Paleozoic shell-Boring Annelids and their Trace Fossils

Polychaete shell-borings are widespread but not often commonin Paleozoic strata of most continents, occurring in pelecypod,gastropod, cephalopod, coral, stromatoporoid, crinoid, brachiopod,ectoproct, and calcareous algal skeletons of Ordovician to Permianage. Four genera are known: Vermiforichnus (Spionidae), Ordovicianto Permian; Caulostrepsis (Spionidae) , Devonian to Oligocene;Myzoslomites (Myzostomidae), Ordovician to Jurassic: and possiblyConchotrema, Devonian to Permian. The Silurian Citonia siphois a worm-boring, not a calcareous worm tube, referable to Vermiforichnus. An exceedingly well preserved Devonian fossilized polychaete,Vermiforafacta rollhisi, with complex setigerous parapodia,dorsal cirri, peristomial cirri, prostomium, and tentacle-likepalps, occurs entombed in an agglutinated tube-lined worm-boring(Vermiforichnus) . It may have been a shell-borer consideringits many similarities to the spionid, Polydora, which apparentlyecologically replaced it. Like Polydora, Vermiforafacta probably filtered food and sedimentfrom sea water and constructed agglutinated tubes which linedits borings. In bivalves, borings parallel valves and are usuallyperpendicular to commissures; in massive skeletons, they radiateoutward and laterally. Distorted later growth and "blisters"indicate that the host was often alive. Commensal to pathogenicparasitism existed and worms benefited from their hosts's feedingcurrents and protective shells. One polychaete nestler is reported.Life positions of hosts are sometimes indicated.     

Conformation and elasticity of the isolated red blood cell membrane skeleton.

We studied the structure and elasticity of membrane skeletons from human red blood cells (RBCs) during and after extraction of RBC ghosts with nonionic detergent. Optical tweezers were used to suspend individual cells inside a flow chamber, away from all surfaces; this procedure allowed complete exchange of medium while the low-contrast protein network of the skeleton was observed by high resolution, video-enhanced differential interference-contrast (DIC) microscopy. Immediately following extraction in a 5 mM salt buffer, skeletons assumed expanded, nearly spherical shapes that were uncorrelated with the shapes of their parent RBCs. Judging by the extent of thermal undulations and by their deformability in small flow fields, the bending rigidity of skeletons was markedly lower than that of either RBCs or ghosts. No further changes were apparent in skeletons maintained in this buffer for up to 40 min at low temperatures (T less than 10 degrees C), but skeletons shrank when the ionic strength of the buffer was increased. When the salt concentration was raised to 1.5 M, shrinkage remained reversible for approximately 1 min but thereafter became irreversible. When maintained in 1.5 M salt buffer for longer periods, skeletons continued to shrink, lost flexibility, and assumed irregular shapes: this rigidification was irreversible. At this stage, skeletons closely resembled those isolated in standard bulk preparations. We propose that the transformation to the rigid, irreversibly shrunken state is a consequence of spectrin dimer-dimer reconnections and that these structural rearrangements are thermally activated. We also measured the salt-dependent size of fresh and bulk extracted skeletons. Our measurements suggest that, in situ, the spectrin tethers are flexible, with a persistence length of approximately 10 nm at 150 mM salt.     

The nature and origin of nucleus‐like intracellular inclusions in Paleoproterozoic eukaryote microfossils

