The taphonomy of colour in fossil insects and feathers

Colouration is an important multifunctional attribute of modern animals, but its evolutionary history is poorly resolved, in part because of our limited ability to recognize and interpret fossil evidence of colour. Recent studies on structural and pigmentary colours in fossil insects and feathers have illuminated important aspects of the anatomy, taphonomy, evolution and function of colour in these fossils. An understanding of the taphonomic factors that control the preservation of colour is key to assessing the fidelity with which original colours are preserved and can constrain interpretations of the visual appearance of fossil insects and theropods. Various analytical approaches can identify anatomical and chemical evidence of colour in fossils; experimental taphonomic studies inform on how colour alters during diagenesis. Preservation of colour is controlled by a suite of factors, the most important of which relate to the diagenetic history of the host sediment, that is, maximum burial temperatures and fluid flow, and subsurface weathering. Future studies focussing on key morphological and chemical aspects of colour preservation relating to cuticular pigments in insects and keratinous structures and nonmelanin pigments in feathers, for example, will resolve outstanding questions regarding the taphonomy of colour and will enhance our ability to infer original colouration and its functions in fossil insects and theropods.     

Fossilized biophotonic nanostructures reveal the original colors of 47-million-year-old moths

Structural colors are generated by scattering of light by variations in tissue nanostructure. They are widespread among animals and have been studied most extensively in butterflies and moths (Lepidoptera), which exhibit the widest diversity of photonic nanostructures, resultant colors, and visual effects of any extant organism. The evolution of structural coloration in lepidopterans, however, is poorly understood. Existing hypotheses based on phylogenetic and/or structural data are controversial and do not incorporate data from fossils. Here we report the first example of structurally colored scales in fossil lepidopterans; specimens are from the 47-million-year-old Messel oil shale (Germany). The preserved colors are generated by a multilayer reflector comprised of a stack of perforated laminae in the scale lumen; differently colored scales differ in their ultrastructure. The original colors were altered during fossilization but are reconstructed based upon preserved ultrastructural detail. The dorsal surface of the forewings was a yellow-green color that probably served as a dual-purpose defensive signal, i.e. aposematic during feeding and cryptic at rest. This visual signal was enhanced by suppression of iridescence (change in hue with viewing angle) achieved via two separate optical mechanisms: extensive perforation, and concave distortion, of the multilayer reflector. The fossils provide the first evidence, to our knowledge, for the function of structural color in fossils and demonstrate the feasibility of reconstructing color in non-metallic lepidopteran fossils. Plastic scale developmental processes and complex optical mechanisms for interspecific signaling had clearly evolved in lepidopterans by the mid-Eocene.     

The cause of 50 million-year-old colour

Multilayer reflectors cause structural, 'metallic' colours in a diversity of animals today, yet are unknown in extinct species. We identify a multilayer reflector, causing structural colour, in a 50-million-year-old beetle from Messel, Germany. It is proposed that the original material of this reflector has been preserved, although this is not a precondition for determining original colours from ancient multilayer reflectors. Therefore, the potential exists to reveal the original colours of other (particularly arthropod) extinct species.     

The role of experiments in investigating the taphonomy of exceptional preservation

In the last 20 years, much taphonomic experimentation has focused on the interpretation of exceptionally preserved fossils. Decay experiments have been used to interpret the features preserved in soft‐bodied fossils and to determine the sequence of character loss and its impact on phylogenetic position. Experiments on the impact of microbial communities on decay and mineralization have started to illuminate the processes involved in the fossilization of soft tissues, including embryos. The role of decay in promoting authigenic mineralization has been used to investigate the formation of Ediacaran macrofossils and concretions. Maturation experiments have shown how the constituents of animals and plants are transformed over time to a macromolecular material that converges on a similar stable composition. Other maturation experiments have explained how structural colours in fossils are altered from the original. A major area requiring investigation is the role of specific types of microbes in decay and their impact on sediment and pore water chemistry, as well as the environmental controls that determine their presence and level of activity. Microbial activity has received less attention than other factors in attempts to explain why the occurrence and nature of exceptional preservation varies in time and space through the fossil record.     

