Palaeoredox geochemistry and bioturbation levels of the exceptionally preserved early Cambrian Indian Springs biota,Nevada, USA

The early Cambrian Indian Springs biota of western Nevada, USA, exhibits Burgess Shale‐type (BST) preservation of a diverse array of animal phyla, including the earliest definitive echinoderms. It therefore provides an important window on animal life during the Cambrian radiation. The objective of this study was to analyse the trace metal palaeoredox geochemistry and bioturbation levels of this BST deposit in order to characterize the palaeoenvironmental conditions in which these animals lived and their remains preserved. A total of 28 rock samples were collected from outcrops at three previously reported intervals of exceptional preservation at the Indian Springs locality, as well as from one interval not exhibiting such preservation. An additional 20 random samples were collected from talus for comparison. In the laboratory, the samples were analysed for trace metal palaeoredox indices (V/Cr and V/(V + Ni) ratios). Bioturbation levels were assessed through X‐radiography and petrographic thin sections using the ichnofabric index (ii) method. Additional samples from coeval strata of the Poleta Formation in the White‐Inyo Mountains, CA, that lack BST preservation were also analysed with the same methodology. Results indicate that oxic bottom water conditions dominated during deposition of these strata, despite consistently low bioturbation levels. This pattern holds for intervals with BST preservation and those without. Although ephemeral incursions of low‐oxygen waters may have taken place, there is no evidence for persistent oxygen restriction in these palaeoenvironments. The low levels of bioturbation indicate limited mixed layer development and a redox boundary near the sediment–water interface, likely allowing post‐burial BST preservation to occur even in this setting dominated by oxic bottom waters. Palaeoecological reconstructions and taphonomic hypotheses relating to the Indian Springs Lagerstätte must consider the palaeoredox conditions revealed in this study. With the dispensing of anoxic bottom waters as a requirement for BST preservation, other models proposing a role for clay minerals, the presence of hypersaline brines and the actions of Fe‐reducing bacteria as mechanisms for exceptional preservation warrant renewed consideration.     

Taphonomy and compositional fidelity of Quaternary fossil assemblages of terrestrial gastropods from carbonate-rich environments of the Canary Islands

Quaternary aeolian deposits of the Canary Islands contain well‐preserved terrestrial gastropods, providing a suitable setting for assessing the taphonomy and compositional fidelity of their fossil record over ~13 kyr. Nine beds (12, 513 shells) have been analysed in terms of multivariate taphonomic and palaeoecological variables, taxonomic composition, and the stratigraphic and palaeontological context. Shells are affected by carbonate coatings, colour loss and fragmentation. Shell preservation is size‐specific: juveniles are less fragmented and show colour preservation more commonly than adults. In palaeosols, the adult shell density correlates negatively with the proportion of fragmented adults, negatively with the proportion of juveniles, and positively with the proportion of adults with coatings. High bioturbation intensity in palaeosols is associated with low shell fragmentation and high proportion of shells with coatings. These relationships imply that high adult density in palaeosols was driven by an increase in shell production rate (related to a decrease in predation rates on adults and a decrease in juvenile mortality) and a decrease in shell destruction rate (related to an increase in durability enhanced by carbonate precipitation). In dunes, the relationships between taphonomic alteration, shell density and bioturbation are insignificant. However, dune assemblages are characterized by a lower frequency of shells with coatings and higher rates of colour loss, indicating lower shell durability in dunes than in palaeosols. Additionally, non‐random differences in the coating proportion among palaeosols imply substantial temporal variation in the rate of carbonate crust formation, reflecting long‐term changes in bioturbation intensity that covaries positively with shell preservation. Dunes and palaeosols do not differ in species abundances despite differences in the degree of shell alteration, suggesting that both weakly and strongly altered assemblages offer data with a high compositional fidelity. Carbonate‐rich terrestrial deposits originating in arid conditions can enhance the preservation of gastropods and result in fossil assemblages that are suitable for palaeoecological and palaeoenvironmental studies of terrestrial ecosystems.     

