa are faithful representations of a clade's entire evolutionary history. Many factors can make this assumption problematic. Fossil taxa do not simply lead‐up to extant taxa; they represent now‐extinct lineages that can substantially impact interpretations of character evolution for extant groups. Here, we analyze body mass data for extant and fossil canids (dogs, foxes, and relatives) for changes in mean and variance through time. AIC‐based model selection recovered distinct models for each of eight canid subgroups. We compared model fit of parameter estimates for (1) extant data alone and (2) extant and fossil data, demonstrating that the latter performs significantly better. Moreover, extant‐only analyses result in unrealistically low estimates of ancestral mass. Although fossil data are not always available, reconstructions of deep‐time organismal evolution in the absence of deep‐time data can be highly inaccurate, and we argue that every effort should be made to include fossil data in macroevolutionary studies.     

The late Sandbian – earliest Katian (Ordovician) brachiopod immigration and its influence on the brachiopod fauna in the Oslo Region, Norway

Bulk samples of brachiopods from the middle and upper parts of the Arnestad Formation and the entire Frognerkilen Formation in the Oslo Region demonstrate major vertical changes in the Sandbian to Katian amphicratonic fauna of this part of the Baltic Province. The main influx of new taxa occurred in the upper part of the Arnestad Formation (uppermost Sandbian), and in the succeeding Frognerkilen Formation (basal Katian). Faunal change is initially reflected in an increase in diversity and not as a replacement of the previously incumbent genera, which remain throughout the studied sequence. The majority of the new genera migrated from the East Baltic Region or through this region from Avalonia, while the marginal Laurentian taxa first occupied the Scandinavian part of Baltica. Six taxa migrated from Laurentia, three from Avalonia, two from Gondwana and one apparently originated on the South China palaeoplate. The faunal shifts and immigration of brachiopods appear to have been in response to an initial transgression together with the movement of Baltica into more warm temperate latitudes, but the diverse faunas developed both against a background of subsequent regression and in response to an offshore shift of biofacies. The new amphicratonic fauna was thus generated by faunal shifts from elsewhere in the Baltic Province to the marginal environments of the Oslo Region together with more exotic elements from neighbouring continents and microcontinents.     

内蒙古中部新近纪动物群的演替与生物年代

内蒙古中部地区陆相新近系出露广、含化石丰富。对这一地区新近纪的研究,可以追溯到20世纪初期瑞典地质学者安特生(J．G．Andersson)、法国古生物学者德日进(P．Teilhar de Chardin)和以美国探险家安德鲁斯(R．C．Andrews)为首的美国自然博物馆中亚考察团分别对二登图、高特格和通古尔的考察与化石采集。他们的开拓性工作使这些地方成为中国十分重要的新近纪经典地点。特别是通古尔,由于其产出的化石丰富、具有中中新世动物群的特征, 已引入中国地质年表,作为新生代中一个“阶”的名称。最近20多年对这一地区新近纪生物地层学的研究又取得了很大的进展,新发现了数个不同时代的化石地点和层位,同时采集到大批哺乳动物化石标本。内蒙古中部各地点化石层的厚度一般不大,但所含的哺乳动物化石种类多、材料丰富。由于具有这一特点,使其化石组合能比较接近地反映短期内动物群体的结构面貌,较客观地指示沉积时期的生态环境。利用这些组合进行动物群相对时代的确定,以及对其生态环境的恢复无疑都会很有意义。但是,这里的地层缺乏测试绝对年龄的材料,化石组合间少见有直接的叠置关系,使得在这一地区建立独立的动物群时间顺序,确定动物群的演替序列和生物年代只能更多地依赖于对动物系统发育和动物群体变化的研究。本文对这一地区各地点发现的哺乳动物化石组合进行了审定,提供了最新的动物群名单;根据默尔根地点上部层位产出的化石组合特征,提议把该组合命名为铁木钦动物群;通过对哺乳动物系统发育关系的分析,将动物群进行先后排序,并阐述了这些动物群在各生物年代的演替特征;同时展示了各动物群与有关岩石地层和磁性地层的关系。文中进一步认定了苏尼特左旗的嘎顺音阿德格动物群为内蒙古中部地区现知新近纪动物群中的最早代表,其后依次为推饶木动物群、默尔根动物群、铁木钦动物群、阿木乌苏动物群、沙拉动物群、宝格达乌拉动物群、二登图动物群、哈尔鄂博动物群、比例克动物群、高特格动物群。内蒙古中部被认为是新近纪生物年代学研究的重要地点,在地质时代上这一哺乳动物群系列跨越了新近纪中新世至上新世的大部分时段。其中的嘎顺音阿德格动物群具有中国陆生哺乳动物年代山旺期的典型持征;推饶木动物群、默尔根动物群、铁木钦动物群构成的广义通古尔动物群,正是定义东亚中中新世陆生哺乳动物年代的依据;阿木乌苏动物群、沙拉动物群、宝格达乌拉动物群和二登图动物群符合保德期动物群的含义;比例克动物群和高特格动物群具有榆社期动物群的性质。虽然目前还无法根据这些动物群对我国陆生哺乳动物年代的时限进行精确界定, 但依某些动物阶元(主要为科和属一级)的最早迁入或在该区的最早出现,以及在该区地层中的最后出席,概述了内蒙古中部地区新近纪动物群所指示的哺乳动物年代特征,并分别把通古尔期和保德期细分为3个和4个非正规亚期。深入的研究,包括在这一地区发现新的化石层位和材料,不仅会为内蒙古中部地区生物年代的厘定提供更多的资料,而且有助于完善中国新近纪地质年代的内涵。     