Chemical preservation of tail feathers from Anchiornis huxleyi,a theropod dinosaur from the Tiaojishan Formation (Upper Jurassic,China)

A panel of geochemical techniques is used here to investigate the taphonomy of fossil feathers preserved in association with the skeleton of the Jurassic theropod Anchiornis huxleyi. Extant feathers were analysed in parallel to test whether the soft tissues morphologically preserved in the fossil also exhibit a high degree of chemical preservation. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) indicate that clays and iron oxide pseudomorphs occur in the surrounding sediment and also reveal the preservation of melanosome-like microbodies in the fossil. Carbon gradient along a depth profile and co-occurrence of carbon and sulphur are shown in the fossil by elastic backscattering (EBS) and particle-induced x-ray emission (PIXE), which are promising techniques for the elemental analysis of fossil soft tissues. The molecular composition of modern and fossil soft tissues was assessed from micro-attenuated total reflectance fourier transform infrared spectroscopy (micro-ATR FTIR), solid-state ¹³C nuclear magnetic resonance (CP-MAS ¹³C NMR) and pyrolysis gas chromatography mass spectrometry in the presence of TMAH (TMAH-Py-GC-MS). Results indicate that the proteinaceous material that comprises the modern feathers is not present in the fossil feathers. The fossil feathers and the embedding sediment exhibit a highly aliphatic character. However, substantial differences exist between these samples, revealing that the organic matter of the fossil feathers is, at least partially, derived from original constituents of the feathers. Our results suggest that, despite the morphological preservation of Anchiornis feathers, original proteins, that is keratin, were probably not preserved in the 160-myr-old feathers.     

Early Triassic coprolites from Australia and their palaeobiological significance

Abstract:  Coprolites from the Arcadia Formation, Queensland, Australia, were studied in conjunction with the vertebrate fossil assemblages from two localities to maximize our understanding of the palaeoecology of these Early Triassic deposits. Criteria used by other researchers to identify the producers of coprolites were found to be of little value in the Arcadia Formation specimens. Using a combination of shape, biostratigraphic distribution, size and included remains some of the coprolites are attributed to basal archosauromorphs and fish whereas others could not be identified. Perhaps the most important attribute of the Arcadia coprolites is that they preserved rare organisms such as cyanobacteria, insects and other arthropods, and a diversity of fish. Estimates of the number of actinopterygians and dipnoans preserved in coprolites significantly increased relative abundance estimates based on skeletal elements alone. Although coprolites are an important source of palaeobiological information, this information is limited by our poor understanding of the taphonomic processes involved in the fossilization of faecal matter and by the near impossibility of assigning coprolites to specific producers.     

中国东北中生代时期的传粉昆虫与虫媒植物

昆虫与植物的相互作用在昆虫与植物协同进化和发展中起着至关重要的作用。化石记录中发现了昆虫取食花粉、授粉滴、访问中生代裸子植物具胚珠的繁殖器官等多方面的昆虫化石证据。20世纪90年代以来,研究和报道了大量采自中国东北地区保存良好的昆虫与植物化石。例如发表于Science上的2篇具有长喙的双翅目和长翅目昆虫化石文章,暗示着它们很可能参与各种裸子植物的授粉。在本篇文章中,作者回顾了已报道的中国东北晚中生代时期的昆虫化石,并把它们与授粉或访"花"相联系。另外,作者对采自同一层位的同时代的植物化石进行了初步研究并介绍了可能涉及到与昆虫相互作用的代表性植物。今后将进一步深入研究,以期在化石中找到昆虫授粉和访花的直接证据。     

An ant-associated mesostigmatid mite in Baltic amber

Fossil mesostigmatid mites (Acari: Parasitiformes: Mesostigmata) are extremely rare, and specimens from only nine families, including four named species, have been described so far. A new record of Myrmozercon sp. described here from Eocene (ca 44–49 Myr) Baltic amber represents the first—and so far only—fossil example of the derived, extant family Laelapidae. Significantly, modern species of this genus are habitually myrmecophilous and the fossil mite described here is preserved attached to the head of the dolichoderine ant Ctenobethylus goepperti (Mayr, 1868). It thus offers the oldest unequivocal evidence for an ecological association between mesostigmatid mites and social insects in the order Hymenoptera.     

