重庆万州下侏罗统自流井组湖相遗迹化石新类型及其古环境意义*

描述在重庆万州区铁峰山下侏罗统自流井组大安寨段首次发现的遗迹化石,鉴定为新种Palaeophycus tiefengshanensis。该种以潜穴表面瘤状凸起特征与较大的潜穴尺寸区别于古藻迹其他遗迹种。遗迹组构分析表明该遗迹化石产出层位的层面生物扰动指数为最高级5,说明原始沉积环境的食物供给充足,氧含量高,造迹生物大量繁盛并活动频繁。根据沉积相变化特征,四川盆地东部地区自流井组沉积期经历了与四川盆地北部地区类似的古环境变迁即湖退过程。两者区别在于四川盆地东部自流井组局部层段可能更适宜底栖动物生存。     

云南早寒武世化石库中的鳃足类和遗迹化石的共生标本

笔者在参加中国古生物学会 2 2届学术年会期间 ,有幸听了贵州工业大学的王约老师作的关于凯里生物群中的一些水母状动物化石和遗迹化石共生保存研究的学术报告 ,在王老师的报告中 ,展示了很多奇特的水母状化石的标本 ,在这些水母状化石的标本上都可以看到有很多虫迹化石分布。有的穿插整个水母状动物而过 ,有的从边缘穿插 ,有的在动物的中部向下潜穴。目前认为这些遗迹是由于造迹生物去吃死去的水母状动物的腐烂尸体而形成的 ,这个理论得到了多数人的认可。回云南之后 ,我观察了我们云南出产的很多甲壳类生物的表面 ,同样发现了很多遗迹化石…     

遗迹歧异度（ichnodisparity）：另眼看寒武纪生命大爆发

遗迹歧异度作为评估生物成因构造中形态轮廓变化的概念被引入,它揭示出造迹生物个体轮廓、运动系统和行为过程的主要创新。遗迹歧异度是基于形态结构设计的测量鉴别,而遗迹多样性是指遗迹分类的数量,即遗迹属或遗迹种的数量。本文统计前寒武纪-寒武纪之交(埃迪卡拉纪和寒武纪纽芬兰世、第二世)的88个遗迹属,并鉴定出40个形态结构设计类型,其中前寒武纪包含22个形态结构设计类型,遗迹多样性为32;寒武纪遗迹形态结构设计类型为38个,遗迹多样性为82。前寒武纪-寒武纪之交的遗迹化石资料显示,埃迪卡拉纪和寒武纪幸运期之交是遗迹多样性与遗迹歧异度的突变期,两者数量均显著增加。这表明造迹生物在数量上急剧增加,在形态类型上更加多样,造迹生物的个体轮廓、运动方式以及行为过程都渐趋复杂、多样,有力地支持了寒武纪生命大爆发事件。遗迹歧异度和遗迹多样性相结合,将会进一步增强遗迹学在演化古生物学中的重要性。     

西南极乔治王岛早第三纪遗迹化石

南极乔治王岛始新统化石山组含多种类型遗迹化石,常与鸟类足迹相伴产出。记述的１新遗迹属及所属的５新遗迹种,从遗迹化石形态两侧对称,纵向延伸,缺乏疣足及其它附肢构造等特征看,推测造迹者为软体蠕虫类,很可能属于寡毛纲的动物。这些化石反映了浅水河湖的沉积环境。     