The well‐known debate on the nature and origin of intracellular inclusions (ICIs) in silicified microfossils from the early Neoproterozoic Bitter Springs Formation has recently been revived by reports of possible fossilized nuclei in phosphatized animal embryo‐like fossils from the Ediacaran Doushantuo Formation of South China. The revisitation of this discussion prompted a critical and comprehensive investigation of ICIs in some of the oldest indisputable eukaryote microfossils—the ornamented acritarchs Dictyosphaera delicata and Shuiyousphaeridium macroreticulatum from the Paleoproterozoic Ruyang Group of North China—using a suite of characterization approaches: scanning electron microscopy (SEM), transmission electron microscopy (TEM), and focused ion beam scanning electron microscopy (FIB‐SEM). Although the Ruyang acritarchs must have had nuclei when alive, our data suggest that their ICIs represent neither fossilized nuclei nor taphonomically condensed cytoplasm. We instead propose that these ICIs likely represent biologically contracted and consolidated eukaryotic protoplasts (the combination of the nucleus, surrounding cytoplasm, and plasma membrane). As opposed to degradational contraction of prokaryotic cells within a mucoidal sheath—a model proposed to explain the Bitter Springs ICIs—our model implies that protoplast condensation in the Ruyang acritarchs was an in vivo biologically programmed response to adverse conditions in preparation for encystment. While the discovery of bona fide nuclei in Paleoproterozoic acritarchs would be a substantial landmark in our understanding of eukaryote evolution, the various processes (such as degradational and biological condensation of protoplasts) capable of producing nuclei‐mimicking structures require that interpretation of ICIs as fossilized nuclei be based on comprehensive investigations.     

The controlling factors limiting maximum body size of insects

The purpose of this study is to consider the controlling factors limiting maximum body size of insects. For this analysis, we set up and quantitatively verify the following working hypothesis: insect body sizes can be explained only by the historical changes in the oxygen supply. The present study focuses on the body size of the Protodonata and Odonata. The amount of oxygen needed and that of oxygen entering the insect body was calculated using allometric equations. The theoretical maximum sizes at each geologic time were estimated from palaeo‐atmospheric oxygen partial pressure and compared with the maximum size of known fossilized insects. The historical change in fossilized insect sizes was much larger than that in theoretical sizes. Additionally, from the Jurassic, despite an increase in the partial pressure of oxygen, which would theoretically increase maximum size, the maximum size of fossilized insects became smaller. These findings are inconsistent with the expectations of the working hypothesis. Oxygen supply is likely to partially limit the maximum size of insects with additional factors.     

Proteomic analysis of a membrane skeleton fraction from human liver

The cytoskeleton networks around liver cell cortex can resist Triton extraction and co-pellet with their tightly associated integral membrane proteins, forming assemblies called "membrane skeletons". Despite their important roles in determining cell shape and in signal transduction pathways, the membrane skeletons of human liver cells are uncharacterized to a great extent. In the present work, we prepared a membrane skeleton fraction by Triton extraction of human liver plasma membranes and then separated its protein components by 2-D gels. We optimized the detergent used for protein solubilization and found that 2% ASB-14 allowed the best recovery of membrane skeleton proteins. By analyzing the protein spots with MALDI-TOF and MALDI-TOF-TOF MS, we identified 104 nonredundant proteins, wherein 38 were cytoskeletal proteins that were further classified into several groups, including proteins in fodrin-based meshworks, adhesion proteins (proteins involved in adherens junctions, focal adhesions, desmosomes, hemidesmosomes and tight junctions), proteins that regulate F-actin dynamics, motor proteins, and some other cytoskeletal proteins. To the best of our knowledge, this is one of the largest data sets of membrane skeleton proteins to date. All the results suggested that the liver cells had complex actin- and cytokeratin-based membrane skeletons. This work provided a representative 2-DE map of membrane skeletons from human normal liver, for the purpose of helping to elucidate the composition and function of the membrane skeletons.     

THE GROWTH AND MORPHOLOGY OF THE SILICOFLAGELLATE DICTYOCHA FIBULA EHRENBERG IN CULTURE1,2

Dictyocha fibula was cultured in an enriched seawater medium from collections taken at Edmonds, Washington. The optimum temperature for growth is 10 C at salinity 24% and 160 ft-c illumination in Provasoli enriched seawater at the concentration of 7.5 ml/liter seawater. Average generation time is 49 hr. In addition to swimming cells with skeletons, swimming cells without skeletons and nonswimming coenocytes were observed in clonal cultures at 15 C.     

