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1.
    
Diversity indices (dominance and evenness) and ecological spatial structure (lifestyles and relative abundances) are important features of Changhsingian brachiopod communities prior to the end-Permian mass extinction (EPME) and could predict temporal and spatial extinction patterns during the EPME. In South China, Changhsingian brachiopod communities show higher diversity than other contemporaneous brachiopod communities in the world and have been reported from a variety of sedimentary environments. In this paper, brachiopods from 18 sections in South China were selected to divide communities and compare their ecological structure. Based on the results of network analysis, cluster analysis and quantitative data from the selected sections, we show that Changhsingian brachiopod communities in South China can be categorized into three assemblages along a marine depth gradient: the Neochonetes–Fusichonetes–Paryphella Assemblage from the shallow-water clastic-rock facies, Spinomarginifera–Peltichia–Oldhamina Assemblage from the shallow-water carbonate platform facies and Fusichonetes–Crurithyris Assemblage from the deep-water siliciclastic intracontinental basin facies. Compared with communities from carbonate platform facies, the communities from siliciclastic facies were characterized by high dominance, low evenness and low lifestyle diversity, which might be important biotic factors leading to earlier extinctions. After the extinction began in all environments, the whole earliest Triassic brachiopod community was first dominated by Fusichonetes and then by Crurithyris. These patterns of domination and replacement could be explained by morphological and ecological advantages. The domination of these two genera, which were already adapted to the oxygen and food-limited deep-water habitat, indicates that the cooler deep-water environment might have been a relatively less stressed habitat after the beginning of the EPME. This suggests that global warming might be the main trigger among the previously proposed synergistic environmental stresses, while anoxia might not, at least for the beginning of EPME.  相似文献   

2.
报道了新种子摩,新变种勐海醉藤;云南新记录种石核木,多香木,兰屿山矾及归并新异名微毛越南山矾。  相似文献   

3.
    
Aim Various methods are employed to recover patterns of area relationships in extinct and extant clades. The fidelity of these patterns can be adversely affected by sampling error in the form of missing data. Here we use simulation studies to evaluate the sensitivity of an analytical biogeographical method, namely tree reconciliation analysis (TRA), to this form of sampling failure. Location Simulation study. Methods To approximate varying degrees of taxonomic sampling failure within phylogenies varying in size and in redundancy of biogeographical signal, we applied sequential pruning protocols to artificial taxon–area cladograms displaying congruent patterns of area relationships. Initial trials assumed equal probability of sampling failure among all areas. Additional trials assigned weighted probabilities to each of the areas in order to explore the effects of uneven geographical sampling. Pruned taxon–area cladograms were then analysed with TRA to determine if the optimal area cladograms recovered match the original biogeographical signal, or if they represent false, ambiguous or uninformative signals. Results The results indicate a period of consistently accurate recovery of the true biogeographical signal, followed by a nonlinear decrease in signal recovery as more taxa are pruned. At high levels of sampling failure, false biogeographical signals are more likely to be recovered than the true signal. However, randomization testing for statistical significance greatly decreases the chance of accepting false signals. The primary inflection of the signal recovery curve, and its steepness and slope depend upon taxon–area cladogram size and area redundancy, as well as on the evenness of sampling. Uneven sampling across geographical areas is found to have serious deleterious effects on TRA, with the accuracy of recovery of biogeographical signal varying by an order of magnitude or more across different sampling regimes. Main conclusions These simulations reiterate the importance of taxon sampling in biogeographical analysis, and attest to the importance of considering geographical, as well as overall, sampling failure when interpreting the robustness of biogeographical signals. In addition to randomization testing for significance, we suggest the use of randomized sequential taxon deletions and the construction of signal decay curves as a means to assess the robustness of biogeographical signals for empirical data sets.  相似文献   

4.
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5.
    

Motivation

We have little understanding of how communities respond to varying magnitudes and rates of environmental perturbations across temporal scales. BioDeepTime harmonizes assemblage time series of presence and abundance data to help facilitate investigations of community dynamics across timescales and the response of communities to natural and anthropogenic stressors. BioDeepTime includes time series of terrestrial and aquatic assemblages of varying spatial and temporal grain and extent from the present-day to millions of years ago.

Main Types of Variables Included

BioDeepTime currently contains 7,437,847 taxon records from 10,062 assemblage time series, each with a minimum of 10 time steps. Age constraints, sampling method, environment and taxonomic scope are provided for each time series.