豫西寒武系苗岭统张夏组Talassinoides bacae 中莓状黄铁矿的成因及其生态学意义

豫西寒武系苗岭统张夏组薄层微晶灰岩中发育了大量的Thalassinoides bacae遗迹化石,利用微区X射线荧光光谱仪和扫描电镜观察,并结合能谱分析,对Thalassinoides bacae遗迹化石的元素分布及微观特征进行分析。结果表明:衬壁与围岩的元素特征相似,晕圈的Fe、Mg富集;在填充物与衬壁的边界处Fe的含量高,且有大量的莓状黄铁矿(微晶呈八面体、五角十二面体、立方体、球体和不规则形)、黄铁矿的自形单晶及其铁的氧化物。认为晕圈构造是受到铁白云石流体的影响而形成的成岩晕;莓状黄铁矿的特征表明其为生物成因,为Thalassinoides bacae的耕作行为习性提供了重要依据,表明造迹生物在潜穴衬壁的边缘培植微生物以提供食物来应对食物贫乏,这是早期生物行为习性进化及后生动物向不同环境辐射的重要标志。     

埃迪卡拉纪疑难化石Shaanxilithes在云南王家湾剖面的发现及地层意义

Shaanxilithes是一类广泛分布于埃迪卡拉纪地层中的疑难化石,其重复而边缘模糊的圆盘状单元体、简单的躯体构型以及缺乏有效的对比化石给确立其生物亲缘关系带来很大的困难。本文报道了云南晋宁六街镇三印村渔户村组旧城段发现的大量保存精美化石——宁强陕西迹(Shaanxilithes ningqiangensis)。通过形态学及精细的显微结构观察表明Shaanxilithes具有稳定的形态结构,外形呈带状,由许多紧密相连的圆盘状结构组成,是一类不同于遗迹化石的实体化石。随着研究地区的扩大,Shaanxilithes相继在扬子板块的陕南、黔中、川北地区,华北板块的青海、宁夏以及西伯利亚和印度西北边缘埃迪卡拉纪晚期地层中发现和报道。此次Shaanxilithes在滇东晋宁地区的大量发现进一步表明此类化石有更广泛的地理分布,揭示了其重要的古生物地层意义,表明Shaanxilithes不仅是区域间而且是洲际之间埃迪卡拉纪晚期地层对比的潜在标准化石。依据形态学分析,结合埋藏学信息,文中对Shaanxilithes的生物属性以及谱系关系进行了讨论,为理解从埃迪卡拉纪晚期到早寒武世古生物学特征的演化带来新的启示。     

豫西寒武系第二、三统馒头组固底控制的遗迹化石北大核心CSCD

依据沉积学及遗迹学特征,豫西寒武系第二、三统馒头组共识别出固底遗迹化石11属15种,包括抓痕、爬痕类和潜穴类遗迹化石。节肢动物抓痕、爬痕类固底遗迹化石形成在沉积-水界面很浅处,保存为极为清晰、完整、精细的附肢痕迹,多形成于细粒的泥岩或粉砂质泥岩层面上,部分保存为上覆粗粒沉积物的底面铸型;潜穴类固底遗迹化石不发育外壁,以水平或近水平分布为主,保存有清晰的潜穴形态,潜穴表面发育精美的纹饰,充填物与围岩反差较大,被动充填上覆的粗粒沉积物或者聚集海底迂回的砂粒得以保存。发育遗迹化石的固底底质主要由沉积物长期或间歇性暴露和低的沉积物混合程度所致。     

川中-川南地区上三叠统滨浅湖沉积中的遗迹化石

川中-川南地区上三叠统滨浅湖沉积中产有丰富的动物遗迹化石,识别为3大类6属8种,包括Sko-lithos linearis,S.verticalis,Ophiomorpha nodosa,Planolites beverleyensis,P.montanus,Palaeophycus tubularis,Taenidiumsatanassi和Cochlichnus anguineus,另外,逃逸构造也很发育。这些遗迹化石主要是无脊椎动物的居住迹、进食迹和觅食迹,大多为全浮痕和上浮痕保存。根据遗迹化石的组合特征及其沉积环境,可识别出3个遗迹组合:1)Skolithos linearis遗迹组合,主要由长的垂直或高角度倾斜的悬食居住潜穴构成,反映高能的砂质滨湖环境;2)Cochlichnus-Planolites遗迹组合,主要由进食迹和牧食迹组成,形成于低能的滨湖沼泽环境;3)Skolithos-Planol-ites遗迹组合,以居住潜穴和进食潜穴为主,遗迹化石的丰度较高,代表潮湿气候条件下的浅湖环境。根据生物扰动的分布及扰动强度,浅湖中可识别出两类扰动类型,即1)砂泥边界扰动,扰动主要发育于砂泥交界处,代表了浅湖下部环境;2)薄砂层扰动,扰动主要发育于薄砂层中,主要出现于浅湖中下部沉积中。     