The fossil record of fish ontogenies: Insights into developmental patterns and processes

One of the properties of fossils is to provide unique ontogenies that have the potential to inform us of developmental patterns and processes in the past. Although fossilized ontogenies are fairly rare, size series of relatively complete specimens for more than 90 fish species have been documented in the literature. These fossilized ontogenies are known for most major phylogenetic groups of fishes and have a broad stratigraphic range extending from the Silurian to the Quaternary with a good representation during the Devonian. Classically, size series have been studied in terms of size and shape differences, where subsequently allometric changes were used as indicators of heterochronic changes in Paleozoic placoderms and sarcopterygians. Quantitative analyses of fossilized ontogenies of dipnoans have been interpreted in terms of morphological integration and fluctuating asymmetry. Recently, reconstructed sequences of ossification have been used to identify recurrent patterns of similar development in actinopterygians and sarcopterygians in order to infer phenotypic developmental modularity and saltatory pattern of development. Phylogenetic and temporal landmarks are put forward for some of the major developmental patterns in the evolution of fishes.     

A posttranslational modification of beta-actin contributes to the slow dissociation of the spectrin-protein 4.1-actin complex of irreversibly sickled cells

Irreversibly sickled cells (ISCs) remain sickled even under conditions where they are well oxygenated and hemoglobin is depolymerized. In our studies we demonstrate that triton extracted ISC core skeletons containing only spectrin, protein 4.1, and actin also retain their sickled shape; while reversibly sickled cell (RSC) skeletons remodel to a round or biconcave shape. We also demonstrate that these triton extracted ISC core skeletons dissociate more slowly upon incubation at 37 degrees C than do RSC or control (AA) core skeletons. This observation may supply the basis for the inability of the ISC core skeleton to remodel its shape. Using an in vitro ternary complex dissociation assay, we demonstrate that a modification in beta-actin is the major determinant of the slow dissociation of the spectrin-protein 4.1-actin complex isolated from the ISC core skeleton. We demonstrate that the difference between ISC and control beta-actin is the inaccessibility of two cysteine residues in ISC beta-actin to labeling by thiol reactive reagents; due to the formation of a disulfide bridge between cysteine284 and cysteine373 in ISC beta-actin, or alternatively another modification of cysteine284 and cysteine373 which is reversible with DTT and adds less than 100 D to the molecular weight of beta-actin.     

A New Algal Fossil from Early Cambrian in Qingzhen County,Guizhou Province,China

A new algal fossil was collected from the lower part of the Lower Cambrian, a Sinian-Cambrian boundary section in Abazhai of Qingzhen County, Guizhou Province. It was discovered in petrographic thin sections of a black laminated chert. The new fossil, Symphysosphaera radialis gen. et sp. nov. is a fossilized muhicellular colony characterized by a surface layer of cells enclosed in an envelope, inner cavity permeated with dark dense mucilage embedded with numerous spherical units. Its difference from all morphs discovered in Precambrian, indicates that the genus may represent member of a new order at the beginning of Cambrian. hs stratigraphic and biological significance merits our attantion.     

周口店田园洞古人类化石点地层学研究及与山顶洞的对比

田园洞主体堆积厚度约2.5m,其动物群可分为上、下两个组合:上部组合物种多样性丰富,化石被啮齿类严重啮咬;下部组合化石种类单调,以鹿类和绵羊类为主,但化石丰富,极少有啮齿类咬痕。人类化石发现于下部组合;东洋界动物主要出现在上部组合,例如猕猴、猪獾、果子狸和鬣羚等。而马鹿和绵羊只出现于下部组合。沟齿鼯鼠和豪猪在下部组合开始出现,但主要发现于上部组合。梅花鹿是田园洞的优势种,在各个阶段都出现。通过统计比较,发现山顶洞3个地层单元(上室、下室和下窨)中所含化石属种基本一致,代表同一个动物群。尽管田园洞动物群中尚未发现可靠绝灭种类,但却有10种地区绝灭种,它与现生动物群有一定差异;而在堆积物特征及化石组合方面,与周口店山顶洞的更为接近。在田园洞和山顶洞出现的沟齿鼯鼠、猪獾、果子狸及鬣羚等是各自在华北地区的最早记录,可能代表了更新世末期自南而北的动物迁徙事件。     