Developing graminoid cuticle analysis for application to Beringian palaeoecology

Much of Beringia was composed of graminoid (grass and sedge) dominated habitats during the Late-Pleistocene, yet the account of the actual gramioids that were present is relatively vague. The spatial and temporal variabilities of palaeoclimate, mega-fauna, archaeology, and vegetation interactions could be significantly enhanced with accounts of Beringian graminoids. Fossil graminoid foliage is well preserved in permafrost sediments from Beringia and is available for identification using the micro-morphologies of the leaf epidermis (cuticles), which are often consistent with taxonomic identity. We present a scanning electron microscope (SEM) guide to the leaf cuticles of 38 graminoid species shown to be, or suspected of being present in former Eastern Beringian habitats during marine isotope stages (MIS) 2 and 3 (∼ 56,000-12,000 cal. yrs BP). We examine whether modern specimens have sufficient cuticle variability to identify fossil foliage. We surveyed SEM images from herbarium specimens for 50 quantitative and qualitative features on both sides (adaxial and abaxial) of leaves, and entered these into an interactive key program (Delta Editor). Individual species were unique based on the combined presence of 2-4 cuticle features. Replicate samples (n = 5) of 10 species were integrated into a cluster analysis and visually compared using a dendrogram. Overall, fossils that match modern specimens with a Gower's similarity coefficient of 0.80 or higher can be considered a reliable identification match. Several fossil graminoid specimens were compared and identified with our reference collection. Cuticle identification appears to be a viable method for future macrofossil analysis in Beringia.     

The colour of fossil feathers

Feathers are complex integumentary appendages of birds and some other theropod dinosaurs. They are frequently coloured and function in camouflage and display. Previous investigations have concluded that fossil feathers are preserved as carbonized traces composed of feather-degrading bacteria. Here, an investigation of a colour-banded feather from the Lower Cretaceous Crato Formation of Brazil revealed that the dark bands are preserved as elongate, oblate carbonaceous bodies 1-2mum long, whereas the light bands retain only relief traces on the rock matrix. Energy dispersive X-ray analysis showed that the dark bands preserve a substantial amount of carbon, whereas the light bands show no carbon residue. Comparison of these oblate fossil bodies with the structure of black feathers from a living bird indicates that they are the eumelanin-containing melanosomes. We conclude that most fossil feathers are preserved as melanosomes, and that the distribution of these structures in fossil feathers can preserve the colour pattern in the original feather. The discovery of preserved melanosomes opens up the possibility of interpreting the colour of extinct birds and other dinosaurs.     

云南中新世杉科化石木研究

利用光学显微镜和扫描电镜首次对云南省楚雄州晚中新世石灰坝组石鼓村层的钙化木材进行了解剖学研究.鉴定出两种类型的木材:柳杉型落羽杉型木(Taxodioxylon cryptomeripsoides Schonfeld)和杉木型落羽杉型木(Taxodioxylon cunninghamioides Watari).二者分别与现代柳杉属和杉木属具有最接近的亲缘关系.根据这两种杉科化石木现存最近亲缘种的生态环境,并综合其他资料,推测该地区在晚中新世为温暖湿润的亚热带气候环境.     