The role of clay minerals in the preservation of Precambrian organic-walled microfossils

Precambrian organic-walled microfossils (OWMs) are primarily preserved in mudstones and shales that are low in total organic carbon (TOC). Recent work suggests that high TOC may hinder OWM preservation, perhaps because it interferes with chemical interactions involving certain clay minerals that inhibit the decay of microorganisms. To test if clay mineralogy controls OWM preservation, and if TOC moderates the effect of clay minerals, we compared OWM preservational quality (measured by pitting on fossil surfaces and the deterioration of wall margins) to TOC, total clay, and specific clay mineral concentrations in 78 shale samples from 11 lithologic units ranging in age from ca. 1650 to 650 million years ago. We found that the probability of finding well-preserved microfossils positively correlates with total clay concentrations and confirmed that it negatively correlates with TOC concentrations. However, we found no evidence that TOC influences the effect of clay mineral concentrations on OWM preservation, supporting an independent role of both factors on preservation. Within the total clay fraction, well-preserved microfossils are more likely to occur in shales with high illite concentrations and low berthierine/chamosite concentrations; however, the magnitude of their effect on preservation is small. Therefore, there is little evidence that bulk clay chemistry is important in OWM preservation. Instead, we propose that OWM preservation is largely regulated by physical properties that isolate organic remains from microbial degradation such as food scarcity (low TOC) and low sediment permeability (high total clay content): low TOC increases the diffusive distances between potential carbon sources and heterotrophic microbes (or their degradative enzymes), while high clay concentrations reduce sediment pore space, thereby limiting the diffusion of oxidants and degradative enzymes to the sites of decay.     

Exceptional fossil preservation and the cambrian explosion

Exceptionally preserved, non-biomineralizing fossils contributeimportantly to resolving details of the Cambrian explosion,but little to its overall patterns. Six distinct "types" ofexceptional preservation are identified for the terminal Proterozoic-Cambrianinterval, each of which is dependent on particular taphonomiccircumstances, typically restricted both in space and time.Taphonomic pathways yielding exceptional preservation were particularlyvariable through the Proterozoic-Cambrian transition, at leastin part a consequence of contemporaneous evolutionary innovations.Combined with the reasonably continuous record of "Doushantuo-typepreservation," and the fundamentally more robust records ofshelly fossils, phytoplankton cysts and trace fossils, thesetaphonomic perturbations contribute to the documentation ofmajor evolutionary and biogeochemical shifts through the terminalProterozoic and early Cambrian. Appreciation of the relationship between taphonomic pathwayand fossil expression serves as a useful tool for interpretingexceptionally preserved, often problematic, early Cambrian fossils.In shale facies, for example, flattened non-biomineralizingstructures typically represent the remains of degradation-resistantacellular and extracellular "tissues" such as chaetae and cuticles,whereas three-dimensional preservation represents labile cellulartissues with a propensity for attracting and precipitating earlydiagenetic minerals. Such distinction helps to identify theacuticular integument of hyolithids, the chaetae-like natureof Wiwaxia sclerites, the chaetognath-like integument of Amiskwia,the midgut glands of various Burgess Shale arthropods, and themisidentification of deposit-feeding arthropods in the Chengjiangbiota. By the same reasoning, putative lobopods in the SiriusPasset biota and putative deuterostomes in the Chengiang biotaare better interpreted as arthropods.     