Spatial Location and Grain

The database includes 8752 unique sampling locations from freshwater, marine and terrestrial ecosystems. Spatial grain represented by individual samples varies from quadrats on the order of several cm2 to grid cells of ~100 km2.

Time Period and Grain

BioDeepTime in aggregate currently spans the last 451 million years, with the 10,062 modern and fossil assemblage time series ranging in extent from years to millions of years. The median extent of modern time series is 18.7 years and for fossil series is 54,872 years. Temporal grain, the time encompassed by individual samples, ranges from days to tens of thousands of years.

Major Taxa and Level of Measurement

The database contains information on 28,777 unique taxa with 4,769,789 records at the species level and another 271,218 records known to the genus level, including time series of benthic and planktonic foraminifera, coccolithophores, diatoms, ostracods, plants (pollen), radiolarians and other invertebrates and vertebrates. There are to date 7012 modern and 3050 fossil time series in BioDeepTime.

Software Format

SQLite, Comma-separated values.  相似文献   

6.
( 1 ) Some taxonomical problems of the genus Clematis mainly about misidentificationsare discussed, and some treatments including the reinstatement of Clematis montana var. brevifoliola Kuntze, C. apiifolia var. biternata Makino, C. subumbellata Kurz, C. goudotiana Planch.& Triana, C. insidiosa Baill., C. kockiana Schneid. and C. longicauda A. Rich., and the reduction of subsect. Africanae M. Johnson, C. umbellifera Gagnep., C. pubescens Benth., C.rhodocarpa Rose, C. edentata Baker, C. stoltzi Engler, C. tibetana ssp. vernayi var. dentataGrey-Wilson, C. clarkeana var. stenophylla Hand.-Mazz., C. subfalcata Pei ex M.Y. Fang,C. angustifoliola W. T. Wang, C. dasyandra var. polyantha Finet & Gagnep. etc are given.(2) The new diagnoses for the two subsections of the sect. Meclatis are provided; C. sericea H.B.K. ex DC. and C. grossa Benth. are treated as two varieties of one species; and a new classification of the infraspecific taxa of C. hirsuta Perr & Guill. is made. (3) one subsection, one series,eight species and one variety are described as new. (4) The new occurrences of C. montana var.brevifoliola Kuntze in southern Xizang, China, Nepal, Bhutan and northern Myanmar, C. burmanica Lace in southwestern Yunnan, C. armandii Franch. in Assam, India and northern Myanmar,and C. yui W. T. Wang in northern Myanmar are reported.  相似文献   

7.
于1999年5月至9月,作者先后访问了K、BM、P和S四个植物标本馆,在查阅他们收藏的铁线莲属植物标本的过程中,发现该属的一些分类学问题：(1)发现过去一些学者分别错误地将Clematis montana var．brevifoliola Kuntze,C．apiifolia var．biternata Makino,C．subumbellata Kurz,C．goudotiana Planch．&; Triana,C．insidiosa Baill.,C．kockiana Schneid．和C．longicauda A．Rich．等加以归并,这些均应予以恢复。(2)发现过去发表的subsect．Africanae M．Johnson,C．umbellifera Gagnep.,C．pubescens Benth.,C．rhodocarpa Rose,C．edentata Baker,C．djalonensis Cheval.,C．oliveri Kuntze,C．tibetana ssp．vernavi var．dentata Grey-Wilson,C．yunuanensis var．brevipedunculata W．T .Wang,C．clarkeana var．stenophylla Hand．-Mazz,C．subfalcata Pei ex M．Y．Fang,C．angustifoliola W．T .Wang,C．dasyandra var．polyantha Finet &; Gagnep.等学名不能成立,应加以归并。(3)对构成黄花铁线莲组sect．Meclatis的二亚组给出新的特征集要;根据C．sericea B．H．K．ex DC．与C．grossa Benth．的形态区别不大,有时甚至难以区分以及二者的分布区一南一北互相邻接的分布格局,认为二者可能为一对姊妹群,并将其等作为一个种的两个地理变种处理;认为在非洲大陆广布并分布到阿拉伯半岛的C．hirsuta Perr．&; Guill．包含4变种;将过去置于C．oweniae Harv．的变种var．jonodii移到此种中,并根据C．inciso-dentata A．Rich．特殊的绵毛毛被和内面无毛的萼片等特征,否定过去一些学者将其归并于C．hirsuta的意见,也将其作为C．hirsuta的一个变种处理。(4)描述了单性铁线莲组sect．Aspidanthera的一个特产马达加斯加岛的新亚组subsect．Insid iosae W．T．Wang和尾叶铁线莲亚组subsect．Connatae的一个特产非洲大陆的新系ser．Grandiflorae W．T． Wang以及8新种、1新变种。(5)发现杨宗愈等(1991)报道的秀丽铁线莲C．grata Wall．在我国7省区 (西藏东部、云南、四川、贵州、湖北、湖南、江西)有分布所依据的8号标本均非C．grata,而分别是与此 种相近缘的5个种或变种。(6)发现了伏毛绣球藤C．montana var．brevifoliola Kuntze(原知分布于锡金和印度西北部)在我国西藏、尼泊尔、不丹和缅甸北部,缅甸铁线莲C．burmanica Lace(原知分布于缅甸和 泰国)在我国云南西南部,小木通C．armandii Franch．(原知分布于我国长江流域、越南)在缅甸北部和印 度东北部,以及俞氏铁线莲C．yui W．T．Wang(原知分布于我国云南西北部和西藏东南部)在缅甸北部 的新分布。  相似文献   