粪化石在古生态研究中的应用综述

粪化石(coprolite)是石化的动物粪便,而广义上粪化石(bromalite)是石化的动物消化物、排泄物和排出物的总称。作为一类重要遗迹化石,粪化石蕴含了大量实体化石难以提供的生物学信息,为古生态学研究提供以下依据:1)粪化石作为媒介帮助理解远古动物的行为习性、消化系统的结构和功能、食谱特征以及古生态系统食物链/食物网;2)粪化石中保存的古寄生虫线索能有效地解读古生物寄生关系和某些常见肠道寄生虫的起源问题;3)新生代以来古人类粪化石证据可以直接解开早期古人类的食谱、疾病特征及其迁移路径;4)中、新生代以来的粪化石中保存的植物残留信息(孢粉化石和植硅体)是重建古植被面貌、恢复古气候和探索早期动植物关系的重要依据。本文回顾了粪化石研究历史,并针对粪化石在上述古生态各研究方向的最新进展进行了系统总结和综述,认为粪化石可有效解读古生态。文章最后对粪化石的最新研究技术方法(如CT扫描技术)及未来发展方向进行了展望。     

贵州清镇早寒武世早期藻类化石

从贵州清镇阿坝寨震旦系一寒武系界线剖面,寒武系底界附近的燧石岩石薄片中,发现的一种保存很好的藻类化石——一种内部具浓密胶状物质的多细胞球形群体化石。它不同于以往在前寒武纪发现的所有藻类化石,故建新属 Symphysosph(?)era gen.nov.(属型种 Symphy-sosphaera radiaalis gen.et sp.nov.)。文中详细比较了新属和几个已知属的区别及可能的亲缘关系。     

Lansing man: a half century later

One of the major fossil man finds from the Plains Area of the United States and one of the few from Kansas are the “Lansing Man” skeletons. The discovery was in February 1902 on the west bank of the Missouri River, south of Leavenworth near the town of Lansing, Kansas. Much was written about this skeleton following its discovery and Ale? Hrdli?ka's only trip to Kansas in October 1902 was to observe the skeletons and the site of its discovery. Numerous articles were written suggesting that “Lansing Man” was many thousands of years old. Geologists could not agree on an age of the skeletons, an adult male and a six to seven year old child, because they were discovered in deposits of slumped loess, confusing the geological picture. Hrdli?ka states that the skeletons were physically identical to Indians of that region at the period of historical contact. William Holmes had the skull sent to the U. S. National Museum and the remaining bones were placed in the Museum of Natural History at the University of Kansas. While on the staff of the University of Kansas, I had Carbon-14 tests conducted on bones from the lower limbs by three separate laboratories. These dates range from 2660 to 5020 B.C. with an average date of four samples (1 each from Geochron Laboratories and the University of Michigan and two from the Smithsonian Institution) of 3579 B.C. This suggests that the “Lansing Man” skeletons are Early Middle Archaic and not Paleoindian. They do, however, represent the oldest known human skeletons from Kansas.     

Evolutionary genomics: a dinosaur's view of genome-size evolution

Estimates of cell volume in fossilized bones of extinct dinosaurs indicate that genome size underwent a significant reduction in the early theropods, from which birds later evolved. This suggests that birds' small genomes are not an adaptation to metabolic demands associated with flight.     

Remarkable preservation of undigested muscle tissue within a Late Cretaceous tyrannosaurid coprolite from Alberta,Canada

Exceptionally detailed soft tissues have been identified within the fossilized feces of a large Cretaceous tyrannosaurid. Microscopic cord-like structures in the coprolitic ground mass are visible in thin section and with scanning electron microscopy. The morphology, organization, and context of these structures indicate that they are the fossilized remains of undigested muscle tissue. This unusual discovery indicates specific digestive and taphonomic conditions, including a relatively short gut-residence time, rapid lithification, and minimal diagenetic recrystallization. Rapid burial of the feces probably was facilitated by a flood event on the ancient coastal lowland plain on which the fecal mass was deposited.     

Binding of mutagenic pyrolyzates to fractions of intestinal bacterial cells.