Infrared mapping resolves soft tissue preservation in 50 million year-old reptile skin

Non-destructive Fourier Transform InfraRed (FTIR) mapping of Eocene aged fossil reptile skin shows that biological control on the distribution of endogenous organic components within fossilized soft tissue can be resolved. Mapped organic functional units within this approximately 50 Myr old specimen from the Green River Formation (USA) include amide and sulphur compounds. These compounds are most probably derived from the original beta keratin present in the skin because fossil leaf- and other non-skin-derived organic matter from the same geological formation do not show intense amide or thiol absorption bands. Maps and spectra from the fossil are directly comparable to extant reptile skin. Furthermore, infrared results are corroborated by several additional quantitative methods including Synchrotron Rapid Scanning X-Ray Fluorescence (SRS-XRF) and Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS). All results combine to clearly show that the organic compound inventory of the fossil skin is different from the embedding sedimentary matrix and fossil plant material. A new taphonomic model involving ternary complexation between keratin-derived organic molecules, divalent trace metals and silicate surfaces is presented to explain the survival of the observed compounds. X-ray diffraction shows that suitable minerals for complex formation are present. Previously, this study would only have been possible with major destructive sampling. Non-destructive FTIR imaging methods are thus shown to be a valuable tool for understanding the taphonomy of high-fidelity preservation, and furthermore, may provide insight into the biochemistry of extinct organisms.     

The importance of Planolites in the Cambrian substrate revolution

Early Cambrian subtidal shelf substrates were characterized by low water content and steep chemical gradients, conditions likely facilitated by the presence of microbial mats as reflected by an abundance of microbially-mediated sedimentary structures in Lower Cambrian strata. Such substrate conditions would have been unfavourable for burrowing by benthic metazoans. A combination of environmental restrictions and a lack of adaptations to vertical burrowing likely prevented most benthic metazoans from burrowing infaunally in Early Cambrian subtidal shelf substrates. The eventual acquisition of burrowing adaptations by benthic metazoans later in the Cambrian promoted an increase in the depth and intensity of bioturbation and initiated a transition toward well-hydrated substrates in which extensive infaunal activity was possible.Siliciclastic units of the Lower Cambrian succession in the White–Inyo Mountains, eastern California, contain abundant horizontal bioturbation on bedding planes, as documented by bedding plane bioturbation indices, but little vertical bioturbation, as shown by ichnofabric indices and x-radiography. Planolites, a simple horizontal trace fossil, represents the dominant type of bioturbation in these units. Planolites is found in a range of diameters, indicating that more than one species of tracemaker likely produced this type of trace. Although these Planolites do not have a vertical component, their abundance on bedding planes indicates that the activities of Planolites tracemakers had a significant impact on subtidal shelf substrates, represented by Lower Cambrian units in the White–Inyo Mountains, early in the Cambrian substrate revolution.     

Biomats, biofilms, and bioglue as preservational agents for arthropod trackways

Due to divergent taphonomic selection, corresponding body and trace fossils are rarely found in the same rocks. In addition to this general rule, arthropod trackways are preferentially preserved in particular settings: (1) lithographic limestones, where toxic bottom waters account for the exceptional preservation of body fossils at the end of their “mortichnial” trackways; (2) estuarine and lacustrine biolaminites that yield blurred surface tracks as well as the sharper undertracks; and (3) Cambrian intertidal sands before the Precambrian/Cambrian substrate revolution had reached this environment. In all these ichnotopes, the original presence of protective microbial films can be inferred from sedimentary structures. By analogy, it is hypothesised that microbes (“bioglue”) may have been involved in the preservation of trackways in eolian dune sands. The absence of arthropod tracks in Ediacaran sands and silts means either that arthropods had not yet evolved or that they were as yet too tiny to pierce the tougher biomats of the time.     