8.
    
We present a summary of the fossil evidence documenting the worldwide occurrence of the family Hydrophilidae (Insecta: Coleoptera: Polyphaga: Hydrophiloidea) in the Late Jurassic and Early Cretaceous. We present the first known fossils of the family from the Mesozoic, being c. 100 Myr older than the fossil record available until now. Two Late Jurassic fossils are documented: P rotochares brevipalpis gen. nov., sp. nov. from the Talbragar Fish Bed (New South Wales, Australia) and ‘Mesosperchus’ schultzi Ponomarenko, 1985 from Solnhofen (Bavaria, Germany). The occurrence of the Hydrophilidae in the Early Cretaceous is documented by six species, all of which may be already assigned to modern subfamilies/tribes: B aissalarva hydrobioides gen. nov., sp. nov. from the Baissa outcrops (Buryat Republic, Russia) and C retoxenus australis gen. nov., sp. nov. from Koonwarra outcrops (Victoria, Australia) are both assigned to the tribe Hydrobiusini (Hydrophilinae); A legorius yixianus gen. nov., sp. nov. and Alegorius sp. from the Yixian Formation (Liaoning, China) may represent the Acidocerinae or Enochrinae, H ydroyixia elongata gen. nov., sp. nov. and H . latissima sp. nov. from the same locality are assigned to the Acidocerinae. The phylogenetic position of Baissalarva hydrobioides is also tested by a phylogenetic analysis. The presence of extant clades (Hydrophilinae: Hydrobiusini, Acidocerinae) in the Early Cretaceous and the wide distribution of the Hydrobiusini in both Gondwana and Laurasia at the same time suggests that the principal extant clades of the Hydrophilidae are at least of Early–Middle Jurassic origin. © 2014 The Linnean Society of London  相似文献   

9.
最近在中国十个省市发现了一个新记录属——巴克斯霉属Backusella,包括一个种的两个变种,即卷曲巴克斯霉原变种B.circina var.circina和卷曲巴克斯霉改级光孢变种B. circina var. lamprospora stat. nov. ≡ B. lamprospora。文章对这两个变种提供了形态描述和线条图,还提供了属内区分所有可以承认的分类群的检索表。把这两个分类群从种级降为变种级的理由亦有所讨论。ITS rDNA序列分析表明,卷曲巴克斯霉是一个多系类群,与放射毛霉属Actinomucor、毛霉属Mucor和根毛霉属Rhizomucor有着密切的谱系关系。这一结果暗示目前的卷曲巴克斯霉种的概念较大,可称为广义卷曲巴克斯霉B.circina s.l.;如果仅仅依靠分子数据,很有可能给出错误的分类学鉴定结果。  相似文献   

10.
    