Fossilization of melanosomes via sulfurization

Fossil melanin granules (melanosomes) are an important resource for inferring the evolutionary history of colour and its functions in animals. The taphonomy of melanin and melanosomes, however, is incompletely understood. In particular, the chemical processes responsible for melanosome preservation have not been investigated. As a result, the origins of sulfur‐bearing compounds in fossil melanosomes are difficult to resolve. This has implications for interpretations of original colour in fossils based on potential sulfur‐rich phaeomelanosomes. Here we use pyrolysis gas chromatography mass spectrometry (Py‐GCMS), fourier transform infrared spectroscopy (FTIR) and time of flight secondary ion mass spectrometry (ToF‐SIMS) to assess the mode of preservation of fossil microstructures, confirmed as melanosomes based on the presence of melanin, preserved in frogs from the Late Miocene Libros biota (NE Spain). Our results reveal a high abundance of organosulfur compounds and non‐sulfurized fatty acid methyl esters in both the fossil tissues and host sediment; chemical signatures in the fossil tissues are inconsistent with preservation of phaeomelanin. Our results reflect preservation via the diagenetic incorporation of sulfur, i.e. sulfurization (natural vulcanization), and other polymerization processes. Organosulfur compounds and/or elevated concentrations of sulfur have been reported from melanosomes preserved in various invertebrate and vertebrate fossils and depositional settings, suggesting that preservation through sulfurization is likely to be widespread. Future studies of sulfur‐rich fossil melanosomes require that the geochemistry of the host sediment is tested for evidence of sulfurization in order to constrain interpretations of potential phaeomelanosomes and thus of original integumentary colour in fossils.     

Biogenic Iron Preserves Structures during Fossilization: A Hypothesis

It is hypothesized that iron from biological tissues, liberated during decay, may have played a role in inhibiting loss of anatomical information during fossilization of extinct organisms. Most tissues in the animal kingdom contain iron in different forms. A widely distributed iron-bearing molecule is ferritin, a globular protein that contains iron crystallites in the form of ferrihydrite minerals. Iron concentrations in ferritin are high and ferrihydrites are extremely reactive. When ancient animals are decaying on the sea floor under anoxic environmental conditions, ferrihydrites may initialize the selective replication of some tissues in pyrite FeS₂. This model explains why some labile tissues are preserved, while other more resistant structures decay and are absent in many fossils. A major implication of this hypothesis is that structures described as brains in Cambrian arthropods are not fossilization artifacts, but are instead a source of information on anatomical evolution at the dawn of complex animal life.     

Chemical signatures of soft tissues distinguish between vertebrates and invertebrates from the Carboniferous Mazon Creek Lagerstätte of Illinois

The chemical composition of fossil soft tissues is a potentially powerful and yet underutilized tool for elucidating the affinity of problematic fossil organisms. In some cases, it has proven difficult to assign a problematic fossil even to the invertebrates or vertebrates (more generally chordates) based on often incompletely preserved morphology alone, and chemical composition may help to resolve such questions. Here, we use in situ Raman microspectroscopy to investigate the chemistry of a diverse array of invertebrate and vertebrate fossils from the Pennsylvanian Mazon Creek Lagerstätte of Illinois, and we generate a ChemoSpace through principal component analysis (PCA) of the in situ Raman spectra. Invertebrate soft tissues characterized by chitin (polysaccharide) fossilization products and vertebrate soft tissues characterized by protein fossilization products plot in completely separate, non‐overlapping regions of the ChemoSpace, demonstrating the utility of certain soft tissue molecular signatures as biomarkers for the original soft tissue composition of fossil organisms. The controversial problematicum Tullimonstrum, known as the Tully Monster, groups with the vertebrates, providing strong evidence of a vertebrate rather than invertebrate affinity.     

Unlocking the early fossil record of the arthropod central nervous system

Extant panarthropods (euarthropods, onychophorans and tardigrades) are hallmarked by stunning morphological and taxonomic diversity, but their central nervous systems (CNS) are relatively conserved. The timing of divergences of the ground pattern CNS organization of the major panarthropod clades has been poorly constrained because of a scarcity of data from their early fossil record. Although the CNS has been documented in three-dimensional detail in insects from Cenozoic ambers, it is widely assumed that these tissues are too prone to decay to withstand other styles of fossilization or geologically older preservation. However, Cambrian Burgess Shale-type compressions have emerged as sources of fossilized brains and nerve cords. CNS in these Cambrian fossils are preserved as carbon films or as iron oxides/hydroxides after pyrite in association with carbon. Experiments with carcasses compacted in fine-grained sediment depict preservation of neural tissue for a more prolonged temporal window than anticipated by decay experiments in other media. CNS and compound eye characters in exceptionally preserved Cambrian fossils predict divergences of the mandibulate and chelicerate ground patterns by Cambrian Stage 3 (ca 518 Ma), a dating that is compatible with molecular estimates for these splits.     