Quantitative paleoecology of Cambrian (Series 2–Miaolingian) communities from central Sonora,Mexico

This work presents a paleoecological approach to study benthic communities preserved in Cambrian strata exposed at the Sahuaral locality in central Sonora, northwestern Mexico. Based on species richness and abundance, this work analyzed 627 individuals corresponding to 33 species from five distinctive Cambrian formations: the lowermost Proveedora Formation characterized by bioturbation horizons that record the occurrence of a benthic-infaunal biota from coastal shallow seas, followed by the Buelna Formation which contains reef deposits dominated by autotrophic epibenthic communities. The Cerro Prieto Formation was deposited in a high-energy shallow marine environment, dominated by primary consumers-epifaunal and suspensions feeders. The uppermost unit, the El Gavilán Formation, is an intercalation of shale and fossiliferous limestone characterized by the fossil remains of suspension feeders, detritus feeders and nektobenthic organisms of low energy deep water environments. The paleobiota consist of ichnofossils, microbial oncolites, chancellorids, brachiopods, hyolithids, and trilobites in a sequence of increasing diversity and complexity. Paleoecological indices (Simpson Dominance, Shannon-Weaver Index, Evenness Index, and Total Richness) were determined and compared in the study area. In addition, the effective number of species and the true diversities were obtained, which are similar between each station distributed in each formation. However, it is possible that the high degree of dominance is a factor to indicate an inequality between the true diversity and the species richness identified. These results provide new analytical and paleoecological criteria for better understanding depositional environments and fossil associations where the spatial distribution of benthic organisms, richness and abundance provide a valued window to Cambrian biotas. The structure of the marine community of the El Sahuaral area has a great affinity with other Cambrian communities, such as those from the Stephen Formation (Burgess Shale, British Columbia) and the Chengjiang biota of the Yangtze Shelf deposits in South China.     

Buoyancy mechanisms limit preservation of coleoid cephalopod soft tissues in Mesozoic Lagerstätten

Coleoid cephalopods are characterized by internalization of their shell, and are divided into the ten‐armed Decabrachia (squids and cuttlefish) and the eight‐armed Vampyropoda (octopuses and vampire squid). They have a rich fossil record predominantly of the limited biomineralized skeletal elements they possess: arm hooks, statoliths, mouthparts (the buccal mass) and internal shell (gladius or pen), although exquisitely preserved soft tissue coleoids are known from several Lagerstätten worldwide. Recent studies have shown that although morphological similarities between extant decabrachian gladii and fossil examples exist, no known examples of fossil decabrachians are currently known. However, molecular clock data and phylogenetic bracketing suggest that they should be present in Lagerstätten that are rich in vampyropod soft tissue fossils (i.e. Hâkel and Hâdjoula Lagerstätten, Cretaceous, Lebanon). We propose that a hitherto unknown taphonomic bias pertaining to the differing methods of buoyancy control within coleoid groups limits preservation potential. Both negatively and neutrally buoyant decabrachians use chemical buoyancy control (ammonia) whereas vampyropods do not. In the event of rapid burial in an environment conducive to exceptional preservation, ammonia dramatically decreases the ability of the decabrachian carcass to generate the required pH for authigenic calcium phosphate replacement, limiting its preservation potential. Moreover, the greater surface area and comparatively fragile dermis further decrease the potential for fossilization. This taphonomic bias may have contributed to the lack of preserved labile soft‐tissues in other cephalopods groups such as the ammonoids.     

A scratch circle origin for the medusoid fossil Kullingia

Kullingia is considered a key taxon in demonstrating the presence of terminal Proterozoic-early Cambrian chondrophorine hydrozoans. However, Kullingia concentrica from the Lower Cambrian of northern Sweden possesses several features that show that it is not a body fossil but that it was formed by current or wave-induced rotation of an anchored tubular organism, possibly a sabelliditid. A scratch circle interpretation applies also to several other reports of Lower Cambrian Kullingia , including Kullingia delicata from the Chapel Island Formation of Newfoundland. Given the considerable number of problematic fossils that have been interpreted as chondrophorines, it is difficult to put an age on the oldest fossil chondrophorines, but it may be as late as the Devonian. Overall, scratch circles appear to be rarely preserved. The occurrence of these scratch circles in Lower Paleozoic storm deposits is probably related to low levels of bioturbation that enhanced both the likelihood of formation and preservation of these structures.     