Abstract: The quality of the Triassic–Jurassic bivalve fossil record in northwest Europe has been measured using the Simple Completeness Metric (SCM). The SCM has been applied to the fossil record of total bivalve diversity and to the records of different ecological guilds. The Westbury and Lilstock Formations record high SCM values for most ecological groups. The ‘Pre‐Planorbis Beds’ of the lower Lias Group, however, witness a precipitous decline in the completeness of most guilds and emigration of taxa due to localized marine anoxia is a likely cause. Neither variation in lithofacies, shell mineralogy, sedimentary rock outcrop area, nor sequence architecture can convincingly explain the observed patterns of completeness. Our SCM data reveal that the Early Jurassic fossil record of infaunal suspension‐feeding bivalves is significantly poorer than that of epifaunal bivalves. Any differences in the apparent Rhaetian extinction rates between these two guilds should therefore be viewed with caution. Analyses of selectivity during the Late Triassic mass extinction based on studies of global databases appear robust in light of our SCM data. Nevertheless, future investigations of the Triassic–Jurassic benthic marine ecosystem undertaken at a finer‐resolution, may need to account for the poor quality of the Early Jurassic fossil records of certain ecological guilds, such as the infaunal suspension‐feeding taxa.  相似文献   

11.
Abstract:  Palaeodiversity curves are constructed from counts of fossils collected at outcrop and thus potentially biased by variation in the rock record, specifically by the amount of sedimentary rock representative of different time intervals that has been preserved at outcrop. To investigate how much of a problem this poses we have compiled a high-resolution record of marine rock outcrop area in Western Europe for the Phanerozoic and use this to generate a model that predicts the sampled diversity curve. We find that we can predict with high accuracy the variance of the marine genus diversity curve (itself dominated by European taxa) from rock outcrop data and a three-step model of diversity that tracks supercontinent fragmentation, coalescence and fragmentation. The size and position of two of the five major mass extinction spikes are largely predicted by rock outcrop data. We conclude that the long-term trends in taxonomic diversity and the end-Cretaceous extinction are not the result of rock area bias, but cannot rule out that rock outcrop area bias explains many of the short-term rises and falls in sampled diversity that palaeontologists have previously sought to explain biologically.  相似文献   

12.
植物名称是人类对植物研究与利用等活动的基础。植物名称的变化可能成为不同行业之间交流的障碍, 错误或含混的植物名称可能会造成不便甚至损失。北京作为中国的首都, 在生物多样性保护与生态文明建设的背景下, 对于植物多样性信息变化的管理水平和能力要求更高。及时并准确地更新植物名称的变化及其过程, 对于植物学工作者、园林工作者和与植物相关产业从业者都十分重要。本文基于过去30年间(1992‒2021年)北京各类维管植物的名称信息, 记录了自1993年《北京植物志》(1992年修订版)以来的维管植物名称的变化过程: 包括34个新类群、175个新记录、509个新异名, 49个错误鉴定, 以及50个存疑类群。过去30年间, 北京的维管植物发生了很大的变化。本文结果可作为北京维管植物多样性监测和保护的重要参考。  相似文献   

13.
    
Abstract:  The heterodont bivalve Sinbadiella pygmaea gen. et sp. nov. is described from the Sinbad Limestone Member (Olenekian, Smithian) of the Lower Triassic Moenkopi Formation of Utah (USA). The new taxon is tentatively assigned to the Lucinidae on the grounds of its external morphology, larval shell morphology and hinge characters. It is the only definite representative of the Superorder Heterodonta in the Olenekian, removing this major clade of bivalves from the long list of Early Triassic Lazarus taxa. Although at least locally very abundant, the new taxon has been overlooked by earlier workers, probably due to its minute size. Dwarfism is a widespread phenomenon in Early Triassic faunas, which has been attributed to ongoing reduction of primary production. If S .  pygmaea was a lucinid, a chemosymbiotic feeding mode can be inferred, which might explain why it was able to thrive in conditions that suppressed filter feeding heterodonts.  相似文献   

14.
    
The pollen content of 31 honey samples from 19 different apiaries of El Hierro (Canary Islands) were subject to qualitative and quantitative melissopalynological analysis. The quantitative analysis demonstrated that 13% of the honey belonged to Maurizio Class I (<2?000?grains), 68% to Class II (2?000–10?000?grains) and 19% to Class III (10?000–50?000?grains). The pollen density ranges from 1?042?grains/g of honey to 24?478?grains/g with an average of 7?471?grains/g. According to the qualitative analysis, six honeys were typified as unifloral and 25 as multifloral. The unifloral honey samples were broken down as follows: two of heather (Erica arborea L.), two of Chamaecytisus proliferus (L. f.) Link‐type (“tagasaste”), one of Fabaceae (Genisteae sp.) and one of Lamiaceae Origanum vulgare L. ssp. virens (Hoffmanns. &; Link) Ietsw.‐type (thyme: Micromeria hyssopifolia Webb &; Berthel.). Honeydew elements were practically absent. Sixty‐nine pollen types were identified belonging to 42 families. The number of pollen types range between 18 and 39 (mean of 27.42). Foeniculum vulgare Mill.‐type pollen is present in all the samples. Galactites tomentosa Moench‐type, Echium plantagineum L., Echium L. sp., Bituminaria bituminosa (L.) C. H. Stirt., Chamaecytisus proliferus ‐type and Origanum vulgare ssp. virens ‐type pollen were found in 96.8% of the samples. The sensorial analysis indicated that honey types are generally of good quality, because 62% were evaluated as very high (16%), high (23%), and good (23%).  相似文献   

15.
    