The binding of mutagenic pyrolyzates to cell fractions from some gram-negative intestinal bacteria and to thermally treated bacterial cells was investigated. 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) were effectively bound by several of the bacterial cells. The cell wall skeletons of all bacteria effectively bound Trp-P-1 and Trp-P-2. Their cytoplasmic fractions retained Trp-P-1 and Trp-P-2, but to a lesser extent than the cell wall skeletons. 2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) was not found in their cytoplasmic fractions. These cell wall skeletons also bound 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1), 2-amino-5-phenylpyridine (Phe-P-1), IQ, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQX). The amount of each mutagen bound differed with the type of mutagen and the bacterial strain used. The outer membrane of Escherichia coli IFO 14249 showed binding of about 123.7 micrograms/mg of Trp-P-2, and its cytoplasmic membrane bound 57.14 micrograms/mg. Trp-P-2 bound to the bacterial cells was extracted with ammonia (5%), methanol, and ethanol but not with water.     

Occurrence and diversity of lipids in modern coral skeletons

Coral skeletons are composite acellular structures, in which organic macromolecules are intimately associated with mineral phases. Previous studies focussed on proteins and sugars of the soluble organic matrices extracted from the skeletons. Here we report the occurrence of diverse lipids which were extracted from the aragonitic skeletons of seven modern coral species. Using thin layer chromatography, we show that these lipids differ in quantity and composition between the species. Higher proportions of sterols and sterol esters in skeleton extracts as compared to a much higher abundance of waxes and triglycerides in previously studied extracts from scleractinian soft tissues suggest a specific, although not yet determined, role in biomineralisation. The occurrence of intraskeletal lipids along with other organic components should also be taken into account when using coral skeletons as bone allografts, as well as in fossilisation processes.     

Estimating body weight and habitat type from extinct avian and avian‐like theropod footprints

The relationship between body weight and footprint area of modern avians was derived and used to estimate the body weights of non‐avian theropods taxa from the Triassic to Cretaceous and extinct avian taxa from the Cretaceous periods. Geometric information, such as the area and shape of fossil tracks of extinct avians and non‐avian theropods, was used to estimate body weight and habitat type. The percentage prediction and standard error of estimates indicated that the body weight estimated from track area is comparable with body weight estimated from body fossils bones. Therefore, this approach is useful when the fossilized track record is richer than the fossilized skeletal record. The data sets for avians and reptiles were combined and used to derive a body weight–area relationship that may be applicable to a broader range of organisms, such as plantigrade quadrupeds and digitigrade bipeds. Additionally, scatter plots of the relationship between habitat type and footprint shape of modern avians were used to infer the habitat type of extinct avians. This finding suggests that the pes of animals, living in areas characterized by fluctuating water levels, and under conditions facilitating the preservation of footprints, were similar in form to those of extant semi‐aquatic avians.     

Feulgen-positive staining of the cell nuclei in fossilized leaf and fruit tissues of the Lower Eocene Myrtaceae

The Feulgen reaction and the staining of preparations with two DNA-specific fluorochromes, Hoechst 33258 and 4',6-diamidino-2-fenilindol (DAPI), were used to study the preservation of DNA in the fossilized leaf and fruit tissues of the Lower Eocene Myrtaceae, Paramyrtacicarpus plurilocularis and Paramyrtaciphyllum agapovii collected in Yakutia (Siberia, Russia). It was shown that chromatin structures of the fossilized plants form stable red-purple complexes with the Schiff's fuchsin sulphuric acid reagent in situ . This coloration is specific for DNA, in particular, for the deoxyribose residues. It means that the cell nuclei of these 53–55 Myr old plants preserve a part of the deoxyribose backbone of DNA molecules. On the other hand, there was no, or only a very weak, staining of the cell nucleus with fluorochromes DAPI or Hoechst 33258, which specifically bind to the double-stranded DNA and do not bind to either the single-stranded DNA or RNA molecules. The stainability of fossil plant cell preparations with alcian blue shows that there are also polysaccharides containing carboxyl groups in the cell walls of fossilized leaf and fruit tissues of the Lower Eocene Myrtaceae.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 315–321.