Taphonomic field experiments and the role of the Shelf and Slope Experimental Taphonomy Initiative

Fossilization of organism remains is the result of biological, physical, and chemical processes at work in the environment of deposition. The pathways taken by the remains of organisms through death, decay, burial, and diagenesis (known as taphonomic pathways) affect the fossil record of life in important ways, from complete removal and recycling of remains to preservation of hard parts and sometimes to exceptional preservation of soft tissues. Our understanding of taphonomic processes informs our interpretations of the fossil record and helps in the reconstruction of ancient environments. Research into taphonomic pathways in modern environments provides important insight into the fossilization process. In 1993, a group of paleontologists formed the Shelf and Slope Experimental Taphonomy Initiative (SSETI) and began a long-term comparative study of taphofacies and differential decay of taxonomic groups by placing experimental arrays containing bivalves, gastropods, decapod crustaceans, sea urchins, and wood species at multiple marine shelf and slope sites in the Bahamas and Gulf of Mexico. The goal of SSETI is to observe taphonomic processes over a period of decades to better understand taphonomic pathways for these various groups of taxa in a wide variety of depositional environments beyond the shallow near shore region. This special volume brings together eight studies that are the result of the SSETI program. The focus of this contribution is to first review the body of published work concerned with the fossilization process through the experimental manipulation of the remains of organisms in modern marine environments. We also present the methods of the SSETI project and its contributions to our understanding of taphonomic processes in relation to carbonate and wood recycling and preservation.     

Interpreting ‘shelly’ fossils preserved as organic films: the case of hyolithids

Most studies of Burgess Shale‐type preservation have focussed on soft‐bodied organisms, but ‘shelly’ fossils are also preserved as carbonaceous films. These films are usually interpreted as coherent organic layers – often external sheaths or periostracal layers – that were present in the original mineralized elements. The example of hyolithids shows that the organic films of skeletal parts do not represent original ‘layers’, but a composite resulting from the coalescence, into a single carbonaceous film, of all the preservable organic matter present in the skeletal element. The diagenetic processes that led to Burgess Shale‐type preservation, which involve the polymerization of organic matter and the loss of original internal structure and chemical integrity of the original tissues, are entirely compatible with – and could account for – the characteristics observed in the fossil films of hyolithid skeletal elements. These observations have general implications for the interpretation of other organisms preserved as carbonaceous films, such as the diverse and often problematic Cambrian sponges.     

Taphonomic experiments imply a possible link between the evolution of multicellularity and the fossilization potential of soft‐bodied organisms

The reliability of evolutionary reconstructions based on the fossil record critically depends on our knowledge of the factors affecting the fossilization of soft‐bodied organisms. Despite considerable research effort, these factors are still poorly understood. In order to elucidate the main prerequisites for the preservation of soft‐bodied organisms, we conducted long‐term (1–5 years) taphonomic experiments with the model crustacean Artemia salina buried in five different sediments. The subsequent analysis of the carcasses and sediments revealed that, in our experimental settings, better preservation was associated with the fast deposition of aluminum and silicon on organic tissues. Other elements such as calcium, magnesium, and iron, which can also accumulate quickly on the carcasses, appear to be much less efficient in preventing decay. Next, we asked if the carcasses of uni‐ and multicellular organisms differ in their ability to accumulate aluminum ions on their surface. The experiments with the flagellate Euglena gracilis and the sponge Spongilla lacustris showed that aluminum ions are more readily deposited onto a multicellular body. This was further confirmed by the experiments with uni‐ and multicellular stages of the social ameba Dictyostelium discoideum. The results lead us to speculate that the evolution of cell adhesion molecules, which provide efficient cell–cell and cell–substrate binding, probably can explain the rich fossil record of soft‐bodied animals, the comparatively poor fossil record of nonskeletal unicellular eukaryotes, and the explosive emergence of the Cambrian diversity of soft‐bodied fossils.     