The distribution of last occurrences of fossil taxa in a stratigraphic column are used to infer the pattern, timing and tempo of extinction from the fossil record. Clusters of last occurrences are commonly interpreted as an abrupt pulse of extinction. However, stratigraphic architecture alone can produce clusters of last occurrences that can be misinterpreted as an extinction pulse. These clusters will typically occur in strata that immediately underlie facies changes and sequence‐stratigraphic surfaces. It has been proposed that a basin‐wide analysis of the fossil record within a sequence‐stratigraphic framework can be used to distinguish between clusters of last occurrences caused solely by extinction pulses from those generated by sequence‐stratigraphic architecture. A basin‐wide approach makes it possible to observe lateral facies shifts in response to sea‐level change, mitigating the effects of stratigraphic architecture. Using computer simulations of plausible Late Ordovician mass‐extinction scenarios tuned to an inferred Late Ordovician sea‐level curve, we show that stratigraphically‐generated clusters of last occurrences are observed even in basin‐wide analyses of the simulated fossil records due to the basin‐wide loss of preferred facies for many taxa. Nonetheless, we demonstrate that by coarsening the stratigraphic resolution to the systems‐tract level and identifying facies preferences of simulated taxa, we can filter out taxa whose last occurrences coincide with the basin‐wide loss of their preferred facies. This enables consistent identification of the underlying extinction pattern for a wide variety of extinction scenarios. Applying this approach to empirical field data can help to constrain underlying extinction patterns from the fossil record.  相似文献   

16.
    
The Paleogene (Paleocene-Oligocene) fossil record of birds in Europe is reviewed and recent and fossil taxa are placed into a phylogenetic framework, based on published cladistic analyses. The pre-Oligocene European avifauna is characterized by the complete absence of passeriform birds, which today are the most diverse and abundant avian taxon. Representatives of small non-passeriform perching birds thus probably had similar ecological niches before the Oligocene to those filled by modern passerines. The occurrence of passerines towards the Lower Oligocene appears to have had a major impact on these birds, and the surviving crown-group members of many small arboreal Eocene taxa show highly specialized feeding strategies not found or rare in passeriform birds. It is detailed that no crown-group members of modern 'families' are known from pre-Oligocene deposits of Europe, or anywhere else. The phylogenetic position of Paleogene birds thus indicates that diversification of the crown-groups of modern avian 'families' did not take place before the Oligocene, irrespective of their relative position within Neornithes (crown-group birds). The Paleogene fossil record of birds does not even support crown-group diversification of Galliformes, one of the most basal taxa of neognathous birds, before the Oligocene, and recent molecular studies that dated diversification of galliform crown-group taxa into the Middle Cretaceous are shown to be based on an incorrect interpretation of the fossil taxa used for molecular clock calibrations. Several taxa that occur in the Paleogene of Europe have a very different distribution than their closest extant relatives. The modern survivors of these Paleogene lineages are not evenly distributed over the continents, and especially the great number of taxa that are today restricted to South and Central America is noteworthy. The occurrence of stem-lineage representatives of many taxa that today have a restricted Southern Hemisphere distribution conflicts with recent hypotheses on a Cretaceous vicariant origin of these taxa, which were deduced from the geographical distribution of the basal crown-group members.  相似文献   

17.
    