豫西寒武系第二、三统馒头组固底控制的遗迹化石

依据沉积学及遗迹学特征,豫西寒武系第二、三统馒头组共识别出固底遗迹化石11属15种,包括抓痕、爬痕类和潜穴类遗迹化石。节肢动物抓痕、爬痕类固底遗迹化石形成在沉积-水界面很浅处,保存为极为清晰、完整、精细的附肢痕迹,多形成于细粒的泥岩或粉砂质泥岩层面上,部分保存为上覆粗粒沉积物的底面铸型;潜穴类固底遗迹化石不发育外壁,以水平或近水平分布为主,保存有清晰的潜穴形态,潜穴表面发育精美的纹饰,充填物与围岩反差较大,被动充填上覆的粗粒沉积物或者聚集海底迂回的砂粒得以保存。发育遗迹化石的固底底质主要由沉积物长期或间歇性暴露和低的沉积物混合程度所致。     

铁球菌菌落与埃迪卡拉纪盘状化石的形态对比研究

从自然环境中分离出多种微生物分别进行纯培养获得其稳定的菌落形态,并将其与埃迪卡拉纪某些生物属性归属存在较大争议的化石进行形态对比研究,发现其中从砂岩型铀矿矿石分离出的铁球菌(Sphaerococcus),在利用Winogradsky培养基进行富集和纯培养后,形成的菌落与埃迪卡拉纪的某些盘状化石(如Tirasianaco...     

Infaunal augurs of the Cambrian explosion: An Ediacaran trace fossil assemblage from Nevada,USA

Morphologically complex trace fossils, recording the infaunal activities of bilaterian animals, are common in Phanerozoic successions but rare in the Ediacaran fossil record. Here, we describe a trace fossil assemblage from the lower Dunfee Member of the Deep Spring Formation at Mount Dunfee (Nevada, USA), over 500 m below the Ediacaran–Cambrian boundary. Although millimetric in scale and largely not fabric‐disruptive, the Dunfee assemblage includes complex and sediment‐penetrative trace fossil morphologies that are characteristic of Cambrian deposits. The Dunfee assemblage records one of the oldest documented instances of sediment‐penetrative infaunalization, corroborating previous molecular, ichnologic, and paleoecological data suggesting that crown‐group bilaterians and bilaterian‐style ecologies were present in late Ediacaran shallow marine ecosystems. Moreover, Dunfee trace fossils co‐occur with classic upper Ediacaran tubular body fossils in multiple horizons, indicating that Ediacaran infauna and epifauna coexisted and likely formed stable ecosystems.     

Trace fossils from lower Cambrian Hongjingshao Formation,Yunnan, China: Taxonomy,palaeoecology, palaeoenvironment

The Hongjingshao Formation (Cambrian Series 2, Stage 3) yields abundant, complex trace fossils that have not been systematically investigated up till now. Our detailed ichnological study of the traces from this formation in Malong area, Yunnan, China, recognizes four groups: (1) simple horizontal or sub-horizontal burrows; (2) complex branched burrow systems; (3) arthropod trails and; (4) simple vertical burrows belonging to the Cruziana ichnofacies. A trophic web is reconstructed for the community in Hongjingshao Formation based on both trace and body fossils. The ichnological and sedimentological features of the formation indicate an intertidal setting. The trace fossil assemblage demonstrates that Early Cambrian organisms were able to colonize very shallow marine environments, which further supports the landward expansion of the Early Cambrian ecosystems.     