Benthic foraminiferal distributions in Chilean fjords: 47°S to 54°S

Surface sediment samples collected from the fjord region of southern Chile (47° to 54° South) were analyzed for benthic foraminifera. A total of 175 species were identified including agglutinated and calcareous benthic taxa. Hierarchical cluster analysis of the foraminiferal data resulted in the recognition of three distinct biofacies: inner-fjord, intermediate fjord and channel, and oceanic biofacies, geographically controlled by relative position between the Pacific Ocean and fjord heads. Similarity percentage (SIMPER) analysis identified key taxa in the definition of the biofacies that include Globocassidulina rossensis, Cassidulina laevigata and Bulimina notovata. Principal components analysis resulted in two principal components representing sediment size, and bottom water temperature and salinity.Regional distributions are strongly controlled by the oceanographic conditions influenced from the Pacific in the west and the glacial/freshwater input from the east. Localized distributions of foraminifera are controlled by conditions influenced by the physiography of the individual fjords and channels. The distribution of Chilean fjord foraminifera and their environmental associations are consistent with results from other temperate to high latitude fjord foraminiferal studies.     

The Cladocera (Crustacea: Branchiopoda) as a relict group

According to the fossil record and DNA data, the Cladocera is an ancient crustacean group. Recent revisions make their taxonomy amenable to zoogeographical analysis. A bipolar (antitropical) disjunct distribution of faunal complexes and taxa ( Daphnia , Daphniopsis , Pleuroxus , Tretocephala , etc.), the wide ranges of some species and narrow restriction of others, the presence of isolated populations and the concentration of endemics in the warm temperate – subtropical zone of both hemispheres are traits of cladoceran zoogeography. These enable us to compare them with better studied (both living and fossil) plants, invertebrates and vertebrates, and to analyse their faunal formation by the modern version of the concept of 'ejected relicts' instead of vicariance. This reveals the extant Cladocera as a relict group, whose taxa were widely distributed in the past. Tertiary climatic changes, primarily within the present tropical and boreal latitudes, resulted in mass extinction of their biotas, while the warm temperate – subtropical regions remained comparatively unchanged. Although most recent Cladocera have relict status, others such as the D. pulex and D. longispina species groups and the subgenus Eubosmina are evolutionary young and show recent speciation.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 147 , 109–124.