Elucidating the mechanisms underlying microbial succession is a major goal of microbial ecology research. Given the increasing human pressure on the environment and natural resources, responses to the repeated introduction of organic and inorganic pollutants are of particular interest. To investigate the temporal dynamics of microbial communities in response to pollutants, we analysed the microbial community structure in batch microcosms that were inoculated with soil bacteria following exposure to individual or combined pollutants (phenanthrene, n‐octadecane, phenanthrene + n‐octadecane and phenanthrene + n‐octadecane + CdCl2). Subculturing was performed at 10‐day intervals, followed by high‐throughput sequencing of 16S rRNA genes. The dynamics of microbial communities in response to different pollutants alone and in combination displayed similar patterns during enrichment. Specifically, the repression and induction of microbial taxa were dominant, and the fluctuation was not significant. The rate of appearance for new taxa and the temporal turnover within microbial communities were higher than the rates reported in other studies of microbial communities in air, water and soil samples. In addition, conditionally rare taxa that were specific to the treatments exhibited higher betweenness centrality values in the co‐occurrence network, indicating a strong influence on other interactions in the community. These results suggest that the repeated introduction of pollutants could accelerate microbial succession in microcosms, resulting in the rapid re‐equilibration of microbial communities.  相似文献   

18.
不同生境毁坏速度下的物种灭绝机制   总被引：1，自引：0，他引：1       下载免费PDF全文
刘会玉  林振山  温腾  梁仁君 《生态学报》2007,27(6):2410-2418
已有似Levins的多物种模型,在研究生境毁坏的影响时,一方面主要集中在对瞬间毁坏影响的研究,另一方面主要研究生境毁坏对强物种影响的研究。在Tilman的多物种竞争共存模型的基础上,同时考虑了生境毁坏直接效应和生境毁坏时间异质性,提出了全新的普适的多物种竞争共存的非自治动力模式。通过模拟物种灭绝对不同速度的生境毁坏时间异质性的响应发现：（1）物种灭绝既存在强物种由强到弱的灭绝,也存在弱物种由弱到强的灭绝。同时,弱物种灭绝机制进一步分为弱物种瞬间集体灭绝,以及较长时间由弱到强的灭绝。（2）生境毁坏速度越快,物种灭绝的时间越短,弱物种灭绝的越多,因此,生境毁坏速度越慢,越有利于弱物种的长期续存。（3）最强物种的多度越大,强-强物种抵御生境毁坏的能力越强,而弱-弱物种抵御生境毁坏的能力越弱,集体灭绝的弱-弱物种就越多。最强物种的多度大的群落（如温带森林）,主要发生的是弱-弱物种灭绝,而最强物种多度小的群落（如热带雨林）同时发生强-强和弱-弱物种的灭绝。因此,争对不同结构的集合种群,不同的保护对象,应采取不同的管理策略。  相似文献   

19.
本文总结了2022年国内外学者发表的中国鳞翅目新分类单元的情况。经过统计, 2022年共发表与中国鳞翅目物种相关的论文98篇, 涉及新分类群238个, 其中新属8个, 新亚属1个, 新种214个, 新亚种15个; 报道中国新记录属5个, 中国新记录种76个(包括5个亚种), 新组合28个; 提出26个异名, 4个物种降为亚种, 5个亚种提升为种。229个新种(新亚种)隶属于鳞翅目的27科103属, 其中127个新种隶属于小蛾类, 86个新种隶属于大蛾类, 蝶类有3个新种和13个新亚种。2022年发表的分布于云南省的鳞翅目新种和新记录种数仍然显著高于其他地区, 分别占全国发表总数的24.02%和55.26%, 我国南方新种和新记录种的数量仍显著高于北方。  相似文献   

20.
Palaeobiodiversity analysis underpins macroevolutionary investigations, allowing identification of mass extinctions and adaptive radiations. However, recent large-scale studies on marine invertebrates indicate that geological factors play a central role in moulding the shape of diversity curves and imply that many features of such curves represent sampling artefacts, rather than genuine evolutionary events. In order to test whether similar biases affect diversity estimates for terrestrial taxa, we compiled genus-richness estimates for three Mesozoic dinosaur clades (Ornithischia, Sauropodomorpha and Theropoda). Linear models of expected genus richness were constructed for each clade, using the number of dinosaur-bearing formations available through time as a proxy for the amount of fossiliferous rock outcrop. Modelled diversity estimates were then compared with observed patterns. Strong statistically robust correlations demonstrate that almost all aspects of ornithischian and theropod diversity curves can be explained by geological megabiases, whereas the sauropodomorph record diverges from modelled predictions and may be a stronger contender for identifying evolutionary signals. In contrast to other recent studies, we identify a marked decline in dinosaur genus richness during the closing stages of the Cretaceous Period, indicating that the clade decreased in diversity for several million years prior to the final extinction of non-avian dinosaurs at the Cretaceous–Palaeocene boundary.  相似文献   

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