The proterozoic and earliest cambrian trace fossil record; patterns, problems and perspectives

The increase in trace fossil diversity across the Neoproterozoic-Cambrianboundary often is presented in terms of tabulations of ichnogenera.However, a clearer picture of the increase in diversity andcomplexity can be reached by combining trace fossils into broadgroups defined both on morphology and interpretation. This alsofocuses attention on looking for similarites between Neoproterozoicand Cambrian trace fossils. Siliciclastic sediments of the Neoproterozoicpreserve elongate tubular organisms and structures of probablealgal origin, many of which are very similar to trace fossils.Such enigmatic structures include Palaeopascichnus and Yelovichnus,previously thought to be trace fossils in the form of tightmeanders. A preliminary two or tripartite terminal Neoproterozoic tracefossil zonation can be be recognized. Possibly the earliesttrace fossils are short unbranched forms, probably younger thanabout 560 Ma. Typical Neoproterozoic trace fossils are unbranchedand essentially horizontal forms found associated with diverseassemblages of Ediacaran organisms. In sections younger thanabout 550 Ma a modest increase in trace fossil diversity occurs,including the appearance of rare three-dimensional burrow systems(treptichnids), and traces with a three-lobed lower surfaces.     

The origin of the animals and a ‘Savannah’ hypothesis for early bilaterian evolution

The earliest evolution of the animals remains a taxing biological problem, as all extant clades are highly derived and the fossil record is not usually considered to be helpful. The rise of the bilaterian animals recorded in the fossil record, commonly known as the ‘Cambrian explosion’, is one of the most significant moments in evolutionary history, and was an event that transformed first marine and then terrestrial environments. We review the phylogeny of early animals and other opisthokonts, and the affinities of the earliest large complex fossils, the so‐called ‘Ediacaran’ taxa. We conclude, based on a variety of lines of evidence, that their affinities most likely lie in various stem groups to large metazoan groupings; a new grouping, the Apoikozoa, is erected to encompass Metazoa and Choanoflagellata. The earliest reasonable fossil evidence for total‐group bilaterians comes from undisputed complex trace fossils that are younger than about 560 Ma, and these diversify greatly as the Ediacaran–Cambrian boundary is crossed a few million years later. It is generally considered that as the bilaterians diversified after this time, their burrowing behaviour destroyed the cyanobacterial mat‐dominated substrates that the enigmatic Ediacaran taxa were associated with, the so‐called ‘Cambrian substrate revolution’, leading to the loss of almost all Ediacara‐aspect diversity in the Cambrian. Why, though, did the energetically expensive and functionally complex burrowing mode of life so typical of later bilaterians arise? Here we propose a much more positive relationship between late‐Ediacaran ecologies and the rise of the bilaterians, with the largely static Ediacaran taxa acting as points of concentration of organic matter both above and below the sediment surface. The breaking of the uniformity of organic carbon availability would have signalled a decisive shift away from the essentially static and monotonous earlier Ediacaran world into the dynamic and burrowing world of the Cambrian. The Ediacaran biota thus played an enabling role in bilaterian evolution similar to that proposed for the Savannah environment for human evolution and bipedality. Rather than being obliterated by the rise of the bilaterians, the subtle remnants of Ediacara‐style taxa within the Cambrian suggest that they remained significant components of Phanerozoic communities, even though at some point their enabling role for bilaterian evolution was presumably taken over by bilaterians or other metazoans. Bilaterian evolution was thus an essentially benthic event that only later impacted the planktonic environment and the style of organic export to the sea floor.     