中国中生代昆虫化石研究新进展

回顾了1990年以来中国中生代昆虫化石研究的新进展,简述了我国学者在古昆虫分类学、昆虫内部形态学、昆虫系统学、古生态学、昆虫生物地层学、昆虫区系的历史演变、生物古地理学、昆虫与植物的关系等8个方面取得的突出贡献,并给出了我国发现的世界最低层位昆虫科级类群表。     

Organic preservation of fossil musculature with ultracellular detail

The very labile (decay-prone), non-biomineralized, tissues of organisms are rarely fossilized. Occurrences thereof are invaluable supplements to a body fossil record dominated by biomineralized tissues, which alone are extremely unrepresentative of diversity in modern and ancient ecosystems. Fossil examples of extremely labile tissues (e.g. muscle) that exhibit a high degree of morphological fidelity are almost invariably replicated by inorganic compounds such as calcium phosphate. There is no consensus as to whether such tissues can be preserved with similar morphological fidelity as organic remains, except when enclosed inside amber. Here, we report fossilized musculature from an approximately 18 Myr old salamander from lacustrine sediments of Ribesalbes, Spain. The muscle is preserved organically, in three dimensions, and with the highest fidelity of morphological preservation yet documented from the fossil record. Preserved ultrastructural details include myofilaments, endomysium, layering within the sarcolemma, and endomysial circulatory vessels infilled with blood. Slight differences between the fossil tissues and their counterparts in extant amphibians reflect limited degradation during fossilization. Our results provide unequivocal evidence that high-fidelity organic preservation of extremely labile tissues is not only feasible, but likely to be common. This is supported by the discovery of similarly preserved tissues in the Eocene Grube Messel biota.     

Palaeophytochemical Constituents of Cretaceous Ginkgo coriacea Florin Leaves

Chemical investigation of the organic solvent extract of Cretaceous Ginkgo coriacea Florin leaves by liquid chromatography-mass spectroscopy （LC-MS） and gas chromatography-mass spectrometry （GC-MS）, analogous to those from extant leaves of Ginkgo biloba L., led to the detection of a group of natural flavonoids and other volatiles. The similarity of the chemical constituents in these two species of Ginkgo suggest that the secondary metabolism of extant G. biloba is close to that of the Cretaceous species. The remaining natural products may be one explanation why the leaves of the Cretaceous G. coriacea have been preserved morphologically in fossilization. The detection of flavonoids suggests that the leaves of G. coriacea experienced a mild post-depositional environment during their fossilization. This appears to be the oldest occurrence of flavonoids in plant fossils.     

Proteins in the fossil bone of the dinosaur, seismosaurus

Proteins have been successfully extracted from the fossil vertebra of a 150-million-year-old sauropod dinosaur (Seismosaurus) recently excavated from the Morrison Formation of New Mexico. HCl and guanidine·HCl extracts of the fossil bone and its sandstone matrix were concentrated, demineralized, and resolved into a number of different protein fractions by reversed-phase high-performance liquid chromatography (HPLC). One of these fractions had the same retention time as collagen. Amino acid analysis (Pico-Tag method) of these fractions confirmed they were proteins. Comparison of the correlation coefficients of the amino acid analyses with that of collagen standards indicated that none of the fractions contained significant amounts of collagen. Similar HPLC profiles were obtained for the HCl extracts of fossil bone and its sandstone matrix suggesting they contained the same proteins. However, different HPLC profiles were obtained when these HCl extracts were dried and reextracted with guanidine·HCl. These different fractions represent proteins unique to the fossil and were not found in the sandstone matrix. These differences were confirmed by amino acid analysis. Such information on fossil bone proteins might provide useful knowledge concerning the evolution of skeletal molecules and the fossilization process. Similar information on the proteins from the geological matrix might provide useful fingerprints for reconstructing ancient environments and for assessing sedimentary rocks for fossil fuel exploration.