贵州剑河中寒武世中期甲劳组水母状化石的发现

贵州剑河革东镇八郎村南甲劳组中部钙质白云岩中新近发现的具有粗强放射状辐管的水母状化石和其下凯里组中具细辐管及同心环的拟轮盘水母(Pararotadiscus)有明显区别,属于伊尔东钵科(Eldoniidae)。其层位晚于中寒武世早期凯里生物群中拟轮盘水母(Pararotadiscus)层位1个化石带,属中寒武世中期,是该类化石在中国的最高层位,相当于北美布尔吉斯页岩生物群中Eldonia化石层位。     

The Sirius Passet Lagerstätte of North Greenland—A geochemical window on early Cambrian low‐oxygen environments and ecosystems

The early Cambrian Sirius Passet fauna of northernmost Greenland (Cambrian Series 2, Stage 3) contains exceptionally preserved soft tissues that provide an important window to early animal evolution, while the surrounding sediment holds critical data on the palaeodepositional water‐column chemistry. The present study combines palaeontological data with a multiproxy geochemical approach based on samples collected in situ at high stratigraphic resolution from Sirius Passet. After careful consideration of chemical alterations during burial, our results demonstrate that fossil preservation and biodiversity show significant correlation with iron enrichments (Fe_HR/Fe_T), trace metal behaviour (V/Al), and changes in nitrogen cycling (δ¹⁵N). These data, together with Mo/Al and the preservation of organic carbon (TOC), are consistent with a water column that was transiently low in oxygen concentration, or even intermittently anoxic. When compared with the biogeochemical characteristics of modern oxygen minimum zones (OMZs), geochemical and palaeontological data collectively suggest that oxygen concentrations as low as 0.2–0.4 ml/L restricted bioturbation but not the development of a largely nektobenthic community of predators and scavengers. We envisage for the Sirius Passet biota a depositional setting where anoxic water column conditions developed and passed over the depositional site, possibly in association with sea‐level change, and where this early Cambrian biota was established in conditions with very low oxygen.     

A myriapod-like arthropod from the Upper Cambrian of East Siberia

Although the fossil record of biramous arthropods commences in the Lower Cambrian, unequivocal uniramous arthropods do not appear until the Upper Silurian, in association with terrestrial biotas. Here we report an Upper Cambrian marine arthropod from East Siberia that possesses some significant myriapodan features. The new arthropod,Xanthomyria spinosa n. gen., n. sp., closely resembles examples of archipolypodans from the Late Palaeozoic. If this resemblance genuinely represents myriapod affinities, this would be the first convincing myriapod from the Cambrian. Suggestions of an early branching point of the myriapods from other arthropods would be consistent with this. Conversely, an as yet poorly known clade of multi-segmented arthropods may exist in the Cambrian, with no close affinities to the myriapods.      

Taphonomy of the middle Cambrian (Drumian) Ravens Throat River Lagerstätte,Rockslide Formation,Mackenzie Mountains,Northwest Territories,Canada