Architectural complexity of marine crustacean burrows: unusual helical trace fossils from the Miocene of Mallorca,Spain

Gibert, J.M. de, Mas, G. & Ekdale, A.A. 2012: Architectural complexity of marine crustacean burrows: unusual helical trace fossils from the Miocene of Mallorca, Spain. Lethaia, Vol. 45, pp. 574–585. Unusual helical trace fossils occur in Tortonian shelfal calcarenites in the island of Mallorca. Their morphology may be either simple (ichnogenus Gyrolithes) or, more commonly, consist of two concentric helical burrows (ichnogenus Lapispira). They bear a very characteristic pelleted lining and are associated and probably connected to Thalassinoides and Ophiomorpha burrow systems very abundant in the same unit. These features allow the interpretation that the tracemaker was a thalassinidean shrimp. The complex and compound nature of these trace fossils is comparable to that seen in other modern and fossil crustacean burrow systems, and it reflects the behavioural plasticity of the architects. □Trace fossils, ichnology, ichnofabrics, crustacean burrows, Miocene, shallow marine, Lapispira.     

Paleoecology of the marine endobenthos

Endobenthic animals, which reside within the sea bottom, include stationary suspension feeders, mobile deposit feeders and both stationary and mobile carnivores. Their activities, especially with regard to dwelling, feeding, walking/crawling and resting/nesting, are recorded as trace fossils.Abundance, diversity and density of some kinds of trace fossils allow interpretation of the population strategies of the trace-makers in terms of opportunistic (r-selected) and equilibrium (K-selected) strategies. Opportunistic ichnotaxa tend to be faciesbreaking traces, which are highly localized in low-diversity, high-density trace fossil associations in rocks representing environmental extremes (e.g., variable salinities, harsh temperatures, low oxygen levels or shifting substrates). Equilibrium ichnotaxa usually are restricted to particular sedimentary facies and are characteristic of high-diversity, low-dominance trace fossil associations in sediments reflecting stable, predictable environmental conditions.The most important environmental factors influencing the composition of trace fossil assemblages in marine settings are bathymetry, substrate, oxygen and hydrodynamic energy. The four factors are closely interrelated, because as water depth increases, there is a general decrease in sediment grain size and hydrodynamic energy of the depositional environment. As depth below the water—sediment interface increases, the firmness of the sediment (due to compaction and dewatering) increases and the oxygen content of interstitial waters drops drastically.Marine ichnofacies are largely substrate-controlled. Soupgrounds are water-saturated, incompetent substrates typified by highly compressed and usually unidentifiable burrows. Softgrounds commonly contain numerous distinctive burrows and are zoned bathymetrically by the Skolithos, Cruziana, Zoophycos and Nereites Ichnofacies. Firmgrounds are characterized by stiff, compacted sediments, in which traces of the Glossifungites Ichnofacies are excavated. Hardgrounds are cemented substrates, in which bioerosion traces of the Trypanites Ichnofacies are bored. Woodgrounds are woody materials that have been exposed to the sea and bored by bivalves, which produce characteristic traces of the Teredolites Ichnofacies. Tiering of endobenthic communities is common and is related to substrate preference of the burrowers and oxygen stratification of interstitial waters.     

The earliest fossil record of the animals and its significance

The fossil record of the earliest animals has been enlivened in recent years by a series of spectacular discoveries, including embryos, from the Ediacaran to the Cambrian, but many issues, not least of dating and interpretation, remain controversial. In particular, aspects of taphonomy of the earliest fossils require careful consideration before pronouncements about their affinities. Nevertheless, a reasonable case can now be made for the extension of the fossil record of at least basal animals (sponges and perhaps cnidarians) to a period of time significantly before the beginning of the Cambrian. The Cambrian explosion itself still seems to represent the arrival of the bilaterians, and many new fossils in recent years have added significant data on the origin of the three major bilaterian clades. Why animals appear so late in the fossil record is still unclear, but the recent trend to embrace rising oxygen levels as being the proximate cause remains unproven and may even involve a degree of circularity.     

Quantitative analysis of horizontal bioturbation from Brioverian (Ediacaran - Fortunian) deposits of Brittany (Armorican Massif,NW of France)

Ediacaran-Cambrian bioturbation on bedding planes provides physical and chemical data about the environmental conditions and biological activities of early metazoans. We propose a quantitative method to estimate horizontal disruption of the substrate using bedding-plane trace fossils from Brioverian deposits. This methodology provides the first quantitative analysis of the trace fossil assemblage from the Armorican Massif (Brittany, NW of France). The Ediacaran-Cambrian transition within the Brioverian series is characterized by the abundance of simple and horizontal trace fossils such as Helminthopsis, Helminthoidichnites, and Palaeophycus as well as rare Gordia and Spirodesmos. Recent U-Pb dating has been carried out on detrital zircon grains from the upper Brioverian series suggesting a late Ediacaran to Fortunian age of the fossiliferous deposits (ca. 550 to 530 Ma). With Arc-Gis software, we use a semi-quantitative approach to estimate the relative 2D bioturbation rate recorded on bedding planes. The dataset is used to discuss the feeding strategies and how the seafloor ecospace was colonized by the early bilaterian metazoans. This approach combines new values such as: the length of a trace fossil, the surface of a trace, the cumulative length, and the cumulative surfaces from all of the ichnofossils recorded on the same slate surface, to finally suggest that the bioturbation rate of the microbial grazers impacted the use of the seafloor ecospaces and feeding strategies through the biomats.     

ECHINOID AND CRUSTACEAN BURROWS AND THEIR DIAGENETIC SIGNIFICANCE IN THE MAASTRICHTIAN-DANIAN OF STEVNS KLINT, DENMARK

The increase in species and specimens of fossils in the uppermost part of the Maastrichtian White Chalk is interpreted as a result of reduced depth. The absence of bryozoans, brachiopods, and regular echinoids in the Cerithium Limestone indicates sedimentation in tidal pools. After sedimentation of the Cerithium Limestone, burrowing activity followed. A burrow of Brissopneustes danicus similar to burrows of the recent Echinocardium cordatum is described. Callianassa and its burrows are found in the Upper Danian calcarenite but not in the Lower Danian or Maastrichtian of Denmark. The dominant type of burrows along the Maastrichtian-Danian boundary has presumably been formed by the crustacean Ctenocheles.
The early post-Maastrichtian burrowing activity was succeeded by (1) induration of the bottom sediment and a slight abrasion (2) dissolution of aragonite shells and siliceous sponges, (3) offshore sedimentation and filling of the burrows with Lower Danian chalk mud, bryozoan fragments and other fossil remains, and (4) settling in the deeper part of the soft chalk sediment and precipitation of flint in or around burrows near the surface of the sediment.     

How spatangoids produce their traces: relationship between burrowing mechanism and trace structure

Kanazawa, K. 1995 11 30 How spatangoids produce their traces: relationship between burrowing mechanism and trace structure.
Two spatangoid echinoids, Echinocardium cordatum and Lovenia elongata , were allowed to produce their traces in poorly and well-sorted sediments in aquaria. In poorly sorted sediments they formed distinct traces, comparable to fossil traces. Sorting of sediment occurred during transportation by the lateroventral spines and brought about characteristic patterns in grain size at the bottoms of the burrows and in redeposited sediment, which made the traces visible. Differences in the burrowing mechanism between E. cordatum and L. elongata are reflected in their trace structures. E. cordatum formed a laminated backlill structure which resulted from periodic accumulation of excavated sediment behind it, while L. elongata simply pushed excavated sediment by compression to the posterior sides of the test, so that their traces lack a distinct laminated structure and the width of the trace becomes larger than that of the animal. In well-sorted sediment, the echinoids burrowed in the same way as in poorly sorted sediment, but no visible trace was produced other than a drain tube. These observations reasonably explain some characteristic modes of occurrence of fossil spatangoid traces. Their different morphological expressions depend on sediment texture and the uneven lithification of traces. Spatangoids, trace, burrowing mechanism .