The Middle Cambrian (series 3, Drumian, Bolaspidella Biozone) Ravens Throat River Lagerstätte in the Rockslide Formation of the Mackenzie Mountains, northwestern Canada, contains a Burgess Shale‐type biota of similar age to the Wheeler and Marjum formations of Utah. The Rockslide Formation is a unit of deep‐water, mixed carbonate and siliciclastic facies deposited in a slope setting on the present‐day northwestern margin of Laurentia. At the fossil‐bearing locality, the unit is about 175 m thick and the lower part onlaps a fault scarp cutting lower Cambrian sandstones. It consists of a succession of shale, laminated to thin‐bedded lime mudstone, debris‐flow breccias, minor calcareous sandstone, greenish‐coloured calcareous mudstone and dolomitic siltstone, overlain by shallow‐water dolostones of the Broken Skull Formation, which indicates an overall progradational sequence. Two ~1‐m‐thick units of greenish calcareous mudstone in the upper part exhibit soft‐bodied preservation, yielding a biota dominated by bivalved arthropods and macrophytic algae, along with hyoliths and trilobites. It represents a low‐diversity in situ community. Most of the fossils occur in the lower unit, and only the more robust components are preserved. Branching burrows are present under the carapaces of some arthropods, and common millimetre‐sized disruptions of laminae are interpreted as bioturbation. The fossiliferous planar‐laminated calcareous mudstone consists of chlorite, illite, quartz silt, calcite and dolomite and is an anomalous facies in the succession. It was deposited via hemipelagic fallout of a mixture of platform‐derived and terrestrial mud. Geochemical analysis and trace‐element proxies indicate oxic bottom waters that only occasionally might have become dysoxic. Productivity in the water column was dominated by cyanobacteria. Fragments of microbial mats are common as carbonaceous seams. Complete decay of soft tissues was interrupted due to the specific sediment composition, providing support for the role of clay minerals, possibly chlorite, in the taphonomic process.     

贵州寒武纪杷榔组古蠕虫类埋藏特征及意义*

贵州剑河寒武纪杷榔组辣子寨剖面含有丰度较高的古蠕虫类化石。化石鉴定为Wronascolex geyiensis, 主要保存在三个层位。在对三个层位的岩石、沉积特征、化石成因及埋藏特征探讨分析后, 证实W. geyiensis化石保存于快速的沉积事件导致的浊流沉积层内, 而化石埋藏的完美程度受到成岩过程中埋藏位置、沉积物中矿物结晶和充填方式的影响, 这些后期的成岩、成矿作用对先期形成的化石精细结构产生了直接和间接的破坏作用。本文通过对W. geyiensis化石体上黏土矿物、草莓状黄铁矿、自形–半自形黄铁矿的成因分析后, 获得最适合保存软躯体化石的环境应该为缺氧且生物体与孔隙水中的硫酸盐无接触的原地和近原地埋藏条件。     

Taphonomic experiments resolve controls on the preservation of melanosomes and keratinous tissues in feathers

Fossils are a key source of data on the evolution of feather structure and function through deep time, but their ability to resolve macroevolutionary questions is compromised by an incomplete understanding of their taphonomy. Critically, the relative preservation potential of two key feather components, melanosomes and keratinous tissue, is not fully resolved. Recent studies suggesting that melanosomes are preferentially preserved conflict with observations that melanosomes preserve in fossil feathers as external moulds in an organic matrix. To date, there is no model to explain the latter mode of melanosome preservation. We addressed these issues by degrading feathers in systematic taphonomic experiments incorporating decay, maturation and oxidation in isolation and combination. Our results reveal that the production of mouldic melanosomes requires interactions with an oxidant and is most likely to occur prior to substantial maturation. This constrains the taphonomic conditions under which melanosomes are likely to be fossilized. Critically, our experiments also confirm that keratinous feather structures have a higher preservation potential than melanosomes under a range of diagenetic conditions, supporting hitherto controversial hypotheses that fossil feathers can retain degraded keratinous structures.     

关山生物群中始海百合化石的再研究*

关山生物群是继澄江生物群之后云南寒武纪早期地层中发现的又一个特异埋藏的化石宝库。现已报道10多个门类的化石动物,对研究寒武纪生命大爆发、后生动物起源及演化、寒武纪早期生态系统的复原等重大学术问题具有特殊的意义。始海百合属于棘皮动物门海蕾亚门,于寒武纪早期出现,志留纪灭绝。笔者将荧光显微镜等先进成像方式与传统的研究手段相结合,对新采集到的关山生物群始海百合化石标本进行深入细致的系统古生物学研究,对其精细形态学构造和生活习性获得更深入的了解。这对于认识寒武纪早期的生物多样性和棘皮动物的演化都具有重要的意义。